What is a G04 Code? [With Lots of Examples]

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

G04

Name

Dwell

Description

The machine will stop moving for a set amount of time

What does a G04 code do?

A G04 code makes the cutting tool stop moving for specified amount of time. Following that amount of time the machine will proceed to the next line of code.

When to use a G04 code?

G04 codes are used for multiple reasons. They are used on lathes specifically, to break the chips. This way you don’t end up with one super long, razor-sharp chip.

They are also used to improve surface finishes on both lathes and mills.

What to think about when using a G04 code?

There is some variation to how G04 codes are called out. The difference is how the dwell times are listed.

Depending on what brand/controller your machine is, the following can change:

Letter used in callout to list time

Common letters are F, P, U, and X.

Seconds vs milliseconds

1 second = 1000 milliseconds

Decimal or no decimal

Some controllers require a decimal. Some don’t allow a decimal. Some allow either way but treat the number different based on whether you use the decimal or not. Real standardized stuff ain’t it?

Still, these differences should help you troubleshoot any program issues you have related to a G04 dwell code. Check out the examples below to get a better understanding of how you might see dwell codes on your machine.

I am not experienced enough with all brands of CNC machines. I would like to add a list here that tells the most common ways to callout a G04 command based on the CNC manufacturer.  If anyone has experience with a variety of machines, please leave a comment below and I will make sure to add the info to the post.

4 G04 code examples and descriptions of what they do

Example #1

N005 G04 P3

This is line number 5 of the program.

G04 sets the movement mode as dwell

P3 is the amount of dwell time = 3 seconds.

Example #2

N040 G04 F5.0

This is line number 40 of the program.

G04 sets the movement mode as dwell

F5.0 is the amount of dwell time = 5 seconds.

Example #3

N040 G04 F5

This is the same line as above, on the same controller. The decimal changes how the machine reads the code.

This is line number 040 of the program.

G04 sets the movement mode as dwell

F5 is the amount of dwell time. In this case, 5 milliseconds = .005 seconds.

A big difference. Watch those decimals.

Example #4

N100 G04 U5

This is line number 100 of the program.

G04 sets the movement mode as dwell

U5 is the amount of dwell time = 5 second.

CNC codes that are similar to G04

The table below lists all of the other G codes that control movement like a G04 code does.

What is a G03 Code? [With Lots of Examples]

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

G03

Name

Circular interpolation, counterclockwise

Type

Modal - stays on until changed

Description

Circular movement at a specified feed rate in a counterclockwise direction

What does a G03 code do?

A G03 code is a circular movement CNC G code. It is used to move the CNC table and/or spindle from its current location to an end location along a specified radius (R) in a counterclockwise direction.

When to use a G03 code?

G03 codes will usually be in the lines of the program that are used to cut the part. The G03 code allows the programmer to cut a full circle or portion of a circle.

F and S codes are used together with a G03 code to specify the feed rate and spindle speed. An R code is used as well to tell the machine what size radius to move along.

What to think about when using a G03 code?

Units

First, make sure you know what units you are working in. Moving 10 inches instead of 10 millimeters is a big difference.

A G20 (inches) or G21 (mm) code should identify the units you are working in before your G03 code.

Absolute vs incremental mode

The second thing to look for is whether you are working in absolute (G90) or incremental (G91) coordinates. The most recent G90 or G91 code in the program will determine which mode you are in.

Absolute coordinates will move from a set zero location such as your machines home location or a specified location on your part.

Incremental coordinates will move relative to your current position. See our posts on G90 and G91 codes to learn more about the differences between absolute and incremental coordinates.

Start and stop locations

Lastly, make sure you understand where you are currently position wise (X, Y & Z location), where you will be moving to and if there is anything in between the two locations.

The G03 code will move the machine in a circular arc to your new location. You don’t want anything in the way or to miscalculate your stop point. Clamps or vises can be easy to forget about and run into. Crashing your machine is never a good time.

3 G03 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

N085 G03 X1.0 Y2.0 R1.0

This is line number 85 of the program.

G03 sets the movement mode as circular, counterclockwise.

X1.0 Y2.0 is the location the machine will move to. There is no Z axis movement in this line.

R1.0 specifies the size of the radius that the machine will move along.

Example #2

N060 G03 X3.5 Y3.5 R0.5

This is line number 60 of the program.

G03 sets the movement mode circular, clockwise.

X3.5 Y3.5 is the location that the machine will move to. There is no Z axis movement in this line.

R0.5 specifies the size of the radius that the machine will move along.

Example #3

N477 G03

This is line number 477 of the program.

G03 sets the movement mode circular, clockwise.

There is no location specified on this line. The machine will not move based on this code line.

CNC codes that are similar to G03

What is a G02 Code? [With Lots of Examples]

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

G02

Name

Circular interpolation, clockwise

Type

Modal - stays on until changed

Description

Circular movement at a specified feed rate in a clockwise direction

What does a G02 code do?

A G02 code is a circular movement CNC G code. It is used to move the CNC table and/or spindle from its current location to an end location along a specified radius (R) in a clockwise direction.

When to use a G02 code?

G02 codes will usually be in the lines of the program that are used to cut the part. The G02 code allows the programmer to cut a full circle or portion of a circle.

F and S codes are used together with a G02 code to specify the feed rate and spindle speed. An R code is used as well to tell the machine what size radius to move along.

What to think about when using a G02 code?

Units

First, make sure you know what units you are working in. Moving 10 inches instead of 10 millimeters is a big difference. A G20 (inches) or G21 (mm) code should identify the units you are working in before your G02 code.

Absolute vs incremental mode

The second thing to look for is whether you are working in absolute (G90) or incremental (G91) coordinates. The most recent G90 or G91 code in the program will determine which mode you are in.

Absolute coordinates will move from a set zero location such as your machines home location or a specified location on your part.

Incremental coordinates will move relative to your current position. See our posts on G90 and G91 codes to learn more about the differences between absolute and incremental coordinates.

Start and stop locations

Lastly, make sure you understand where you are currently position wise (X, Y & Z location), where you will be moving to and if there is anything in between the two locations.

The G02 code will move the machine in a circular arc to your new location. You don’t want anything in the way or to miscalculate your stop point. Clamps or vises can be easy to forget about and run into. Crashing your machine is never a good time.

3 G02 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

N035 G02 X4.0 Y4.0 R2.0

This is line number 35 of the program.

G02 sets the movement mode as circular, clockwise.

X4.0 Y4.0 is the location the machine will move to. There is no Z axis movement in this line.

R2.0 specifies the size of the radius that the machine will move along.

Example #2

N090 G02 X7.5 Y1.5 R0.5

This is line number 90 of the program.

G02 sets the movement mode as circular, clockwise.

X7.5 Y1.5 is the location that the machine will move to. There is no Z axis movement in this line.

R0.5 specifies the size of the radius that the machine will move along.

Example #3

N250 G02

This is line number 250 of the program.

G02 sets the movement mode as circular, clockwise.

There is no location specified on this line. The machine will not move based on this code line.

CNC codes that are similar to G02

What is a G01 Code? [With Lots of Examples]

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

G01

Name

Linear movement

Type

Modal - stays on until changed

Description

Straight line movement at a specified feed rate

What does a G01 code do?

A G01 code is a linear movement CNC G code. It is used to move the CNC table and/or spindle.

When to use a G01 code?

G01 codes will usually be in the lines of the program that are used to cut the part. The G01 code allows the programmer to specify where the tool will move to. F and S codes are used together with a G01 code to specify the feed rate and spindle speed.

The location movement, speeds, and feeds are the main factors that influence your cut.

What to think about when using a G01 code?

Units

First, make sure you know what units you are working in. Moving 10 inches instead of 10 millimeters is a big difference. A G20 (inches) or G21 (mm) code should identify the units you are working in before your G01 code.

Absolute vs incremental mode

The second thing to look for is whether you are working in absolute (G90) or incremental (G91) coordinates. The most recent G90 or G91 code in the program will determine which mode you are in.

Absolute coordinates will move from a set zero location such as your machines home location or a specified location on your part.

Incremental coordinates will move relative to your current position. See our posts on G90 and G91 codes to learn more about the differences between absolute and incremental coordinates.

Start and stop locations

Lastly, make sure you understand where you are currently position wise (X, Y & Z location), where you will be moving to and if there is anything in between the two locations.

The G01 code will move the machine in a straight line to your new location. You don’t want anything in the way or to miscalculate your stop point. Clamps or vises can be easy to forget about and run into. Crashing your machine is never a good time.

6 G01 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

N015 G01 X7.0 Y5.0 Z3.0

This is line number 15 of the program.

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

X7.0 Y5.0 Z3.0 is the location the machine will move to. If the Z location of the machine was already at 3.0, then the Z axis will not move. This is the same for each axis.

Example #2

N070 G01 X6.0 Y2.0

This is line number 70 of the program.

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

X6.0 Y2.0 is the location that the machine will move to. The Z axis of the machine will not change and remain at the location it was previously set at.

Example #3

N120 G01 Y2.5 Z1.0

This is line number 120 of the program.

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

Y2.5 Z1.0 is the location that the machine will move to. The X axis of the machine will not change and remain at the location it was previously set at.

Example #4

N020 G00 Y4.0

This is line number 20 of the program.

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

Y4.0 is the location that the machine will move to. The X and Z axes of the machine will not change and remain at the location they were previously set at.

Example #5

N100 G01

This is line number 100 of the program.

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

There is no location specified on this line. The machine will not move based on this code line.

Example #6

N256 G01 X8.0

This is line number 256 of the program.

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

X8.0 is the location that the machine will move to. The Y and Z axes of the machine will not change and remain at the location they were previously set at.

CNC codes that are similar to G01

Note that all the movement codes listed below are modal. This means they will stay in the movement mode identified by the code until switched to a different mode.

Micrometers vs Calipers [Similarities, Differences & Everything Else]

micrometer vs caliper

Micrometers and calipers are both precision measuring tools.

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

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

Micrometers

Calipers

Accuracy

0.0001"

0.001"

Measuring Range

1" increments

0-6"

Types of Measurements

Outside Measurements

Inside, Outside & Depth Measurements

Micrometer and caliper comparisons

Accuracy

Micrometers are more accurate. 

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

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

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

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

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

Measuring range

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

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

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

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

Calipers have larger measuring ranges but they are less accurate.

Types of measurements they are capable of

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

Most calipers will measure inside, outside and depth measurements. 

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

Micrometers are capable of only performing one type of measurement. 

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

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

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

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

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

Ease of use

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

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

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

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

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

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

Speed

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

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

Cost comparison

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

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

More info about micrometers and calipers

Parts of a micrometer

parts of a micrometer

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

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

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

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

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

Parts of a caliper

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

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

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

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

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

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

Digital vs analog micrometers

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

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

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

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

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

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

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

Digital vs dial vs vernier calipers

mitutoyo 6 inch vernier caliper
Mitutoyo vernier caliper

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

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

anytime tools dial caliper dial face
Dial caliper

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

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

Summary

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

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

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

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

Ultimate Guide to Measuring Caliper Accuracy

Measuring calipers can be extremely capable measuring devices when in the right hands.

Knowing the limitations of your calipers and how you affect them is what will make you the “right hands” for the job.

I’m going to run you through the different aspects that affect caliper accuracy. I’ll start with the most basic topics and work from there so feel free to skip ahead if you already know about a subject.

Size of calipers

0-6" calipers

mitutoyo digital caliper
0-6" Mitutoyo Digital Caliper

The most common type of measuring caliper is a 0-6” caliper. If you are working in metric, this will be a 0-300mm caliper.

There is some variety in what they are capable of but in general they will be able to measure inside, outside and depth measurements over a 6” measuring range.

Larger and smaller calipers

Calipers do come in many different size measuring ranges. They are used much less often but you will still run into them.

0-12” calipers are the next logical choice when it comes time to measure a bigger part. The reason you wouldn’t use them all the time is because they are big and can be awkward to use.

0-24” calipers have the same issue and are even more awkward. Typically, you would only use the larger calipers in a situation where you could not use a caliper.

There 0-4” and 0-8” varieties that can be found as well and all types of specialized measuring ranges can be special ordered.

0-24" Calipers

Larger calipers will be more expensive than small calipers. The added expense is for accuracy. It gets much harder to maintain the accuracy seen in smaller calipers over larger measuring ranges.

Note: Calipers with larger measuring ranges tend to be less accurate. For example, the same Mitutoyo caliper in a 0-6” version has a specified accuracy of +/- 0.001” and the 0-24” version has an accuracy of +/- 0.002”. They are only half as accurate. This only gets worse when you realize larger calipers from lesser known manufacturers may be even less accurate.

Types of calipers

There are three main types of calipers. They are very similar with the main difference being how the actual measurement is read.

Vernier calipers

vernier caliper measuring thickness of brass part
Vernier Caliper Scale

Often referred to as simply “verniers”, these calipers have multiple scales on the face of the tool that are used together to take your measurement reading.

Because they do not have any internal mechanisms, they are the most durable type of caliper and most likely to remain accurate.

Verniers are the most difficult type of caliper then it comes to reading a measurement, especially for beginners. While they are not necessarily difficult to use, they take a little more understanding than using a dial or digital caliper.

Dial calipers

anytime tools dial caliper dial face
Dial Caliper Face

Dial calipers use a geared system to spin a needle on a dial. They have an easy to ready scale on the body of the caliper. This scale is often in .100” increments. The distance between the rulings makes them easier to read compared to the small lines which are used on a vernier.

The scale reading is used with the reading from the needle on the dial face of the tool to calculate your measurement.

Dial and vernier calipers are very similar in cost. Both do not require batteries which means they are always ready to take a measurement.

Digital calipers

digital caliper measuring coin
Digital Caliper Display

Digital calipers use electronic sensors to give a measurement reading. They are easily the simplest caliper to take a reading with.

The values get read off the LCD display like an alarm clock.

At one time they were very expensive and still somewhat are. In recent years, they have dropped in price and gotten more reliable. Tools made in China and other lower labor cost countries have improved in quality, though they can be hit or miss when compared to established tool and gauge companies.

There are many digital calipers available which are not nearly as accurate as they would lead you to believe. This is because their resolution is finer than their accuracy.

Typical accuracies for different types of calipers

A caliper should be accurate to .001”. There are cheap ones or shoddy quality ones that will fail to meet this accuracy but when most people think about calipers, they expect it to be accurate to .001”.

Accuracy is similar across the different types of 0-6” calipers and it may look like digital calipers have better resolution but that isn’t exactly true.

Often digital calipers will have displays that read out farther than they are accurate to. There isn’t any point taking a reading to 5 tenths of an inch or .0005” if the tool isn’t accurate to that level.

Be careful. Some digital calipers will make you think they are more accurate than they actually are.

How cost affects accuracy

Small calipers are easier to make than large ones at the same accuracy. To get a caliper accurate to .001” at 6” will be much easier than at 24”. This is why the cost goes up quickly for larger calipers or their accuracy goes down.

Some calipers will sacrifice accuracy to keep costs down. Some budget level calipers do not meet an accuracy of +/- 0.001” for a 0-6” caliper. Pay attention to the specified accuracy when comparing different tools.

Keep in mind that if something seems too good to be true then it probably is such as a cheap, large range caliper that claims accuracy to +/- 0.001”.

What tools are more accurate than a measuring caliper?

outside micrometer
0-1" Outside Micrometer

Micrometers are another tool frequently used by people who also use calipers to take measurements. The typical accuracy of a micrometer is a tenth of an inch or .0001”. This is 10x more accurate than a caliper.

Dial and test indicators are another type of tool used in machine shops. They usually have dial faces with a needle, or occasionally you will find digital versions.

The accuracy of these indicators varies from .001” for many dial indicators to .00001” for test indicators. Test indicators can be 1000x more accurate than dial indicators and calipers.

dial indicator
Dial Test Indicator

Accuracy vs resolution

Resolution is the how finely your tool will give for a reading. It is not how accurate it is.

Imagine you measure a box.

A less capable digital caliper may measure the length of the box at 6.5005”. The problem is that the caliper may only be accurate to +/- 0.001”. This means you could take that same caliper and measure the same box again, in the same exact location and get a reading of 6.4995” or 6.5015”

Tips for increasing your accuracy using calipers

Know what accuracy you need

The first step is knowing how accurate of a tool you need. You might not need a caliper at all. You might need a micrometer to measure down to a tenth (0.0001”). Maybe you can get away with using a good tape measure.

I don’t know. Only you can decide what accuracy you will need.

General advice would be to get a caliper with an accuracy of +/- 0.001” or better.

Be careful how you hold your caliper

You affect the accuracy of your caliper a lot.

You want to make sure that the jaws of your caliper sit flat when you take a measurement. If they are cock-eyed when you use them, the readings will be larger than the actual size.

Luckily, for outside measurements, such as the length or width of a part, this is easy to do. You can gently rock, again I said gently, and you will feel the caliper settle in when it sits flush.

Inside measurements are slightly more difficult because the jaws do not have a flat spot to settle into. Still, you will want to use the same rocking motion, but be even more careful with it.

Repeatability

No matter what type of measurement you plan to take, take multiple readings to develop an assurance that your measurement is accurate. It is not uncommon to take a measurement and get a reading, only to take two more measurements that are both 0.005” off.

At this point you would want to take more measurements to verify that your first measurement was indeed wrong. Maybe it was dirt, or you had the tool at an angle. Either way, verifying your repeatability will help you take more accurate measurements.

Depth measurements are easy to get wrong

caliper depth base attachment
Caliper With Depth Attachment

Outside and inside measurements aren’t too bad but depth measurements are where things get tricky.

Not all calipers will have the ability to take depth measurements. However, for those that do it is easy to get bad readings when using them to take depth readings.

The shape of the caliper makes them top heavy which means they have a tendency to want to tilt. If your tool moves even just a small amount, it will throw your measurement off by quite a bit.

There are attachments that you can get for your caliper to help steady your tool when taking depth measurements, but they are not a perfect solution.

Another factor affecting accuracy is that the depth measuring rod on a caliper can easily get bent or otherwise out of alignment. This is a common occurrence and even brand-new calipers can come from the factory unable to make accurate depth measurements.

Depth measurements are the most difficult type of measurement to take with a caliper and also the most difficult aspect for a tool maker to build accurately.

Be consistent with your measurements

The amount of force you use when taking measurements with your calipers will change your readings. This is called your “touch”.

If you take a measurement using a small amount of pressure on the caliper and then do the same measurement squeezing the caliper shut and holding it with some force, you will see that your readings can easily vary by a thousandth or two (0.001”-0.002”).

The easiest way to practice being consistent with the force you use to take measurements is to check the same thing over and over.

Checking the accuracy of your caliper

Cheaper calipers can be accurate, but not every cheap caliper will be. Premium tools from Mitutoyo, Starrett or other well-known manufacturers can be off too, but the odds are much less likely.

The problem is that you won’t know the caliper is accurate until you check it. This process is called calibrating. If you don’t have access to everything you need to calibrate a caliper, a less precise version of the process would be called zeroing.

Zeroing your caliper

Zeroing your calipers requires you to close them all the way and reset the zero point.

Zeroing procedure

parts of a caliper

Make sure your tool is clean, especially the jaws of the caliper.

Slide the caliper closed.

For a digital caliper, hit the origin button – this will sometimes be labeled differently (such as Zero) based on the manufacturer of the caliper.

For a dial caliper, loosen the bezel lock screw, twist the dial until the needle reads zero and then lock the bezel lock screw again.

Once you have reset the zero location, make sure to verify it. Do this by opening the calipers up and then closing to the zero position again.

You want to verify that the caliper reads zero each time. The amount of pressure you put on the tool affects the measurement so make sure to use the same amount of force to close your caliper.

Consistent, gentle movements will help you get the most accurate readings out of your tool.

At this point you know your caliper is accurate at the zero location. What is not known is how that same caliper will measure at another location. It may be perfectly accurate at zero but off by ten thousandths or 0.010” at 6 inches.

This process is for your external jaws only and it is entirely possible that your jaws for measuring internal measurements such as holes may not be aligned with the external jaws. The zero location may be different for your internal and external jaws.

This is why ideally you would calibrate your calipers to verify their accuracy over the whole measuring range. Calibration requires additional equipment so many people won’t take the extra step.

What is important is to consider is what level of accuracy you need for your measurement.

Precision measuring tools = be gentle

These things are not hammers. You need to treat them gingerly. They won’t shatter into a million pieces when you set them on a bench but banging them or dropping them means you’re going to have a bad time.

The most common types of damage, all of which would affect accuracy are

  • Shock to the internal workings. This can cause excess drag in the mechanism or simply give bad measurements.
  • Damage to the jaws of the caliper such as nicks or burrs. Even a very small nick can cause your measurement to be off. The inside measurement jaws are more likely to be damaged than the outside measurement jaws.
  • The depth measuring rod can get bent or otherwise damaged and give bad readings. The rods tend to be long and thin which means it doesn’t take much force to damage them.

Calibration

gauge block set
Set of Gauge Blocks

Calibration involves taking a known length standard such as a set of gauge blocks and using them to check the accuracy of the caliper over its whole measuring range.

You would check the caliper at 0 inches, 6 inches and at random intervals between the two. This is the super simplified version of a calibration procedure. If you want a more detailed instruction, then check out our guide to caliper calibration.

Related articles

Ultimate Guide To Reading Machine Shop Numbers & Values

math on chalkboard

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. 

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).

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

texas instruments ti-30xa calculator

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. 

Ultimate Guide to Basic Dimensions

Basic dimensions are shown on a blueprint enclosed in a box. But what do they mean?

Keep reading to find out.

What is a basic dimension?

A basic dimension is a theoretically exact size or location.

Basic dimensions do not have a tolerance applied to them, this includes any general tolerance blocks.

Instead a separate is listed on the drawing that uses the basic dimension.

An example of this would be a true position callout for a hole or set of holes. The basic dimension(s) specify the location of the hole.

The true position of the hole is calculated based on the difference of the actual location compared to the basic dimensions theoretically exact location.

What is a basic dimension used for?

Basic dimensions are used for calculations. They are used to calculate various geometric dimensioning and tolerancing (GD&T) characteristics such as true position, profile or angularity.

In the example above, the 120 degree callout and the 42 diameter bolt circle are the basic dimensions and the true position of 0.2 is the characteristic controlling the basic dimensions.

Using basic dimensions

How is a basic dimension shown on a drawing?

basic dimension example

The symbol for a basic dimension is the dimension shown enclosed in a rectangular frame or box.

This is the convention identified in the blueprint drawing standard ASME Y14.5.

Some drawings may list a basic dimension not in a rectangular frame but instead the dimension will be followed by a Bsc. notation. This is more common on older drawings and does not change the way basic dimensions are used.

Basic dimension examples

basic dimensions for a bolt hole circle
This example has 2 basic dimensions. Both the size of the bolt hole circle and the angle between the holes are basic dimension.

Basic dimensions and tolerances

Can a basic dimension have a tolerance?

A basic dimension itself does not have a tolerance. General tolerance blocks do not apply to a basic dimension.

Instead its value is used to compute another characteristic such as angularity, profile or true position.

general tolerance block
An example of a general tolerance block

Basic dimensions compared to other types of dimensions

Basic dimension vs reference dimension

Basic dimensions are associated with another tolerance or dimension. While they don’t have a tolerance tied to themselves, they are used to calculate another toleranced feature such as the true position of a hole.

Reference dimensions are simply placed on a drawing or blueprint for reference. They have no tolerance associated with them. No matter how far off the given value a reference dimension is, it would never be cause for rejection.

A basic dimension being far off its nominal value would not be cause for rejection itself, but its effect on another feature referencing the basic dimension could be cause for rejection. So if a basic dimension was far off the nominal location, another tolerance would likely be out of spec. 

reference dimensions
Reference dimension examples

Basic dimension vs regular dimension

Regular dimensions have a tolerance assigned to them. This can be directly assigned to the individual dimension or it can be the general tolerances. The regular dimension must fall within the limits of the tolerance.

A basic dimension is instead controlled by another characteristic. The basic dimension can vary by any amount but it must not deviate from the nominal value to the point that the other characteristic (true position callout, profile callout, etc.) is no longer within the specified limits.

How to measure a basic dimension

A basic dimension is measured just like any other dimension. The only difference is that the basic dimension doesn’t have a tolerance directly associated with it. Instead another dimension uses the basic dimension to calculate its value.

How to report basic dimensions

Do basic dimensions need to be listed on an inspection report?

While there isn’t a strict requirement anywhere to include them, I would recommend reporting their values on an inspection report. 

The features have been measured and you likely already have the values. By recording them, you will provide more information and value for your customer. 

You must report the feature control values such as true position, profile value, etc. that use the basic dimension to be calculated.

What about on FAIs?

The requirement for reporting basic dimensions is the same for first article inspection reports. Be aware that some customers may require them even though there is no requirement per AS9102.

Best Woods For CNC Routing

cnc router engraving design

Let’s say you have some extra time on your hands, and you decide to build your own computer. Countless people do this every year, so surely it can’t be too difficult to find the necessary materials, right?

Then you realize you’re going to need some basic electrical wiring. Would you go search through a pile of old electronics and rip out whatever you can find?

Of course not.

You’re going to go find something that is meant for your build.

The same goes for CNC routing. You can’t (or at least shouldn’t) use just any old piece of wood you see lying around.

To build a nice project, you need quality material, and we are going to help you figure out which ones are right for your projector in some cases, experience level.

We do our best to run through as many different types of wood for CNC routing that we could come up with, but if you just want the short and sweet version to help you pick a wood to work with check out our list of the best woods below.

Category

Wood Type

Easiest wood for CNC routing (best for beginners)

Cherry

Best wood for CNC carving

Walnut

Best wood for CNC sign making

Cypress

Best cheap wood for CNC routing

Poplar

Best plywood for CNC routing

Birch

Below is a lengthy list of various types of woods that you can use for CNC woodworking.

While the list may not include absolutely every type of wood you might want to use, it does hit the main ones

The cost of the different woods will vary by region and availability, but we have tried our best to assign a relative cost score to them.

Cost rating system

Keep it simple right? We used a scale of 1-5 dollar signs

$ = cheaper woods

$$$$$ = very expensive woods

Alder

Cost: $

Alder wood is generally light and soft. Its structure is even with straight fibers. Highly pliant, alder wood is one of the preferred woods for furniture makers the world over.

Alder is pretty good for carving, though it can be a bit stringy at times.

Ash

Cost: $

Ash wood is strong, durable and generally light in color. It is coarse, but the grain is fairly straight. As a result of its strength and durability, ash wood has an array of uses but is commonly used in the making of tools, furniture and frames.

For routing, you might find moderate resistance with ash because it’s a stronger wood. Ash can tend to wear your cutters quicker than other, softer woods. If you’re going to use ash, make sure your cutters are sharp before you start.

Balsa

Cost: $

Balsa is the lightest and softest timber used commercially. Though it’s lightweight, balsa is also fairly coarse. It possesses an unusually high degree of buoyancy, and the wood is adaptable to a great number of special uses.

If you’re using softer balsa, it can be prone to tearing along the grain as the cutter goes past. It can also be hard to get a nicely finished edge with balsa.

Beech

Cost: $

Beech wood is known for its fine-textured straight and attractive grain, pliability, strength, and finishing ease. However, Beech wood has a fairly high shrinkage rate, which is why most beech wood ends up as paper.

When routing beech, you’ll likely want to have the router moving at a lower speed to avoid burning.

Birch

birch wood grain

Cost: $

Birch is a stiff wood with light color and wavy grain.

When working with birch, you should go slow and take shallow passes. If routing in one direction causes a lot of splintering, turn the board around and go in the opposite direction. This hits the grain from a different direction. The splintering is caused by the bit digging into the grain. Going the other way stops that.

Birch plywood

Cost: $

For birch plywood, some good advice is to cut the chip load down to about half of what you would normally do.

You should also have your spindle speed as high as you can get it without overheating the cutting tool. For engraving, you will find that it is best to outline the toolpath first.

Cedar

cedar wood grain

Cost: $$

Cedar has a nice smell and good color, but the knots in the wood can make it a bit difficult to work with.

Also, because it’s a softer wood, you need to be careful with tear outs – this is a common problem with cedar. To avoid the tear-out issue, try doing multiple passes.

There are some who swear by soaking and freezing cedar before working with it as a way to get a better finished product.

Cherry

Cost: $$$$

Cherry wood is hard, durable, resistant to rot and decay, and has a pretty good ability to withstand shock.

It’s also easy to carve, cut, and mold.

Cherry is interesting because it is a relatively soft hardwood.

In other words, cherry wood is a fantastic option for CNC wood routing, and you’ll find that it is popular among hobbyists and professionals alike. Cherry has a reputation for being easy to work with due to its versatility.

Cyprus

Cost: $

Cypress wood is extremely soft, and a lot of woodworkers will tell you that this stuff carves like butter.

Cypress is a really great option if you’re looking at making signs. Cypress also holds up extremely well outdoors. It is a decay-resistant wood.

One downside to cypress would be that it can be a knotty wood, similar to cedar.

In other words, cherry wood is a fantastic option for CNC wood routing, and you’ll find that it is popular among hobbyists and professionals alike. Cherry has a reputation for being easy to work with due to its versatility.

Elm

Cost: $$$

Elm wood has fairly open pores, which can lead to a lot of tear-outs if you’re not careful.

Some people also find Elm to be a bit stringy. However, elm is also known for being extremely tough, so if you can avoid tear-outs and your project isn’t too stringy, you will have your elm wood project for a long time to come.

Elm is a little pricier now than it used to be because “Dutch Elm Disease” wiped out a good portion of elms around the world.

Fir

Cost: $$

Fir has a nice consistent pattern and is pretty easy to work with.

Fir can have some issues with tear-outs, but most people can easily avoid these through climb cuts. Though Fir can splinter a bit, it isn’t known for having knots, which makes it easier to work with.

Mahogany

Cost: $$$$$

Many woodworkers the world over will consider genuine mahogany to be the best wood on the market.

It’s durable, stable, and looks beautiful. It’s a fairly hardwood but is easy to work with. Its mostly straight, open grains mean the wood rarely tears out.

When working with mahogany, you should go a bit slower in terms of your feeding, and don’t overload your carvers.

Maple

maple wood grain

Cost: $$$$$

If you don’t have a ton of experience, maple can be a little bit difficult to work with.

The wood is extremely hard, so you’ll need very sharp cutters, though the maple will dull them while cutting.

You should also cut at a lower speed to prevent any burning. Though maple might be hard to work with, you’ll love the final product because it’s a beautiful wood.

MDF

Cost: $

Medium-density fiberboard is super cheap and versatile. MDF is basically sawdust and glue, so be prepared for a sandstorm when you’re working with it.

Still, people find MDF super easy to work with as it carves and cuts extremely easily.

Oak

red oak wood grain

Cost: $$$$

Oak is a heavy, hard wood that rarely breaks. Since it’s so hard, you want to be a little careful when it comes to cutting.

Make smaller passes, and take multiple passes, so you don’t break any of your bits. Also, watch out for any burning.

Paduak

Cost: $$$

You’ll really like the way padauk carves but be sure to bring a sharp bit. The reason people like to work with Padauk is that it has nice, straight grains.

One thing to watch out for when working with Padauk is the dust. When you start cutting this wood, you’ll get a lot of dust, so you might find a dust boot helpful.

Pine

pine wood grain

Cost: $

Pine generally machines well, but sometimes certain cuts can get a little bit gummy on you.

Another thing about pine is that it’s a fuzzy wood, so it can be helpful to sand the wood down both before and after you work with it.

Making multiple passes can also reduce some of the fuzz. Pine may not be your first choice to work with, but you should learn how to machine pine because it’s reasonably cheap and available everywhere.

Pine plywood

Cost: $

Like with regular pine, again get a lot of fuzz. The benefit here, though, is that this stuff is so easy to find and it’s cheap.

Be sure not to cut too deep and take multiple passes when working with pine plywood. Patience will be key if you want the project to turn out well.

Poplar

poplar wood grain

Cost: $

Similar to pine, Poplar is widely available, cheap, and leaves behind a lot of fuzz.

So, like with Pine, be sure to sand the Poplar down well. You will also want to have sharp bits and a slower speeds and feeds to avoid any tearing.

Poplar will take paint really well, so if you’re working on a project that you’ll ultimately want to paint poplar might be your choice of wood.

Red gum

Cost: $$$

Due to its softness and low density, people generally find red gum easy to work with.

However, red gum does have interlocked fibers, so be careful to avoid tear-outs. Another criticism of red gum is that it can warp a lot when drying out.

Redwood

Cost: $$$

While Redwood is light but strong, it does splinter fairly easily. Make sure you’re using shallow cuts to avoid tear-outs.

If you’re just looking for a carving project, redwood will be fantastic due to its softness.

Spruce

Cost: $

Spruce is not really known for being great wood to route with. It splinters easily and can have hidden sap pockets that can’t be cut through and will make your bit super sticky.

With short fibers and many knots, you may find it difficult to work with spruce.

Walnut

Cost: $$$$

Walnut is a very popular wood when it comes to routing. It cuts well. If you have a sharp bit, then cutting through walnut is like passing a hot knife through butter.

Another great feature of walnut is that it is not really known to burn while routing. However, Walnut dust can be highly irritating, so be sure to protect your eyes. A dust collection system of some sort would be advised.

Western red cedar

Cost: $$$

Western red cedar has a really wide grain which can be helpful for routing. That said, this wood can easily tear out if you’re not careful. This red cedar can be a better option than regular cedar because it has fewer knots.

Another benefit of red cedar is that it is good to use for outdoor projects.

Yew

Cost: $$$$

Yew can be a tough wood to work with. For one, when yew trees grow, they can contort in a way to that creates a lot of cross-fibers, which can lead to tear-outs.

Additionally, Yew wood can come with a whole lot of knots that you’ll have to work around.

Things to consider when choosing your wood for CNC routing

Clean up

Some woods that create more fuzz – such as pine and poplar – are going to require additional sanding. You can’t just pull these woods off the machine and expect a finished product.

Other woods may not have fuzz, but the cutting action will create rough edges that have to be sanded out. Keep this in mind when creating a project timeline.

Additionally, some of these woods are heavy on the dust. All of the woods listed will create some dust, but some woods are worse than others. You’ll definitely need a shop vac or other form of dust collection in use, and it could be very helpful to have a dust boot.

Knots

A knot is a portion of a branch or limb that has become incorporated in the trunk of a tree. Knots can change the direction of the wood, which make the wood vulnerable to tear-outs.

Your machining parameters should be reduced when working with a knotted portion of the workpiece to avoid shock loading.

Before you can machine them, use 5-minute epoxy to lock loose and loosening knots into place and fill any gaps and voids. When the epoxy cures, you can saw, joint, or plane the wood without fear of knocking the knot out, or worse, sending it flying across the shop or hurting you or your machine.

Price

Depending on what wood you use, your project can skyrocket up in price.

The more exotic woods you use, the more expensive they will be.

Redwood, for example, only grows in a very specific location and environment, so that makes it rarer. Pine, on the other hand, is easily available so it’s cheap.

Expensive woods can be worth it if you’re making a nice project, but don’t spend a bunch of money on wood if you’re not sure how the project will turn out. It is best to practice with the cheap stuff until you get things more figured out.

When you do start moving up to more expensive woods, run some test cuts or small test projects to try out your setup before committing to a large project.

Where to buy wood for CNC routing

You can go to your local hardware store to check out their wood selection. Some stores will have scrap or damaged pcs that can be had for free or at a large discount.

This can be a good way to get material for a small project or for testing out cuts on different types of wood.

You can also find a lumber mill near you and see if they’ll sell you any wood. Oftentimes, lumber mills will have excess wood that they can’t use that they will sell you for cheap.

Break Edge – All About

break edge blueprint examples

A break edge means the removal of material, usually in the form of a chamfer or radius to remove the sharp edge.

Machining a surface will often leave a corner which can be dangerous for both the part and the part handler. Many times there will be a burr (raised piece of material), left on the edge which can be razor sharp. Using a deburring tool can break the edge to remove the sharp 

A broken edge is usually specified as a maximum value or with no value at all. If no value is specified, the break edge has not been constrained sufficiently.

A break edge callout with no maximum size referenced would normally be assumed to be approximately .005-.010” though in some instances it could be larger.

What does a break edge look like?

Break edge on a physical part

In the brass cube below, notice how the corners have all the sharp edges removed. This is an example of a break edge.

metal cube with break edge

Break edge on a blueprint

Break edge symbol

There is no GD&T symbol for a break edge. Break edges are also not referenced in the engineering drawing standard ASME Y14.5.

Break edge callouts are specified directly on the drawing to reference a certain surface or as a note e.g. “Break all sharp edges”.

At times, the break edge specification may be contained in the general tolerance block such as shown below.

Break edge note example

general break edge note on blueprint
Break edge note example

How to make a break edge

Break edge on wood

Using 180 grit fine sandpaper is the easiest way to create a break edge on a wooden workpiece. This can also be used together with a block plane to chamfer the edge and then soften it with a light sanding.

Break edge on metal

Because metal tends to be more durable, you have more choices for creating a break edge on your piece of metal.

You can use:

  • A chamfer deburring tool which is a specialty tool designed to remove burrs from the edges of parts
  • A file to knock the edge off a part
  • Sandpaper
  • A grinding wheel
  • A rotary tool such as a Dremel

Break edge on glass

To create a break edge on a piece of glass, use one of the following:

  • Diamond file
  • Grinding wheel
  • Rotary tool with diamond wheel

How to measure a break edge

Which measuring tools to use

igaging pocket comparator with reticles and case
A pocket comparator with various reticles for measuring

The size of a break edge is measured the same as a standard chamfer or radius. If a measurement is required, a pocket comparator or eye loupe with a reticle are the most common inspection tools to use. 

An optical comparator with or without an overlay could also be used. See the examples below to better understand how the size of a break edge would be determined.

How to measure the break edge based on your blueprint

break edge examples

On the left is a chamfered break edge. The size is measured from the left edge of the part to the intersection of the break edge and the top of the part. This is done in both the x and y directions (up and down, left and right). 

On the right is a break edge created by a radius. The same measurement technique applies with the exception that the intersection would now be called the tangent point or point where the radius meets the straight edge.

Break edge compared to similar features

Break edge vs chamfer

The difference between a break edge dimension and a chamfer dimension is generally in the tolerancing of the two. A chamfer is usually thought of as being toleranced in a way that places tighter constraints on the feature. 

Often a chamfer callout will have a tolerance associated with the angle and a break edge will not.

Break edge vs radius

A break edge can be a radius. Many times, the person or company machining the part will round the edge using a variety of techniques including tumbling, specialty tools or even sandpaper.