# Caliper vs Micrometer



## David Morrow (Mar 16, 2009)

I'm not sure if this is an either / or question. 

I have a relatively inexpensive digital caliper that I really like. It does almost everything that I need it to do. Occasionally though it's a bit awkward to use but nothing insurmountable. I often wonder if I should be using a micrometer in some instances instead.

Any comments or suggestions ?


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## Stan (Mar 16, 2009)

A caliper will make measurements that can't be done with a conventional micrometer but it is less accurate.


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## rake60 (Mar 16, 2009)

For an O.D. measurement a micrometer is much more accurate.
A properly zeroed caliper might miss that reading by .0005"
 scratch.gif

I have mics and calipers in my home hobby shop.
The purists won't like this comment, but I use my digital
calipers for almost everything and my finished models still run...

Maybe it's just dumb luck. 

Rick


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## marcel beaudry (Mar 16, 2009)

Hello to all

a micrometer and a caliper will only mesure a distance between two points , will not mesure how round it is ,both will mesure as precise for usual jobs, for high precision a micrometer is usually used, but remember it will only mesure a distance. Go see


www:howround.com/


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## Mike N (Mar 16, 2009)

If you can hold +-.001" with a caliper what more could you ask for? I use my caliper for almost everything, if I want to hold .0005" or better I use a micrometer or bore gage.


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## Philjoe5 (Mar 16, 2009)

The problem I have with calipers is that it easy to put a slight twist on the jaws and throw a reading off, especially when checking dimensions on a workpiece chucked in the lathe. For me, I need to use a micrometer if I want any measurement within 0.002". I think the answer to the original question is best answered by the user. 

Cheers,
Phil


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## Maryak (Mar 17, 2009)

rake60  said:
			
		

> I use my digital calipers for almost everything.



Me too except mine are the analog type.

My golden rule is don't mix on the same dimension, i.e. if you start with calipers finish with them and likewise with micrometers. Both are only as good as they are adjusted and both are subject to operator feel, although the ratchet on a micrometer goes some way to removing this variable.

Best Regards
Bob


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## Tin Falcon (Mar 17, 2009)

Digital calipers for quick easy measurement. Calipers for accuracy . I have been known to use both to check measurements. IMHO it is easy to miss a line on the mics so check with calipers or a magnifying glass.
Tin


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## Stan (Mar 17, 2009)

My biggest error with a caliper is with flat, not round, surfaces. It is easy to measure the width of a 1/8" tool bit but to measure the length of a 3" X 3" cylinder (or a wide piece of plate), I have difficulty holding the caliper square to the work. Is there a proper way to do it? It is so simple with a mic.


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## mklotz (Mar 17, 2009)

I find it very awkward to use calipers to measure a diameter on a lathe so I generally use a micrometer even though the part may not demand the accuracy of a mike. YMMV.

Good quality micrometers will easily measure to a thousandth IF USED PROPERLY. If you hold the calipers with the right hand only and close the jaws on the part, the fact that the part is not in line with the beam means that the movable jaw can angle slightly on the beam and thus produce a (slightly) erroneous reading.

Avoid this by using the thumb and forefinger of the left hand to press the jaws in contact with the part. Additionally, this helps to avoid the other source of error, cocking the jaws so they are not parallel to the surfaces of the part being measured.

Arguably the hardest shape to measure accurately with calipers is the length of a rod with large L/D ratio, e.g., a micrometer standard. If you want to develop your technique with calipers, practice measuring mike standards rather than gage blocks. Gage blocks are useful for checking the caliper's accuracy over its range but they're not the best item for honing your technique with the tool.


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## rklopp (Mar 17, 2009)

I find it's easier to scratch a nicely finished workpiece with a caliper than with a micrometer. For lathe work, I mostly use a micrometer when I'm getting close to final size. I often work on close fits, e.g., bearings, pistons, press fits, and calipers aren't good enough for those in my taste. Micrometers are about 5x as accurate for me.


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## BobWarfield (Mar 17, 2009)

In my shop, digital calipers for "close enough", digital mics for "gotta be right". 

It is easier to take a more accurate measurement with the mic (at least if you have a quality one with ratchet thimble, if not, may not be easier). Because of that, I often use the mics to train myself how to measure better with the calipers. I'll alternate the two measuring various diameters, but I will treat the mic as the right answer and work on my technique with calipers until I get it right most of the time.

The mics also get taken better care of. Calipers get left all around the shop so there is always one close to hand and handy. I must have 6 or 7. Most are cheap, but 2 are Mitutoyos.

RE digital vs vernier, to each his own. I have both, but I prefer the digital as I don't have enough years to make the verniers completely automatic. Digital is easy to come by. Just make sure you buy plenty of spare batteries!

Cheers,

BW


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## David Morrow (Mar 17, 2009)

It sounds there is a micrometer in my future. I really like the electronic digital type.

Any suggestions there ?

I really appreciate all of your comments. Thanks.


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## joeby (Mar 17, 2009)

It's like anything else, really. How close do you need to be? If you are working to +-.002", calipers are probably ok (operator dependent), closer tolerances than that should be micrometer territory, IMHO. Less than .0005" is getting to indicator and gage block measurement. It's a matter of opinion and how much you trust yourself and your tools, and how you take care of your tools. 

 In your home shop, you are basically making comparative measurements. This part fits that part, etc.. As long as you are using the same tool and YOU are measuring both parts, you can get pretty good results.

 Industry teaches you differently, if you are using micrometers (.001" res) to measure to +-.0005", and the inspection department is using a .0001" indicator to inspect them, an argument can quickly ensue.

 I have several different calipers in my shop, including verniers, and they get a good bit of use for quick measurements. When I was in trade school, however, the instructor insisted that they should be properly called "Mickey Mouse tools" and would not allow their use.

Kevin


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## 90LX_Notch (Mar 17, 2009)

I throw my 2 cents in here. 

Take it from someone who was a mechanical calibration tech who calibrated and repaired mics, calipers, indicators, etc. I also wrote the work instructions on how to calibrate said items. Calipers aren't that great. Tips get bent, jaws get worn, racks are misaligned, frames wear, teeth chip on the gear train, gibs wear, etc. Most calipers will have at least .001 of an error some where in their range. Just because it measures accurately at 1.750 doesn't mean it is accurate at 4.500. Another thing is that all capabilities of the tool should be checked ie: inside, outside, depth and step. The variation here can be very alarming. A caliper that is fine for inside outside and step could .005 off for the depth rod. Also, just because it is digital, with a greater resolution, doesn't mean it is more accurate. 

Real mics, are lapped on both the threads and the faces. What does that tell you. Also, your better mics are accurate to .0001. And yes, they wear and can have problems, but most just need an adjustment and are fine.


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## mklotz (Mar 17, 2009)

Don't trust calipers for accurate measurement of bores - even if the calipers are in good shape.

On most calipers (check yours to be sure) the inside measurement jaws have tiny flats on them. This means that, when measuring a cylindrical hole, you're actually measuring the distance between two (tiny) chords of the hole and the measurement will be smaller than the actual hole diameter. While fine for measuring the distance between two flat planes, use an inside mike, tubular/ball gage or gage pins for accurately measuring holes.


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## 90LX_Notch (Mar 17, 2009)

Correct, and the jaws aren't in the same plane. Unless, it is a critical measurement, the error is negligible until small diameters. 

On the subject of accuracy- Then there are the problems with dial indicators. They suffer from similar mechanical issues as calipers. Also, most people miss the error that occurs from not setting an indicator perpendicular to the plane from which they are measuring.

Gotta go, my wife just got home.


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