Accuracy of vernier

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Accuracy of vernier

Post  Bob Salter on Fri Dec 03, 2010 8:06 am

Ive just ordered a micrometer, but due to the weather its not going to arrive any time soon. I know digital verniers are pretty useless for reamer making but I was raking in a box of old tools and found a mitutoyo manual vernier. Would this be anywhere near good enough to attempt reamer making or should I wait for the micrometer.

Bob

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Re: Accuracy of vernier

Post  verdatum on Fri Dec 03, 2010 12:50 pm

So long as you test that the caliper is properly zeroed, and the probes are nice and sharp/squared, most vernier calipers I see are accurate to at least +/- .2 mm. With a magnifying glass, it's closer to .1mm. I don't know much about reamer making, but assuming you are just trying to make a repeatable chanter bore size, this should be fine, shouldn't it? I should think higher accuracy should only be needed when dealing with interworking machined parts, like high speed gears.

Further, you should be able to do the work with your calipers, and then verify with your micrometer.

I never have been able to understand why (most) digital verniers are so terrible. The one I bought (crazy cheap model from harbor freight) would frequently go buggy and report a random distance that was off by as much as 4 inches.

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Re: Accuracy of vernier

Post  Yuri on Fri Dec 03, 2010 6:47 pm

Wood movement is larger than that. There are timbers which's tangential movement with weather differences is around 8%, while radial around 2%. So a fraction of a mm in the reamer doesn't make any difference at all.
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Re: Accuracy of vernier

Post  Art on Sat Dec 04, 2010 10:01 pm

I've had very good luck with my two Harbor Freight calipers, one long and one shorter. I regularly verify my measurements and haven't had any trouble. When the battery died, it did get flaky, but that's a simple fix.

Am I missing something?
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Re: Accuracy of vernier

Post  Bob Salter on Sun Dec 05, 2010 2:34 pm

Digital vernier calipers have a quoted accuracy of +/- 30 thou. In engineering terms this is a vast amount. There is a split among pipemakers some saying that the wood moves far more than this( which is a real and accurate point) and the others who claim that to accurately reproduce a chanter the reamer shold be accurate to about .0002mm or better. I was never able to make reamers very accurately, grinding reamers from flat stock is imprecise at best and in my case at least fairly inaccurate and believed squarely and unshakably that good results could be had simply by more or less reproducing a given bore and fiddling with hole position and undercutting to produce an in tune chanter. This is more true for single octave pipes than two octave pipes. Ive been messing around with pipemaking for more years than I care to recall and still havent got a chanter Im really proud of, whose tone and pitch are just so. Lately Ive become a little more serious about it and bought a metal lathe( an old myford) for reamer making. Even my early attempts have made a huge difference to the finished item. Im currently working on reamers for an uilleann chanter in C which has 45 measured points. I fully intend to try and make it accurate to a thou( I suspect it will be a while before I can manage 2/10 of a thou, but I know of some who do exactly that) and using a digital vernier I could be 30 thou under on one measurement and 30 over on the next thus making the reamer extremely inaccurate (relatively). A micrometer is WAY more accurate than a vernier and a little easier to read than a manual vernier for those of us with senior eyes.
I cannot say conclusively wether more accurate reamers will give better results but it cartainly cant do any harm. After all, at those tolerances one turn too many with the reamer will change everything anyway. Im on the road to finding out and will report back when I know more

Bob
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Re: Accuracy of vernier

Post  Art on Sun Jan 02, 2011 1:53 am

That's an interesting reply, Bob. I'll be interested in hearing what you learn.

What caused the improvement when you began using the Myford to make reamers? Is it because the Myford allows you to create a much more accurate a taper on the reamer?
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