Ultimate Guide to Digital Calipers

Digital calipers are one of the most versatile measuring tools available. Used by machinists and hobbyists alike, they have found a home in many toolboxes around the world.

Whether you need to learn a little more about how they work, what they are capable of, or maybe you simply want to find the best digital caliper for your application. 

No matter what you seek, we have you covered. Check out our top digital caliper related posts below and drop a comment below if you don’t find what you need. We will be sure to add to our extensive list of posts.

A Beginner's Guide to Digital Calipers

Everything you need to know about calipers. A comprehensive guide for anyone looking to learn all about calipers.

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Digital Calipers Buyers Guide

Find out which digital calipers top our best of list. Includes tips and things to consider when looking for a quality measuring caliper.

Digital Caliper Info Guides

Dive into a selection of articles specifically chosen to help you learn all about digital calipers.

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Digital Caliper Reviews

Check out the latest digital caliper reviews from brands such as Starrett, Mitutoyo, Fowler and many more.

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Guide to Becoming a CNC Operator

Overview

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

cnc operator pushing button on control panel

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

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

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

What does a CNC operator do?

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

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

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

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

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

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

Typical CNC operator job description

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

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

The CNC Machine Operator will:

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

Desired Skills:

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

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

CNC operator skills

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

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

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

How much does a CNC operator make?

20, 10 and 5 dollar bills

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

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

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

How long does it take to become a CNC operator?

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

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

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

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

Is being a CNC operator stressful?

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

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

Is being a CNC operator boring?

cnc operator inspecting part in front of machine

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

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

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

Do you need a degree to be a CNC operator?

high school degree

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

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

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

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

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

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

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

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

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

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

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

Tips for finding a good position as a CNC operator

Research, research, research.

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

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

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

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Ultimate Guide to ISO 9001 Quality Objectives

What are quality objectives?

tablet with goals on it

Quality objectives are goals that are tied to the quality policy of an organization. They are key performance indicators used to measure items identified as being very important to the business. Generally, they are performance metrics tied to items such as delivery, quality, and/or safety.

Does ISO 9001 require quality objectives?

The 2015 revision of ISO 9001 requires that an organization has quality objectives. Section 6.2 of the standard describes the requirements.

Per the ISO standard, the quality objectives must coincide with the quality policy. They also must be measured, monitored and communicated. This means you must pick a criterion, set a goal, measure it over a certain timeframe and communicate the results.

 For example:

  • Criterion = number of customer returns
  • Goal = less than 10 returns
  • Timeframe = per quarter
  • Communication = report the results at management review and to all employees

The communication part can be misleading slightly. The most important people to communicate the results to are the members of the management who are responsible. In the example above, this would likely be someone in a quality control management role.

Communicating to all employees is often done through posting the results on a bulletin board somewhere so the employees can see the quality objective performance.

Who is responsible for the quality objectives?

Management is responsible for setting the quality objectives. Depending on the size of the organization, top management may be responsible or lower-level management may be involved. Smaller businesses are more likely to have heavy involvement from top management.

How do you write a good quality objective?

A good quality objective will follow the rules of SMART. Quality objectives should be specific, measurable, attainable, relevant and time bound.

smart goal banner

Specific = customer returns

Measurable = # of customer returns

Attainable = 10 customer returns per quarter because we know our average is 11

Relevant = customer returns are relevant because it ties into our quality policy with regards to doing the job right

Time bound = per quarter

In summary, our SMART quality objective in this example is customer returns with a goal of 10 per quarter.

Setting a goal is important. Make sure your goals are not too easy or too hard. You want to reasonably be able to attain them, but they should be forcing you to continuously improve.

Not every quality objective needs to be related to customer satisfaction or continuous improvement but having quality objectives that are will link them to your quality policy, an ISO requirement.

How many quality objectives should you have?

The answer to this question will be specific to each organization. However, a good starting point would be to have approximately five quality objectives. See the examples below to get an idea of where to start.

Quality objective examples

The quality objective examples below could apply to both manufacturing companies along with service providers.

Quality Objective

Example Goal

On-time delivery to customer

> 95% on-time delivery

Customer returns

< 10 returns per quarter

Supplier on-time delivery

> 95% on-time delivery

Supplier returns

< 5 returns per quarter

Safety incidents

0 safety incidents per quarter

How often should you review your quality objectives?

Your quality objective performance should be reviewed minimally at every management review meeting. Organizations handle management review in different ways. If you are just getting started then think about starting with quarterly management reviews.

Performing reviews quarterly will allow the organization to address any issues that may arise in a timely manner.

What should you do if you don't meet your quality objectives?

If you don’t meet your quality objectives, you should think about starting corrective action activities. If you miss your quality objective by .1% it doesn’t necessarily require that you generate a corrective action. Continually missing the objective or missing the objective by a substantial margin would be more worrisome and cause for creating a corrective action.

Can you add, remove or change your quality objectives?

Yes, you are free to change your quality objectives as you see fit. You should make sure they are relevant to your organization and its goals (including quality policy). Remember the ISO requirements as listed above when making changes including adding or removing quality objectives.

Quality objectives vs key performance indicators (KPIs)

Every quality objective is a KPI but not every KPI is a quality objective.

Quality objectives are more of an overall picture of the organizational performance such as overall on-time delivery. KPIs can be something much smaller in scope such as customer support response time.

Ultimately, an organization will need to identify the KPIs that are the most important to them and track them as quality objectives. See the examples above to give yourself some ideas of what constitutes a quality objective.

Quality objectives vs quality policy

A quality policy is basically a mission statement. The quality objectives are the items that are measured, monitored and communicated within an organization to ensure that the business is meeting its quality policy.

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Ultimate Guide to ISO 9001 Quality Policies

To get ISO certified there are many requirements which must be met. One of these requirements is establishing a quality policy. A quality policy shouldn’t be complicated. It should be simple to understand and easy to communicate throughout your organization.

What is a quality policy?

A quality policy is similar to a mission statement. It describes how a business or organization will strive to provide the best products or services possible. At times it may include other components such as environmental concerns, but the core message still remains. Do it right. Do it on-time.

What is the purpose of a quality policy?

A quality policy is important because it communicates to the stakeholders such as your employees, suppliers, and customers what your goals are with regards to your business.

Does ISO 9001 require a quality policy?

The 2015 revision of ISO 9001 explicitly requires a quality policy. Per the ISO 9001 standard, the quality policy must include a commitment to meeting applicable requirements and continuous improvement.

Applicable requirements include items such as state and federal regulations, ITAR, OSHA and any other industry relevant requirement.

There are also requirements to make sure that the quality policy is documented, communicated, and understood within the organization.

Who will establish and maintain the quality policy?

org chart example

Top management is responsible for establishing and maintaining the quality policy. Physical and electronic documents are often created and updated by quality personnel or a management representative, but ultimately the members of management at the top of the org chart are the ones who must set the quality policy.

How often should the quality policy be reviewed?

The quality policy needs to be periodically reviewed to ensure its continued suitability for the organization. This can be done by reviewing the quality policy at every management review meeting.

Once established, it won’t need to be changed often unless there is a large organizational change.

Review of the quality policy can be something as simple as a check box like the one below.

quality policy review in management review

Leave a section below the checkbox where you can talk about changes to the quality policy when they do happen.

How to write a quality policy

Keep it simple and make sure to include a statement about continuously improving. Think about what your customers want.

If there is something else that is vitally important to your organization, then it may be worthwhile to include in your quality policy. Examples of this would be environmental or safety concerns.

If you are just getting started with ISO 9001, I recommend keeping it as basic as possible while still describing what is important to your business. If an auditor were to come in and take issue with your quality policy, it would be an easy fix.

How to communicate your quality policy

Communicating your quality policy to your customers and suppliers is easy. Include the quality policy on your company’s website.

Communicating your quality policy to your employees can be a little more challenging. Emails, group meetings, and one on one training sessions are all effective ways to communicate your quality policy.

group meeting
Group meetings are excellent training tools

Teaching employees about your quality policy should also be a component of your new hire onboarding process.

Once established, you will need to train existing employees to the newly created quality policy. Additionally, periodic retraining can be used to keep the quality policy fresh in their minds.

Think about implementing an annual training schedule to communicate the quality policy to your employees.

Quality policy vs quality manual

Your quality manual is the overall view of your quality system. The quality policy is one small component of that system. A vitally important part, but still a small part.

Quality policy vs quality objectives

The quality policy is your mission. The quality objectives are the measurable items you will monitor to make sure you meet that goal.

The “measurable” part is important.

Some common quality objectives are items such as on-time delivery percentage, number of customer returns, supplier on-time delivery percentage, supplier returns, non-conforming material statistics (scrap) and/or safety incidents.

Super simple quality policy example

The example below is as pared back as possible while still including the essential components of a quality policy.

“Company ABC will provide products which meet our customers’ expectations while satisfying applicable requirements and striving to continuously improve our quality performance.”

Quality policy example for manufacturing

We will supply products and services that meet or exceed our customers’ requirements on time, every time. By continually improving the effectiveness of our quality management system (QMS), we strive for excellence in everything we do.

Quality policy example for service business

It is the policy of Company ABC to provide a service that continually meets or exceeds all customer quality and delivery expectations while abiding by all regulatory requirements.

Company ABC will strive to continually improve its process quality and efficiency.

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Printable Quality Control Labels

Below is a list of printable labels for QC, manufacturing and maintenance. I have done my best to keep the labels simple. Fancy pictures or colors will not provide better traceability, they will only cost you more money to purchase. Each label has a picture provided to show what the label will look like.

The label files are in Microsoft Word format and include all of the information you need. The label sizes are listed along with links to the label sheets to use. 

There are three size labels used. These blank crack and peel style labels can be printed on any standard inkjet or laser printer. I have included Amazon links to the various sizes below and in the individual files.

I recommend using the smallest label possible to save on the cost of labels. This is the case unless visibility is a huge concern. 

Please note that these labels will not be water, coolant, or oil resistant. However, a simple piece of scotch tape over the label will provide protection from most things.

Finally, if there is a label you need which you don’t see listed and you think would benefit everyone, please leave a comment below and I will try to update the post over time.

Printable Calibration Labels

Gauge Calibration Labels

calibration label

These calibration labels provide the necessary information to identify your gage inventory. 

Simply list the tool number, who performed the calibration, the date the calibration was performed and the date when the tool is due for next calibration. 

The Calibration labels are available in two formats:

For Reference Use Only Labels

for reference use only label

For reference use only labels can be used for tools which aren’t used for final inspection. I once had an ISO auditor require us to place a For Reference Use Only label on our UPS scale. A little extreme, but an easy enough fix. 

The For Reference Use Only labels are available in two formats:

Do Not Use Labels

do not use label

Do Not Use labels are good for identifying tools or equipment that aren’t functioning properly. They will often be used for labeling gauges that can be used for parts later.

The Do Not Use labels are available in two formats:

Calibrate Before Use Labels

calibrate before use label

Calibrate Before Use labels can be used to identify gauges which function properly but possibly aren’t needed at this time. Calibration takes time and if a tool can be taken out of service and only calibrated when it is needed then you can save yourselves plenty of time and money.

The Calibrate Before Use labels are available in two formats:

In Process QC Labels

QC Passed Labels

qc passed label

The QC Passed labels are available in two formats:

QC Approved Labels

qc approved label

The QC Approved labels are available in two formats:

QC Rejected Labels

qc rejected label

The QC Rejected labels are available in two formats:

QC Inspected Labels

qc inspected label

The QC Inspected labels are available in two formats:

Manufacturing and Maintenance Labels

Preventive Maintenance Labels

preventive maintenance label

Preventive maintenance labels are very similar to the calibration labels because they are on the same type of recall system. 

The PM labels are made in larger sizes because their is usually much more space on a machine than something like a micrometer or caliper. 

The Preventive Maintenance labels are available in two formats:

Limited Shelf Life Labels

limited shelf life label

Limited shelf life labels can be used for items such as paints or adhesives that have expiration dates that need to be monitored.

The Limited Shelf Life labels are available in two formats:

Other labels

If there are any other common labels that I have missed, please let me know in the comments below and I will try to make some up.

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Ultimate Guide to Micrometer Calibration

Outside micrometers are easily one of the most common measuring tools in the machinist’s toolbox. They are so common that they are usually referred to as simply micrometers or mics. For the rest of this post, I will follow the same convention.

A side note, specialty micrometers such as depth micrometers or inside micrometers are more often referred to by their whole name.

Now that you are on a first name basis with your micrometer, let’s think about calibrating it.

So just how important is it to have a properly calibrated micrometer?

 

outside micrometer
0-1" standard micrometer

Considering a 0-1” micrometer is likely the most used inspection tool in the shop… pretty darn important.

Please note that some of what follows might be overkill for a hobbyist but it is certainly still good practice.

Now, let’s learn more about micrometer calibration.

Why do micrometers need to be calibrated?

Micrometers need to be calibrated to ensure their accuracy.

Because they are used for critical measurements, it is important to make sure that any readings taken with the micrometer are correct.

During the calibration process, the micrometer is checked with a standard, such as a gauge block, to verify it is accurate across its entire measuring range.

How often should you calibrate a micrometer?

There are many factors to consider when determining how often to calibrate your micrometer. The visual below lists some of the most common factors.

Micrometers can be calibrated at many different intervals. When setting the calibration frequency, you should take into account factors such as:

  • How the tool will be used? Is the micrometer being used to measure critical product dimensions?
  • How tight are the tolerances it will be used to measure?
  • Will it be subjected to stresses such as heat, humidity, pressure, physical stress or other environmental?
  • How much usage will it see?
  • What is the tool’s past calibration history?

Where I work we take all of these factors into account and develop our calibration intervals based on them. We group tools into different intervals.

The most important tools are calibrated every four months or sooner. Less critical tools are calibrated on a yearly schedule. Occasionally, tools which see little use and have an excellent calibration history get calibrated at a more extended interval.

It all depends on what works for your shop. If you are unsure of where to start, calibrate more frequently and then adjust based on usage and calibration history over time.

Think about all of these factors when determining how often you will calibrate your micrometer.

What equipment do you need to calibrate a micrometer?

Calibration of your micrometer requires only a known length standard such as a gauge block, an adjustment spanner and your micrometer.

Additional supplies such as gage oil and task wipers will also come in handy but aren’t required.

 

gauge block set
Gauge block set

Gauge blocks should be chosen that are at a minimum four times more accurate than your micrometer.

If your micrometer reads to a tenth (.0001”) like most common micrometers, then you will need gauge blocks that are accurate to 25 millionths of an inch (.000025”).

This 4:1 requirement started with the military specification, or mil spec MIL-STD-45662. This specification defined the calibration requirements for companies.

This requirement is a minimum requirement. Using gauge blocks that are 10 times more accurate than the micrometer is even better.

length standards set
Length standard set

Note: For larger micrometers, length standards are often used in place of gage blocks.

Do I need to buy a micrometer that is already calibrated?

No, buying a micrometer that is already calibrated is not required.

In fact, I recommend not purchasing a micrometer that comes with a calibration certificate. The certification process costs extra and adds no extra value.

You will want to check the calibration of the tool once you get it anyways. Shipping companies aren’t always gentle and just because it was in calibration at the time of shipping does not ensure it is in calibration when received.

What do I need to maintain for calibration records?

At a minimum, your records should include calibration labels for your tools and a database where you record calibration information.

Free and printable calibration labels are available on our calibration labels page. All types of stickers are included for everything from tool calibration labels to do not use labels.

What information should the calibration label include?

Calibration labels should include at least the calibration date along with the next calibration due date. It is also a good idea to include the person who calibrated the tool and the tool #.

Note: It is acceptable to place a label on the box of a measuring tool if it isn’t practical to place on the tool such as is the case with a set of gauge blocks.

calibration label
Example calibration label

What information should be included in the calibration database?

The calibration database can come in many forms. Card systems, spreadsheets, database files and specialty programs are often used to maintain calibration records.

The following information should be recorded in the calibration database:

  • Who performed the calibration
  • Date calibration was performed
  • Master standard that was used for calibration
  • Calibration checks to be performed
  • Acceptable limits for calibration checks
  • Actual readings from the calibration checks
  • Next calibration due date

While it isn’t always a strict requirement, it is a good idea to think about recording the environmental conditions such as temperature and humidity when performing your calibration.

Example calibration procedure for a micrometer

  1. Read the entire procedure before beginning calibration
  2. If at any time in the calibration procedure a problem is identified, the problem will be corrected and the process will start over. If the problem can not be fixed, the micrometer will be taken out of service.
  3. Clean anvil and spindle faces along with all exterior surfaces.
  4. Inspect the micrometer for any damage or issues which might prevent accurate calibration.
  5. Close the micrometer using ratchet or friction stop if present.
  6. Hold the micrometer up to light and visually examine. If faces are not parallel, light will show between them. There should be no light visible between the faces of the anvil and spindle.
  7. Remove the spindle assembly.
  8. Clean and oil spindle and measuring screw.
  9. Reassemble the micrometer.
  10. Check measuring screw for wear by pushing thimble in and out. Do this in the direction of the measuring screw axis. There should be no movement.
  11. Close the micrometer by using the ratchet or friction stop if present to check the zero setting.
  12. Check accuracy with gage block(s) having accuracy not less than 0.000025 inch. Verify measurements at sizes that are not even intervals. Use sizes such as .206”, .456” or .784”. Avoid common sizes such as .250”, .500” and .800”. Verifying sizes that are not even increments of .025” will verify the scale around the micrometer.
  13. Place block or block combinations between anvil and spindle of the micrometer and close the micrometer using ratchet or friction stop if present. Use block combinations to check the accuracy of the instrument positions across the total measuring range.
  14. Record all above readings in the calibration database.

Steps 8 and 9 are not required but are good preventative maintenance for your tool.

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Knurling – All About

What is knurling?

Knurling is the process of creating a pattern on a workpiece to improve the visual appearance or to create a better grip on the part. Knurling uses the tool to displace material. This moving of the workpiece material creates the knurled pattern. A great example of knurling is seen on the thimble of most micrometers. Knurling is also often used on various knobs to provide grip.

Types of knurling

straight knurling example
Straight knurling
diamond knurling example
Diamond knurling

There are four main types of knurling. These are straight knurling, diamond knurling, left hand and right hand knurling. Of these different knurling types, straight and diamond are by far the most commonly used. There are many variations of these patterns including fine, medium, and coarse versions of each. Fine knurling has the lowest profile whereas coarse knurling would have prominent ridges to provide greater friction for gripping.

Cut knurling vs form knurling

Cut and form knurling are the two methods of creating knurling.

Form knurling is the standard form of knurling. Form knurling is pressing the knurling tool into the workpiece to create the raised grooves or teeth.

Cut knurling scrapes away material instead to create the knurling pattern. Cut knurling is better for some materials such as plastic or Delrin.

Does knurling increase diameter?

Form knurling does increase the diameter of the workpiece. This happens because the knurling tool is displacing material (moving it) which pushes material in in some locations and out in others. The amount of increase depends upon whether the knurling is fine or coarse. Coarse knurling has more material displaced and therefore creates bigger valleys and mountains in the workpiece.

Cut knurling decreases the diameter of the workpiece. This occurs because material is removed from the part instead of moved around like in form knurling.

Can you knurl wood?

Yes, wood can be knurled but it is not as simple as knurling metal. Knurling really only works for hard woods in the same way as metal. However, a simple pattern can be created through a process called checkering.  

Can you knurl plastic?

Plastics can be knurled though usually in a different way. Cut knurling is often used instead of standard form knurling.

Can you knurl Delrin?

Yes, you can knurl acetal plastic, also known as Delrin. It will be more difficult than knurling metal but if you manage you speeds, feeds, and depth of cut carefully then you can come out with something that looks nice and is functional. Cut knurling is a good choice for Delrin.

Knurling tips

Do your knurling before your final finishing. Knurling applies pressure to the workpiece and can bend it.

Because the force on the workpiece is so big, make sure that everything is secure including the part and the cutter.

Multiple passes frequently yield the best results

Thoughts?

Got any knurling tips? Share them and we will add them to the list.

Thru Hole – All About

What is a thru holes?

A thru hole, also known as a through hole, is a feature on a blueprint or drawing that identifies a hole to be machined with two open ends. The hole goes all the way through the part. In other words, the hole breaks through at two locations on the part.

In the picture below, the thru hole is on the right. The other holes are blind holes.

cutaway example of blind and thru holes

How to dimension a thru hole?

A thru hole is dimensioned by specifying the diameter of the hole along with a tolerance. Additional features can be added if needed such as a countersink or counterbore for the hole. No other features are required.

Thru hole vs blind hole

A thru hole has two open ends. A blind hole has one open end and does not go all the way through the part.

Thru hole symbol

There is no GD&T symbol for a thru hole though often it will be specified with the notation “THRU” on the engineering drawing.

Thru hole examples

thru hole blueprint 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!

Blind Holes – All About

What is a blind hole?

A blind hole is a hole that does not go all the way through a part. A blind hole goes to a specified depth and stops. 

How to dimension a blind hole

To specify a blind hole requires listing the diameter of the hole and a dimension to control the depth. The depth can be controlled by directly specifying the depth of the hole or by identifying the amount of material that will remain.

Blind hole vs thru hole

cutaway example of blind and thru holes

A thru hole, sometimes called a through hole, goes completely through a part. It has two open ends whereas a blind hole has one open end and does not break through to the opposite side. In the image above, the three holes on the left are all blind holes. The hole on the right is a thru hole.

Blind hole symbol

Diameter Blueprint GD&T Symbol o with line through it
Diameter symbol
Depth Blueprint GD&T Symbol line with arrow pointing down
Depth of symbol

There is no GD&T symbol for a blind hole. A blind hole will be specified with a diameter and a depth specification or remaining amount of material. In the example below, the blind holes have a diameter of 0.25 and go to a depth of 0.40.

blind holes blueprint example

Can you make a flat-bottomed blind hole?

You can make a flat bottom blind hole, but it can be difficult depending upon what type of material is being drilled. A modified drill bit or an end mill can work.  This video explains some tips.

Blind hole example

The example below has three blind holes. They all have a diameter of 0.500 but they have different depths. From left to right, the depths are 0.500, 0.250 and 0.100.

blind holes blueprint 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.

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Limit Tolerances – All About

What is a limit tolerance?

limit tolerance example

A limit tolerance is a form of dimensional tolerancing that specifies a tolerance range for a specific feature. Limit tolerances are also known as limit dimensioning and are an effective way to specify requirements on a blueprint. They clearly identify the tolerance range without requiring additional calculations by the blueprint reader.

Limit tolerance symbol

There is no GD&T symbol for a limit tolerance. Per ASME Y14.5, the notation for a limit tolerance is to callout the upper and lower tolerance boundaries for a dimension. The upper end value of the tolerance range goes on top of the lower end value as shown in the examples below.

Limit tolerance examples

limit tolerance example
limit tolerance example

Limit tolerance vs unilateral tolerance

unilateral tolerance blueprint example
Unilateral tolerance example

A unilateral tolerance lists a nominal value along with a plus or minus tolerance. Using these two values allows the blueprint reader to calculate the upper and lower ends of the tolerance range. A limit tolerance skips the calculation step and directly specifies the upper and lower end of the tolerance range. If the unilateral tolerance above was instead specified as a limit tolerance it would be 5.8-6.0.

Limit tolerance vs bilateral tolerance

bilateral tolerance blueprint example
Bilateral tolerance example

A bilateral tolerance lists a nominal value along with a plus/minus tolerance. Using these two values allows the blueprint reader to calculate the upper and lower ends of the tolerance range. A limit tolerance skips the calculation step and directly specifies the upper and lower end of the tolerance range. If the bilateral tolerance above were instead specified as a limit tolerance it would be 16.5-17.5.

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!