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Old January 3, 2013, 08:51 PM   #1
scissorhands
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Dumb question, but I must know

I got a Hornady dial caliper for Christmas. I get all kinds of different readings from it. That range from .001-.005 depending where the brass is on the caliper. What is the proper amount of pressure to apply to the caliper for consistant readings? Its driving me crazy!!!!!!!!!!!
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Old January 3, 2013, 09:05 PM   #2
reynolds357
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Is it plastic or metal? If its plastic you will never get true precision readings. Dont put much pressure at all on a plastic caliper.
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Old January 3, 2013, 09:07 PM   #3
scissorhands
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its metal, stainless I believe
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Old January 3, 2013, 09:10 PM   #4
reynolds357
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Find something flat and practice measuring it. Preferably, mic something and then see if you can get close to the known reading and see hot to apply pressure to get that reading.
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Old January 3, 2013, 09:39 PM   #5
browninghunter86
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just takes "feel". As long as you measure the same way every time you will be good. It doesn't take long to figure out what is needed. Push too hard and reading will be less, not enough reading will be longer.
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Old January 3, 2013, 09:43 PM   #6
NWPilgrim
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It does not take much pressure. Just light yet firm contact. Do not crank it down or force it.

Most calipers have flats and blade sections. I measure most things with the flats, especially COL and case length. If you use the lade section you may not get exactly on the hihest point each time.

Even though case mouths may look even, there can be small variations not noticeable to the eye. The flats will more likely hit on the highest point each time whereas the blades can end up in slight depression.

If you are measuring diameter then have the diameter in pararell with the lades rather than perpendicular so the highest point will defenitely be under the caliper and you are not guessing when you have the greatest point.

Also, be sure that it is zeroed before each use and lock the zero ring.
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Old January 3, 2013, 09:57 PM   #7
Sport45
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Get the feel of it by practicing on the diameter of a quality jacketed bullet. They should be within 0.0005" of their advertised diameter.
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Old January 3, 2013, 10:05 PM   #8
Edward429451
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The only thing I can add to the excellent responses already is to not store them fully closed. Leave them open perhaps.015 for storage.
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Old January 3, 2013, 10:21 PM   #9
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pick up a set of feeler gauges from your local auto store and practice on the different thickness's
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Old January 3, 2013, 11:50 PM   #10
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Yup. Feeler gauges are perfect. I take an old set and remove the .010" and .025" blades and keep them in the case with the calipers to check zero. You only want to apply enough pressure to remove all of the play on the part to be measured and no more.
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Old January 4, 2013, 12:27 AM   #11
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I always suggest going to your local machinist's supply store and buy a "reference standard" 1 inch long. That will be a piece of steel precisely ground to 1.0000 inches and tracable back to the National Institute of Standards and Technology. It's an excellent piece to keep handy to check a caliper or anything else from time to time to be sure it's still accurate.

Close the caliper and the reading should be zero. Then measure the reference standard and the caliper should measure 1.000 inches. This means your caliper is right on the money. You can also use this standard to test the pressure necessary to get an accurate measurement.
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Old January 4, 2013, 03:52 AM   #12
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Clean the caliper first, two or three times, snugly close caliper on a piece of paper and pull paper out. This will remove any dirt on surface of the jaws.
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Old January 4, 2013, 07:41 AM   #13
10 Spot Terminator
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If the cases are fired there can be a slight variance in the neck length around the rim and measurements will be accented at times if the fired primers are not still seated under flush from the base of the brass. Removing all of the measuring tool variables stated above is the place to start but measuring fired brass is just the nature of the beast. Case in point would be to take one of the cases you are referring to and trim it .005 then measure again. Perfecly trued brass equals perfectly true readings.
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Old January 4, 2013, 07:49 AM   #14
Sport45
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Quote:
Perfecly trued brass equals perfectly true readings.
Except then you'll be driven crazy by the small bends and nicks put in the rim by the extractor/ejector.
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Old January 4, 2013, 08:17 AM   #15
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Close the jaws and set the dial at zero. Then see how much pressure you can put on it at zero (fully closed) while still keeping it reading zero. Don't overdo it, just enough to get an idea how rigid the calipers are. Then when measuring anything, zero it first and use the same pressure to take a measurement, but no more than necessary. If the zero varies without much difference in how much pressure you're giving it, you need a more rigid instrument.
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Old January 4, 2013, 09:31 AM   #16
scissorhands
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Thanks for all the replies, they have helped a lot!

Rob
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Old January 4, 2013, 02:43 PM   #17
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Quote:
The only thing I can add to the excellent responses already is to not store them fully closed. Leave them open perhaps.015 for storage.
I have never herd that before, can you explain why?

Thanks
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Old January 4, 2013, 02:51 PM   #18
chris in va
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Keep in mind too, most brass cases are tapered. The leading edge of the caliper will be higher on the brass than the trailing edge.
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Old January 4, 2013, 02:58 PM   #19
mehavey
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Simple:

1. Close the calipers all the way with whatever pressure you want to call "nominal"

2. Set the Zero at that point.

3. Open and close the calipers several times to to that same "Zero" point, and get the feel of the repeatable pressure that gets you that same "0.000" again and again.

5. Lock that amount of pressure in your "organic memory" and use it from them on.

6. Don't sweat it.
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Old January 4, 2013, 03:20 PM   #20
jimbob86
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mehavey has it.

Quote:
measure the same way every time
This is true of any measuring device, whether it is a Lee dipper, a powder measure, a dial caliper, a tape measure, or a spring scale..... or anything.

Varying the procedure will vary the results, sometime a little, sometimes a lot.
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Old January 4, 2013, 03:40 PM   #21
rajbcpa
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I've used non-digital dial calipers for years. Generally, they work great. Hornady products have slipped recently in the quality control department, however, so I do not buy anything from Hornady.

I read somewhere that they moved their production to China, so this may be the reason.
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Old January 4, 2013, 05:23 PM   #22
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Quote:
I have never herd that before, can you explain why?
That goes for Micrometers more than dial calibers. Most dial calibers are either plastic, (Junk) or stainless steel, (good ones), It doesn't matter if they are closed or not. Micrometers are not made from stainless and stand a better chance of rusting if let closed against both surfaces.

I have about 5 pairs of stainless dial calipers left over from my machining days, and they don't seem to care if they are left closed for years on end.

I haven't heard yet weather these calipers are digitol or dial. Digitol calipers are much more sensitive to over presure than dial calipers are because they usually are calibrated for .0001 instead of ,001 of the dial type.

Either way you don't use a lot of pressure with either one. Enough to stabalize the reading.
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Old January 4, 2013, 06:41 PM   #23
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Quote:
The only thing I can add to the excellent responses already is to not store them fully closed. Leave them open perhaps.015 for storage.


Temperature changes will cause the metal to expand and contract thus putting stress on the gears (threads of micrometers) and slop will develop. Leading to accuracy issues and wearing them out prematurely. This is not as big an issue with calipers as it is with micrometers but it sure doesn’t hurt anything to treat your tools with the most care possible.
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Old January 4, 2013, 09:14 PM   #24
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Exactly. There's plenty of room in the case to leave them open a tad.
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Old January 5, 2013, 01:00 PM   #25
grubbylabs
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Well thanks for the responses, it nice to learn something new.
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