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

[milanuk]

Hello,

So... I've got a couple sets of calipers - one Lyman dial caliper, one Mitutuoyo digital caliper, a Mitutuoyo ball micrometer, and a no-name import (Grizzly) dial indicator.

The dial indicator is trying to tell me that Winchester .308 Win brass is about 14 thou in thickness, while the others all say ~12 thou. They seem to all agree pretty well about where the variations are, and how much they are, but the dial indicator seems to read a bit thicker than the others.

Anything to be done for it, or pitch it and get a new one?

Thanks,

Monte

 

[ss7mm]

All of the digital as well as dial type calipers I have can be zeroed, as I assume yours can be.

But, what is the dial indicator on, how is it mounted and can it be zeroed?

And, the calipers probably have flat faces on both jaws. The dial indicator probably has a rounded type point on the indicator rod at least. Don't know about the opposite side or how it's mounted. This would possibly mean that you are trying to read a rounded case neck's internal dimension with a flat faced jaw that doesn't actually touch the inside of the case neck with the center of the caliper jaw.

Is it possible that the difference in flat faces and a rounded face can be giving you the difference in thicknesses but still indicating the same spots for variations.

 

[milanuk]

Everything that can be zeroed easily (the exception being the tubing micrometer) was.

I see what you're saying about the different jaws contacting the rounded contour differently... but normally (in my limited experience) when thats the case, the calipers would be reading *thicker*, not thinner. And the ball mike (a model I purchased from Russ Haydon years ago) has a specially modified anvil to allow closer contact to the neck on smaller cartridges - the flat is on the outside, the inside contact surface is a fairly small ball. It agrees with the calipers, but not the dial indicator.

 

[Mikecr]

I would only believe the ball mic.

 

[eddybo]

I agree.

I would only believe the ball mic.

 

[Winchester 69]

No measuring instrument needs to be zeroed to be used accurately. It IS necessary to adjust the reading by whatever error at zero exists. For what you are doing (measuring wall thickness of the brass necks), the ball micrometer is the appropriate instrument; additionally, it is the most accurate of the selection of instruments.

The calipers are the next most-accurate instrument type. The uniformity of the brass and your skill in making the measurement will influence the accuracy of their measurement.

I don't know how you are using a dial indicator to make this type measurement. It isn't surprising at all that the measurement doesn't agree with the others. Measuring wall thickness requires the use of a fabricated jig to provide an anvil and to hold the indicator. The design of the anvil would need to like that of the ball mic for the instrument to compensate for an unevenness in the metal's surface.

As mentioned, the ball mic is the proper instrument for making your measurement. If the anvils are at zero, then your measurement is correct as read. If the anvils are not at zero, then the measurement should be adjusted by the amount of error.

 

[milanuk]

The dial indicator is being used in a Sinclair case spinner jig - one of those little 'L' shaped brackets that holds a rod w/ a caliber-specific mandrel and when you slide the case in over the mandrel so it stops on the case mouth, a dial indicator should give you a reading of the neck thickness. More to the point, when you spin the case (gently) on the mandrel, the dial indicator should give an idea of how much variation in neck thickness a particular case has.

Basically a much older version (with no base) of their current rendition (shown below):

I don't think it was ever intended to replace a ball mike; I know that when I'm neck turning, that is the tool I rely on. I also know that there are some tools set up to make taking readings around the neck easier, with a micrometer instead of something as 'coarse' as a caliper or dial indicator, such as these two:

but for what I'm trying to do (sort a reasonably large number of cases in a timely fashion)... the spinner seems (seemed) like a better option. Granted, I've had it for years and haven't used it for several, but if the dang dial indicator isn't going to read at least somewhat close it severely undermines my confidence in the tool.

Looking at 'good' dial indicators from Mitutuoyo or Starrett they seem to run in the $125-150 range (this one cost like $20); at that point I would be very tempted to get one of the micrometer gauges shown above. Either that or figure some way to take the measurement with my NECO gauge; darned thing measures everything else known to man but I can't find a description of that particular setup in the manual.

 

[Winchester 69]

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.
.

 

[milanuk]

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.

 

[Winchester 69]

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.

 

[milanuk]

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 ***. Not a bad idea, actually... lightbulb

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'.

 

[boomtube]

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.

 

[nheninge]

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.