# Caliper no-no



## mklotz (Nov 13, 2007)

A friend was complaining to me that he bored a hole oversized a few thou.

Q: With what were you measuring the hole diameter?
A: Dial calipers.

Gag!  You can't measure hole diameters accurately with calipers.

Take a look at the inside jaws on your calipers.  You'll see a tiny* flat.  When you use them to measure a hole, what you're measuring is the distance between two tiny chords on the circle formed by the hole.  Thus the hole will always measure undersize - the worst possible error direction if you're enlarging the hole.

For *precision* applications, always use an inside mike, expanding gages or bore or pin gages to measure.  Never use calipers.

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* I measured the 0.2" standard for my 1.2-2.2" inside mike with my Mitutoyo calipers.  It measured 0.1975".  With a little trig, that makes the flats about 0.030" wide which, to my calibrated eyeball, looks about right.


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## cfellows (Nov 13, 2007)

I wondered why that is!

Chuck


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## compound driver (Nov 14, 2007)

HI

Still in my books the best way is a GO no GO gauge made for the job and then an internal micrometer. Calipers are ok for a few thou but certainly do not come close to a micrometer for either internal or external use.

Cheers kevin


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## greenie (Nov 18, 2007)

AAaaahh, the good 'ole vernier calipers.

I was told many years ago that the word vernier was french, for VERY NEARLY, the old bloke who told me that was sure correct.

regards  greenie  :mrgreen:


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## mklotz (Nov 18, 2007)

greenie said:
			
		

> I was told many years ago that the word vernier was french, for VERY NEARLY, the old bloke who told me that was sure correct.



Like most things told by old blokes to young apprentices, it was utter BS.

Paul Vernier was a French mathematician who first described the sliding scale that now bears his name.


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## compound driver (Nov 18, 2007)

My most used vernier was given to my father in 1935 its a pain to read now but never stops working when dropped in cutting oil or suds. Digit calipers are ok for us hard of seeing but you cant get better than Moore and Wright.

vernier also went on to do a lot more than the vernier scale he's well worth googeling.

Cheers kevin


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## starnovice (Nov 27, 2012)

Hate to drag up an old tip, but this sure made me a little less ignorant.  Thanks!

Pat


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## SmithDoor (Dec 3, 2012)

I found *Caliper *are to ± 0.005" after that use a mic they good to ±0.0001"
When had my no could use a caliper for any turning. 

Dave


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## Tin Falcon (Dec 3, 2012)

Pat the tip was probably worth dragging up. 

In my personal experience a caliper is good for .002 accuracy on an outside measurement.  . For real measurements use a micrometer that reads in tenths.  the tenth reading ones are usually only a little more money and worth the extra. 
Hole gauges T_ gauges and inside mics are meant for inside holes not calipers. 
Tin 

 .


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## rdhem2 (Dec 5, 2012)

BS or not, very nearly is so much easier to remember.  Like all things from noble people, time has a way of enhancing any accomplishments.
My caliper shows me, for example that a piece of material is somewhere between 1" and 2".  After that I use a mike.
Like all the other posts show, *very nearly* is closer to *absolute fact*.     ;D


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## Tin Falcon (Dec 5, 2012)

digital calipers close measurement will keep you out of trouble. while a good mic will be accurate to the ten thousands you can miss a line and be off by .025 DAMHIKT .  I use both the digi's  get the measurement close the mics get me the rest of the way.   
Tin


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## sharlotendo (Dec 6, 2012)

The thing with a Caliper is "Feel"just touching on the internal bore..then the same touch on the mic.Its suprising how accurate you can get with a bit of practice.


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## Ken I (Dec 6, 2012)

As Marv pointed out the ability of a vernier on bores is limited and worse the error varies with size, being less "accurate" on small bores - a quick and dirty method is to calibrate against a known bore size approximately the same size as you are measuring - I have a drawer full of ball bearings which I presume are way more accurate than my vernier or measuring technique.

Ken


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## Forestgnome (Aug 20, 2013)

I've always found my calipers to agree with my snap gage/micrometer measurements. I did a little calculation. The flats on my caliper jaws are pretty small, guesstimation to be 1/64". If this is so, then measuring a bore 1" in diameter gives a calculated diameter error of -0.00012". As you go up in diameter the error get smaller. Are you accurate enough with an inside mic or snap gage to know you're within a tenth?


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