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Calipers, micrometer, & dial indicator - one not like the others

 
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  #8  
Old 03-16-2009, 06:14 PM
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Re: Calipers, micrometer, & dial indicator - one not like the others

Monte,
I tried to add some info earlier, but I got logged off (Apple, I guess) and the forum wouldn't let me edit afterward. Anyway, we have a better idea of what you're working with. I had tried to suggest earlier that you check your dial indicator with a gauge block or feeler gauge, but that was all lost. I assume that you are running your brass through an expander before measuring, as the dial indicator device will measure dings and out-of roundness that the others won't.

Actually, I thought that your NECO apparatus would measure wall thickness, and I prefer the run-out gauge to a dial indicator any day.

I haven't used any of the Sinclair mic rigs like you show, but i would think that a hand-held mic would at least as easy to use as one of them (mic laying in palm of hand with the thumb and fore-finger manipulating the thimble, brass in the other hand).

Maybe we're closing in on some resolution.
.

Last edited by Winchester 69; 03-16-2009 at 06:31 PM.
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  #9  
Old 03-16-2009, 07:41 PM
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Location: Wenatchee, WA
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Re: Calipers, micrometer, & dial indicator - one not like the others

I know what you mean. Sometimes it seems like the world is against us (Mac users) <sniff>

I swapped that dial indicator out... I was diggin' around under the work bench and realized I *do* have a couple extra... bad news is that at least one of 'em reads kind of wonky also. I do have some feeler gauges that I can try; not a bad idea at all.

The NECO gauge probably *can* do the reading, and it's GEM indicator is supposed to be pretty high zoot so I guess I'd trust it ;) I just have to sit down and stare at it and play with it a bit to figure how to best go about it. Right now I have it set up for doing case wall runout, and have a *lot* more cases to go, so I'm not inclined at all to tear it down just yet ;)

The ball mike I have would work as you describe... I just feel a bit uncoordinated with it in my (big) hand.
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  #10  
Old 03-16-2009, 09:55 PM
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Re: Calipers, micrometer, & dial indicator - one not like the others

With a small mic, I think it's mostly a matter of getting used to it. You just let it lay in your hand with your fingers supporting it no more than is necessary to maintain a balance. Easiest of any instrument to use once you've become acclimated. If you get a mic stand for it, you'll have the equivalent of one of Sinclair's deals, but hand held should be easier.

The more I think about your disparity with the dial indicator, the more I think that you're simply measuring something in the brass that the others don't. If the brass is rotating on a mandrel rather than an anvil, an eccentric or bent neck will influence the measurement even though it has nothing to do with thickness of the brass. A straight anvil rather than a raised ball can also have an influence.

The dial indicator is a simple rack and pinion drive; very linear. Problems with one shouldn't present themselves as generous measurements. Usually you'll feel a rough drive and see a jerky movement if you have a problem.
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  #11  
Old 03-16-2009, 10:07 PM
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Re: Calipers, micrometer, & dial indicator - one not like the others

Eh... I've got one of Grizzly's stands that clamps it in place and rotates a bit. Not my favorite tool, and one I've about chucked in the trash on a number of occasions. I think two Jorgensen wooden hand-screws clamped together would work better than that POS. Not a bad idea, actually...

Took the feeler gauges and measured the one marked 0.012"... with the ball mike it measured 0.0116-0.0117". With the Mitutuoyo calipers, 0.0115-0.0120". With the dial indicator (any of them) I had a bloody hard time getting that feeler in there without influencing the reading, but the minimum reading I could get was about 13 thou.

The indicator seems fairly repeatable, even if its readings are a bit 'off'.
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  #12  
Old 03-17-2009, 05:54 PM
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Re: Calipers, micrometer, & dial indicator - one not like the others

The ONLY way to find out if a mic, capiper, etc, reads "right" is to measure a known accurate block with it. That can require a trip to a standards and calibration lab, expensive too.

Alternate, and likely just a good for most of us, is to find a machine shop that has a set of Johanson Blocks and see if they will let you take a few readings off them. Jo blocks are VERY accruate even tho they are rarely sent to a standards lab for certfication.

I lucked onto two Jo blocks, .33" and 1.0", a few years back. They insure all the accuracy I really need for my reloading gages.
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  #13  
Old 03-17-2009, 10:26 PM
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Re: Calipers, micrometer, & dial indicator - one not like the others

The terminology here I think is absolute vs. relative measurements. Neck variance and runout on dial mics are only a relative measurement. Ball mics etc are absolute. However like boomtube states you need some measure of confidence in a known value. At least two should be used of different sizes to determine flat error (0.002 off throughout the range) vs. increasing/decreasing error as the measurement range changes.
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