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Guide to Becoming a CNC Operator

July 12, 2022September 23, 2021 by Brandon Fowler

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.

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.

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

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?

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?

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?

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.

For more information check out these related articles:

Spotfaces – All About

May 6, 2022February 19, 2021 by Brandon Fowler

What is a spotface?

A spotface is a machined section of a part that allows a fastener to sit flat. This is usually a bolt head or washer but can be other fasteners. A spotface is generally very shallow and removes just enough material to create the clean, even, flat surface. Spotfaces are most often used when machining castings or forgings. Spotfacing is done using a manual or CNC milling machines.

Spotface vs counterbore

A spotface is functionally no different than a counterbore. A counterbore usually references a feature that is deeper than a spotface. While a spotface creates a flat mounting surface, a counterbore acts to recess the fastener. It would be safe to call a spotface a counterbore but not the other way around.

Spotface vs countersink

The primary difference between a countersink and a spotface is that the countersink has an angled bottom whereas a spotface has a flat bottom.

Spotface symbol

The symbol used to callout a spotface is the counterbore symbol with the letters SF in the middle. This is per the engineering drawing standard ASME Y14.5. At times, a blueprint may indicate a spotface feature simply through the use of a counterbore symbol. Additionally, older drawings and blueprints may reference a spotface as SF or SFACE instead of using the symbol.

How to dimension a spotface

A spotface is dimensioned by specifying its diameter and depth. At times the amount of remaining material may be specified instead of the depth. The symbols for diameter and depth are shown below.

Spotface example

Want to learn more?

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

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

Luckily, we know someone.

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

For more information see these related articles:

TYP & Typical on Blueprints [What They Mean & How to Inspect Them]

May 6, 2022January 20, 2021 by Brandon Fowler

What does typical mean on a blueprint?

Typical on an engineering drawing identifies a repeated feature. This is identical to a feature which is identified as 2x or 5x.

A typical dimension callout will occasionally be followed by a 2x, 5x or similar, to specify the quantity of features which are tolerance the same.

The typical callout will most often be used as part of a repeating pattern such as a bolt hole circle, to identify the hole sizes or angle between the holes.

Another common application is to identify a common chamfer size on a component. It should be noted that the notation of “typical” is not a part of the current revision of the ASME Y14.5 standard and therefore not a recommended notation for use on an engineering drawing. There are however countless blueprints in the wild which may already use this language.

What is the symbol for a typical dimension?

There is no GD&T symbol for a typical dimension. A typical dimension callout is identified with either TYP. or TYPICAL. In the example below, the typical notation is used to reference that the slot on both sides of the part is to be machined to the same depth.

A better way to identify the same dimension would be as shown below. It is best to not leave anything to the imagination of the person interpreting the blueprint.

Want to learn more?

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

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

Luckily, we know someone.

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

For more information see these related articles:

Best CNC and Machining Books

A Beginner’s Guide to Calipers – Dial and Digital

Engineering, Manufacturing and Quality Abbreviations and Acronyms

January 29, 2020 by Brandon Fowler

OMG why are there so many acronyms and abbreviations? FYI here is a huge list of common meanings. Hopefully it helps decipher some of the jargon and gibberish.

8D – method of problem solving commonly used in the automotive industry.

AQL – acceptance quality limit, previously acceptable quality limit

APQP – advanced quality product planning

AS9100 – aerospace quality standard

ATP – acceptance test procedure

BOM – bill of materials

CAD – computer aided design

CAGE – Commercial and Government Entity code

CAM – computer aided manufacturing

CAPA – corrective and preventive action

CAR – corrective action report

CFE – customer furnished equipment

CFM – customer furnished material

CNC – computer numerical control

COA/C of A – certificate of analysis

COC/C of C – certificate of conformance or certificate of compliance

COTS – commercial off the shelf

CSM – customer supplied material

CT – center thickness

DFARS – Defense Federal Acquisition Regulation Supplement

DFMEA – design failure mode effects analysis

DPA – destructive physical analysis

DPAS – Defense Property Accountability System

DPPM – defective parts per million

DSS – data summary sheet

ECN – engineering change notice

EIDP – end item data package

ERP – enterprise resource planning

ESD – electrostatic discharge

ETV – edge thickness variation

FAI – first article inspection

FAIR – first article inspection report

FMEA – failure mode and effects analysis

FOB – free on board

FOD – foreign object damage

FW – face width

GFE – government furnished equipment

GFM – government furnished material

GFP – government furnished property

GIDEP – government industry data exchange program

GMIP – government mandatory inspection points

GSI – government source inspection

GSS – government source surveillance

HIC – humidity indicator card

IAQG – International Aerospace Quality Group

IAW – in accordance with

IOT – internet of things

ISO – International Organization for Standardization

ITAR – International Traffic in Arms Regulation

JIT – just in time

KPI – key performance indicator

MBB – moisture barrier bag

MRB – material review board

MSDS – material safety data sheet

NADCAP – National Aerospace and Defense Contractors Accreditation Program

NC – non conformance

NCM – non conforming material

NDT – non destructive testing

NIST – National Institute of Standards and Technology

OCM – original component manufacturer

OD – outside diameter

ODM – original design manufacturer

OEM – original equipment manufacturer

OTD – on-time delivery

PCB – printed circuit board

PDCA – plan, do, check, act

PEM – plastic encapsulated microcircuits

PFMEA – process failure mode and effects analysis

PID – product identification document

PL – parts list

PM – preventative maintenance

PPAP – Production Part Approval Process

PO – purchase order

QA – quality assurance

QAPP – quality assurance program plan

QC – quality control

QML – qualified manufacturers list

QPL – qualified product list

QTP – qualification test plan

QTR – qualification test report

RCA – root cause analysis

REACH – registration, evaluation, authorization and restriction of chemicals

RFI – request for information

RFQ – request for quote

RMA – return material authorization

RoHS – Restriction of Hazardous Substances

SCAR – supplier corrective action request

SDS – safety data sheets

SMP – supplier management process

SOP – standard operating procedure

SOW – scope of work

SPC – statistical process control

TDP – technical data package

TIR – total indicator runout

WI – work instruction

WIP – work in progress

XRF – x-ray fluorescence

Ballooning/Numbering A Blueprint

February 13, 2021January 22, 2020 by Brandon Fowler

What is a ballooned or numbered blueprint?

Commonly referred to by many different names including ballooned drawing, bubble drawing, numbered print, etc. A numbered drawing or blueprint is a way to identify individual attributes of a part or assembly as depicted in an engineering drawing. The numbers and balloons or bubbles are ordinarily done in red ink or a red font as seen above.

What are ballooned drawings used for?

Numbered drawings are a common component in the inspection process. They can be a part of your in house inspection procedure or a requirement which you provide to your customers. Ballooned drawings are also frequently used as part of a first article inspection report package. They allow the reader to connect an individual measurement to its location on the blueprint. This is especially handy when multiple attributes with the same nominal values are present.

How to number a drawing

Numbering or ballooning a blueprint is a process that has some flexibility to the order in which attributes are labeled. The most important aspect is that all attributes are assigned a number including all notes and general tolerances as needed. When in doubt, number it. Where to start is a matter of preference but make sure that your numbering sequence is easy to follow. Generally the person numbering the drawing will start in the top left view and work their way clockwise assigning numbers to attributes in that particular view. This process is repeated for all views present on the drawing in a top to bottom, left to right manner similar to the way you read a book. Some users will list attributes in the notes first such as material, but this is simply a matter of preference. Just make sure to number all the relevant attributes in the notes. If you work in a logical manner, it will be much easier for the customer or reader to follow along.

Example of a fully numbered drawing

What to include in a numbered drawing

Assign a number to every attribute on the print including all notes and applicable general tolerances. Some notes may include more than one attribute in a single note which requires a numbered attribute.

For more information see these related articles:

Chamfers – All About

Datums – All About

May 6, 2022January 22, 2020 by Brandon Fowler

What is a datum?

A datum is a reference point for measurements. A datum is a theoretically perfect feature. It is often a main surface of a part called a plane but can also be a point such as the center of a diameter or an axis such as the center of a cylinder.

How are datums used?

Datums are used to orient measurements. In the case of something simple such as a perpendicularity specification, the datum is the surface against which the toleranced feature is checked. For a positional tolerance, features are located relative to a datum.

Symbol for a datum

Datum names

Datum names are identified with a capital letter. The most important reference feature is usually identified with a capital A. In order of importance datums will be assigned consecutive letters (B, C, etc).

How is a datum used in a feature control frame?

Datums are placed at the end of a feature control frame.

Primary datums

A primary datum is the main locating surface used for alignment.

Think of a box set on a table. In this case the bottom of the box is the primary datum.

The table would be used to simulate the primary datum. In this example measurements could be taken from the table to other features of the box to verify they meet the required dimensions.

The primary datum controls one axis of freedom. The box can move back and forth or spin in place on the table but it can not turn end over end. This is similar to the way a granite surface plate is used in machine shops all over the world.

Secondary datums

A secondary datum is the secondary alignment feature. In the box on a table example, if the table and the box were pushed up against a wall then the wall would be the secondary datum.

The box would contact the wall at a minimum of two points. Contacting the wall would constrain the movement in another axis.

The table controls end over end movement. The wall stops the box from spinning. It is however still able to move back and forth along the wall.

Tertiary datums

A tertiary datum is the third alignment feature. In the box on a table example, if the box on a table which is now against a wall was pushed into a corner then the new wall would be the tertiary datum. This new datum works to control the last remaining axis of movement.

What is a datum target?

A datum target is a specified location that is used to measure a part. It identifies the point(s) from which measurements will be taken.

The use of datum targets or points provides a level of control over the datum surface. Some surfaces are incapable of being used like a normal datum.

A very large datum surface or a surface that has a lot of variation in its form are two common reasons why datum targets are used.

Datum targets are also used to mimic real world use such as contact points in an assembly.

Datum target symbol

The top half of the datum target symbol is often empty. The upper half lists the area of the datum target when specified. The lower half of the datum target symbol lists the datum target name.

Is a datum real or theoretical?

Both really. The real datum is the actual surface referenced. This surface is imperfect and will have variation to it.

No surface is perfectly true.

In practice though a datum is used as a theoretically perfect surface.

A good example would be placing a datum surface down on a surface plate which is known to be very flat. The imperfect actual surface of the part will come to rest on the high points sitting on the surface plate. Measurements can be taken from the surface plate as if it was the datum surface itself.

Examples

True position callout referencing datums A & B

Perpendicularity callout referencing datum A

Circular runout referencing datum A

Datum dimensioning vs chain dimensioning

Chain dimensioning is the process of dimensioning features of one another in a row. Datum dimensioning is used when features are referenced from a common point. Take a look at the differences in the examples below.

A disadvantage of chain dimensioning is that the tolerances stack up. This means that the location of the far right hole can actually vary by as much as +/- 0.040”.

The example which uses datum dimensioning maintains the +/- 0.010” tolerance for each location. Chain dimensioning can be a perfectly acceptable way to tolerance your parts, just make sure you have taken into account the additional tolerance that can apply to the feature.

Plural of datum

Nothing too strange. More than one datum would be multiple datums.

Want to learn more?

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

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

Luckily, we know someone.

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

For more information see these related articles:

Feature Control Frames – All About

May 6, 2022January 19, 2020 by Brandon Fowler

What is a feature control frame?

A key component of geometric dimensioning and tolerancing (commonly referred to as GD&T). On engineering blueprints, the feature control frame consists of a symbol to identify the type of tolerance, the amount of tolerance and reference datums if applicable.

How to read a feature control frame

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

Examples

True position of 0.2 to datums A and B

Perpendicularity of 0.001 to datum A

Cylindricity of 0.001

Circular runout of 0.010 to datum A

Composite feature control frame

A composite feature control frame controls both a pattern on a part and the location of individual items in the pattern.

The upper section of a composite feature control frame specifies the tolerance for the pattern to the overall part.

The lower section specifies the tolerance for individual features to the pattern. In the example of a bolt hole circle, the upper section controls the tolerance for the location of the bolt hole circle on the part. The lower section would control how closely the individual holes must follow the pattern.

Feature control frame symbols

For more information see our GD&T Symbols Quick Reference

Basic dimensions

Basic dimensions are identified by a rectangular frame around the dimension.

They are dimensions that are theoretically exact. They do not have a tolerance themselves (general blueprint tolerances do not apply).

Instead they are controlled by another characteristic. This is often seen with positional tolerances such as the true position of a hole. The hole location will be specified as basic dimensions.

A true position tolerance will then be assigned to the hole which will control how far off the nominal location the hole can be.

Want to learn more?

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

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

Luckily, we know someone.

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

For more information see these related articles:

A Beginner’s Guide to Depth Micrometers

August 31, 2021December 31, 2019 by Brandon Fowler

What is a depth micrometer?

A depth micrometer (or depth mic) is a measuring tool commonly used to check precise measurements of slots, keyways, grooves and various other locations. They are a very accurate measuring device.

Depth micrometers are commonly used to take measurements to an accuracy of .001″ or .0001″ in inches. Measurements in millimeters can be made down to .01mm or .001mm.

How to use a depth micrometer

Depth mics can be used to measure many different types of part characteristics. I will explain how to check a hole depth.

Before using your micrometer, ensure that the measuring tool and surface to be measured are free of dirt, debris, chips, etc. The micrometer thimble should spin freely. Place the tool on part over the hole. Spin the micrometer thimble until the rod extends to the bottom of the hole. Use the ratchet or friction stop if available on your tool.

Note: The depth mic should be checked for accuracy whenever a rod is changed to measure a different size. It can be easy for something to get contamination in between the micrometer and the depth rod where they come together.

Keeping things as clean as possible will help with this problem.

How to read a depth micrometer

I recommend a digital depth micrometer for ease of measurement especially if the measurer will only occasionally be taking readings with their micrometer. Unfortunately the price of a digital depth mic can be quite high so if you must use an analog micrometer then please keep reading.

The most common varieties of depth micrometers read in increments of one thousandth of an inch (.001″) or one ten-thousandth of an inch (.0001″). The process of reading a measurement from either type is similar. Along the sleeve of the depth micrometer will be graduations similar to a ruler.

The graduations at every fourth interval are most often numbered 0, 1, 2 and so forth. These numbers represent .100″ or one hundred thousandths of an inch. If using a depth micrometer with a 1-2″ rod, the graduation marked 6 would correspond to a measurement of 1.600″. The graduations between the numbers are each .025″ or twenty five thousandths of an inch. If we were to use a depth micrometer with a 4-5″ rod and obtained a measurement at the 3rd graduation after the .200″ mark, then our reading would be 4.275″. This would be the reading if the 0 on the thimble lined up exactly with the 3rd graduation after the .200 mark on the reading line.

If instead the number ten lined up with the reading line and we could still see the 3rd graduation after the .200″ mark, then our measurement would be 4.285″. For micrometers that read to .0001″ we would additionally rotate the micrometer without turning the spindle to determine which numbers line up on the sleeve and thimble. If a number lines up on the thimble with the number 7 on the sleeve, our reading would now be 4.2857″.

Formula for depth micrometer readings

Base depth micrometer rod size + (.100″ x largest visible number) + (.025″ x graduations visible after the largest number) + (.001″ x reading from thimble) +(.0001″ x reading from sleeve for .0001″ micrometers)

Example for a depth micrometer with a 1-2″ rod

1.000″ + (.100″ x 4) + (.025″ x 2) + (.001″ x 3) + (.0001″ x 8) =

1.000″+ .400″ + .050″ + .003″ + .0008″ = 1.4538″

When to use a depth micrometer

Depth micrometers while very accurate have one downfall. Depth micrometers like most standard micrometers are most commonly found in 1″ measuring range increments (3-4″, 4-5″, etc.). For a depth micrometer, this means that multiple sized rods are needed to be capable of covering the measurer’s measurement needs. Because of this depth micrometers are commonly sold in sets.

A 0-3″ micrometer set will cover the needs of most applications while a 0-12″ set is more than most people, especially hobbyists will need.

What makes a good depth micrometer

A good depth micrometer needs two things: precision and accuracy. Some adjustments can be made with most depth micrometers to account for small errors in accuracy but nothing can be done to fix a tool that isn’t precise.

Quality depth micrometers will turn smoothly without any drag. This is the telltale sign of a good tool. If your depth micrometer ever feels like it is rubbing internally, disassemble the micrometer and clean per the manufacturers instructions to eliminate any possible contamination that may be causing the issue.

Where to buy depth micrometers

Depth micrometers are available from a number of online retailers. For a more in depth guide of which depth micrometer is best for your situation, please see our reviews section.

Some general advice, as usual for most products Amazon has a number of good options available. Walmart sells depth micrometers but we do not recommend any that they currently offer.

Are cheaper depth micrometers as good as expensive ones?

While some of the cheaper (made in China) type depth micrometers have gotten much better than they were in years past, they are nowhere near the same quality that you will see in a depth micrometer from one of the tried and true manufacturers such as Starrett or Mitutoyo.

A depth micrometer is the type of tool that is best to purchase once. In most cases it can be more beneficial to search for a used option on Craigslist or Facebook marketplace. Ebay can also be a good alternative. For more information on the best depth micrometers for your application, see our Best Depth Micrometers article.

How to calibrate a 0-1" depth micrometer

Verify that the micrometer is clean.

Visually examine the micrometer for any condition that could cause errors in the calibration.
Whenever necessary to disassemble for adjustment, use care and cleanliness to assure no damage to the internal threads of the tool.
Spin the thimble until the depth rod is inside the tool.

Place the tool on a surface plate and spin the thimble to extend the depth rod to the zero position. Use the ratchet or friction stop if available.
Repeat the process by placing the depth micrometer on gage blocks and overhanging the tool to allow the depth rod to extend down to the surface plate.
Check accuracy of the micrometer at various locations within the tool’s measuring range. Gage blocks which have been calibrated themselves should be use for this operation. Block sizes which are used should test the micrometer at different positions of the thimble and not only increments of .025″. This ensures the scale on the thimble is accurate.

Adjustments can be made at this step as needed. Different depth micrometers have different procedures for adjustment. Consult manufacturer documentation for instructions regarding the adjustment of your micrometer if needed. If adjustments are made, the calibration procedure should be started over to verify the adjustments were adequate.
Calibration results are commonly recorded in a register or database for traceability of measurement history.

For more information check out these related articles:

GD&T Symbols Quick Reference

May 6, 2022December 31, 2019 by Brandon Fowler

A cheat sheet type reference for the most common GD&T symbols.

Symbol	Name	Description
	Straightness	Straightness is how close to a straight line a feature is.
	Flatness	Flatness is how flat a feature is. All points on the feature must lie within two parallel planes that are spaced the tolerance width apart.
	Circularity	Often called roundness. Circularity refers to how close to a perfect circle a single location is. Circularity is at one location. This can be thought of as a single circle on a cylinder. Usually circularity would be checked at multiple locations along the cylinder. This cylinder can be the inside of a hole, the outside of a shaft or various other features.
	Cylindricity	Cylindricity is the same as circularity (often called roundness) with the exception that the requirement applies across the whole surface instead of at a single location. Cylindricity works to control taper whereas circularity does not.
	Parallelism	Parallelism refers to how close to 180 degrees two surfaces are.
	Perpendicularity	Perpendicularity is how close to 90 degrees two features are. This can be any combination of planes or axes.
	Angularity	Angularity is the same as perpendicularity with the exception that the two features are not at 90 degrees to one another but instead at a different specified angle.
	Concentricity	Concentricity is how close the axes of two features run together.
	True Position	True position is a theoretically exact location of a feature.
	Symmetry	Symmetry is the same as concentricity but is applied to features that aren’t round. This means that the axes or centers of two features must run together.
	Profile of a Line	Profile of a line controls the shape of a cross section of a feature. It can control size, form and location.
	Profile of a Surface	Profile of a surface is similar to the profile of a line tolerance but it controls the entire surface instead of a single cross section.
	Circular Runout	Circular runout controls the runout in a single location of a circular feature such as a cylinder.
	Total Runout	Total runout controls the runout of an entire surface of a circular feature instead of at a single location. When compared to circular runout, total runout would check the entire cylinder.

Want to learn more?

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

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

Luckily, we know someone.

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

Get the Best GD&T Training Available

For more information see these related articles:

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A cheat sheet type reference for the most common GD&T symbols.

Symbol	Name	Description
	Straightness	Straightness is how close to a straight line a feature is.
	Flatness	Flatness is how flat a feature is. All points on the feature must lie within two parallel planes that are spaced the tolerance width apart.
	Circularity	Often called roundness. Circularity refers to how close to a perfect circle a single location is. Circularity is at one location. This can be thought of as a single circle on a cylinder. Usually circularity would be checked at multiple locations along the cylinder. This cylinder can be the inside of a hole, the outside of a shaft or various other features.
	Cylindricity	Cylindricity is the same as circularity (often called roundness) with the exception that the requirement applies across the whole surface instead of at a single location. Cylindricity works to control taper whereas circularity does not.
	Parallelism	Parallelism refers to how close to 180 degrees two surfaces are.
	Perpendicularity	Perpendicularity is how close to 90 degrees two features are. This can be any combination of planes or axes.
	Angularity	Angularity is the same as perpendicularity with the exception that the two features are not at 90 degrees to one another but instead at a different specified angle.
	Concentricity	Concentricity is how close the axes of two features run together.
	True Position	True position is a theoretically exact location of a feature.
	Symmetry	Symmetry is the same as concentricity but is applied to features that aren’t round. This means that the axes or centers of two features must run together.
	Profile of a Line	Profile of a line controls the shape of a cross section of a feature. It can control size, form and location.
	Profile of a Surface	Profile of a surface is similar to the profile of a line tolerance but it controls the entire surface instead of a single cross section.
	Circular Runout	Circular runout controls the runout in a single location of a circular feature such as a cylinder.
	Total Runout	Total runout controls the runout of an entire surface of a circular feature instead of at a single location. When compared to circular runout, total runout would check the entire cylinder.

Want to learn more?

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

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

Luckily, we know someone.

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For more information see these related articles:

Micrometers vs Calipers

A Beginner’s Guide to Calipers – Dial and Digital

July 24, 2022July 24, 0202 by Brandon Fowler

What is a caliper?

A caliper is a measuring tool used to check precision measurements.

The biggest strength of calipers is how versatile they are.

Calipers come in many forms, including digital, dial and vernier versions.

They are commonly used to take measurements to an accuracy of .001″ or .01mm.

What are calipers used for?

Below is a list of the most common caliper uses:

Inside measurements – hole sizes, slot widths

Outside measurements – lengths, widths, diameters, thicknesses
Depth measurements – depth of holes, slots, step locations

Many precision measuring tools such as micrometers or dial indicators are specialized and only take a single type of measurement. Calipers can take a larger variety of measurements and their measuring range is usually much larger than more accurate alternatives.

Types of calipers

There are three main types of measuring calipers. They are:

Digital calipers
Dial calipers
Vernier calipers

They all perform the same types of measurements and to the same level of accuracy. The main difference between the three types of calipers is the display/scale that is used to read measurements.

The display/scales for each type of caliper are shown below.

Digital calipers

Dial calipers

Vernier calipers

Parts of a caliper

The parts are very similar on all three types of calipers; digital, dial and vernier.

You can see the slight differences in the pictures below.

Digital caliper parts

Dial caliper parts

Vernier caliper parts

Calipers vs micrometers

Micrometers are another kind of precision measuring tool.

Micrometers are more limited in what they can measure. See the two types of measuring tools compared below.

	Micrometers	Calipers
Accuracy	0.0001"	0.001"
Measuring Range	1" increments	0-6"
Types of Measurements	Outside Measurements	Inside, Outside & Depth Measurements

How to use a caliper

The most common type of measurement that calipers are used for is internal and external measurements.

To take a measurement with your caliper follow these simple steps:

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

For an outside measurement, slide the jaws of the caliper open until they are far enough apart to be placed over the part to be measured.
Now proceed to close the jaws while trying to keep the jaws perpendicular to the surface being measured.
Multiple measurements should be taken to verify that the caliper has yielded the true reading. For example, if a measurement is taken where the jaws of the caliper are not perpendicular to the surface being measured then the reading obtained can be larger than the true size.

Note: Do not exert a large amount of force on the caliper in the direction of measurement. This can cause the tool to flex and distort the true measurement. It is best to place the same amount of force that is used to zero the caliper.

How to read digital caliper

Reading a digital caliper is easy.

The digital readout display clearly shows the measurement value.

Because they are so easy to read, I highly recommend anyone who is looking to get started working with calipers starts with a good set of digital calipers first.

Digital calipers have the ability to quickly switch between metric and inch readings. Some also allow you to switch between fractional measurements as well.

How to read a dial caliper

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

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

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

Dial calipers come in multiple varieties, but most have their measurement read in the same way. A reading is taken on the main scale and the dial face. The two readings are added together to get the final measurement.

Still need more info?

See our full guide to taking and understanding measurements with your dial calipers.

What makes a good caliper

Whether digital, dial or vernier, a good digital caliper needs two things: precision and accuracy.

Some adjustments can be made with most calipers to account for small errors in accuracy but nothing can be done to fix a tool that isn’t precise.

A quality caliper will move smoothly without any drag. This is the telltale sign of a good tool.

If your caliper ever feels like it is rubbing or dragging then it is most likely the result of damage from being dropped or contamination exposure.

Unfortunately if you caliper isn’t moving smoothly there isn’t usually much that can be done besides oiling the tool and sliding back and worth. Then wipe off the oil and repeat the process over again.

Make sure to consult the manufacturer’s instructions before performing this operation as calipers can vary and only use machine tool oil such as this one by Starrett.

Caliper calibration

Calibrating measuring tools such as calipers is important because it allows you to have confidence that your measurements are correct.

Check your calipers regularly to make sure they are accurate.

For more information check out these related articles:

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What is a caliper?

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