Brandon Fowler

Guide to Becoming a CNC Operator

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Overview

Being a CNC operator is easily the simplest of all CNC jobs. A CNC operator is typically an entry level position and they are tasked with keeping the machines running and constantly making parts.

cnc operator pushing button on control panel

In most cases, someone else will program and setup the machine while an operator is asked to keep it between the lines. This often means checking parts in some fashion as they come off the machine and occasionally making small adjustments to keep everything within the allowable tolerances.

CNC operators are often referred to as button pushers. Quite honestly, operating a CNC isn’t the most highly skilled position. As a result, the pay isn’t that high, but most will find it still beats working retail and isn’t nearly as backbreaking as something you might find in one of the construction trades.

So, let’s jump right in to some of the most frequently asked questions about becoming a CNC operator.

What does a CNC operator do?

A CNC operator pushes buttons to keep the CNC machines running while performing basic inspection of the machined parts.

As an entry-level position, all of the skills necessary for a CNC operator to possess would be taught to a new employee. Any experience or knowledge that an applicant bring with them would be icing on the cake.

Operators will be expected to do simple math such as adding and subtracting. Additionally, they will use measuring gauges such as micrometers, calipers, a pocket comparator and often dial indicators.

mitutoyo digital caliper
A digital caliper
anytime tools 1-2" micrometer
Typical outside micrometer

Basic hand tools including screwdrivers, mallets and deburring tools will get everyday use as well. The real benefit of being a CNC operator is that it can be a great stepping stone to an extremely in demand profession once you have expanded your skillset and advanced to the level of CNC setup and/or programming.

Experience with blueprints, trigonometry or handheld measuring equipment such as micrometers and calipers would be very sought after for any company.

Typical CNC operator job description

MachinistGuides.com is seeking a quality-oriented CNC Machine Operator to join our dynamic team.

The CNC Machine Operator will work with other team members and report to the Shop Manager. This role is responsible for reading blueprints, checking finished parts, and operating CNC mills and/or lathes.

The CNC Machine Operator will:

  • Safely operate a CNC machine to create precision components
  • Read and interpret blueprints, diagrams, sketches, and verbal instruction
  • Maintain pace of production to meet scheduled demands
  • Safely load and unload CNC production equipment
  • Have the ability to lift 50+lbs and stand for several hours

Desired Skills:

  • CNC machine operator/manufacturing experience
  • Thorough knowledge of standard manufacturing concepts, practices, and procedures
  • Have a strong work ethic and a positive attitude
  • Attentive to detail and instruction

Compensation commensurate with experience. A list of benefits which may include paid time off, 401k, medical, dental, life insurance, and/or holidays.

CNC operator skills

basic dimensions of bolt hole circle on blueprint
Blueprint example
  • Blueprint reading
  • Simple math including addition and subtraction of decimals
  • Hand tools
  • Handheld measuring equipment use
  • Some light trigonometry

Check out our Beginner’s Guide to Blueprint Reading to gain a leg up on the competition. 

Our guide to machinist lingo will help you talk the talk at your new job as well.

How much does a CNC operator make?

20, 10 and 5 dollar bills

According to GlassDoor.com, the average pay for a CNC operator is $38,490 per year. With a typical 40-hour week that comes out to $18.50 an hour.

Keep in mind that pay will vary by region, but this should give you a good idea of where you will start. The nice thing about CNC and machining work is that there is often quite a bit of room for growth.

For reference, CNC programmers can often make $30+ an hour.

How long does it take to become a CNC operator?

Being a CNC operator is an entry level position and as a result, you can be a CNC operator on your first day on the job.

You might not the most productive employee on day one, but you will be tackling the normal everyday responsibilities of more experienced operators.

Is it difficult to learn how to be a CNC operator?

CNC operation is not a difficult job to learn. As an entry level position, the skills needed to be a great CNC operator can be learned in a pretty short amount of time.

Is being a CNC operator stressful?

Generally speaking, CNC operation is not a stressful job. Of course this will vary from company to company but because the position is entry level, there is very little responsibility on the operators part.

It will be possible to find some businesses that work with a very heavy “produce, produce, produce” mentality and in these cases, the job can get more stressful. This is more of a product of the management style than the actual position itself so make sure to do some research online to check out some reviews for any potential employers.

Is being a CNC operator boring?

cnc operator inspecting part in front of machine

This is a very subjective question, but I believe many would find the position boring. A CNC operator job will usually be fairly repetitive while not being overly difficult mentally or physically.

The good news is that if your are looking for something to keep things a little more interesting then there will often be opportunities for advancement if you are willing to learn and put in a little effort.

You should also know that boring is also a term for precision machining of a hole by a machine such as a CNC mill or lathe.

Do you need a degree to be a CNC operator?

high school degree

Being a CNC operator does not require a college degree in any form. Local community colleges often offer certificate programs or crash course type coursework that will be looked upon very favorably for any new hire.

Many companies however will require a high school degree or equivalent. Larger companies are usually the ones who have this requirement. Smaller shops are generally more lenient.

What kinds of certifications and training are available to become a CNC operator?

Training, courses, classes, and certifications are available at colleges across the country with many community colleges leading the way.

Check out your local community college’s website to see if they offer training that may be beneficial. You will likely be surprised at the number of different options they offer.

Another valuable resource is your states manufacturing extension program. These organizations are usually aimed more at helping businesses with workforce development, but they often offer subsidized training that can give you a huge leg up in the job market.

YouTube is a great resource as well and there are thousands of high-quality videos out there to teach you all about every aspect of CNC work.

If you want a more structured approach, then check out our post on the best CNC and machining books. Many of these books are the same reference material that the college classes mentioned above will use.

What should you put on a resume to get a position as a CNC operator?

To get a job as a CNC operator make sure to mention any of the following items that may apply:

  • Math skills, especially anything related to trigonometry
  • Blueprint reading experience of any kind
  • Mention your attention to detail
  • Describe how reliable and dependable you are

Tips for finding a good position as a CNC operator

Research, research, research.

Actually it’s not that hard. A single research is probably enough. It is actually pretty easy to find a good job as a CNC operator.

Look for company reviews on sites such as Indeed or GlassDoor. Take it all with a grain of salt but in my experience, any company who has more than a few reviews will be pretty easy to determine the overall “vibe” of the business.

Look for a company that stresses quality over quantity and you will be headed in the right direction.

Related articles

For more information check out these related articles:

Beginner’s Guide To Reading Machine Shop Numbers & Values

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Confused? If you’re reading this page then I’m pretty sure you are. Dealing with numbers, values and calculations when machining or 3d printing can be hard for those just starting. 

The lingo and terminology used by many people both online or at a new job can be hard to understand. My hope is that after this quick lesson in dealing with machine shop numbers, you will not only be comfortable reading your numbers and measurements but also will know how to perform some simple calculations using them. 

math on chalkboard

Let’s begin

First we need to understand what the numbers we are working with represent.

Whether they are a reading on a micrometer, a spec on a blueprint or a stack of gage blocks, the goal is the same.

We need to know how to read them and work with them. 

Below is a graphic that shows the name (including machine shop lingo) for different values.

Pay attention to how far each number is from the decimal place when looking at the chart.

Please note that not everyone will be working down to millionths of an inch but I included them for reference. Many will only work down to the the values shown in this table. 

Value

Machinist Lingo

Technical Math Term

0.001"

Thousandth or Thou

Thousandth of an Inch

0.0001"

Tenth

Ten Thousandth of an Inch

Keep in mind that all these numbers and terms apply to imperial units (inches).

machine shop terminology for numbers

How to say the value

Machine shops usually speak in terms of thousandths of an inch. Because of this when we describe the value to someone else we will read it a little different than you might expect.

As noted above, if we give the example of 7.489136″ a machinist would describe the value as 7 inch, 489 thousandths, 1 tenth, 36 millionths. 

Read that last sentence over a couple times to really understand the terms your typical machine shop speaks in.

As a note, not all machine shops or hobbyists will deal in millionths of an inch and some might not even work with tenths but I have included them for reference.

Note: Thousandths of an inch is often abbreviated as “thou” especially when discussing values verbally. 

Machine shop number reading examples

Below are some more examples to show how machinists communicate values:

Value

Machinist Lingo

1.325"

1 inch 325 thousandths

0.5001"

500 thousandths 1 tenth

0.021

21 thousandths

0.6532"

653 thousandths 2 tenths

9.792345"

9 inch 792 thousandths 3 tenths 45 millionths

Gage blocks

A common scenario for someone new in a machine shop is learning how to set up a stack of gage blocks.

I’m not going to show you how to pick the right gage blocks for your stack here. If you need those instructions then head over to Starrett’s website. They have great instructions that show you how to select your gage blocks and make a stack of a specific height. 

The link also contains information related to the use and care of your gage blocks. Take care of your gage blocks people, those things are expensive.

How to setup calculations

Now I said I would show you how to work with these numbers, so let’s demonstrate how to do that.

The important part when dealing with numbers or values in a machine shop context is to line up the decimal point. Below you will see some examples of addition and subtraction of numbers:

Simple calculation examples

addition and subtraction of values

For practice, let’s list out how to say those answers!

Value

Machinist Lingo

1.610"

1 inch 610 thousandths

0.7206"

720 thousandths 6 tenths

0.6249"

624 thousandths 9 tenths

There aren’t any other special tricks here. Once you line up the decimal places everything else is just like you learned early in school. Also consider yourself lucky we have calculators.

That’s it. Now you should know how to speak in terms that a machinist would understand and use the values in simple calculations. 

If you need more in depth training when it comes to machine shop math, check out the training linked below. It breaks all the hard subjects down into bite sized pieces to make them easy to understand.

Ready to master machining math?

Get the tips and tricks you need to master the math needed for CNC and manual machining. Includes easy-to-follow guidance to make learning the math you need to succeed a breeze!

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Complete Guide to Comments in G Code

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a cnc machine running with g code overlaid

What are g code comments?

Comments in CNC g code are portions of the program that are ignored by the CNC controller and/or help the machine operator understand the program.

There are many different machine manufacturers and they can each have their own format for handling and identifying comments. In other words, what works on one machine may not work on another.

When in doubt try to find a manual or research your specific brand of CNC. We have outlined some of the most common CNC manufacturers and how they call out comments in the table below.

You can see that the two most common ways to identify a comment are by enclosing it in parentheses () or placing a semicolon symbol ; before the comment.

How to insert a comment into a g code program

The table below lists the symbol or character that is used to identify g code comments on a specific line of the program.

Take note that when parentheses () are used, everything between the open and closed parentheses will be ignored.

When the semicolon ; is used, all code after the semicolon on that line will be ignored and treated as a comment. Placing a semicolon inside a parentheses will not make the machine ignore the rest of the line, only what is inside the parentheses in this case will be ignored.

Remember, there are dozens or possibly hundreds of machine tool manufacturers and some may not adhere to these rules but this guidance will work for the majority of machines.

Machine Control Manufacturer

G Code Comment Character

Fanuc

Parentheses ()

Haas

Parentheses ()

Heidenhain

Semicolon ;

Hurco

Parentheses ()

Mitsubishi

Parentheses ()

Sinumerik (Siemens)

Semicolon ;

Yasnac

Parentheses ()

Ready to master CNC programming?

Try the free 30 minute intro course to see how simple and easy G code can be. Take the shortcut to becoming a G Code Master today!

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What should be included in a g code comment?

Comments can include anything that can help to operator or setup person to better understand how the program is operating.

Placing comments at key moments in the program can be a great way to help an operator. Letting them know if they need to perform an action or if the program is about to start a new operation (switching from roughing to finishing or starting to drill a set of holes) can be extremely helpful.

The best practice is to be brief but provide enough info. You don’t want to write a book and clutter up the program, but too little information can leave a person guessing or assuming what is happening in the program.

Creating good comments can help someone who isn’t highly trained in reading g code but they can also help you when you go to troubleshoot the program or try to edit or improve it later on down the road.

Where should you put comments in your CNC program?

In general, g code comments should be placed at the end of the program line to describe the current action. Some machines allow comments, specifically ones in parentheses (), to be added in the middle of the line.

I recommend avoiding this practice as much as possible. It can cause issues with some machines. Sticking with a semicolon or parentheses at the end of the line will help ensure your program is the most compatible with a wider assortment of machines.

As we noted above, it is also a good idea to include comments at the start of a new section of your program.

Tooling descriptions, offset information and descriptions of the operations being performed are all great info to include in the comments at the start of a new section.

A block of comments at the start of your program is a welcome addition that many CAM programs will automatically insert with information such as the program creators name, a date or revision of the program and miscellaneous other information.

When should you use comments in your g code?

Comments add to the size of the CNC program (not as much of an issue with newer machines) and also clutter up the code.

Use them sparingly and in the important places. You don’t need to comment ever move.

Comments work great at the start of program sections to help operators know what to expect or what is expected of them.

Ready to master CNC programming?

Try the free 30 minute intro course to see how simple and easy G code can be. Take the shortcut to becoming a G Code Master today!

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How to Learn CNC Programming [Best Resources]

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What is CNC programming?

CNC programming is the process of creating and running a program consisting of G code in a CNC machine to move the machine and control its functions.  

There are a large range of CNC machine types available, from industrial mills and lathes to home machines such as 3d printers, laser engravers and CNC routers.

All of these CNC machines use the same G code language to control the machine.

How difficult is it to learn CNC programming?

Learning basic CNC programming is fairly easy. It involves learning how the CNC machine will react to a series of codes. Most of the codes are easy to remember with a little practice (F for feedrate, S for spindle speed) and for any of the harder to remember codes, cheat sheet type references are usually not too far away.

Learning advanced CNC programming will take more time. Practice and repetition help, as does attending local training programs or completing an online training course.

When learning CNC programming expect to apply math skills, learn to read manufacturing blueprints and work with specialized computer programs.

Ready to master CNC programming?

Try the free 30 minute intro course to see how simple and easy G code can be. Take the shortcut to becoming a G Code Master today!

View Free G Code Course

What are the steps involved in CNC programming?

infographic that shows three steps to making a cnc program

Plan the program

The first step in CNC programming is planning out your program. In this step you will choose the machine and tools that will use to make your part. The operations to create the part (shape part, drill hole, mill slot, etc.) as well as the order of those steps will be determined.

Write the program

Now that you know what you will use to make the part (machine and tools) and how you will make the part (the order of operations), the program can be written.

When writing the program, you will create code either by hand or with the help of software to create the instructions for the machine to run.

In this step, documentation is usually created that lists any special requirements for running the program such as the tooling to be used, offset information, and fixturing information.

Setup the CNC machine

The role of the CNC programmer will sometimes end once the program is written and documented. However, in many machine shops programmers are also responsible for setting up and/or operating the machines too.

Setting the CNC machine up will involve loading the correct tools, setting offsets, loading the program and running a first piece to verify everything is running as planned.

Types of CNC programming

Manual programming

Manual programming is when the programmer creates the G code by hand. This involves controlling all of the machine’s functions and movements through the use of code.

Manual programming of CNC programs is usually only done with very simple programs.

Conversational programming

Conversational programming involves giving the machine specific parameters or dimensions that are required and the CNC machine generates the code for you based on the input.

Conversational programming is a middle point between manual programming and programming with CAD/CAM systems. Conversational programming simplifies the programming of features that may be difficult to program manually.

Conversational programming can allow quicker programming times when compared to CAD/CAM programming options. It also generally requires far less training than what is required to work with CAD/CAM packages.

Programming with CAD/CAM

two computer monitors with CAD-CAM software running
Example CAD/CAM software

The majority of CNC programming today is done with the use of various computer aided drafting (CAD) and computer aided manufacturing (CAM) software packages. These software programs allow the creation of long, complex CNC programs with much less work when compared to manual or conversational programming.

CAD/CAM programs are capable of programming things that wouldn’t be possible with manual or conversational programming. There are many different CAD/CAM software programs available with some of the most common being AutoCAD, Fusion 360, SolidWorks, Mastercam & EDGECAM.

How to start learning CNC programming

Local college/training

One of the best ways to start learning CNC machining is to look for local education resources such as colleges, community colleges, training programs and your state’s manufacturing extension partnership (MEP).

These resources often provide unequaled instruction and hands on use of equipment.

In some areas, companies have created their own training programs which they operate to help educate their local workforce.

Self-guided training

If you don’t have local training options available, there are a large number of resources that allow you to learn CNC machining and programming on your own schedule.

YouTube has a wealth of informative instructional videos and there is an abundance of information available on other online resources such as MachinistGuides.com.

We recommend reviewing our list of the Best CNC and Machining Books to find the best reference material available.

Learning on your own can be daunting, especially when you don’t know where to start. For this reason, we have put together A Roadmap to Learn CNC Programming to help guide you and make sure you focus on the important stuff first.

Online training

For those looking for a more structured approach, there are online CNC training resources and courses available such as GCodeTutor.

The biggest benefit of online training is that it allows you to work at your own pace. The best online training programs will have help resources available as well as quizzes and projects to test your knowledge.

Types of CNC machines

CNC machines used to be extremely expensive machines that only large companies were capable of purchasing.

In recent years, the cost of CNC machines has come down quite a bit. Large scale industrial machines are still available, but they are accompanied by a new generation of machines aimed at hobbyists and makers.

Home/hobbyist machines

cnc wood router
CNC router
  • CNC routers
  • CNC plasma cutters
  • CNC laser engravers
  • 3d printers

Industrial level machines

a cnc mill with multiple fixtures and coolant lines
Industrial CNC
  • Mills
  • Lathes
  • Electrical discharge machines (EDM)

Frequently asked questions

Do you need a degree to get a job in CNC programming?

No degree is needed to become a CNC programmer, although previous training or certifications are looked at very favorably by employers.

Many employers are willing to provide on the job training to teach new employees the skills needed to perform the job.

How long does it take to learn CNC programming?

The basics of CNC programming can be learned in a short amount of time.  Learning the basics will only take a few short months.

However, CNC programming is a wide field, and it will take much longer to have a solid understanding of everything that goes into CNC programming.

To become a highly skilled CNC programmer will likely take years. Training programs vary in length from 1-4 years on average. In addition, hands on experience will be needed to truly become a master of the craft. Certainly, anyone who applies themselves and works hard to learn will shorten that timeframe considerably especially when working in a good training program.

Is CNC programming a good career?

CNC programming is a great potential career. There is a high level of demand for skilled CNC workers across the globe. Many experienced CNC programmers and machinists are expected to retire in the coming years and a lower rate of younger workers entering the field has created a high demand for skilled CNC workers.

The demand for skilled CNC workers is so large that many in the CNC industry refer to it as “the skills gap”.

This skills gap has created a good opportunity for anyone seeking a well-paying job in the industry.

What is the salary for a CNC programmer?

According to GlassDoor.com, the average CNC programmer makes about $85,000 per year.

That comes out to about $40 an hour.

CNC programming is similar to other skilled trade jobs and can pay quite well without the need for a college degree. Getting training or certifications will help improve your chances of landing that well-paying position.

What skills does a CNC programmer need?

Because most CNC programming positions require the use of specialized CAD/CAM software, the best programmers have solid computer skills.

CNC programming positions often require math skills as well. Trigonometry, geometry and algebra are all commonly used when programming. Often the computer software will perform the necessary calculations but there are many times where calculations must be verified by hand.

Luckily, most of the math skills only use a limited number of formulas. To get a better idea of the type of math skills involved, check out our Beginner’s Guide to Machine Shop Math.

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

What other jobs take similar skills to CNC programming?

CNC and machine operators are the closest related job to CNC programming. Often, operators are the ones who will be running the CNC programs.

It is quite common for operators to gain some experience in their machine shop and work their way up to a position in CNC programming.

CNC and machine operator positions are typically much less demanding when it comes to computer and math skills and are a great starting point for anyone interested in learning CNC machining.

Micrometers and Calipers [Similarities, Differences & Everything Else]

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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

Most calipers will measure inside, outside and depth measurements. 

Caliper measuring internal hole
caliper depth base attachment
Depth measuring rod extended from caliper – depth base attachment shown
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.

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

Calipers are capable of taking a much larger variety of 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

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.

Related Articles

For more information see these related articles:

Geometric Dimensioning and Tolerancing Font – GD&T Keyboard Shortcuts

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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 listed below will 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

Related Articles

Best Engraving Pens for Every Budget and Material

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Engraving pens come in a wide range shapes, sizes and capabilities. You want to find the one that is just right for you project.

As you read our guide to the best engraving pens, make sure to keep your planned project in mind to determine what tool will work best for you.

Some applications such as jewelry engraving will benefit from a smaller tool for more precise strokes. Other materials such as metal or glass will engrave better with a more powerful tool such as one of the engravers by Dremel below.

No matter what you are working with, we have laid out the best tools on the market and an extensive list of items at the bottom of the article for you to consider when looking for your right fit tool.

Name

Awards

Where to Buy

Culiau Customizer

Best Overall Cordless Engraving Pen

Check Price

Tidalpool Easy Etcher

Best Budget Cordless Engraving Pen

Check Price

Tacklife PCG01B

Best Value Cordless Engraving Pen

Check Price

Dremel 290-01

Best Corded Engraving Pen

Check Price

IMT Scriber

Best Manual Engraving Pen

Check Price

Best Overall Cordless Engraving Pen

box/packaging for the culiau customizer

Culiau Customizer

plus symbol

Pros

Easy to handle and use
Customer service
Plenty of included bits

minus symbol

Cons

Not the cheapest option

The Culiau Customizer Engraving Pen is excellent choice for novices. Because the tool is so light, engraving is as simple as using a pen. 

Don’t get me wrong, it will still take practice to get a nice, finished product but the Customizer is easier to use than some of the other bulkier engraving pens on the market.

The Customizer is roughly the size of a regular marker. The grip and light weight make controlling the engraver while in use a snap.

culiau customizer compared to sharpie, pen and pencil
Size comparison

You can sketch with it just like a normal pen or pencil.

One of the biggest indicators of the quality is the feel of the tool. This is a well-built tool that feels good in the hand.

The flexibility of the Customizer makes the job as simple as drawing on paper. It works well on wood, including hardwoods, glass, and metals like steel, silver, and others.

culiau customizer in box with engraving bits
Plenty of included bits

It is ergonomic, lightweight, and small. Because of this it is exceptionally comfortable to use and handle. The Customizer truly is a pocket-sized engraving machine.

The quality comes with a price though and the Customizer does cost more than many of the other engraving pens on the market. The cheaper engraving pens aren’t built as well, but if you only plan to use it for the occasional project then it might not be a big deal.

If you plan to use it a lot, I recommend going with an engraving pen that is a step above such as the Customizer from Culiau and skipping all the generic cheapy ones.

Check Current Price

Best Budget Cordless Engraving Pen

tidalpool easy etcher with bits

Tidalpool Easy Etcher

plus symbol

Pros

Lightweight
Easy to control
Included stencils

minus symbol

Cons

Underpowered

The Easy Etcher is an excellent engraving pen for beginners. The tool is so lightweight that engraving with it is as close to using an actual pen as you will get. The Easy Etcher is actually about the size of a standard marker.

The rubberized grip also helps keep the engraver under control while using it. While the 12,000 RPM speed may seem under powered when compared to other engraving pens, it actually helps keep the tool stable during use.

Runtimes will vary depending on the type of material you are working with, but the Easy Etcher runs on AAA batteries which means there is no waiting around for the tool to recharge. The batteries aren’t included but other extras are.

The Easy Etcher comes with 10 sets of stencils that make engraving text or designs on your material a piece of cake. It also comes with a nice starter selection of bits that allow you to create a variety of textures and finishes.

The Easy Etcher won’t be the be all, end all for engraving every material but it is a great tool to get you started without breaking the bank.

Check Current Price

Best Value Cordless Engraving Pen

tacklife pcg01B rotary tool with accessories

TACKLIFE PCG01B

plus symbol

Pros

Good power

minus symbol

Cons

Charge time

While the TACKLIFE PCG018 is not as nimble as the Easy Etcher it does a good job of making up for it in the power department. With similar price points, it would be wise to determine whether power or maneuverability is more important to you.

The PCG018 has 3 speed settings of 5, 10 and 15,000 RPMs. This means it will work well for a variety of materials.

This TACKLIFE engraving pen is cordless and rechargeable. It charges over USB which has some benefits and drawbacks.

The charge time is fairly long at 2 hours but with a runtime of 90 minutes it lasts long enough to complete most jobs.

Additionally, the tool comes with 31 different accessories for engraving, sanding and finishing along with a case to contain them all. Two collets to accommodate different bit sizes of 3/32” and 1/8” is also a nice addition.

The TACKLIFE PCG018 is a solid choice when it comes to cordless engraving pens.

Check Current Price

Best Corded Engraving Pen

dremel 290-01 with stencil

Dremel 290-01

plus symbol

Pros

Adjustable depth setting
Warranty

minus symbol

Cons

Cost

The Dremel 290-01 is different than most of the other engravers on this list. Instead of being a rotary engraver, it has a vibrating tip that moves in and out. Basically, it operates like a mini jackhammer.

Corded engraving pens like this Dremel have some advantages and disadvantages.

Being corded means that you are tethered to your power outlet and it can be slightly cumbersome to work with the power cord snagging on objects in your work area. The 290-01 is pretty lightweight though which makes maneuvering it around your workpiece a little easier.

A nice benefit of using a corded engraver is that you won’t ever run out of power. This is helpful for harder materials that may take multiple passes to get the amount of engraving you desire.

The power of the 290-01 is controlled with a dial that allows five depth settings. This works well to adjust for different material types such as wood or rock. All that power comes with the side effect that the tool is quite loud when running. You should expect it to be noisy. It is a power tool after all but take note that the other tools on this list are quieter.

There are a couple minor downfalls for the 290-01. The biggest one is that the bit can be difficult to install. The set screw that locks it is tiny and it can be challenging to work with.

Also, the provided stencil comes in handy but is somewhat lacking. Many other engravers come with a wider variety of stencils so keep in mind that you may want to purchase some extra stencils if you plan on engraving a lot.

On the plus side, just like this engraving pen’s cordless counterpart, the Dremel 290-01 comes with a two-year warranty which is well above what most competing engravers come with.

Overall, the Dremel 290-01 is a solid engraving pen. A couple minor inconveniences are balanced nicely by the higher, non-stop power that comes from being always plugged in.

Check Current Price

Best Manual Engraving Pens

imt scriber two pack

IMT Scriber

plus symbol

Pros

No power required

minus symbol

Cons

Doesn’t engrave as deep

If all you need is something basic and reliable for engraving then the manual scriber from IMT may be your best bet.

It requires no batteries or power cord. The tool is extremely lightweight and its tungsten carbide tip will engrave a large variety of materials including steel, ceramics and glass. If you are working with plastics though, a powered tool would be a better choice.

The IMT scriber will actually perform an operation that is more akin to scratching your material than actually engraving it. For many use cases, this is more than enough. Just keep this in mind when choosing your engraving pen.

It also comes with extra tips in case one snaps. They are somewhat brittle because they are so hard. They aren’t fragile but can break if you aren’t dropped or handled roughly. Luckily, the scriber comes with a protective cap that will help shield the point from damage.

The IMT scriber is definitely more low tech than some of the other engraving pen options available but if all you need is a simple engraver then it may be a great choice at a cheap price.

Check Current Price

Things to consider when buying an engraving pen

Safety

Remember that these tools can be dangerous, especially to your eyes. Be careful handling them and use eye protection to protect you from things such as flying chips or broken bits.

Corded vs cordless engraving pens

Corded engraving pens generally have more power than their cordless counterparts. The downside is that the cord can get in the way and make the tool more difficult to maneuver. The easiest engraving pens to use are those that are lightweight and battery operated.

Cord length

If you choose to use a corded engraving pen to have more power, keep in mind that the length of the power cord is very important. If the cord is short, then make sure that you have an extension cord handy because some of the power cords can be very short.

Speed

RPMs do not equal power. Being able to adjust your RPMs over a wider range is more beneficial than simply having a higher RPM overall. Different materials will require different RPMs. In general, materials such as glass or metal which are harder will benefit from a higher RPM and softer materials will engrave better at lower RPMs.

Bits and accessories

It is a nice bonus for an engraving pen to come with a good selection of bits and accessories but not a necessity. There are many bit or accessory kits available that allow you to perform different types of engravings or finishing to your piece for a fairly cheap price.

Extra bits aren’t required to start but before too long you will definitely want to expand your bit collection if your engraving pen doesn’t come with many. Different bits will allow you to different styles of engraving.

Battery

If you go the cordless route, make sure you find a tool that charges quick and has a long runtime.

Cheaper tools tend to run off standard AA or AAA batteries which means they can run out of power quickly but also that more power can easily be on standby. Keep extra batteries nearby but consider the amount of power you will need for your project when choosing which engraving pen to go with. Harder materials require more power.

Warranty

Pay attention to the length of the warranty for your tool. Just like many other power tools, a good warranty is a solid indicator of the quality of the tool. This doesn’t mean that good tools don’t come with shorter warranties, just that it is something to be mindful of.

Stencils

Stencils can be very important for getting the correct design on your part. There are many different stencil kits available but it is definitely a bonus to have a couple to start with. Creating visually appealing designs freehand is going to take some practice so having a template to follow when getting started will be helpful.

Engraving vs cutting

Engraving pens are just that, engravers. They generally are not meant for cutting. If you are looking for a tool that is capable of doing more than simply scratching the surface of a part, then you will want to look into something with more power like the various Dremels or other higher power rotary tools. 

Related articles

For more information check out these related articles:

Quick Guide to CNC Safety Lines [Common Codes]

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What are CNC program safety lines?

Safety lines, sometimes called a safety block, are a section of code within a CNC program which are used to protect the machine, the workpiece, and the operator.

Safety lines are used to make sure the machine is in the proper mode/state which means that the machine will understand all the commands we give it correctly.

If you need the machine to work in inches (or mm in some parts of the world), it is important to frequently set the machine to work in those units. 

This is especially true if you will be switching between units when machining.

While many won’t switch between imperial and metric units, it is common to switch between absolute and incremental positioning modes.

The safety lines used will vary by machine, however there are many which are common between the majority of machines.

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Types of codes found in a safety line

Safety lines can contain G codes for coordinate systems, measurement units, tool compensation, and cancel functions. 

Each one of these commands is necessary to move the tool safely. 

Modal commands and cancel commands are two of the most common codes used in CNC safety lines.

Below are the most common safety codes found in CNC programs:

Positioning mode – G90/G91

The first code normally found in a safety line will be the machine’s positioning mode.

There are two positioning modes available to use. Absolute and incremental positioning.

Absolute positioning uses the G90 command. 

Absolute positioning mode tells the machine to interpret all locations it is given as measured from a fixed zero location (origin).

graph paper example of absolute positioning with multiple points as examples

Incremental positioning uses the G91 command.

Incremental positioning modes tells the CNC that the zero location is wherever the machine currently is. 

Once the CNC makes a move in incremental mode, the new location becomes the zero location.

graph paper example of incremental positioning with multiple points as examples

Units mode – G20/G21

Selecting the system of units you will be working in is important. This is why the units mode is found in the safety lines of the program.

Imperial units are set with G20 (inches) and metric units are set with G21 (mm).

You don’t want to move 4 inches when you meant to 4 millimeters.

Setting the units mode is critical to running your CNC.

comparison of units of measurement for cnc programming

Plane selection – G17/G18/G19

Selecting the plane you will be working with is necessary. Not because you will often switch between planes, but because it’s possible.

Most people will never use anything other than the standard XY plane with G17, but setting it will make sure that it is set correctly.

The alternatives to G17 are G18 for the ZX plane and G19 for the YZ plane.

Canned cycle cancel – G80

G80 is the g code used to cancel any active canned cycle.

Canned cycles are used to perform repetitive machining. This includes drilling, reaming, boring, counterboring and other operations.

Canned cycles are modal which means they are on until they are switched or turned off. 

In the case of a drilling canned cycle, once it is turned on every new location the machine reads will be a spot where it drills a hole.

Obviously, you need to stop drilling holes eventually. Using G80 cancels the drilling canned cycle or another other canned cycles that might be active.

Cutter compensation cancel – G40

Cutter compensation is when the CNC machine control changes how it reads the program. With cutter compensation on, the machine will shift a set distance based on the size of the cutting tool when running the program.

illustration that shows how a CNC will act when using cutter compensation left with the G41 code

Cutter compensation is turned on with either G41 or G42. G41 shifts the tool left and G42 shifts it right.

illustration that shows how a CNC will act when using cutter compensation right with the G42 code

The G40 code turns cutter compensation off.

illustration that shows how a CNC will act when there is no cutter compensation mode active

Tool length compensation cancel – G49

Cutter compensation is accounts for the diameter of the cutting tool.

Tool length compensation accounts for the length of the cutter from the CNC spindle.

G49 is the code used to cancel tool length compensation.

Both compensation modes adjust for the size of your cutter. This allows you to run the same program with different tools.

Other safety codes

Codes will vary by machine. Check your instruction manual for the specific codes you need to use in the safety lines.

The codes listed here are certainly a good start.

an illustration of a cnc machine that shows how a g43 code offsets the program

Safety lines for starting up your CNC

Setting the initial modes for your machine is an important part of every CNC program. If the modes are not set then the machine will stay in it’s initialized state.

Modes such as the unit system (mm/inch) can be set in the machine parameters. If no code is specifically given in the program then the machine will remain in the initialized state.

This is not a good programming practice because there is plenty of opportunity for errors to occur. Use safety lines to make absolutely sure your CNC is in the correct mode.

Here is an example of a safety line to use at the beginning of a program:

O1000
(Start of safety code)
G20 G17 G40 (G20 inch, XY plane, cancel cutter compensation)
G49 G64 G80 (cancel tool length compensation, normal cutting mode, cancel canned cycles)
G90 G94 G98 (absolute mode, feed per minute, initial plane for canned cycles)
(end of safety code)

Frequently asked questions about CNC safety lines

Can you put all of your safety codes on the same line?

The number of codes that can fit in the same line depends on the CNC machine.

Many machines have limitations for how many M-codes you can put on one line. G codes are generally only limited to one code from each group.

For example, G00, G01, G02 and G03 are all in the same group (movement). Only one of the codes from this group should be used on any particular line.

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CNC Spindle Controls Explained [M03, M04, M05 and More]

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Getting started with CNC spindle controls

The most basic codes to control your CNC spindle are:

But there is more to controlling your CNC spindle than simply turning it on and off.

For instance, most CNC machines have multiple ways to turn the spindle off and each way has it’s own use case. 

Controlling the spindle speed is another function that has multiple modes. Choosing the wrong one could potentially be disastrous. 

Learn the ins and outs of controlling your spindle below.

picture of the inside of a cnc machine with the spindle identified

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Codes for turning your spindle on

There are two CNC commands for turning the spindle on, M03 and M04.

The S code is used together with these codes to set the speed of the spindle.

Spindle direction

M03 [spindle on, clockwise]

The M03 code turns the spindle on in a clockwise direction at a set speed.

The speed is set with the most recent S code.

Clockwise rotation with M03 is the most common spindle rotation direction when CNC machining. 

Clockwise rotation is used with right hand cutting tools.

M04 [spindle on, counterclockwise]

The M04 code turns the spindle on in a counterclockwise direction at a set speed. 

Just like M03, the set speed is the value used with the most recent S code.

M04 is used with left hand cutting tools.

Counterclockwise spindle rotation is much less common than clockwise. 

This is especially true for machining centers (mills). For lathes, M03 is still more common but M04 gets more use.

Codes for turning your spindle off

The M05 code is the only code that just turns the spindle off.

However, there are other codes listed below that turn off multiple machine functions and the spindle is included in those functions.

M05 [spindle off]

The M05 code is used to stop the spindle.

It is normally used when there is a tool change or other change in the machining process.

When the spindle is turned back on with an M03 or M04 code after being stopped, the spindle will return to the same speed it was previously set at with the last S code.

M00 [program stop]

The M00 code is called a program stop. It stops the current program in the middle of running.

Using the M00 code turns off the following functions:

  • Movement of all axes
  • Spindle rotation
  • Coolant flow
  • The machine pauses reading the program

When the M00 code is used, nothing is reset. In other words, any active modes or parameters will stay as they are.

The program is merely paused when it reads the M00 code.

fanuc cnc control panel with cycle start button highlighted
Cycle start button on a Fanuc control panel

The machine will resume reading the program when the cycle start button is pressed after the program stop has occurred.

One thing to keep in mind is that the machine doesn’t turn on functions when cycle start is pushed. 

If the M00 code turns something off such as the spindle, it will need to be turned back on in the program.

M01 [optional stop]

The M01 code is called an optional stop. 

It stops the current program in the middle of running, but only if the optional stop switch or button is on.

If the optional stop switch is not on, then the machine will ignore any M01 codes it reads and continue running the program like normal.

haas cnc control panel with optional stop button highlighted
Optional stop button on a Haas CNC

When the machine reads an M01 code and the optional stop switch is on, it will turn off the following functions:

  • Movement of all axes
  • Spindle rotation
  • Coolant flow
  • The machine pauses reading the program

When the M01 code is used, nothing is reset. Same as with the M00 code.

In other words, any active modes or parameters will stay as they are. The program is merely paused when it reads the M01 code.

The machine will resume reading the program when the cycle start button is pressed after the program stop has occurred.

One thing to keep in mind is that the machine doesn’t turn on functions when cycle start is pushed. 

If the M01 code turns something off such as the spindle, it will need to be turned back on in the program.

M30 [program end]

The M30 code ends the program. 

This makes it different from M00, M01 or M05.

M00 and M01 shut down various machine functions and pause the program.

M30 shuts down machine functions and ends it. 

Pressing cycle start after an M30 code will start the entire program over again.

How to set spindle speeds

CNC spindle speeds are set using the S code.

S code

Using the S code sets the spindle speed that will be used whenever the spindle is turned on. The units are revolutions per minute (RPM).

The same spindle speed value will be maintained until it is changed.

Below is a small section of code with comments in parentheses that show what will happen as the machine reads the code.

M03 S3000   (Spindle On CW, Speed = 3,000 RPM)
M05              (Spindle Off)
M04              (Spindle On CCW, Speed = 3,000 RPM)

Notice how the spindle turns back on at the same set speed. This happens even if the spindle rotation direction is changed from clockwise to counterclockwise or vice versa.

S codes show up frequently in programs at the beginning of a new section of code. This can be switching tools or switching machining operations such as going from cutting the outside profile of the part to drilling holes.

Some other notes about the S code:

  • Must be a whole number (no decimals such as 3000.5)
  • Most machines have a limit to the range of spindle speeds that can be used. 1-9999 is common but 1-99999 is also used by some machines

Spindle speed modes

In CNC programming there are two codes that control the spindle speed mode, G96 and G97.

G97 is the most common and sets the spindle mode to RPM.

G96 sets the spindle mode to constant surface speed which adjusts the speed of the spindle based on the size of the part being machined.

G97 [speed in RPM]

When the G97 mode is active, the machine will maintain a constant spindle speed based on the RPM value set with the most recent S code.

If G97 is active, spindle speed will only change when the S code is changed.

G96 [constant surface speed]

When the G96 mode is active, the machine will maintain a constant surface speed.

Imagine a monster truck tire. Now picture rolling the monster truck tire one complete revolution in one minute. In that one minute, you might move 20 feet.

Now imagine you have a normal car tire. If you roll the car tire one revolution in one minute, you might only travel 4 feet.

You covered a lot less distance in that one minute, which means you traveled at a slower speed.

When things are spinning based on an RPM speed, the actual speed that the cutting edge of the tool is traveling can change.

Using constant surface speed with the G96 code tells the machine to change the spindle speed over time as the size of the part changes so that the speed where the cutting action is happening remains the same.

This is a simplified explanation of how G96 works. For more information about G96 see our full guide to the G96 command.

How to change the tool in your spindle

Most machining centers have automatic tool changers that can switch tools into and out of the CNC spindle.

an automatic tool changer on a dmg mori cnc machine
Automatic tool changer holding multiple tools in a DMG Mori CNC

The tool to be placed into the spindle is called up with the T code. This places the new tool in location so that it is ready to be switched.

The M06 command is then used to perform the tool change.

Here is an example section of code:

T01    (Tool 1 is readied for change)
M06    (Tool 1 is placed in the spindle)
T02    (Tool 2 is readied for change)
T03    (Tool 3 is readied for change)
M06    (Tool 3 is placed in the spindle)

Notice that even though tool 2 was readied for change, it never actually was put in the spindle. Instead, tool 3 was readied before the tool change occurred and it was placed in the spindle instead.

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CNC Offsets Explained [D, H and Work Offsets]

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What is a CNC offset?

Offsets are the adjustments that the CNC machine will make based on different features of the machine.

There are three types of offsets:

  • Diameter offsets
  • Height offsets
  • Work offsets

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Types of CNC offsets

Each of the three offset types has a specific purpose. 

They each allow for flexibility when running your program. This includes allowing you to use the same program even if you need to change cutting tools.

Height (H) offsets

illustration of a cnc cutting tool that shows what an H offset is

The height offset refers to the location difference between the spindle and the cutting tool.

This difference in location is stored in the machines offset library. Height offsets are usually stored in the same number location as the tool.

mach 3 tool offset table
Example offset library

For instance, T01 (tool 1) and H01 (height offset 1) or T05 (tool 5) and H05 (height offset 5).

This makes it easier to match up the necessary offset with the correct tool.

The G43 code is used to turn on tool length compensation using an H offset.

For example, G43 H01 turns on tool length comp with the first H offset.

Once tool length compensation is turned on with the G43 code, it will stay on until it is turned off with the G49 cancel code or switched to a new H offset such as H02 or H05.

Diameter (D) offsets

illustration of a cnc cutting tool that shows what an D offset is

While H offsets adjust for the length of the cutter, D offsets compensate for the diameter of the cutting tool.

D offsets are also stored in the machines offset library. D offsets are usually stored in the same number location as the tool they are used with.

T04 (tool 4) and D04 (diameter offset 4) would usually be matched together.

G41 and G42 are the two cutter compensation modes that are used with D offsets.

They tell the machine to adjust the path of the cutter so that the edge of cutter follows the path given in the CNC program. G41 shifts the cutter left and G42 shifts the cutter right.

illustration that shows how a CNC will act when using cutter compensation left with the G41 code
illustration that shows how a CNC will act when using cutter compensation right with the G42 code

With cutter compensation off using the G40 code, the machine will move the center of the cutter along the path in the program. 

This can make it difficult to get the correct size, especially when using different or multiple cutters.

illustration that shows how a CNC will act when there is no cutter compensation mode active

Telling the machine the size of the cutters with your D offsets allows it to account for them and run the same program with different tools ang get the same size part. 

If you didn’t have cutter compensation, then you would need to create a new version of the program every time you wanted to use a new tool.

Just like tool length compensation with G43, cutter comp with G41 and G42 are modal commands so those adjustments will stay on until switched or turned off with the G40 code.

Work offsets (G54-G59)

Work offsets are basically the stored location of your part in the machine. 

You use them to set the XYZ zero location when working in absolute positioning mode.

There are multiple work offsets available. 

The six most common are G54 through G59. Most machines will also have others available, but the format varies from machine to machine.

visual to show cnc work offsets G54-G59 with the zero locations shown
Multiple work offsets being used in one CNC machine

Fanuc controls are one of the most common controllers. If they allow additional work offsets, the Fanuc format for using them is G54.1 P1, G54.1 P2 and so on. The P number is the additional offset.

In most cases the six offsets of G54 through G59 that are common on all machines will be more than enough.

One benefit of having multiple work offsets is how easy they make it to run multiple parts at once. You can set the work offset for multiple parts and run the same program with a new work offset each time.

This works well when you a fixture that holds multiple parts in your CNC.

Where are offsets stored?

Offsets are stored in the tool offset table or library.

This tool table allows you to describe the different dimensions of the tool that will affect the program.

This includes the tool radius or diameter (D offset) and its length (H offset).

Offset Library
Tool offset library on an Okuma CNC machine

Some machines allow you to store the H and D offsets together in one offset. In this example, tool T01 would use both H01 and D01 as offsets. 

Other machines may require the offsets to be stored individually. 

When the offsets are stored individually, the programmer should maintain a system so that the offset numbers used are consistent. 

In other words, the first H offset would always be stored in the 01 location and the first D offset would always be stored in the 51 location.

Having a system like this will help prevent errors in your program.

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