Geometric Dimensioning and Tolerancing Font – GD&T Keyboard Shortcuts

How to insert symbols into a Microsoft Word document

To insert GD&T symbols into Word, take note of the codes in the table below.

There are two types of symbols below. Some are alt codes (ALT+248) and some are Unicode characters (25B1 then ALT+X). Alt codes are entered by holding the ALT key and pressing the number code. Unicode characters are entered by typing the code and then holding the ALT key and pressing X.

How to insert GD&T symbols into a Microsoft Excel document

Not all the codes work in Excel. The ALT codes (ALT+248 style) work but the Unicode characters (25B1 then ALT+X style) do not. The best way to insert the GD&T symbols into Excel is to copy and paste the symbols.

GD&T Symbols Alt Codes

Symbol Name

Symbol

Code

Straightness

ALT+22

Flatness

25B1 - ALT+X

Circularity

25EF – ALT+X

Cylindricity

232D – ALT+X

Profile of a Line

ALT+239

Profile of a Surface

2313 – ALT+X

Angularity

2220 – ALT+X

Perpendicularity

ALT+8869

Parallelism

//

2225 – ALT+X

True Position

2316 – ALT+X

Concentricity

ALT + 10686

Symmetry

232F – ALT+X

Circular Runout

↗

2197 – ALT+X

Total Runout

2330 – ALT+X

Free state

ALT + 9403

Least material condition

ALT + 9409

Maximum material condition

Ⓜ

ALT + 9410

Projected tolerance zone

ALT + 9413

Regardless of feature size (RFS)

ALT + 9416

Tangent plane

ALT + 9417

Unequally disposed tolerance

ALT + 9418

Common Blueprint Symbol Alt Codes

Symbol Name

Symbol

Code

Degree

°

ALT + 248

Plus or Minus

±

ALT+241

Diameter

Ø

ALT+0216

Depth

ALT + 8615

Greater Than or Equal To

ALT+242

Less Than or Equal To

ALT+243

Counterbore

ALT+9012

Countersink

ALT+9013

Micro

µ

ALT+230

Surface Finish

2713 - ALT+X

Centerline

ALT + 8452

Want to learn more about 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!

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

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

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 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
A 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.

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 used in a machine shop

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.

calculators are good, phones are bad

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.

More difficult math skills used in a machine shop

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. 

Remember, that none of it is too hard and someone has already figured out all of the formulas you will need after all.

Use the formulas listed at the bottom of this post and the calculators that I have linked to hit the “easy button” when it comes to machine shop math.

Don't overthink it, take the easy route

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

Where to Sell Your CNC Projects

person on phone in front of map with pins in it and text that reads best places to sell you cnc projects

Who doesn’t like to earn a little extra dough?

Whether you have a CNC router, laser engraver or plasma cutter, selling your projects locally or online can bring in a pretty penny.

But where is the best place to sell those cool creations?

We picked the best spots to set up shop and turn a tidy profit with tips to help you make the most of each marketplace.

Fire up the CNC, it’s time to make some money!

Best Places to Sell Your CNC Projects

You can sell your products both locally and on the internet. Billions of people buy and sell goods online thanks to the widespread internet access. Here are some of the places you should explore:

Facebook Marketplace

hand holding a phone that shows the facebook login page

Facebook Marketplace is one of the best and easiest ways to market your CNC projects to a local audience for free.

Through the marketplace, people can browse through your product portfolio and message or call you with offers. Getting started is super easy, especially if you’re already a Facebook user. You can use your personal account or create one for your business.

All you need are a couple nice pictures of your CNC projects, a thorough description of the products, their conditions (new), price, and where willing buyers can pick them from.

The pictures are very important because they are what will help get people to share and tag others on your listing. Spend a little time getting good pictures.

Locally, it is best to meet buyers face to face and cash is always best. You can sell and ship products through Facebook Marketplace, but Facebook charges a 5% fee.

Tip: Be careful accepting some forms of payment such as PayPal or Venmo. People have been known to dispute transactions leaving sellers without their payment or their product.

Craigslist

Craigslist has been around since 1995 and is still one of the most popular online marketplaces to sell all sorts of items. This makes it a great place to sell your CNC projects and best of all there is not cost for selling.

It has taken a hit in popularity since the introduction of Facebook Marketplace, but plenty of buyers and sellers still use the site.

Creating a Craigslist ad is so simple that you don’t even need a Craigslist account.

How to list your CNC projects on Craigslist

  • Go to the Craigslist website and set it to your current city or area
  • Click on the ‘Create a Posting’ link
  • Answer ‘what type of posting is this’. In your case select ‘ for sale by owner’
  • Select your item category. For you that would be ‘furniture by owner’ or ‘arts & craft’
  • Write a clear and precise product description. Add price. Provide your contact information. Add mode of payment. Always prefer cash transactions. Meeting your customers face to face is safer.
  • Upload photos of your project and publish your ad.
the new york craigslist home page

Once posted you will simply need to monitor your email for interested buyers.

Craigslist is a great zero fee option for selling CNC products online locally.

Craft Fairs

Craft fairs or craft shows are local craft events organized for artists to showcase and sell their products. Craft fairs are a superb way to show off your brand to the locals and hopefully make some sales while you’re at it.

CNC products can get a lot of attention at craft fairs because often there isn’t much competition. Many of the other vendors at the show will be focused on things such as jewelry, knitting and painting.

Get your products to stand out and put yourself out there and you can make sales even after the fair is over. Craft shows allow you to bring your CNC projects to the masses, network with peers, and acquire a new set of skills and techniques.

Most craft fairs and shows will charge a fee to display your wares. They can range from $10 to hundreds of dollars, it varies a lot by event. Bigger venues with more traffic are going to be more costly to attend but they also have the potential for much larger sales.

Some tips for selling at craft fairs:

  • Make sure that you’re adequately prepared before the show
  • Be friendly with your potential customers. Friendly conversation is a great way to generate sales.
  • Showcase your best work so more people come visit your booth or table.
  • Pricing your products correctly can be tricky, but don’t undercut yourself. Make sure you are turning a profit and account for your time as well.
  • Keep track of what sells. Keeping good records will help you plan for future events.
  • Hand out your business cards to increase your brand awareness.

Flea Markets

various things for sale at a flea market

Flea market are an outdoor street market where organizers rent spaces to vendors to sell their products. Some events will be indoors, but most flea markets are done outside in the warmer months.

Vendors commonly sell secondhand or used products at flea markets, but this doesn’t mean your unique brand-new CNC creations can’t be sold. You can make a pretty penny selling your CNC projects at flea markets the same way you would at craft shows.

Flea markets tend to have lower space rental fees which can increase your overall profits.

Many flea markets are temporary and open mainly in the summer late spring to early fall depending on your local climate. Some of the larger markets will be open year-round.

Renting a space in a flea markets will vary in cost much like craft fairs but can be anywhere between $10 to a couple hundred.

Tip: Check local newspapers and Facebook groups to find nearby markets to sell your wares and don’t be afraid to ask your friends and family if they have visited any that were particularly busy.

Craft Stores

Craft stores can be an interesting and extremely profitable proposition if done right.

The first step is finding a good craft store. A quick Google of “craft stores near me” may do the trick. Another good way to find the best craft stores to sell your projects is by talking to other sellers at events. This is only one of the reasons why networking with other makers is helpful.

Not all craft stores are created equal. They vary in the type and amount of fees they charge as well as their rules. Some may be strict on keeping your product stocked and others might not allow you to setup shop if someone else is already selling similar products there.

All this means you need to put some boots on the ground and get out there and check some local shops out. The best ones are close to you for easy stocking or not far from your normal commute.

Don’t be afraid to ask shop owners for suggestions to increase your sales. They see firsthand what people want and it will be best to stay on their good side after all.

Our best tip is to try out multiple craft stores over time and find out which ones work best for you and your product. Different locales will have varying tastes that may or may not cater to your specific product. Find your target market.

Yard Sales

yard sale sign on a mailbox with people browsing in the background

Think of it like a pop-up craft store and a good excuse to get rid of some stuff you don’t need at the same time. A good old fashion garage sale can be an excellent opportunity to kick start your side hustle.

Even better if you are near an area that gets a decent amount of traffic. If possible put up signs to advertise that are easy to read at a distance. Some towns or cities even hold town wide yard sales which brings even more traffic and potential customers in.

Make sure you price everything ahead of time and expect people to negotiate. Seriously, people can be brutal. I once saw an old lady offer a dime for a $10 item. And it sold! Don’t be afraid to stand firm on your prices as they won’t be normal yard sale fare but giving in a little is likely to improve your overall sales numbers.

Special events

people browsing tents at a special event

Local festivals, fairs, and events offer valuable opportunities to sell your CNC projects. Often people are in a happy mood and ready to buy more than they usually would.

What might seem like a small town event can be huge for the local community and bring out a large portion of the population. More eyes on your products means more potential customers.

Fees to set up shop at these types of events tends to be low so take advantage and make a killing even if the event is only once per year.

Some sample events to look for that usually have vendor spots available:

  • State, county and local fairs
  • Holiday events such as Halloween and 4th of July
  • Farmers markets
  • Chili cook offs
  • Food truck festivals
  • Music festivals

Etsy

Laptop computer displaying logo of Etsy

Etsy is a popular global marketplace for artisans with nearly 82 million monthly active users. The platform is dedicated to sellers and buyers of “handmade, vintage, custom, and unique” products.

This platform is crawling with buyers who are willing to splurge on unique items on sale. Don’t expect cookie cutter type products to do well here.

Your best bet to gain customers on Etsy is to highly customize your art to make sure nothing like it exists on the platform or any other place. When done correctly, sellers can often get top dollar for their products.

The best products on Etsy are unique. Etsy is a great market to sell products that cater to a specific audience. Custom board game tiles, 3d topographic maps of specific locales and personalized products of all kinds are just some examples of the types of things sold on Etsy.

Having the right product to list might not be simple but creating an Etsy account is super easy:

  • On the Etsy, landing page click the ‘Sell on Etsy’ link
  • Edit your shop’s settings including language, location, and your preferred currency among other customizations
  • Add a creative name that communicates your brand to potential buyers
  • List your products with titles, descriptions, photos, prices and how much inventory you have
  • Add shipping information for your products. Include the shipping fee, where the product is being shipped from, the time it will take to process the order and the weight of the product, and size.
  • Add a payment method. Most electronic payment methods including PayPal are accepted on Etsy. Select your preferred payment method.

Etsy charges a transaction fee of 6.5% for every product sold on its platform.

EBay

magnifying glass looking at ebay website

EBay is huge player in the ecommerce industry. Recent statistics show that EBay is used by nearly 35% of all active US mobile users. That’s a huge group of potential buyers.

EBay also has the potential to open your side hustle up to a global market giving you limitless possibilities.

You can list your item for sale as either a standard bidding auction or for a buy it now price. Buy it now prices tend to work best if you will be consistently offering the same products.

One of the best things about using EBay is how easy it is to set up a listing. Typical EBay listings requires a photo, product description, price, payment method, and shipping information.

EBay does a great job of integrating shipping and keeping the overall shipping cost low which helps drive more sales.

EBay takes a percentage of nearly every sale, ranging from 1.5% and 15%.

Amazon

Amazon logotype printed on cardboard box

Everyone knows Amazon. Over 197 million people around the world visit Amazon.com every month, making it by far, the most popular ecommerce site worldwide.

You can monetize most of your CNC project ideas on Amazon under their different categories and go about creating unique products for the worldwide market.

Furniture, arts & craft, ornaments, customized signs, and personalized nameplates, among others, can sell pretty quickly on Amazon.

Setting up an Amazon listing is simple but you should take care to accurately list your products to make sure that customers get what is expected.

To create a listing you will need to:

  • Adding your product title
  • Uploading high-quality images
  • List any variations of your products i.e. color, measurements, material, et al
  • Create a detailed description of the item including a bulleted summary of the most important features

You may sell your products on your Amazon customer account or create a seller’s account.

Amazon takes a cut of between 6% and 15% of every sale made on the platform. The percentage can go to as high as 45% for Amazon devices accessories.

While the platform is huge. You need to be ready for the potential demand. Because of this, it is best to make sure you have your business running smoothly before selling on Amazon.

Things to consider as a seller

Identifying where you can sell your CNC projects solves only a part of the puzzle. The other equally important part is getting the item ready for sale and shipping.  Even after finding the ideal outlet for your products, there are a couple of things you need to consider when selling. They include:

Project materials and supplies

CNC projects can be created on wood, plastic, light metals (aluminum, brass, and copper), and acrylics among others. You will want to create your projects on high quality materials, but make sure you don’t overpay because buyers like a good bargain as well.

Packaging

First impressions are important. Besides its main job of protecting your product from damage during shipment, the packaging is the first introduction the customer has to your brand.

Make it memorable. This can mean custom printed labels or laser engraved packaging but no matter which way you go try to stand out.

And toss a few business cards in the box. Happy customers are often willing to spread the word of your quality work. Make it easy for them.

Including a card or code that offers 5 or 10% off another purchase can also be a great way to keep the customers you already have coming back for more.

Shipping

Shipping can be costly and makes selling your products a little more complicated. This is why it is a great idea to start locally and work your way up to online only marketplaces.

Pay close attention to the sizes and weights of your products because they can make big changes in your shipping cost which can end up hurting your bottom line.

Warranties and returns

What happens when a product is faulty when it reaches the buyer? Can you refund their money or send them a replacement quickly?

It is bound to happen eventually when you start your own business. Make sure you are prepared for it to happen and act quickly. Quality customer service can make or break the customers opinion of your brand.

Make sure you clearly list your warranty and return policies because you will be expected to follow them and customers take them into account when making purchasing decisions. 

That’s plenty of ideas and tips about where to sell your projects, but what if you don’t know what to build?

Then check out our guide to the Best CNC Projects That Really Sell to kickstart your imagination.

Beginners Guide to Rapid Traverse for CNCs

What is rapid traverse?

Rapid traverse, sometimes referred to as rapid transverse or rapid travel, is used for moving a machine tool around the workpiece as fast as possible. 

Depending on the type of machine tool, this is accomplished in different ways. See below for more information related to CNC and manual machines.

How fast does the machine move in rapid traverse?

industrial cnc machine
Industrial grade CNC mill

First let’s talk about speed.

Rapid traverse speeds vary based on the machine.  A good quality desktop CNC will usually be capable of speeds around 100 inches per minute (IPM).

Larger, industrial grade CNC can often move at speeds of 1,000 inches per minute or more. No matter what type of CNC you are using, you will want to make sure that nothing is in the way when these moves are being made in a CNC machine. 

Crashing a CNC at normal speeds is bad enough, crashing a CNC at rapid speeds could be catastrophic.

Can rapid traverse speed be adjusted?

cnc control board with rapid travel dial identified with arrow
Rapid Override Dial

Most CNC machine controls have an adjustment to dial back the rapid travel speed. This is often referred to as Rapid Override or something similar. This override allows the CNC operator to adjust the rapid speed, usually in the form of a percentage of the full speed.

Some shops need to run full speed. Time is money after all, but many machine shops will dial things back a little for safety.

How does the CNC move during rapid travel?

straight line movement example

Newer CNCs will move in a true straight line fashion, however some older CNCs can process the command in different ways.

Some machines may only move one axis at a time while others will move in other strange ways. The most important thing is to be aware how your specific CNC control will process the rapid travel command and create your program to account for this movement.

Because various machines will process commands in different ways, this means you may not be able to take a program and a setup and run it on a different machine.

What is the G code for rapid traverse?

rapid traverse code example

The G code for rapid movement is G00. This applies to both CNC mills and lathes. In the example above, G00 is the code for rapid traverse and the X and Y values are the position that the machine is to rapidly move to.

Rapid movement can happen in the Z axis as well.

Want to learn more about CNC G codes?

What should you think about when using rapid travel?

When you are zipping your CNC back and forth think about:

  • Part location – it can be easy to forget about a step in your part and attempt to move over the top of you part at a Z height that is too low
  • Fixturing – similar to your part location, remember that you often have clamps, vises, etc. that will be in your machine and it’s best to avoid them
  • Removing material – don’t cut in rapid mode, it will result in size issues and poor surface finishes at best

Rapid traverse in manual machining

bridgeport milling machine with rapid power feed pointed out
Power feed marked by red arrow

Many manual machines, such as a Bridgeport mill, use a power feed to rapidly move around the workpiece. These power feeds are not as fast as a CNCs rapid moves but they are still much quicker than the standard speed which usually involves cranking a handle to position the machine.

Beginners Guide to Micrometer Ratchets [Tips and Tricks for Use]

micrometer ratchets

Click, click, click. 

Is that the sound of a good measurement?

If you follow our guide to using your micrometer ratchet, then maybe. You can’t say we didn’t try.

Some of these tips might just surprise you. After all, it is all the little details coming together that let you get a good reading from your micrometer.

Check them out but remember that no amount of reading will beat some quality time practicing with your mic.

What is the ratchet on a micrometer used for?

Ratchets on a micrometer are used for consistency of measurement. The ratchet allows the micrometer user to apply a consistent amount of force to the tool resulting in more consistent measurements.

Micrometers are capable of taking measurements with a great deal of accuracy, most often to 0.0001” or 0.002mm. That is about 30 times smaller than a human hair.

The ratchet mechanism on a micrometer limits the amount of force that can be applied to applied to the tool.

Imagine taking a measurement with your micrometer by gently closing the tool on the part you are measuring. By doing this you get a measurement reading of 0.5000”.

Now with that same part you twist the thimble as hard as you can. Now the micrometer reads .4995”. Notice how the excess force has caused your reading to change.

 

Closing the micrometer quickly can have the same effect (too much force) and the ratchet mechanism will help in this situation as well.

Ratcheting mechanisms are especially helpful for anyone who is not used to working with a micrometer. The biggest thing to remember is that they aren’t perfect and there are many old micrometers out there with ratchets that don’t function properly.

Take multiple measurements and verify your tool to a known standard such as a calibrated gauge block to give yourself the best chance at an accurate measurement.

Will using a ratchet stop on your micrometer make your measurements more accurate?

This one is tricky.

No, using a ratchet stop will not immediately mean that your readings are more accurate. They can however make it easier to get accurate measurements.

If you are new to working with a micrometers we recommend you use the ratchet mechanism. But don’t assume this removes you from the equation. You should still do your best to be consistent in your measurements.

This means using a fairly gentle and above all consistent amount of force when using your micrometers. Spin it as fast as you want (within reason) until you are just about to contact the part you will measure. Improving the accuracy of your measurements happens in those last few thousandths of an inch.

yellow and black quick tips icon

Count your clicks

To improve your consistency, use the same amount of ratchet clicks when taking your measurements. We recommend starting with three clicks.

Ratchet or not, make sure to take multiple measurements to improve your skill using your micrometer. In fact, with enough practice, many people prefer to use their micrometer without the ratchet and instead relying on their “feel or touch” with the micrometer.

This isn’t beginner level stuff though, it will take some time and practice to develop the touch and even once you have gotten good with your tool, you should still be taking multiple measurements.

It only takes a spec of dust or lint, or a slight twist of your micrometer to give a measurement that is a few “thou” off. A few thousandths can often be the difference between perfect parts and scrap.

Ratchet stops vs friction thimbles

Ratchet stop
micrometer friction thimble example
Friction thimble

Ratchets aren’t the only type of mechanism used on micrometer to improve accuracy. Not only are there multiple types of ratchets with different levels of force, but there are also other options from different manufacturers such as friction thimbles.

With a friction thimble, once a certain amount of force has been applied the thimble will spin freely. No click, click, click.

Friction thimbles are still subject to the same issues as ratchet stops. They still require you to be consistent with the amount of force applied and it is best practice to take multiple measurements.

Friction thimbles, like ratchets, will lessen the effect that the micrometer user will have on their measurements, but they don’t eliminate that effect.

Tips for getting the most accurate measurements with your micrometers

The goal when using a micrometer is always to get the most accurate reading possible. To do this follow the tips below and give yourself the best shot at getting that measurement right on the money each and every time.

Keep it clean

contaminants that affect measurements

Your micrometer, your part, your workspace. Just keep everything clean.

Dirt, grime, lint, and oil are all enemies of accuracy. Clean everything with low lint wipes whenever possible. A quick visual inspection can help you determine whether your tool and part are free of contaminants.

Verify your micrometer

gauge block set
Check your micrometer with gauge blocks regularly

Whenever possible, check your tool at a size as close to the measurement size you are checking as feasible. If you are going to measure a 0.510” thickness, then grab a calibrated 0.500” gauge block and give it a quick check. This will provide some confidence that your tool is functioning correctly.

I always say that you never know what happened to your micrometer when you weren’t looking. Don’t think your kids or coworker wouldn’t knock it on the concrete floor, give a shifty glance around, put it back on your workbench and then walk away never saying a thing.

Right measurements are at right angles

a micrometer measuring a part at 90 degrees

You should be measuring your parts normal, or 90 degrees, to the surface being measured. What this means is that if you try to take a reading and your mic is cock-eyed, then you will get a bad measurement.

When at an angle other than 90 degrees, you will be measuring the hypotenuse of a triangle which will result in a larger than actual measurement.

This can largely be avoided by using a slight, gentle rocking of your micrometer when taking your measurements. With a little practice, you will feel the tool and part settle in and know that you aren’t getting a crooked measurement.

Be consistent

I covered it quite a bit earlier, but it is so important I want to touch on it again.

Consistency is king when it comes to measurement. Practice, practice, practice and you will develop that consistency. Some of it is just muscle memory so grab a known standard such as a gauge block or the standards that come with your mics to practice with. Measuring them over and over will allow you to develop that consistent form and force that will give you the most accurate readings possible.

Take multiple measurements

headline that says check, check and check again

Even the best machine shop inspectors can get a bad reading once. The tolerances are just too tight and the margin of error is too small.

A good inspector might get one bad reading, but you can bet that they won’t get three in a row.

Check your part multiple times to increase your confidence that you got a good reading. If you find that your measurements vary, then practice some more on a known size to work on your feel and form.

Check your tool again when finished measuring

Imagine you just finished taking multiple readings on a dozen parts with your micrometer. What should you do now?

Go check a gauge block! If you don’t have one, then at least check the zero of your micrometer. Too often something can happen to cause your measuring tool to be out of whack.

If you check the tool when you start and check it when you are done then you will only add to the confidence that all the measurements taken in between were accurate.

Safe storage

black plastic case for mitutoyo caliper
Many measuring tools come with plastic cases. Use them!

Take care of those precision measuring tools. If it came with a case, then put it back in the case and stash it in a desk, cabinet or somewhere else out of harms way.

Keep them away from those who would do harm to your precious instruments. I have never known anyone to have regretted putting their tools away and locking them up.

What can a micrometer measure? [Uses and comparisons]

a photo of someone holding a micrometer measuring a part with text that says what can a micrometer measure

Micrometers can measure a large variety of things, but they do have their limitations.

Those limitations are based on their accuracy and their measuring range as well as the type of micrometer.

Because they are specialized measuring tools, you need to make sure that you use micrometers for the right application and wouldn’t be better off with another measuring tool.

How accuracy affects what a micrometer can measure

Accuracy is one of the most important features of a micrometer.

Micrometers are commonly used to measure parts or features of a part, such as its thickness, to a high level of accuracy. Engine components are just one example of the types of highly accurate parts that micrometers are used to check.

Micrometers that read in inches are commonly accurate to +/- 0.0001” while metric micrometers usually measure to +/- 0.002mm.

There are some that do better and some that do worse, but in general most will measure with the above listed accuracy.

Because they are so accurate, they don’t work well for all measurements. For example, if you need to measure a board for a cut and you only need it accurate to 1/16 of an inch (which equals .0625”), then the micrometer is major overkill. It measures 625 times more accurate than you need!

They are slower too. If you only need accuracy of 1/16 of an inch, then bust out the tape measure, take your measurement and keep on trucking.

Micrometer measuring ranges

The other major limitation of a micrometer is its measuring range.

Inch micrometers measure in increments of 1”. So you will have a 0-1”, 0-2”, 0-3” micrometer and so on. This is why micrometers are often sold as a set with 0-3”, 0-6” and 0-12” sets being the most common.

starrett micrometer set in case with reference standards
A 0-6" set of micrometers

Having a set of micrometers allows you to take accurate measurements over a larger range of sizes.

Metric micrometers are found in 25mm increments. 0-25mm, 25-50mm and so on. They too are sold as sets to cover larger measuring ranges.

Basically, a micrometer will take a very accurate measurement at the sacrifice of speed and the range of measurements it is capable of.

For many measuring devices you will find that as the accuracy of the tool gets better, the range it can measure over will get smaller.

Types of micrometers

Micrometers are also called screw gauges. There are many different types of micrometers that use the same screw gauge mechanism to measure different types of features. It’s doubtful you need to know about all of them so let’s stick to the basics.

Standard micrometer

outside micrometer
Analog micrometer
mitutoyo digital micrometer
Digital micrometer

First off is your standard micrometer. If someone simply says micrometer then they are referring to an outside micrometer or ‘mic’.

Outside mics are used to measure external dimensions such as the length, width, or thickness of a part.

They are by far the most common micrometer used.

Inside micrometer

mitutoyo inside micrometer set
Inside micrometer set

Inside micrometers get used to measure internal features such as hole diameters or slot widths. One thing to know about inside mics is that they are often not as accurate as outside micrometers.

The most common accuracy for an inside micrometer is +/- 0.001”.

Depth micrometer

depth micrometer
0-1" Depth micrometer

You are never going guess what a depth micrometer measures. Wait… you already know?!

Well thanks for ruining the surprise.

Depth mics measure the depth of features such as holes or slots. Just like an inside micrometer, they are often not as accurate as outside micrometers and usually measure to an accuracy of +/- 0.001”. Their design also means that they can be easier to get an incorrect measurement.

Practice using them on a known standard such as a gauge block is the best way to get good with them.

Accuracy vs resolution

We’ve talked a lot about the accuracy of micrometers, but we haven’t yet talked about their resolution.

Accuracy is how close to a true measurement the micrometer is capable of.

Resolution is how small the graduations that it can resolve are. At times the resolution of a micrometer, especially digital micrometers, may be better than the accuracy which can lead you to believe that you are measuring to tighter tolerances than you actually are.

When comparing micrometers make sure to pay attention to the accuracy of the tool.

Alternatives to micrometers

When it comes to picking a tool other than a micrometer to use, it all comes back to your accuracy needs and the speed of the measurement.

Let’s discuss the two main alternatives to micrometers:

Calipers

digital caliper measuring gauge block
Set of digital calipers measuring a gauge block

Calipers, whether digital, dial or vernier, are less accurate than micrometers. They typically measure to an accuracy of +/- 0.001”.

But what they sacrifice in accuracy they gain in versatility and speed of measurement.

While micrometers only measure a single type of measurement such as an outside, inside or depth measurement, most calipers will take all three.

They also have a larger measuring range with the most common type being able to take readings from 0-6”. You would need six separate micrometers to match the outside dimension measuring capability of a single set of calipers.

We discussed earlier how micrometers aren’t the fastest measuring tool to use. When compared to calipers this really becomes noticeable. A set of calipers could take dozens of measurements across their entire measuring range in the time it would take to take a few readings with a micrometer.

Calipers compared to micrometers have their advantages and their disadvantages. Pay attention to these differences when deciding which one is right for your measurement.

Dial indicators

dial indicator
Dial test indicator

Dial indicators come in a couple different varieties. First is the dial test indicator.

Dial test indicators are used to take comparison measurements. They get set up or “zeroed” to a known standard such as a stack of gauge blocks and measurements are taken relative to that standard.

A dial test indicator will have a relatively small measuring range, usually measured in thousandths of an inch (0.001”) and will measure to a high degree of accuracy such as 0.0001” or better.

They specialize in taking very accurate measurements repeatedly. If they are used to check a variety of measurements, then they will be quite slow to use because they need to be set up for each different measurement.

mahr drop indicator
Drop indicator

Another type of dial indicator is drop indicator. They most often come with a larger dial face, usually about 2-3” across, and they have larger measuring ranges.

A typical measuring range for a drop indicator is one inch but they do vary and can be smaller or larger. When compared to dial test indicators, they have significantly less accuracy. Most drop indicators are accurate to 0.001”. Their most common application is set up in either a snap gauge or a height stand which allows them to be used to take quick, repetitive measurements.

What is a G21 Code? [With Lots of Examples]

a graphic of a cnc machine with text that says learn g code today G21 metric mode

The information below is meant for beginners. If you are experienced with CNC programming, then you probably already know this stuff and much more. If you are new to CNC programming, this is the place for you.

Please note that some of the topics below could include more information on the subject. However, in the interest of keeping things simple for those just starting out, they have been left out of this G code guide.

Ready to learn? Let’s go.

Code

G21

Name

Metric mode

Type

Modal - stays on until changed

Description

The machine will interpret all size and location values as metric

What does a G21 code do?

A G21 code will switch the CNC into metric mode. Once the G21 code is used, all sizes and locations in the program will be treated as millimeter values until the mode is changed.

This type of G code is called a modal command.

Modal commands remain in effect until they are canceled. This holds true even if you restart your program. Until you cancel the command or change it, the G21 code would remain.

This can cause trouble if you aren’t paying attention.

For this reason, most CNC programs will be created with start-up or safety commands. The safety commands make sure that the machine is always in the correct modes.

When to use a G21 code?

A G21 code can be found at any point within the program but the most likely location is at the start of the program or at the start of a new block of code.

For instance, you might switch the CNC into metric mode by using the G21 command immediately before starting to cut a slot in the part.

The machine could already be in metric mode or it could be in inch mode but placing the G21 command immediately before the new block of code for the slot operation will make sure you are working in the correct units. All kinds of things can happen when machining and it isn’t uncommon for the machine to crash or some part of a program needs to be re-run.

Placing the safety commands (G21 in this case) at the start of the new block of code makes sure your machine does exactly what was intended.

What to think about when using a G21 code?

When you use a G21 code you simply need to be aware of what type of units you are working in. Most machine shops will work in either inches or mm.

There are definitely some shops out there that will use mixed units, but in most cases CNC programs will be written in one or the other for every program they make.

Know whether your parts are in inches or millimeters.

4 G21 code examples and descriptions of what they mean

For the examples below, we will assume your machine is in absolute mode (G90). If you are working in incremental mode (G91), the resulting movements will be different. Check out our guides to G90 and G91 G codes to understand the difference between the two movement types.

Example #1

N010 G21 G00 X3.5 Y4.2 Z1.3

N010 is line number 5 of the program.

G21 sets the units as metric

G00 sets the movement mode as rapid travel.

X3.5 Y4.2 Z1.3 is the location the machine will move to. If the Z location of the machine was already at 1.3 inches, then the Z axis will not move. This is the same for each axis.

Example #2

N125 G21

N130 G01 X3.5 Y4.2 Z1.3

N125 is line number 125 of the program.

G21 sets the units as metric

G01 sets the movement mode as straight line (linear interpolation).

X3.5 Y4.2 Z1.3 is the location the machine will move to. If the Z location of the machine was already at 1.3 inches, then the Z axis will not move. This is the same for each axis.

This example is at a different spot in the program (N010 vs N125) but will act the same as the previous example with the exception that this example will not move in a rapid travel manner.

Notice that the G21 code can be called out on the previous line and it will still be in effect on the next line.

Example #3

N025 G20 G00 X1.0

N030 G21 X1.0

N035 X25.4

N025 is line number 25 of the program

G20 sets the units as inches

G00 sets the movement mode as rapid travel

X1.0 moves the machine to a location where X=1.0 inches

N030 is line number 30 of the program

G21 sets the units as millimeters

X1.0 moves the machine to a location where X=1.0 mm

Example #4

N010 G80 G40

N020 G21 G90

This is an example of a safety or startup command. They vary though and you need to know you machine to make sure you use the correct codes. Do not assume that using the code above will be correct for your machine.

N010 is line 10 of the program

G80 cancels all canned cycles

G40 cancels cutter compensation

N020 is line 20 of the program

G21 puts the machine in metric mode

G90 sets the movement mode as absolute

CNC codes that are similar to G21

All of the codes listed in the table below are modal commands that affect the way the CNC machine interprets size and location values that are entered.

Code

Mode

G20

Inch Mode

G21

Metric Mode

G90

Absolute Mode

G91

Incremental Mode

What is a G20 Code? [With Lots of Examples]

a graphic of a cnc machine with text that says learn g code today G20 inch mode

The information below is meant for beginners. If you are experienced with CNC programming, then you probably already know this stuff and much more. If you are new to CNC programming, this is the place for you.

Please note that some of the topics below could include more information on the subject. However, in the interest of keeping things simple for those just starting out, they have been left out of this G code guide.

Ready to learn? Let’s go.

Code

G20

Name

Inch mode

Type

Modal - stays on until changed

Description

The machine will interpret all size and location values as in inches

What does a G20 code do?

A G20 code will switch the CNC into inch mode. Once the G20 code is used, all sizes and locations in the program will be treated as inch values until the mode is changed.

This type of G code is called a modal command.

Modal commands remain in effect until they are canceled. This holds true even if you restart your program. Until you cancel the command or change it, the G20 code would remain.

This can cause trouble if you aren’t paying attention.

For this reason, most CNC programs will be created with start-up or safety commands. The safety commands make sure that the machine is always in the correct modes.

When to use a G20 code?

A G20 code can be found at any point within the program but the most likely location is at the start of the program or at the start of a new block of code.

For instance, you might switch the CNC into inch mode by using the G20 command immediately before starting a drilling cycle.

The machine may already be in inch mode but placing the G20 command immediately before the drill cycle will ensure the program is in inch mode. All kinds of things can happen when machining and it isn’t uncommon for the machine to crash or some part of a program needs to be re-run.

Placing the safety commands (G20 in this case) at the start of the new block of code makes sure your machine does exactly what was intended.

With this example, the customer won’t be happy if you give them holes that are 1mm instead of 1 inch. If it goes the other way and you make a hole that is 1 inch instead of 1mm just tell them that the extra work is on the house.

What to think about when using a G20 code?

When you use a G20 code you simply need to be aware of what type of units you are working in. Most machine shops will work in either inches or mm.

There are definitely some shops out there that will use mixed units, but in most cases CNC programs will be written in one or the other for every program they make.

Know whether your parts are in inches or mms.

4 G20 code examples and descriptions of what they do

For the examples below, we will assume your machine is in absolute mode (G90). If you are working in incremental mode (G91), the resulting movements will be different. Check out our guides to G90 and G91 G codes to understand the difference between the two movement types.

Example #1

N005 G20 G00 X4.0 Y5.0 Z2.0

N005 is line number 5 of the program.

G20 sets the units as inches

G00 sets the movement mode as rapid travel.

X4.0 Y5.0 Z2.0 is the location the machine will move to. If the Z location of the machine was already at 2.0 inches, then the Z axis will not move. This is the same for each axis.

Example #2

N360 G20

N365 G01 X4.0 Y5.0 Z2.0

N365 is line number 365 of the program.

G20 sets the units as inches

G01 sets the movement mode as straight line (linear interpolation).

X4.0 Y5.0 Z2.0 is the location the machine will move to. If the Z location of the machine was already at 2.0 inches, then the Z axis will not move. This is the same for each axis.

This example is at a different spot in the program (N005 vs N365) but will act the same as the previous example with the exception that this example will not move in a rapid travel manner.

Notice that the G20 code can be called out on the previous line and it will still be in effect on the next line.

Example #3

N025 G20 G00 X1.0

N030 G21 X1.0

N035 X25.4

N025 is line number 25 of the program

G20 sets the units as inches

G00 sets the movement mode as rapid travel

X1.0 moves the machine to a location where X=1.0 inches

Example #4

N030 is line number 30 of the program

G21 sets the units as millimeters

X1.0 moves the machine to a location where X=1.0 mm

N010 G80 G40

N020 G20 G90

This is an example of a safety or startup command. They vary though and you need to know you machine to make sure you use the correct codes. Do not assume that using the code above will be correct for your machine.

N010 is line 10 of the program

G80 cancels all canned cycles

G40 cancels cutter compensation

N020 is line 20 of the program

G20 puts the machine in inch mode

G90 sets the movement mode as absolute

Codes that are similar to G20

All of the codes listed in the table below are modal commands that affect the way the CNC machine interprets size and location values that are entered.

Code

Mode

G20

Inch Mode

G21

Metric Mode

G90

Absolute Mode

G91

Incremental Mode