11 Best 3018 Series CNC Upgrades and Accessories

Why do they have to make so many cool toys for adults?

Actually, I suppose it’s not the toys that are the problem, but instead it’s the cost of the toys.

Luckily if you recently purchased a 3018 series CNC such as the SainSmart Genmitsu series, MYSWEETY or one of the numerous other manufacturers out there, there are some relatively cheap or homemade upgrades to trick out your new machine.

Check out our list below to find out how to improve your 3018 CNC without breaking the bank.

Safety glasses

First and foremost, you should make sure you have a quality set of safety glasses. While these are small machines that are not as high powered as industrial CNCs, they are still dangerous.

Read your instructions. Wear safety glasses and it’s a good idea to have ear protection too.

Enclosure

An enclosure is one of the best upgrades for any hobbyist CNC. These machines can create a lot of dust and noise. It is a good idea to reduce both, especially if running the machine in your normal living area.

The enclosures are pretty straight forward. Assemble the box and place it over your machine to start reducing the volume of dust and noise created by your CNC.

If you have a 3D printer and are so inclined, it is possible to construct your own with some PLA, pieces of plexiglass and a little elbow grease.

Vise clamp

Larger CNCs use a machinist vise to hold the workpiece. This vise is a smaller version for the 3018 series of CNC machines. They work great to secure a variety of materials.

This tool is especially useful for holding parts which are an unusual shape such as jewelry or some electronics.

Many different forms of work holding are available such as clamps and T nuts but a vise is a simple way to hold a large assortment of material. Compared to other types of workholding, a vise will decrease setup time and increase productivity.

T nuts

If a vise is too costly for securing your workpiece. Think about some T nuts. They aren’t as fast but they are versatile and a vast improvement over the typical clamps included with most of the 3018 series CNCs.

Check out our bonus tips for ways to protect your workpiece while using T nuts.

Router bits and cutters

Upgraded router bits and end mills are an important addition. 

But not every type of bit is worth buying. 

Check out our Beginner’s Guide to CNC Router Bits to figure out which ones you need to get started and which ones are fun toys for later on.

Rotary engraving module

The 3018 series of CNC are capable of laser engraving but for anyone looking to laser engrave cylindrical objects such as cups, tumblers, etc. this is the perfect solution.

The rotary engraving module will allow you to rotate the workpiece to allow the part to stay in the lasers ideal path. This will allow uniform engraving of the workpiece around the circumference of the engraved piece.

This isn’t an upgrade for everyone but if you have a specific application in mind which requires laser engraving a circular object then think about checking out this upgrade.

Collets

Different collets are a great addition for a 3018 series CNC. They allow you to use many different size bits or end mills to machine your workpiece with. At the bare minimum it would be wise to consider adding a ¼” ER11 collet. For a little more you can get a set that will allow just about any bit or end mill that you would want to use.

There is no need to break the bank on ER11 collets for a 3018 CNC. The added quality and reduction in runout won’t translate to a big difference in quality for your projects. A simple set is the best choice.

Z axis touch setting probe

No one likes setting Z axis heights with paper. It feels imprecise and clumsy. Luckily, there is a simple and cheap upgrade which will allow you to make the process simpler and more accurate.

The probe is very easy to use. First connect the probe to your control board. Now measure the height of the probe with a tool such as a digital caliper or micrometer.

The thickness of the probe now needs to be entered into the CNC software. Place the probe on the workpiece and then connect the clip to the cutting tool. Run the probing program and lower the cutting tool slowly until it contacts the probe. The Z axis will now be set.

For more detailed instructions check the manufacturer’s website, they have a nice tutorial.

You can make your own if you wish but for the price it is hard to justify messing with a homemade tool.

If a homemade tool is more your speed then check out this tutorial which will walk you through creating your own Z axis touch setting probe.

The cost of the homemade tool is close to the cost of an actual probe but you might have some of the supplies on hand already which will bring the cost down.

Limit switches

Limit switches are a great addition to a 3018 CNC machine. Without them it is all too easy to crash your machine. While crashing the machine won’t always cause damage, it is a definite possibility.

Honestly, the machines should all come with limit switches to protect the machine from damage but I am sure that the manufacturers are trying to keep the cost down as much as possible and therefore did not include them in some versions of the 3018 CNC.

The 3018 series of CNC machines are pretty budget friendly but that doesn’t mean you want to scrap the machine right away.

Take note that adding limit switches will reduce your work area by a small amount. While this is unfortunate, it is definitely a recommended upgrade to protect your machine especially at the relatively small cost of the upgrade.

Storage tray

As you gain more experience with your CNC machine, it is inevitable that you will develop quite the collection of bits and end mills. A good storage solution is a must to protect your bits from damage.

The storage tray has holes for many different sizes of bits and end mills along with storage for miscellaneous other tools. The tray from Genmitsu does a great job of organizing all the little odds and ends along with your cutting tools.

If you have a 3D printer then check out Thingiverse for storage trays. You should be able to find something similar that will meet your needs. If you don’t have a 3D printer then you might be able to find something that will work at the dollar store.

The important thing is to keep your tools organized and protected so that they will remain sharp and ready for your next project.

Wire and cable protectors

Those with experience working with a 3D printer will likely recognize the value of a good wire/cable protector. This is often one of the first things printed when someone buys a new 3D printer and for good reason.

The movement of the machine back and forth in the process of cutting or engraving means that there is some risk that the wires will snag on some portion of the machine. The cable protectors will keep this from happening.

If you have a 3D printer already, take a peek on Thingiverse to see if there are any plans or find a premade alternative somewhere else like Amazon.

Bonus tips for your 3018 CNC

One great way to hold down projects that are difficult to secure for all types of reasons is to place blue painters tape on the bed and the workpiece. Now use an adhesive to glue the two sections of painters tape together. The tape and glue combo will hold the part and once you are done, you can simply peel the painters tape off.

3D printed holding fixtures can be a great addition and allow more versatility in what you can machine. Check out Thingiverse for all kinds of 3D printed addons.

Use felt furniture sliders from the dollar store with clamps or t nuts to protect surface of delicate workpieces.

If you have any additional tips you learned experimenting with your 3018 CNC please let us know and we will happily share them here to save others some of the headaches that come with learning how to work with a new machine.

Dial Caliper Reading Quiz

/10

Dial Caliper reading quiz

Test your ability to accurately read a dial caliper.

1 / 10

Enter the value for the measurement shown on the dial caliper above.

Values should be entered to the nearest thousandth of an inch (0.001”).

2 / 10

Enter the value for the measurement shown on the dial caliper above.

Values should be entered to the nearest thousandth of an inch (0.001”).

3 / 10

Enter the value for the measurement shown on the dial caliper above.

Values should be entered to the nearest thousandth of an inch (0.001”).

4 / 10

Enter the value for the measurement shown on the dial caliper above.

Values should be entered to the nearest thousandth of an inch (0.001”).

5 / 10

Enter the value for the measurement shown on the dial caliper above.

Values should be entered to the nearest thousandth of an inch (0.001”).

6 / 10

Enter the value for the measurement shown on the dial caliper above.

Values should be entered to the nearest thousandth of an inch (0.001”).

7 / 10

Enter the value for the measurement shown on the dial caliper above.

Values should be entered to the nearest thousandth of an inch (0.001”).

8 / 10

Enter the value for the measurement shown on the dial caliper above.

Values should be entered to the nearest thousandth of an inch (0.001”).

9 / 10

Enter the value for the measurement shown on the dial caliper above.

Values should be entered to the nearest thousandth of an inch (0.001”).

10 / 10

Enter the value for the measurement shown on the dial caliper above.

Values should be entered to the nearest thousandth of an inch (0.001”).

Your score is

The average score is 64%

0%

How to use a dial caliper

Before using your caliper, check to make sure that the measuring tool and surface to be measured are free of dirt, debris, chips, etc. The body of the caliper should slide freely along the scale or bar.

For an outside measurement, slide the jaws of the caliper open until they are far enough apart to be placed over the part to be measured.

parts of a caliper

Now proceed to close the jaws while trying to keep the jaws perpendicular to the surface being measured.

Multiple measurements should be taken to verify that the caliper has yielded the true reading.

For example, if a measurement is taken where the jaws of the caliper are not perpendicular to the surface being measured then the reading obtained can be larger than the true size.

Note: Do not use a large amount of force on the caliper in the direction of measurement. This can cause the tool to flex and give an incorrect reading. It is best to place the same amount of force that is used to zero the caliper.

How to read a dial caliper?

Reading a dial caliper is easy, though not as easy as a digital caliper.

Because costs have come down substantially in recent years, I recommend purchasing a digital caliper if possible.

If a digital caliper isn’t in the cards either because of budget or because you are working with an inherited tool then keep reading.

mitutoyo digital caliper display in inches
Typical digital caliper display

Dial calipers come in a few varieties, but most have their measurement read in the same way.

Dial calipers have graduations along the bar that are in increments of 0.1″ or one hundred thousandths of an inch. 

Often the 1,2,3, and so on whole inch increments are marked with a number and the 0.1″ increments will be marked with a line.

a dial caliper with text that shows how to read the bar of the tool
This dial caliper has the 0.1" increments marked too

To read the caliper, combine the largest visible whole inch and 0.1″ increments on the beam with the dial reading. 

Your reading = Largest whole inch + largest 0.1 inch + dial reading

In the example below, the 3 inch graduation (line) is visible. So is the 0.1 inch graduation after the 3. 

If we add them together we get 3.1 inches. Now we need to add the dial reading to our beam reading.

The dial reading is 0.006 inches. 3.1″ + 0.006″ = 3.106″

The dial caliper measurement reading is 3.106″

a picture of a dial caliper with the instructions about how to read a measurement
A dial caliper with a measurement reading of 3.106"

How accurate are dial calipers?

A good set of 0-6″ dial calipers is accurate to +/- .001”. Any 6 inch calipers which are less accurate should be ignored.

As the measuring range of the caliper gets larger, the accuracy of the caliper will often be reduced. Pay attention to the specs because it isn’t uncommon for a 24″ set of calipers to only be accurate to +/- 0.002″.

If you are in need of accuracy that is greater than this, you will need to find a nice set of micrometers for your application.

Mitutoyo Micrometer

Micrometers are commonly available with an accuracy of +/- .0001”. Some cheaper sets of micrometers will not quite meet this accuracy, but you can rest assured that a set from the most well-known manufacturers such as Starrett and Mitutoyo will more than meet this standard.

Dial calipers sacrifice some accuracy to gain versatility in measurement.

Dial vs digital calipers

mitutoyo digital caliper measuring 1 inch block
Mitutoyo digital caliper

Both dial and digital calipers have their advantages. For dial calipers, their lack of batteries mean they are always ready to take a measurement.

Digital calipers have the benefit of taking instant measurements as well as switching between units at the press of a button.

There is no difference between the accuracy of digital and dial calipers and they are both available with similar measuring ranges. Ultimately, the choice between which is better comes down to a matter of preference.

For a more complete guide to the differences between dial and digital calipers see our guide on the topic.

Best Machinist Calculators & Calculator Apps

title of article best machinist calculators and calculator apps with graphics of a calculator and a smart phone with apps on screen

Machinists, CNC Machines Operators, and hobbyists often need to work with complex engineering and mathematical equations daily. With practice they get easier to work with, but a good calculator tailored to machining can speed up the learning process.

After all, a miscalculation can be the difference between a scrapped part or crashed machine and a perfect part.

Standard hand-held calculators are designed for basic arithmetic calculations of addition, subtraction, multiplication, and division.

A good machinist calculator will perform all the functions of a standard calculator along with other specialized functions such as trigonometry, logarithms, and exponential functions.

At the very least you will want to get a calculator that can perform all of the necessary operations.

If you want to step things up and make those calculations easier, then some of the specialized calculators below simplify the formulas and calculations.

In this article, we discuss some of the best machinist calculators and apps for machinists available while including tips for making the most out of these mathematical tools.

Best machinist calculator

Our pick for the best machinist calculator is the Calculated Industries 4088 Machinist Calc Pro 2.

The Machinist Calc Pro 2 Model 4088 easily ranks among the best machining calculators because of its ease to use, and rugged build. This calculator is ideal for machinists, engineers, programmers, and hobbyists.

The Machinist Calc Pro 2 Model 4088 makes solving the most common formulas used such as speeds, feeds and trigonometry super simple. Adjusting those calculations, with a larger depth of cut for example, is also easy. A couple button pushes to adjust the value in the calculator and it quickly spits out your new speeds and feeds. No need to run through the whole calculation step by step again.

It also solves right-angle triangle and bolt-circle patterns problems with ease. The trig functions are great. Enter what you know, any combination of angles or sides, and the Calc Pro 2 will spit out all the unknown values.

Also, the calculator comes with built-in charts that you can look up information for calculating milling, boring, spindle speed, cut speed, chip-load, etc.

Back to speeds and feeds because that is a large portion of what this calculator is so good at.

The calculator makes solving for any of these values quick and easy:

  • Surface feet per minute (SFM)
  • Revolutions per minute (RPM)
  • Inches per revolution (IPR)
  • Inches per tooth (IPT)
  • Inches per minute (IPM)
  • Width of cut (WOC)
  • Depth of cut (DOC)
  • Length of cut (LOC)

On top of this, there are a ton of variables that can be adjusted to accurately setup your machine. You can pick the type of cutting tool you are using as well as the material you are cutting.

It comes loaded with material info for various steels as well as aluminum and titanium alloys among others. The tool choices are high speed steel, carbide, and high-performance tools.

The pre-programmed processes built in are:

  • Turning
  • Drilling
  • Boring
  • Slot milling
  • End milling
  • Face milling

The Machinist Calc Pro 2 is handy but also built tough. Things don’t always get treated as carefully as they should in the shop which is why the included case/cover is important. Just remember that the case isn’t waterproof, it is only meant to protect it from a splash, don’t go dipping it in your coolant.

The case has a quick tips guide to the most important functions and this thing practically comes with a textbook. It can seem overwhelming, but it is pretty well laid out and you can find what you need pretty quickly.

The Calc Pro 2 isn’t necessarily a calculator replacement. It isn’t meant to do all math calculations, but it is meant to do a large selection of the ones that anyone working in machine shop would need.

Best budget calculator for machinists

Let’s be real, not everyone wants to break the bank when picking up a calculator. If you fall into this category, keep it simple and go with one of the classics.

The TI-30XIIS scientific calculator by Texas Instruments is solid calculator fully capable of any calculation the average machinist or CNC operator might need.

While it won’t step you through the formulas and calculations like the Calc Pro 2, it is still more than capable of getting to the end result.

The TI-30XIIS has all the functions you will need for solving your machining formulas. Algebra, geometry and trigonometry functions are all built in.

The TI-30XIIS is both solar and battery powered, and the battery practically lasts forever. I have used literally dozens of these calculators in my time working in machine shops and I can’t recall ever having one that had a dead battery.

They are simply built to last. This isn’t cheap plastic. I feel like you could use the thing as a hammer and it would keep on ticking.

Please don’t though. Using the calculator as a hammer will likely void your one-year warranty.

The only thing I have seen kill one of these calculators is chemicals. But in fairness, a heavy dose of acetone will put an end to most things plastic.

If you simply need a calculator to do your job and aren’t looking for something super specialized, then stick with one of the classics and grab a Texas Instruments TI-30XIIS scientific calculator.

Best machinist calculator app

screenshot of CNC machinist Calculator Pro app showing calculator feature

Everyone uses the calculator on their smart phone. But this is not your ordinary calculator app. 

The CNC Machinist Calculator Pro app is an extremely powerful machining tool. It features all the standard calculator functions you would expect along with a wide assortment of specialized functions.

screenshot of CNC machinist Calculator Pro app showing trigonometry solver

It has functions for milling, drilling and turning calculations. 

The app also includes a nice variety of charts and references to use. This is a great all around app that has a little bit of everything and enough of it to help anyone using the app along.

For example, not everyone will need to reference the G code library or the GD&T symbols guide but both sections of the include a nice amount of info and examples to prove useful.

screenshot of CNC machinist Calculator Pro app showing quiz feature

I really like the mini apps that are included in the Machinist Calculator Pro app.

The trigonometry solver and geometry solver are very handy. 

I also really enjoy the quiz function called Brain Check. It has various quizzes on different machining related topics. Seems like a fun way to figure out what you might need to brush up on for subjects.

Overall, the app is well made and easy to use. While it isn’t a $1 or $2 app, it does pack an extensive amount of functions into the package while still being quite a bit less expensive than some of the competing machining apps.

Best premium machinist calculator app

screenshot of Calculated Industries Machinist Calc Pro 2 App showing cutting speed

There’s an app for nearly every gadget, tool, or piece of equipment you can think of. This even applies to calculators for machinists.

The best premium app is a no-brainer. It is Machinist Calc Pro 2. Yeah, you read that right. Calculated Industries have literally made an app that replicates their physical calculator.

screenshot of Calculated Industries Machinist Calc Pro 2 App showing decimal degrees

The mobile app features all the same functions of the handheld version with a built-in help function for when you can’t figure out your next move. By pressing and holding specific keys, the app displays clear explanations of what the key does alongside elaborate examples.

Everything we said about the physical calculator still applies to the digital replica.

screenshot of Calculated Industries Machinist Calc Pro 2 App showing rpm

The app is available for all android and iOS devices and the best part is that you can get it for about half the price of the physical handheld version.

Best free machinist calculator app

screenshot of FS wizard app home screen
FSWizard Home Screen

FSWizard Machinist Calculator by Zero_Divide is an amazing calculator and overall machining resource especially considering the price of admission.

It has a ton of different calculators for things such as speeds and feeds, triangles, bolt circles, and more.

In addition, there are a huge quantity of references and charts that will come in handy. Most of the references aren’t intended to be the ultimate resource on the topic but instead simply a quick reference.

Many machinists, especially those just starting out, will enjoy the all-in-one app that includes GD&T, G code and speeds and feeds info all in one place.

screenshot of FS wizard app showing the navigation menu
FSWizard Navigation Menu

The biggest downfall of the free version of FSWizard is the limited selection of materials available in its speeds and feeds calculator. There are enough to get by, but the numbers won’t be exactly tailored to your workpiece. The additional materials are available in the Pro version of the tool.

Overall, FSWizard provides a ton of value for free. The app is available for all android and iOS devices.

Best online machining calculators

There are a large number of machining calculators available online. It can be a pain to have a bunch of bookmarked sites for all the different calculators you might need.

MachiningDoctor.com has a great selection of machining calculators for everything from speeds and feeds to sine bar calculations all in one place. Most of their online calculators are fairly advanced and allow customization for many different variables.

I also like that they often have a simple mode available for users who might not be as experienced.

Micrometers and Calipers [Similarities, Differences & Everything Else]

micrometers vs calipers

Micrometers and calipers are both precision measuring tools.

The difference between these tools lies in their accuracy and the types of measurements they can take.

Check out the table below for the main differences between the two tools and then keep on reading to gain a better understanding of what those differences mean when it comes time to use them.

Micrometers

Calipers

Accuracy

0.0001"

0.001"

Measuring Range

1" increments

0-6"

Types of Measurements

Outside Measurements

Inside, Outside & Depth Measurements

Micrometer and caliper comparisons

Accuracy

Micrometers are more accurate. 

A typical micrometer is accurate to 0.0001″ and a caliper is only accurate to 0.001″.

This makes a micrometer 10x more accurate than a caliper.

Just keep in mind that you can buy cheap versions of both tools that have worse accuracy. Also, if you were to buy a larger versions of these tools they will often have lower accuracy. 

A 17-18″ micrometer might only be accurate to +/- 0.0002″ and a 0-24″ caliper may only be accurate to +/- 0.002″.

To sum it up, realize that there is some variation in accuracy but in general you will find that micrometers are 10x more accurate than calipers.

Measuring range

starrett micrometer set in case with reference standards
0-6" Micrometer set

Micrometers come with 1″ measuring ranges. 0-1″, 1-2″, 2-3″ and so on. 

The most common measuring calipers measure over a 0-6″ range. Larger varieties can be also be found with 0-12″ and 0-24″ measuring ranges. There are some different ranges available such as 0-4″ and 0-8″ also but they are much less common.

This difference in measuring ranges means that you would need a set of micrometers to measure over the same measuring range a single caliper is capable of. 

Calipers have larger measuring ranges but they are less accurate.

Types of measurements they are capable of

Caliper measuring internal hole
caliper depth base attachment

Most calipers will measure inside, outside and depth measurements. 

digital caliper measuring coin
Standard outside diameter being measure with digital caliper

Micrometers are capable of only performing one type of measurement. 

The most common type of micrometer is an outside micrometer, usually referred to as simply micrometers or sometimes mics.

anytime tools 1-2" micrometer
0-1" outside micrometer

Inside micrometers and depth micrometers are also available to take internal and depth  measurements.

Calipers are capable of taking a much larger variety of measurements.

Depth micrometer with multiple rods for different size measurements
mitutoyo inside micrometer set
Inside micrometer with multiple attachements for different size measurements

Ease of use

To maintain the added accuracy that a micrometer has requires taking more care when using them. 

Something as small as the amount of force you use to close the micrometer can change your measurement. Many micrometers will have a ratchet or friction stops that help alleviate this problem. 

When you are working down to a tenth (machinist lingo for 0.0001″), even temperature comes into play. Metals expand and contract with changes in temperature. To protect against this, most micrometers have plastic pieces that can be used to help insulate your from the tool.

outside micrometer
0-1" outside micrometer with piece of black plastic for thermal insulation

A good micrometer stand can help keep you accurate as well.

The same factors affect the accuracy of a caliper but the effects aren’t as noticeable because they aren’t as accurate.

Speed

Calipers are quicker to use than micrometers. The jaws can open and close in a split second.

Micrometers need to spin the thimble around 40 times to cover an inch of travel. 

Cost comparison

A micrometer and a set of calipers have similar price points. Take for example a 0-1″ micrometer from Mitutoyo and a 0-6″ set of calipers from Mitutoyo.

The difference would be that to cover the same measuring range of a set of calipers, you would need a 0-6″ set of micrometers. A good set of micrometers is going to cost quite a bit more than your typical 0-6″ caliper.

More info about micrometers and calipers

Parts of a micrometer

parts of a micrometer

The part being measured will be placed between the anvil and spindle of the micrometer. The spindle is adjusted in and out by turning the thimble clockwise or counterclockwise. 

Depending on the micrometer being used, the lock nut, lock ring or lock lever can be used to hold the micrometer at a specific size. Some tools will not have any locking feature. 

Measurements are read using the scales on the sleeve and thimble. 

The frame of the micrometer can vary across brands and types of micrometers. Some are made specifically to have smaller frames for different measuring applications. 

Many micrometers also have a ratchet stop or friction stop that limits the amount of force applied to the thimble. This allows more consistent measurements.

Parts of a caliper

The jaws for external measurements are used to measure features such as length, width and thickness.

The jaws for internal measurement are used for measuring features such as hole sizes and slot or groove widths.

The rod for depth measurements is used for measuring depths of holes, counterbores and step heights. 

The scale and dial indicator face are used together to obtain measurement readings.

The slide of the caliper which consists of the moveable jaws along with the dial indicator face are slid along the beam.

The lock screw can be used to hold the caliper at a specific size for repetitive measurements.

Digital vs analog micrometers

Digital micrometers are great for the speed at which measurements can be read. Their display means very little training for the operator. 

Another benefit of a digital micrometer is how quickly measurement values can be converted between inch and metric readings. A simple button press can save time and do the conversion for you. 

starrett 0-1" micrometer
Starrett analog micrometer
mitutoyo digital micrometer
Mitutoyo digital micrometer

The downfall is that they tend to be quite a bit more expensive than a standard analog micrometer and they are more susceptible to contaminants such as water and coolant. Some models are offered with resistance or protection from different contaminants. 

In recent years, prices have dropped for digital micrometers making them more affordable. 

Analog micrometers tend to be a very dependable tool and many have been in use for generations. This also means that there are many used options on the market for analog micrometers. 

If cost is your primary concern, I recommend going with an analog micrometer. If ease of use and operation is important then go with a digital micrometer.

Digital vs dial vs vernier calipers

mitutoyo 6 inch vernier caliper
Mitutoyo vernier caliper

Vernier calipers are the most resilient type of calipers. They will be the least affected by things such as dirt and water or coolant. Unfortunately they are the most difficult to take measurements with. Learning to read the scales takes some practice. 

Dial calipers are a good middle ground with measurements that are relatively easy to take with the dial indicator face. They are reasonably resistant to contamination though they should still be handled with care. 

anytime tools dial caliper dial face
Dial caliper

Digital calipers are by far the easiest to use. The LCD display takes any guesswork out of reading your measurement. They are also the most susceptible to damage from things such as dirt and coolant. 

Unless they are being used in the harshest environment, I recommend getting digital calipers. Digital calipers can be purchased with ingress protection if needed.

Summary

While they are both precision measuring tools, there are some key differences between micrometers and calipers. 

Micrometers are more specialized and have a smaller measuring range. As a result they are generally more accurate and often capable of measurements to .0001″. 

Calipers are more versatile. They have a much larger measuring range. To achieve this they sacrifice accuracy and most often take measurements to an accuracy of .001″. 

As you can see they both have their strengths and weaknesses but in the end they are two of the most important precision measuring tools you can have in your toolbox.

Beginner’s Guide to Blueprint Reading

Learning to read blueprints can be hard. That’s why we’ve broken down the process into bite size chunks. All of the basic components of an engineering drawing are detailed below with links throughout to give you more info on each subject.

Use the table of contents below to jump straight to your topic of choice and if you don’t find what you are looking for please leave a comment at the bottom and we will tackle any blueprint related questions we may have missed.

Components of a drawing

Title block

title block example
Title block example

A blueprint title block contains the high-level identification information. The title block of a blueprint can vary quite a bit across different companies. In general, the title block can be found in the bottom right of the blueprint and will include the following:

  1. Drawing or part number and revision
  2. Part name
  3. Company name
  4. 1st or 3rd angle projection
  5. Scale

Tolerance block

tolerance block example
Tolerance block example

The tolerance block, sometimes referred to as the general tolerance block, is usually located in the bottom right or bottom middle section of the blueprint. The tolerance block identifies the tolerances associated with dimensions that are not directly listed on the drawing.

This can include items such as the blueprint dimensional units (imperial or metric) or surface roughness requirements.

Units of measurement

The units of the print are very important because there is a huge difference between 25.4mm and 25.4 inches. The measurement units will often be called out in the title block or tolerance block but occasionally will be in another section of the blueprint such as in the notes.

Angular units are important also but there is usually less confusion associated with them because decimal degrees and degrees, minutes, seconds are so different.

Types of projections

Projections are different ways of representing parts on a blueprint. Basically this means there are different methods of showing the same part.

1st angle projection, sometimes referred to as the European convention, is a method of displaying the various views of the part as if the part has been flipped to each side.

Notice how the car is flipped below in each view of a 1st angle projection blueprint.

1st angle projection car example
1st angle projection example - click to enlarge

3rd angle projection, the American convention, is a method of displaying the various views of the part as if the part is placed in a bowl and rolled in the bowl to the other views.

Notice how the car is flipped below in each view of a 3rd angle projection blueprint.

3rd angle projection example - click to enlarge

Projections can be hard to describe in words. Just remember that 1st angle projections are a flop method and 3rd angle projection is a roll method. 

Types of tolerances

There are multiple ways of tolerancing a dimension. Below are the ways of directly dimensioning a feature with standard tolerances. GD&T tolerances are a separate topic altogether.

Limit tolerances

limit tolerance example
Limit tolerance example

Limit tolerances list a range that the dimension must fall within. No calculation needed. Simply keep it between the numbers.

Unilateral tolerances

unilateral tolerance blueprint example
Unilateral tolerance example

Unilateral tolerances are given when the allowable variation is in a single direction such as the example below. In this example, the part cannot have a diameter that is over 6mm.

Bilateral tolerances

bilateral tolerance blueprint example
Bilateral tolerance example

Bilateral tolerances, often referred to as plus or minus tolerances, have a nominal size and a tolerance in the positive and negative directions. Often this tolerance will be equal in both directions, but it doesn’t have to be. Sometimes you will see bilateral tolerances that allow more variation in one direction.

Notes section

Notes on a blueprint can have a huge impact on the component requirements. The notes are often where surface treatment requirements such as heat treating, anodizing and other similar requirements are documented.

Literally anything can be listed in the notes section and the items listed can have a large bearing on the complexity of the part.

Pay attention to your notes section, there are often critically important features and characteristics relative to the part listed.

Symbols

A wide range of symbols are used to create engineering drawings. There are also specialty blueprint symbols associated with items such as welding or electronic components, but I will only be covering the standard blueprint symbols including those related to geometric dimensioning and tolerancing (GD&T).

Center lines

Center lines, such as the center of a thru hole are depicted on a drawing with long and short lines spaced alternately.

In the example below, the centerlines are shown as blue lines.

hidden and center line blueprint example
Center lines and hidden lines example

Hidden lines

To show features in a blueprint view that would not actually be visible, hidden lines are used. These hidden lines are show on a drawing as lines made of dashes.

In the example above, the hidden lines are shown as red lines

Diameters

Diameter Blueprint GD&T Symbol o with line through it
Diameter symbol

Diameters are round or cylindrical features. Features such as the outside diameter of a part and the size of a hole or counterbore are examples of diameters. They will be referenced using the diameter symbol shown below.

Countersinks

Countersink Blueprint GD&T Symbol two lines pointing down
Countersink symbol

Countersinks are a chamfer on a hole that allows a fastener such as a screw to sit flush or below the part surface. The blueprint symbol for a countersink is shown below.

countersink blueprint example
Countersink callout example

Counterbores

Counterbore Blueprint GD&T Symbol u shape
Counterbore symbol

A counterbore is a circular hole that is deep enough to allow the head of a fastener to be recessed. Counterbores will be shown on a blueprint with a diameter and depth symbol associated with them.

counterbore blueprint example
Counterbore callout example

Radii

Radius callout example

Radii show up on prints for many different reasons. The most common application of a radius is to specify the maximum radius allowed in the bottom of a slot or hole. They are frequently used as a form of edge relief similar to a chamfer. While these are the most common radius uses, radii can be dimensioned for all kinds of internal and external features.

When a radius smoothly blends into a surface, it will occasionally be called out as a full radius or full R. A full R callout does not change the way a radius is measured or add any additional requirements.

Holes

thru hole blueprint example

Holes are about as simple as they come. They come in two varieties, thru holes and blind holes. When shown on a drawing they will usually be referenced by their size and location to the center of the hole.

Datums

Datum Blueprint GD&T Symbol a in a box with arrow
Datum symbol

Datums are reference points for measurements and are utilized in many GD&T callouts. You will find datums shown on a drawing to identify the feature as a datum or as part of a GD&T callout in a feature control frame.

GD&T Symbols

gd&t symbols
gd&t symbols

Basic dimensions

Basic Dimension Blueprint GD&T Symbol dimension in a box
Basic dimension example

Basic dimensions are the theoretically perfect size or location of a part feature. The variation from this “perfect” size or location will be used to measure another characteristic of the part such as true position or profile. Basic dimensions do not have a tolerance themselves and instead are controlled by another GD&T callout.

Reference dimensions

Reference Dimension Blueprint GD&T Symbol dimension in parentheses
Reference dimension example

Reference dimensions are just what they sound like. They are placed on a print for reference only. They have no requirements associated with them and no tolerances either. They generally get used in one of two ways, they will be used to highlight something that might not be immediately clear without the reference dimension listed or they will be used to show the approximate dimension in another unit system (metric vs imperial units).

Chamfers

chamfer callout blueprint example
Chamfer callout example

Chamfers are used to remove the sharp edges of a part. This provides safety for both the part and the person using the part. Chamfers are frequently specified in many different places. They can be listed directly on the part, in the notes section or in the general tolerance block.

When the chamfers are small, at times they will be listed as a break edge.

Spotfaces

spotface example on mechanical blueprint drawing
Spotface callout example

Spotfaces are a small counterbore that is machined so that a fastener can sit flat on the part. They are essentially just shallow counterbores and will be dimensioned as such.

Bolt hole circles

basic dimensions for a bolt hole circle
Bolt hole circle callout example

A bolt hole circle will be shown on a print using multiple dimensions. This will include the size of the individual holes, the angle between the center of the bolt hole circle and the individual holes along with the size of the bolt hole circle itself.

Knurling

knurling blueprint callout examples
Knurling callout examples

Knurling is a textured pattern on a part. It is added for visual appeal or added grip. Knurls will be called out by the pitch, diameter, and type of knurling.

Surface finish/surface roughness

Surface Finish Blueprint GD&T Symbol check mark
Surface finish/roughness symbol

The surface finish quality is specified with the use of a check mark on the surface. The number above the start of the check is the required surface finish. If there are two numbers present, the surface roughness must fall within the range specified. If only one number is specified, the surface roughness must be less than or equal to the specified value.

Surface finish requirements are frequently specified directly on the applicable surfaces as well as in the notes section and general tolerance block.

Threads

Threads will be specified in either the ISO metric format or Unified National Coarse (UNC) thread format. This article clarifies the details of thread callouts.

Want to learn more?

GD&T is a complicated subject and understanding it correctly can be the difference between a perfect part and scrap.

The best way to learn GD&T is from experienced teachers who can break down the material into manageable pieces.

Luckily, we know someone.

And MachinistGuides.com readers get an exclusive discount on training!

Related articles

Complete Guide to Machining Blueprint Symbols

Common Blueprint Symbols

nominal size dimension with a tolerance

Nominal Size

In the example shown, 24 is the nominal size. It is the size that the tolerance envelope is based on. A reference/starting point.

plus or minus symbol

Plus or Minus

Plus or minus is the most common tolerance type. They are less common, but tolerances can be all negative, all positive or +/- with enequal sizes such as +3/-2.

45 degrees

Degree Symbol

The symbol used to callout angle requirements.

Reference dimensions are shown in parentheses. They are provided for informational use only. They are not size requirements but often help make the print easier to understand.

Symbols For Features

Radius Blueprint GD&T Symbol r

Radii

Half of a circle. The distance from the center of a circle to the edge.

Diameter Blueprint GD&T Symbol o with line through it

Diameters

The distance all the way across a circle. Two times the radius. This symbol gets used with other symbols as well such as counterbores, countersinks, and true position callouts.

Depth Blueprint GD&T Symbol line with arrow pointing down

Depth of

This symbol specifies the depth of a feature.

A counterbore is a flat bottomed, recessed hole.

Countersinks are a round, angled feature added to a hole. They are often used to allow a screw head or other fastener to sit flush with the surface.

A spotface is  a shallow counterbore that allows a fastener to sit straight. The symbol has a few variations that get used. Often the counterbore symbol portion is left out and the SF is used only.

Surface Finish Blueprint GD&T Symbol check mark

Surface Texture

A symbol for defining the surface finish of a part. There are many variations of the surface texture symbol but most often it is used with a microinch or micrometer value callout that specifies the roughness of a surface.

Symbols Used In GD&T Callouts

Basic dimensions represent a  theoretically perfect feature or size. They are shown enclosed in a box and are the basis for many GD&T callouts.

Datums are features that are used to locate a part for measurement. 

Feature control frames contain a geometric dimensioning and tolerance callout.

The example shown reads, the feature is perpendicular to within 0.001 to datum A.

GD&T Symbols

Symbols For Roundness

Circularity Blueprint GD&T Symbol circle

Circularity

Otherwise known as roundness. Circularity only applies at one location. You might check the roundness of a hole at a specific depth.

Cylindricity Blueprint GD&T Symbol circle with two lines coming off it

Cylindricity

Cylindricity is roundness but over all locations of a feature. Cylindricity of a hole would mean the hole must be round at all points.

Symbols Used for Flat Things

Straightness Blueprint GD&T Symbol line

Straightness

A straightforward requirement. The feature must be a straight line within the specified tolerance.

Flatness Blueprint GD&T Symbol parallelogram

Flatness

Similar to straightness but over a whole surface. The high and low of a surface must be within the specified tolerance of each other.

Symbols Used to Control Angles

Perpendicularity Blueprint GD&T Symbol two lines perpendicular to each other

Perpendicularity

Two features must be 90 degrees to each other.

Parallelism Blueprint GD&T Symbol two parallel lines

Parallelism

Two features must run together (180 degrees to each other).

Angularity Blueprint GD&T Symbol two lines at an angle

Angularity

Angularity is used when two features must be have a specific angle between them and the angle between the features is not 90 or 180 degrees.

Symbols Used for Profile

Profile of a Line Blueprint GD&T Symbol half circle not connected

Profile of a Line

Profile of a line controls the shape of a feature. Imagine it as controlling the outline of a feature.

Profile of a Surface Blueprint GD&T Symbol half circle

Profile of a Surface

Profile of a surface controls the shape of a feature but instead of controlling it in one location like profile of a line, it applies to the entire feature surface.

GD&T Symbols That Control Location of a Feature

True Position Blueprint GD&T Symbol target

True Position

Controls location of a feature based on the variation from the basic dimensions.

Concentricity Blueprint GD&T Symbol two concentric circles

Concentricity

A requirement that the centerline or axis of two features are located together. 

Symmetry Blueprint GD&T Symbol three lines

Symmetry

A requirement that a feature must be evenly located based on another feature. Centered based on a feature or location.

Runout Blueprint GD&T Symbol single arrow

Circular Runout

Controls how even a surface is when spun in a circle. 

Total Runout Blueprint GD&T Symbol two arrows

Total Runout

The same as circular runout but at all locations on the feature. Circular runout and total runout have a relationship similar to circularity and cylindricity.

Symbols That Change Tolerance

Maximum Material Condition Blueprint GD&T Symbol m in a circle

Maximum Material Condition

A modifier that can give bonus tolerance based how close or far the features are from nominal size.

Least Material Condition Blueprint GD&T Symbol l in a circle

Least Material Condition

A modifier that can give bonus tolerance based how close or far the features are from nominal size.

Projected Tolerance Zone Blueprint GD&T Symbol p in a circle

Projected Tolerance Zone

Used when a tolerance zone applies outside the boundaries of the physical part.

Regardless of Feature Size Blueprint GD&T Symbol s in a circle

Regardless of Feature Size

The tolerances do not change based on the size of the features. This is the default spec and any tolerance is assumed to be regardless of feature size even if the symbol is not used.

Unequally Disposed Profile Blueprint GD&T Symbol U in a circle

Unequally Disposed Tolerance Zone

Profile tolerance zones are normally centered on the nominal dimensions. When this is not the case, the unequally disposed tolerance symbol is used to move the tolerance zone based off the nominal dimensions.

Want to learn more?

GD&T is a complicated subject and understanding it correctly can be the difference between a perfect part and scrap.

The best way to learn GD&T is from experienced teachers who can break down the material into manageable pieces.

Luckily, we know someone.

And MachinistGuides.com readers get an exclusive discount on training!

Guide to Holes on Blueprints [Types, Symbols & Features]

Hole types

blind holes blueprint example
3 blind holes specified

Blind holes are holes that get drilled or milled to a specified depth but do not go all the way through the part.

thru hole blueprint example

Thru holes

Thru holes get drilled all the way through a part.

They can be specified as “thru” as shown in the example or the blueprint can make it clear visually that the hole goes all the way through the part.

cutaway example of blind and thru holes
3 blind holes and 1 thru hole

Blind holes vs thru holes

This picture of a part cut in half shows the difference between a thru hole and a blind hole. The three holes on the left are blind holes which do not break through to the other surface.

The thru hole on the right goes all the way through the part.

Symbols used to dimension holes

Diameter Blueprint GD&T Symbol o with line through it

Diameter

The diameter of the hole is the size. The diameter is the distance across the hole.

Radius Blueprint GD&T Symbol r

Radii

Less often, holes are specified with a radial dimension instead of a diameter. The radius is the distance from the center of the hole to the edge of the hole. This is equal to 1/2 of the diameter.

Depth Blueprint GD&T Symbol line with arrow pointing down

Depth

The depth of the hole is the distance that it is drilled to. 

Features associated with holes

Counterbore Blueprint GD&T Symbol u shape

Holes often get counterbores that allow a fastener such as a bolt head to be recessed. 

Holes with a counterbore will specify the size and depth of the hole as well as the size and depth of the counterbore.

Countersink Blueprint GD&T Symbol two lines pointing down

Countersinks get added to holes as either a way to specify a chamfer for protective purposes or to allow a fastener such as a screw head to be recessed.

Holes with a countersink will specify the size and depth of the hole as well as the size and angle of the countersink.

Spotface Blueprint GD&T Symbol SF in a u

Spotfaces are functionally no different than a counterbore. They are machined on a part to allow a fastener to sit flush, though not always completely recessed.

Holes with a spotface will specify the size and depth of the holes as well as the size and depth of the spotface.

Note: spotfaces are not always specified with the symbol shown. At times, they will only use the counterbore symbol and other times they will use the SF notation only.

Want to learn more?

GD&T is a complicated subject and understanding it correctly can be the difference between a perfect part and scrap.

The best way to learn GD&T is from experienced teachers who can break down the material into manageable pieces.

Luckily, we know someone.

And MachinistGuides.com readers get an exclusive discount on training!

GD&T Symbols – A Beginner’s Guide

Geometric dimensioning and tolerancing (GD&T) consists of a set of symbols and rules for applying them that communicates the requirements of an engineering blueprint.

GD&T controls variations of size, form, orientation, location and runout individually or in combination.

For help understanding even the most complex GD&T concepts, get comprehensive and practical training with an exclusive discount for MachinistGuides.com readers!

GD&T and Engineering Blueprint Symbols

True Position Blueprint GD&T Symbol target

True Position

Controls how far a feature can deviate from a given location.

Straightness Blueprint GD&T Symbol line

Straightness

A tolerance given that defines how far from a perfect line a feature can be. A 2D (line) requirement. 

Flatness Blueprint GD&T Symbol parallelogram

Flatness

Similar to straightness but the callout applies over the entire surface (plane).

Perpendicularity Blueprint GD&T Symbol two lines perpendicular to each other

Perpendicularity

Defines the maximum allowed deviation of a feature from 90°.

Parallelism Blueprint GD&T Symbol two parallel lines

Parallelism

Describes two features that are equally distanced from each other over their entire surfaces. 

Angularity Blueprint GD&T Symbol two lines at an angle

Angularity

Angularity is the allowed deviation from a theoretically perfect feature at a specified angle other than 90° or 180° from another feature.

Runout Blueprint GD&T Symbol single arrow

Circular Runout

Controls the runout of a rotated circular at any single location on the feature.

Total Runout Blueprint GD&T Symbol two arrows

Total Runout

Controls the runout of a rotated circular at all locations on the feature.

Profile of a Line Blueprint GD&T Symbol half circle not connected

Profile of a Line

A tolerance that identifies how close to a specified design a feature is at specific cross section.

Profile of a Surface Blueprint GD&T Symbol half circle

Profile of a Surface

A tolerance that identifies how close to a specified design a whole feature is.

Circularity Blueprint GD&T Symbol circle

Circularity

A tolerance that defines how round a feature must be at a single location.

Cylindricity Blueprint GD&T Symbol circle with two lines coming off it

Cylindricity

Similar to circularity but it applies over the entire cylinder instead of at a single point.

Concentricity Blueprint GD&T Symbol two concentric circles

Concentricity

A requirement that the centerline or axis of two features are located within a specified tolerance of each other.

Symmetry Blueprint GD&T Symbol three lines

Symmetry

Controls the location of a feature such as a slot to a datum.

Envelope Requirement Blueprint GD&T Symbol e in a circle

Envelope Requirement

Specifies that the feature may not exceed the minimum or maximum total size requirement. This applies at each cross section as well as over the entire feature.

Free State Blueprint GD&T Symbol f in a circle

Free State

For non-rigid parts, the specified GD&T requirements apply when the part is in a free state, where only the force of gravity is affecting the part.

Independency Blueprint GD&T Symbol i in a circle

Independency

Removes the form control for a feature. When independency is called out the feature size is controlled only by the attached requirement.

Least Material Condition Blueprint GD&T Symbol l in a circle

Least Material Condition (LMC)

A modifier that can give bonus tolerance based how close or far the features are from nominal size.

Maximum Material Condition Blueprint GD&T Symbol m in a circle

Maximum Material Condition (MMC)

A modifier that can give bonus tolerance based how close or far the features are from nominal size.

Projected Tolerance Zone Blueprint GD&T Symbol p in a circle

Projected Tolerance Zone

Used when a tolerance zone applies outside the boundaries of the physical part.

Regardless of Feature Size Blueprint GD&T Symbol s in a circle

Regardless of Feature Size (RFS)

The tolerances do not change based on the size of the features. This is an older symbol that is no longer used. This condition is assumed unless specified otherwise now.

Tangent Plane Blueprint GD&T Symbol t in a circle

Tangent Plane

Creates a plane based on the highest contact points of a feature. 

Unequally Disposed Profile Blueprint GD&T Symbol U in a circle

Unequally Disposed Profile

Profile tolerance zones are normally centered on the nominal dimensions. When this is not the case, the unequally disposed tolerance symbol is used to move the tolerance zone based off the nominal dimensions.

Continuous Feature Blueprint GD&T Symbol cf in a hexagon

Continuous Feature

Identifies two or more separate features that should be treated as one such as two planes separated by a keyway.

Statistical Tolerance Blueprint GD&T Symbol st in a hexagon

Statistical Tolerance

Specifies that statistical process controls can be used which may be more cost effective in some situations.

Slope Blueprint GD&T Symbol triangle

Slope

Identifies the rise over run of a feature. Shown as a ratio.

Conical Taper Blueprint GD&T Symbol triangle with line through it

Conical Taper

The ratio of size difference between two diameter sections.

Target Point Blueprint GD&T Symbol x

Datum Target Point

A single point that is to be used as a datum or as part of a datum.

A basic dimension is a theoretically exact dimension used to calculate GD&T tolerances. Shown enclosed in a box. Older blueprints may identify the feature with BSC instead.

Reference dimensions are shown in parentheses. They are not blueprint requirements. They are shown for informational purposes only.

Arc Length Blueprint GD&T Symbol number with an arc over it

Arc Length

Describes the length along an arc. Measures the distance around the outside of the arc. It is not a chord length.

Dimension Not to Scale Blueprint GD&T Symbol number with line underneath

Dimension Not to Scale

Features are not shown with the same relative scale for all features.

Square Blueprint GD&T Symbol

Square

Identifies a feature that has equal sizes for both length and width. 

Diameter Blueprint GD&T Symbol o with line through it

Diameter

The distance across the center of a circle. Two times the radius.

Radius Blueprint GD&T Symbol r

Radius

Half of the diameter. The distance from the center of a circle to the edge.

Spherical Diameter Blueprint GD&T Symbol s and o with a line through it

Spherical Diameter

A sphere or ball shaped feature specified by the diameter of the sphere.

Spherical Radius Blueprint GD&T Symbol SR

Spherical Radius

A sphere or ball shaped feature specified by the distance from the center of the sphere to the outside.

Controlled Radius Blueprint GD&T Symbol cr

Controlled Radius

A radius without flats or reversals.

Common Tolerance Zone Blueprint GD&T Symbol cz

Common Tolerance Zone

Identifies two or more separate features that should be treated as one such as two planes separated by a keyway.

Datum Blueprint GD&T Symbol a in a box with arrow

Datum

A feature which is used for location and measurement of other features.

A flat bottomed, recessed hole

A round, angled feature that allows a fastener such as a screw head to sit flush or below the surface.

A shallow counterbore. Shown as on simply SF on some blueprints.

Depth Blueprint GD&T Symbol line with arrow pointing down

Depth of

Identifies how deep a feature is. Commonly applied to holes, counterbores, etc.

Surface Finish Blueprint GD&T Symbol check mark

Surface Finish

Describes the surface texture or roughness of a surface. Can be specified as a max allowable roughness as  shown above or a range.

Places Blueprint GD&T Symbol 4x or 4 pl.

Number of Places

An identifier that lists the number of instances of a repeated feature.

All Around Blueprint GD&T Symbol a bent arrow with a circle at the bend

All Around

Identifies that a requirement applies around the entire perimeter (edge) of the part.

All Over Blueprint GD&T Symbol a bent arrow with two circles at the bend

All Over

Identifies that a requirement applies to all surfaces and features of a part.

Translation Blueprint GD&T Symbol triangle

Datum Translation

Allows the identified datum locating feature to be adjusted so that the feature is fully engaged.

Movable Datum Target Blueprint GD&T Symbol circle with A1 in it and lines coming off

Movable Datum Target

Identifies datum targets that may be shifted in a specified direction.

Dynamic Profile Blueprint GD&T Symbol triangle

Dynamic Profile Tolerance Zone

Controls the form of a feature. When the dynamic profile modifier is used, the profile callout does not control the size of the feature.

Datum Target Blueprint GD&T Symbol circle with diameter 3 in top and A1 in bottom half

Datum Target

The top section is the size and shape of the target area. The lower section lists the identifying letter and number.

From-To Blueprint GD&T Symbol arrow

From-To

Indicates a gradual change in tolerance between two points. The arrow points in the direction of the tolerance change.

Between Blueprint GD&T Symbol line with arrows on both ends

Between

Feature requirements apply between two specified locations.

Dimension Origin Blueprint GD&T Symbol cross hair with arrow

Dimension Origin

Indicates the feature that another feature should be measured from. Often used to indicate a measurement should be taken from a shorter surface.

Frequently asked questions

What does GD&T stand for?

GD&T stands for geometric dimensioning and tolerancing. 

What is GD&T used for?

GD&T is a way for engineers and designers to more accurately control features and tolerances on manufacturing drawings.

GD&T allows designers to place only the needed controls and tolerances on features which reduces cost and complexity of components.

GD&T is critical for designing mating parts and assemblies effectively. 

What are the 5 categories of GD&T callouts?

The categories of GD&T symbols are form, profile, orientation, location and runout.

In addition there are a large amount of supplementary symbols which are used to identify blueprint requirements.

What standards control GD&T use?

There are two main standards which govern the use of various GD&T symbols.

ASME Y14.5 is the main standard referenced and the current revision is the 2018 version of the standard. The standard is commonly referred to as ASME Y14.5-2018 or on occasion simply, Y14.5-2018.

There are multiple ISO standards which govern the use of symbols and their interpretation. ISO 8015, ISO 1101 and ISO 2768 are the three most common standards that detail GD&T use and interpretation.

How to read a GD&T callout

feature control frame description with parts identified

A GD&T callout comes in the form of a feature control frame.

Feature control frames are read from left to right.

It reads “Type of control” of “Tolerance” to Datum. It should be noted that if a diameter symbol is present before “Tolerance” then it indicates the shape of the tolerance zone is cylindrical.

Here are a couple examples with description of how to read them:

true position callout

True position of 0.2 to datums A and B

perpendicularity callout example with feature control frame

Perpendicularity of 0.001 to datum A

What is the best way to learn GD&T?

GD&T is a complicated subject and understanding it correctly can be the difference between a perfect part and scrap.

The best way to learn GD&T is from experienced teachers who can break down the material into manageable pieces.

Luckily, we know someone.

And MachinistGuides.com readers get an exclusive discount on training!

Dial vs Digital Calipers – Which Is Better?

Somebody is going to get mad about this one. I just know it.

I have had many discussions with coworkers over the advantages and disadvantages of dial vs digital calipers.

What I have learned is that most people have a preference and that there isn’t anything that will change it. I am going to try and put aside any preference I have as I outline the differences between these two types of calipers.

Keep reading to find out more about the differences between digital and dial calipers. When you’re done, maybe you’ll have your own preference. But please, keep a more open mind than my coworkers.

What is a dial caliper?

A dial caliper is a mechanical inspection tool for measuring sizes accurately. Most models are capable of taking internal, external, step and depth measurements to an accuracy of +/- .001” or +/- .02mm.

The most common variety measures from 0-6” but they come in many different measuring ranges including 0-4”, 0-8”, 0-12” and 0-24”.

They can take quick measurements and are a very versatile inspection tool. For many machinists, a set of calipers will be the most frequently used measurement device.

The biggest differentiator for a dial caliper is the rack and pinion system which drives the indicator needle seen on the dial face.

Advantages

  • No batteries required
  • Tried and true design

Disadvantages

  • Can’t switch between inches and mm

What is a digital caliper?

mitutoyo digital caliper display in inches
Mitutoyo Digital Caliper

Digital calipers are the same sort of inspection tool as a dial caliper. They have similar accuracies and are available in comparable measuring ranges.

The main difference is that digital calipers require batteries which power their LCD display. The difference in displays between a dial and digital caliper can be thought of as the same as the difference between a standard analog clock and a digital version.

Advantages

  • Instant measurements
  • Can measure inches and mm

Disadvantages

  • Dead batteries
  • Electronics susceptible to damage

Are dial calipers more accurate than digital?

This can be a tricky question to answer because there are so many different models and manufacturers of both dial and digital calipers out there. In saying that, the short answer is no.

When comparing dial and digital calipers from the same manufacturer there is generally no difference in the accuracy of the tool.

Are digital calipers easier to use than dial calipers?

igaging ip54 digital caliper display mm
Digital Caliper Display - Notice the Button to Switch Between Units

Yes, digital calipers are easier to use than dial calipers. This is because the LCD display gives readings that can be instantly interpreted. Dial calipers require reading both the dial face as well as the scale to determine your measurement value.

Another added benefit of digital calipers that makes them easier to use is that most models are capable of switching between inches and mm at the push of a button. This saves the user from needing to convert measurements to another form of units.

This is an excellent feature for many users because it removes a step from the process which cuts down on the time needed to take a measurement. Removing the conversion step also eliminates the possibility that an error is made in the conversion calculation.

How to adjust or zero a dial caliper

parts of a caliper

To adjust a dial caliper, move the caliper until the jaws are closed.

Once in the zero position, check reading on the indicator needle. If it lines up on zero, then no adjustment is needed. You can proceed to verifying the tools repeatability as noted below.

If it does not line up on zero, loosen the bezel lock screw and turn the dial face until it lines up on zero. Once aligned, tighten the lock screw.

Now open and close the jaws to verify that the caliper repeatedly returns a zero reading.

Once this is verified, if available use a set of known reference standards such as a gauge block set to verify different readings across the calipers measuring range. For a 0-6” caliper, 0”, 2”, 4” and 6” would be a good start.

After the tool has been verified as accurate across its measuring range, you can proceed to take your part measurements.

How to adjust or zero a digital caliper

parts of adoric digital caliper

To adjust a digital caliper, move the caliper until the jaws are closed.

Once in the zero position, check reading on the digital display. If the display reads zero, then no adjustment is needed. You can proceed to verifying the tools repeatability as noted below.

If it does not read zero, press the zero button, sometimes identified as the origin button on some calipers.

Now open and close the jaws to verify that the caliper repeatedly returns a zero reading on its display.

Once this is verified, if available use a set of known reference standards such as a gauge block set to verify different readings across the calipers measuring range. For a 0-6” caliper, 0”, 2”, 4” and 6” would be a good start.

Once the tool has been verified as accurate, you can proceed to take your part measurements.

Things to consider when purchasing dial or digital calipers

Accuracy

Dial and digital calipers have comparable accuracies. There is some variation between makes and models of calipers, but most are accurate to +/- .001” or +/- .02mm. If you need something more accurate then you will likely need to look into purchasing a quality micrometer or micrometer set.

Most micrometers are accurate to +/- .0001” which makes them ten times more accurate than a typical caliper. The downfall is that they are more specialized and therefore are only capable of taking a single type of measurement (inside, outside, etc.) and have a smaller measuring range which is why a micrometer set is often needed to cover the measuring range of a single caliper.

Please note that cheap digital calipers often have reduced accuracy when compared to the usual gauge manufacturers such as Starrett and Mitutoyo. At the very least keep in mind the accuracy you need when purchasing because some of the budget priced tools are only half as accurate.

Measuring units

anytime tools 5 inch dial caliper with inch and metric reading dial
An Example of a Dual Unit Dial Caliper - Notice How It Has Two Indicator Needles

There are exceptions but most dial calipers are capable of measuring in a single set of units, either imperial (inches) or metric units (millimeters).

Some dial calipers are available that take measurements in both types of units, but they are clunky and often can not be calibrated so that both units are accurate. Stick with a single unit version.

Digital calipers are capable of taking measurements in both inches and millimeters while switching between the two at the push of a button. This is one of their primary advantages.

Many models are also able to take fractional measurements which can come in handy for some applications.

Measuring range

The measuring range of digital and dial calipers is similar. The most common version for both is a 6” caliper. Additionally, they can be found in ranges from 0-3” all the way up to 0-24” and beyond. Most will not find a need for measuring over 24”.

One point to keep in mind is that the cost goes up and the ease of use goes down as the caliper gets longer. For this reason, it is recommended to have multiple sets of calipers if you need to measure large sizes.

Imagine trying to measure a two-inch hole with a 0-24” caliper. It is going to be awkward and can easily lead to erroneous measurements. If you are in need of a set capable of measuring larger than six inches, then think about purchasing a quality 0-6” caliper as well as a 0-12” or 0-24” set.

The six-inch set will get the majority of the work and be easy to use and the larger set can be pulled out for use when the time is right.

Batteries

button cell battery for micrometer
Digital Caliper Battery Example

Dial calipers do not require batteries. This means they will always be ready to use, no matter how long they sit in your toolbox between uses.

Digital calipers on the other hand do require batteries and unfortunately not the types most people keep on hand.

Digital calipers typically use a LR44, SR44 or CR2032 battery. They are available at most department stores as well as online.

Modern digital calipers, especially the high-quality ones from Starrett and Mitutoyo, have extremely long battery life. Many people have reported going years between battery changes with a Mitutoyo digital caliper.

For peace of mind think about keeping an extra battery or two around in your toolbox or junk drawer if you decide to go with a digital caliper. This way it will always be ready to use when you need it.

Cases

VINCA digital caliper in case unwrapped
Digital Caliper with Case

Both dial and digital calipers are precision measuring instruments. You will find that most are built well and have no problem handling everyday use.

Unfortunately, the precision nature of these tools means that they are susceptible to damage from contamination such as coolant, oil, or metal chips as well as damage from physical shock.

A caliper that has been bumped off a workbench or dropped on accident can easily damage the jaws of the caliper or affect the internal workings resulting in invalid readings.

Calibration

gauge block set
Gauge Block Set

Calipers should be calibrated periodically at an interval of your choosing. In a machine shop atmosphere, this will be determined by the company. Normal calibration intervals will range from 3 months to 1 year and everything in between. Some shops will even base the calibration frequency on tool use as opposed to length of time.

For home use, I recommend verifying them before each measurement.

With critical measurements, at home or in the shop, this verification becomes even more important. You don’t want to find out that your engine was bored oversize because you neglected to check your caliper before using it right?

Verify your tools and if possible check them against a known calibrated standard such as a set of gauge blocks.

For more info on caliper calibration, please see our post on the Complete Guide to Caliper Calibration.

Calibration certificates

Some of the caliper manufacturers and resellers offer a calibration certificate with their tool. My recommendation would be to skip this unnecessary add-on.

At a minimum you should be verifying your tool when you receive it. Ideally, you would calibrate the tool yourself with a set of calibrated gage blocks.

A calibration certificate will only serve as proof that the caliper was accurate at the time of calibration. Since many tools get ordered online or through a catalog, the tool will get be in a shipping company’s hand between the time of calibration and when you receive it. They aren’t always known for being gentle.

A calibration certificate doesn’t provide much peace of mind when buying a new tool. It should be accurate anyways, that is what you bought it for after all. It would be better to take the added expense of calibration and apply it towards a set of gauge blocks or other reference standard.

Depth base attachments

caliper depth base attachment

Depth measurements with a caliper can be quite tricky. The size and shape of the tool means it is top heavy and as a result it can be easy to get incorrect readings when taking depth measurements.

A depth caliper base attachment can help alleviate some of this by providing a wider, more stable base to take your measurements from. Adding one will make it easier to get consistent, accurate readings.

The base provides stability that is more in line with that of a depth micrometer, thought the tool will still be less accurate than a quality depth mic.

Related articles

Beginner’s Guide to Machine Shop Math

title image that shows a triangle drawn on a paper with pencil next to it

How important is math when working in a machine shop?

Math is something that anyone working in a machine shop will use on a daily basis.

The good news is that everything you need to know can be learned on the job and it isn’t too difficult.

Basic middle school level math skills can take you quite far with machining.

Find out which math skills are the most important and how to do them.

What type of math is used in machining?

a speech bubble that shows how machinists speak
Say what?

First, I want to point out that learning to speak like a machinist isn’t a math skill necessarily, but it is a skill that anyone working in a machine shop will need to have to do math in the shop.

Our guide to learning how to talk like a machinist teaches you the differences between machining terms such as “thou” or “tenth” and how they compare to normal math terms you may have already learned.

Now on to the real math!

Easy math skills

The math skills needed by a machinist are pretty simple, with a few exceptions. Luckily, a good calculator and a cheat sheet of common formulas (like the one provided below) will make almost all the math used in a machine shop easy enough for just about anyone to solve.

1+1=? written on chalkboard
The easy stuff really is this easy

A large portion of the math you will need to do when machining is working with decimals. If you can do the following operations while working with decimals, you will have a solid start to learning machine shop math:

  • Addition
  • Subtraction
  • Multiplication
  • Division

Addition and subtraction are regularly used to calculate the top and bottom of your part tolerance.

Multiplication and division are used to convert between units such as taking a metric value and converting it into inches.

This is easy stuff to do with a calculator, which you should have by the way.

Speaking of calculators, I recommend going with an actual calculator and not just using your phone. You will look much more professional using an actual calculator. It won’t matter if you are using your smartphone for calculating setups and offsets, people are going to assume you are watching cat videos.

There are some good, specialized calculators for machining, but a cheap Texas Instruments calculator will do everything you need it to.

Unless you know you want a calculator with special functions for machining, it’s best to start out with something like a TI-30 series calculator.

One last easy one that helps is knowing how to calculate the decimal equivalent of various fractions. Again, this is simple to do with a calculator. Quick reference cheat sheets work well also.

Harder math skills

On to the fun stuff! 

I say that jokingly because I know that many are scared to even say these words:

  • Trigonometry
  • Geometry
  • Algebra

But they really aren’t that bad, especially because there are so many resources available to make them easier.

Take for example trigonometry.

Trigonometry is math for working with triangles. Sure, some people will use it frequently working in a machine shop, but there are tons of online calculators that basically make it a no brainer. And to top it off, you will only really use a handful of formulas anyways.

Geometry is no different than trig. Knowing where to find the formula or an online calculator is half the battle.

Most shops will have a trusty reference book such as Machinery’s Handbook or another good machining textbook available with all the formulas you will need. If not, luckily Google will usually turn up anything you need pretty quick.

You'll use the same formulas over and over so just keep practicing

Algebra is probably the most difficult math you will work with if you aren’t very good at math. A little bit of rearranging equations goes a long way.

And honestly, even if you will never be good at algebra, you can go pretty far in the machine trade.

There are multiple online algebra calculators/solvers to help you solve those equations without breaking a sweat. What did we do before the internet?

Lastly, statistics gets used in manufacturing, but in most instances this is something left to higher level engineers and/or management. It’s not something that anyone just starting out in a machine shop should be worried about.

What can you use to make machine shop math easier?

I touched on it earlier, but skip the slide rule and get a good calculator!

After that, bookmark some handy references whether they are online or in an actual book.

Lastly, just practice. The more you use the types of math that get used in a machine shop, the better you will get. 

Bookmark the best resources and practice to master machine shop math.

If you want the easy button instead…

Focus on the most important stuff first.

You need to know how to do a limited number of calculations.

Hit the “easy button” for Machine Shop Math and find out what you really need to know.

Don't overthink it, take the easy route

Other resources

Common machining formulas

Speeds and feeds formulas – Make sure you don’t mix inches and mm! Always stay in the same units

  • Feed rate (inches per minute) = RPM x feed per tooth x number of teeth/flutes in cutter
  • Surface feet per minute = RPM x diameter of cutter / 3.82
  • RPM = surface feet per minute x 3.82 / diameter of cutter
  • Inches per Tooth = inches per minute / RPM / number of teeth/flutes in cutter

 

Conversion formulas

  • Inches = mm / 25.4
  • MM = inches x 25.4
  • Diameter = radius x 2
  • Radius = diameter / 2

Best online calculators for machine shop math