{"id":738,"date":"2020-05-14T23:30:00","date_gmt":"2020-05-14T23:30:00","guid":{"rendered":"http:\/\/kylecothern.com\/?p=738"},"modified":"2020-05-17T02:42:25","modified_gmt":"2020-05-17T02:42:25","slug":"tools-calipers","status":"publish","type":"post","link":"https:\/\/kylecothern.com\/index.php\/2020\/05\/14\/tools-calipers\/","title":{"rendered":"Tools: Calipers"},"content":{"rendered":"\n

Well I have a shop in the garage so I figure I should start blogging about useful tools. This is the first post in a series of common (and uncommon) tools you’ll find in a machine shop. <\/p>\n\n\n\n

The most useful tool, for a Mechanical Engineer anyway, seems to be a pair of calipers. I don’t leave home without them. I have 4 pair in my toolbox alone. <\/p>\n\n\n\n\n\n\n\n

What are calipers?<\/h2>\n\n\n\n
\"\"
8″ Mitutoyo Coolant Proof Calipers. This pair got sucked into a Monarch 10EE by some long steel chips whipping around but is still alright. <\/figcaption><\/figure><\/div>\n\n\n\n

Calipers are a measuring instrument for distance, thickness, length, height, depth, diameter, etc. They can be used to accurately measure in one dimension (usually are marked in inches, mm or both) and will generally have a pair of inside and outside measuring jaws juxtaposed, as well as a depth gauge plunger. You may think “why not use a tape measure or ruler?” and the answer is: accuracy, precision and repeatability. <\/p>\n\n\n\n

Accuracy, repeatability, and why if you’re cutting on a lathe you should be using a Micrometer, not calipers.<\/h2>\n\n\n\n

Accuracy<\/strong> – Closeness of a measured value to a standard reference<\/p>\n\n\n\n

Precision <\/strong>(repeatability) – Closeness of two or more measured values to each other<\/p>\n\n\n\n

\"\"
Rulers are great for measuring how jacked the welds are on your hyperloop tube at a glance, but it’s hard to get an accurate reading without touching two surfaces. Calipers with a depth gauge or a weld gauge<\/a> would be a better measuring tool for this application<\/figcaption><\/figure><\/div>\n\n\n\n

Calipers are the weapon of choice for engineers primarily because they quickly can give you accurate, precise data about the length, thickness or diameter of an object, to a higher degree of precision than a ruler or tape measure, about .001″ or .025 mm. <\/p>\n\n\n\n

\"\"
Calipers are great for hand checking width of slots, hole diameters, parth thicknesses, overall dimensions, and distance between features. <\/figcaption><\/figure><\/div>\n\n\n\n

This matters for making sure parts fit together, mating surfaces will be in proper contact, or two moving parts in an assembly will have adequate clearance. They are also superb for in process manufacturing checks, to make sure the proper amount of material has been removed, or a hole is large enough to clear a bolt. <\/p>\n\n\n\n

In modern manufacturing, most bulk material removal processes tend to achieve around .001″ precision or less (at least for metallics, generally) , and more precise manufacturing environments generally use more precise tools. <\/p>\n\n\n\n

\"\"
Parts can be cut more accurately than you can measure with calipers on a lathe. Best stick to micrometers when checking turned parts, but in a jif, calipers can be used for layout or rough dimensional checks. <\/figcaption><\/figure><\/div>\n\n\n\n

Lathes are capable of regularly turning out parts that have diameters precise to .0001″. For measuring tight tolerance parts that have a turning operation, you want to use a micrometer, as it can accurately measure down to .0001″ or less. These tolerances are normally necessary for press fit or slip fit parts, bearings bores, and optical assemblies. <\/p>\n\n\n\n

\"\"
From Machinery’s Handbook- This chart shows common processes and the tolerances they can achieve. Calipers can measure down to .001″ usually, or on the process list, from flame cutting down to about boring. <\/figcaption><\/figure><\/div>\n\n\n\n

What types of calipers are there?<\/h2>\n\n\n\n
\"\"
The oldest calipers had no markings to display the measured dimension, and were primarily used for transferring a measurement from one part to another, or to do a part layout<\/figcaption><\/figure><\/div>\n\n\n\n

There are many kinds of calipers. The earliest calipers were merely two curved bows with a pivot in the middle. The common types of calipers you’d find in a shop for everyday measuring work are the following:<\/p>\n\n\n\n

Vernier – old timey, hardest to break<\/h3>\n\n\n\n

These are seldom used in application in modern shops, due to a tendency for new engineers to misread the vernier scale. <\/p>\n\n\n\n

\"\"
Diagram of Vernier Calipers and how to read them from the Wikipedia article on calipers<\/a><\/figcaption><\/figure><\/div>\n\n\n\n

Dial- The batteries never die<\/h3>\n\n\n\n

These are all over the place, a reliable instrument for quick checks, without batteries to die, they can sit in a toolbox for 10 years and never be dead when you pick them up. These are probably the most sensitive to damage, as a hard drop can break the fragile mechanisms inside. <\/p>\n\n\n\n

\"\"
My first pair of calipers in the professional world, a Fowler set I got at SpaceX. The dial is adjustable to set zero at any point on the slide, though you’ll have to remember what mark you started at.<\/figcaption><\/figure><\/div>\n\n\n\n

Electronic- Easy to read, come in varieties (coolant proof, economy, etc)<\/h3>\n\n\n\n

For the lazy modern engineer, only accept the best. And buy some extra coin cell batteries because these calipers die when you need them the most. The first time, every time. <\/p>\n\n\n\n

\"\"
Even when your spherical bearing races are still covered in nuclear grade anti seize, electronic calipers make your life easy and your hands clean. <\/figcaption><\/figure><\/div>\n\n\n\n

How do you use them? What can you measure with them, what can you not measure with them?<\/h2>\n\n\n\n

Direct Measurement of length, thickness<\/h3>\n\n\n\n
\"\"
Direct Measurement of the thickness of a cube. Notice how I’m not using the sharp part of the jaws. This would scratch the part, and if I used too much force, may give me an undersized measurement. Watch out for burrs on metal parts, as they can throw off a reading. Hit a part straight off the mill with a deburring knife or stone before measuring. <\/figcaption><\/figure><\/div>\n\n\n\n

The easiest ways to measure with calipers is to place an item between the jaws and close the jaws with the thumb wheel.<\/p>\n\n\n\n

Depth measurement<\/h3>\n\n\n\n
\"\"
Measuring the depth of the hole in the center of this tape roll. This isn’t going to be super accurate, but gives you an idea.
<\/figcaption><\/figure><\/div>\n\n\n\n
\"\"
The business end of the depth measurement.<\/figcaption><\/figure><\/div>\n\n\n\n

Most calipers have an integral depth gauge that extends when you open the jaws (be careful not to bend this guy when taking measurements). This allows you to measure hole depth, pocket depth, or features inside a hole like a shoulder or a counter bore.<\/p>\n\n\n\n

Be careful to get the reference edge lined up well and set zero at the top of the hole before taking measurement. Keeping the calipers perpendicular to the measuring surface is more difficult with the depth gauge, so double check measurements. <\/p>\n\n\n\n

\"default\"
Depth base attachment for Mitutoyo Calipers from Mcmaster Carr<\/a> – $51.21<\/figcaption><\/figure><\/div>\n\n\n\n

There are special attachments for making it easier to hold the calipers perpendicular to a flat part surface when using the depth gauge feature. <\/p>\n\n\n\n

Update: Thanks @cyclematch for this rad tip on measuring shallow steps. <\/strong><\/h3>\n\n\n\n

Thanks for the good article on calipers. One more method to add for measuring step height, I learned it a couple months ago from my machining professor. Thanks Prof LaFont! pic.twitter.com\/0BqJ3a299f<\/a><\/p>— Kevin Matocha (@CycleMatch) May 17, 2020<\/a><\/blockquote>