Two Micrometers Don't Agree

[1hole]

For any reloading or casting situation I can't even think of anywhere that .0004 would be meaningful.

Jedman

Ditto.

I've been reloading since '65 and have never seen anything that needed absolute accuracy to a tenth. Mostly I use my old B&S for comparison measurements, such as fired to unfired case heads. In real world reloading I don't think a matter of 4 tenths exists.

[EDG]

I suspect that if you shoot cast bullets .0004 undersize you might find a case for having a little more accurate mike. When shooting a tight neck bench rest rifle you need to use an accurate mike since the clearance between the loaded cartridge neck and the chamber neck is so little.
Most of the time there is little reason to tolerate a mike being off .0004. It costs nothing to set the zero properly.

Ditto.

I've been reloading since '65 and have never seen anything that needed absolute accuracy to a tenth. Mostly I use my old B&S for comparison measurements, such as fired to unfired case heads. In real world reloading I don't think a matter of 4 tenths exists.

[alamogunr]

I've gone back and done another series of measurements with both micrometers. I tried to be much more careful this time.

Plug Gauge Brown&Sharpe Scherr-Tumico

.310 .3099 .3097

.325 .3249 .3247

.360 .3599 .3596

.375 .3748 .3747

.430 .4298 .4300

.454 .4539 .4537

.478 .4779 .4778

I hope that this doesn't get all mixed up when I post it.
Well! I previewed it and it did get compressed. I don't know how to fix it so I hope you can still read it.

[uscra112]

I was about to say that you should check the mikes at a number of different sizes which do NOT coincide with an integral number of turns of the spindle. You did that. If as you say you've zeroed the barrels with the mikes closed up, I'd simply retire the Scherr-Tumpico if it were under my gage management program. Only other thing I would mention is that our MIL-I-45208 protocol specified gage blocks, not pins, as the reference standard.

[country gent]

Looks like it might be as simple as old oil thickened up each of the 3 measuring's is very consistent in the recorded changes. Am betting a good cleaning with clean first use solvent. and very light oiling will fix them right up. This appears to be the oil film being thinned with the repeated measurements.
If it was the faces or thread play adjustments each of the 3 measurements would be off but the 3 would be the same. old oil or some coolants will cause this. A good cleaning is the fix.

What I prefer with the brown and sharpe mics over others is the slant line grads on the barrel makes them much easier to read. Mics are a simple tool and really not a lot to go wrong with them. Its all in the threads, 40 tpi ground and fitted with a take u for play the rest is engraved graduations. Made a few mic heads for gages when a "special" range was needed, or a special size was required. On the gages we sent them out for black anodize then used white paint in grads when they came back. Easy to read and use.

[alamogunr]

I grant you that gauge blocks would be better(easier to use) since they are rectangular but pins are what I have and blocks are not available to me.

I don't use the Sherr-Tumico very often since it is harder to use. The ratchet is small and on the end of the barrel. I feel that I should use the ratchet to close on the object being measured because, as an occasional user, my feel is not well developed.

My post was in response to uscra112. Country gent posted while I was typing.

country gent: The black anodizing sounds great. You can do a lot when it is being paid for by company funds. I had to leave that behind 13 years ago.

[country gent]

Yep company funds go a long ways. I gave it up about the same time you did Medically retired 10 years ago.

All of our gages specified anodizing on the prints. The white was just was a finish touch. Some prints even specified colors. This was for Gages. Parts were bare or in house blued.

[uscra112]

Looks like it might be as simple as old oil thickened up each of the 3 measuring's is very consistent in the recorded changes. Am betting a good cleaning with clean first use solvent. and very light oiling will fix them right up. This appears to be the oil film being thinned with the repeated measurements.
If it was the faces or thread play adjustments each of the 3 measurements would be off but the 3 would be the same. old oil or some coolants will cause this.

Can't write off the old oil hypothesis. I once was called in to evaluate a Moore CNC Jig Grinder with my laser interferometer, and found a kind of "dip" in the X-axis, right where they'd been using it for years and years grinding one particular small die part day in and day out. Just a coupla tenths, but that's big lump of error for a Moore. Moore told him to cycle the axis end-to-end a few times every day, and sure enough a year later the "dip" had disappeared. Shop super was kinda disappointed - he'd been angling with his management for money to get the machine rebuilt, based on my findings.

[gnostic]

I'm definitely not a machinist and I'm ok with being wrong. But, I've always measured a feeler gauge to proof my micrometer and dial caliper. My feel isn't skillful enough to be super accurate....

[country gent]

Here's another little thing. When doing precession measurements always use the same mic, calipers or measuring tool. You develop your feel to the most used of these tools and others just plain feel different. My brown and sharpe mics are a part of my hand and I now when I have the right "touch" with them. I one of those things that's hard to explain. for truly accurate measurements a height gage indicator and gage blocks or CMM. Even the CMM has a "touch" or feel in it thru the electrical connection used to sense the probe touch the piece.

[William Yanda]

I have read through this thread but don't find repeatability addressed. Did I miss something?

[3006guns]

I have read through this thread but don't find repeatability addressed. Did I miss something?

.......or temperature. Most precision tools and their test standards are supposed to be used at room temperature. An ice cold standard and a room temperature mike don't jibe too well....

[1hole]

Seems the reality of obturating bullets, especially cast bullets, i.e., upset and swelling on firing, even jacketed bullets, has been lost. Truth is, it would take a very hard bullet and/or a very mild load to fail to upset a cast bullet 4 tenths. So, such absolute accuracy is nice but effectively meaningless to reloaders because bullets usually exit at bore diameter.

Oil, paint or anything else on a mic's anvil faces obviously affect their zero but the OP stated both his mics zeroed the same so they both must be clean; I took him at his word and didn't question his intelligence.

[uscra112]

A long-time truth in the metrology field is that your instruments should be an order of magnitude more precise than the tolerance you're trying to measure.

----------------

Repeatability is addressed in a way at post #30. Given a micrometer as the subject, it is very much a matter of the operator's skill (feel) with his tool.

Yes, temperature is always an issue when trying to verify accuracy. It is also a small factor in repeatability, if the heat of the operator's hand is enough to make the tool grow over the course of several trials. Bench check stations often mount the mic in some sort of stationary clamp to minimize this.

[EDG]

It seems you are trying to rationalize lack of accuracy with a mike.
A .0004 undersize bullet may permit blow by and cause leading.
If it does how would you know what caused the problem since you seem to be happy with an inaccurate mike.

Seems the reality of obturating bullets, especially cast bullets, i.e., upset and swelling on firing, even jacketed bullets, has been lost. Truth is, it would take a very hard bullet and/or a very mild load to fail to upset a cast bullet 4 tenths. So, such absolute accuracy is nice but effectively meaningless to reloaders because bullets usually exit at bore diameter.

Oil, paint or anything else on a mic's anvil faces obviously affect their zero but the OP stated both his mics zeroed the same so they both must be clean; I took him at his word and didn't question his intelligence.

[JSnover]

A .0004" undersized boolit shouldn't happen at all if we're casting .002"-003" oversized, unless the mic is way off.

[1hole]

It seems you are trying to rationalize lack of accuracy with a mike.

IF someone is working in a precision machine shop with many mics scattered around a production line being used on identical parts THEN absolute accuracy between work stations might be important but even then it would matter ONLY if the work itself required better accuracy (and the formentioned repeatability!) than 4 tenths.

Also, as mentioned above is the FACT that even modest temperature variations quickly become important in highly precise machine work but, for most of us, that level of absolute accuracy is meaningless. That level of accuracy simply isn't often needed even in a common machine shop and virtually never on a home shop reloading bench. I don't believe any reloader's work needs such fine measurement accuracy that he should work in a temperature controlled atmosphere because it would be laughable, we have no need for it and would gain nothing from it.

A .0004 undersize bullet may permit blow by and cause leading. If it does how would you know what caused the problem since you seem to be happy with an inaccurate mike.

You don't know what I'm happy with.

We may prove anything we wish with "mays" or "mights" but that doesn't make it true. IF our bullets were cast iron your example would/could be so. But, our bullet's are cast lead and even the hardest of lead alloys are quite malleable. Most bullet weights and powder charges will upset them to fully obturate our bores. Gas cutting will surely lead a bore but the common reasons for leading are a too soft alloy, poor lube and/or an excessive powder charge. Not from being 4 tenths undersize.

Bottom line, handguns aren't bench guns and cast handgun bullets aren't precision BR projectiles. Nothing we can do will make them so and we would never see any difference on our targets even if we could.

There is no "rationalizing the inaccuracy of a micrometer" about any of that. It's just recognizing the facts of precision mechanical measuring and a common sense recognition of the level of accuracy we reloaders actually need, not what may be needed for the space program.

[JeepHammer]

This is one of my 'Pet Peeves',

If you have precision measuring equipment, you NEED a 'Standard' to check the accuracy of that measuring equipment...

The 'Standard' here would be a 'Gauge Block', or a Rod, to verify your micrometer/caliper (whatever) isn't lying to you.

https://en.m.wikipedia.org/wiki/Gauge_block

You can buy these blocks by the piece, you don't need to buy the entire set,
And I suggest you buy one from a major manufacturers, like Starrett, Mitutoyo, Brown & Sharpe, etc.

DO NOT over handle these, keep them protected!
Just handling wear or rust will ruin them.

To do this CORRECTLY,
You will need two precise measurements, like 1/4" and 3/4" or 1".
If the micrometer shows correct at 1/4" AND 1", it's most likely correct over it's entire range.

Keep in mind the heat from your hand can skew readings, the standard can expand with heat, so do as little 'Touching' as you can.

Some standards have a plastic or foam insulation on them so the heat from your hand doesn't skew readings.
I use a plastic clamp to hold standards when I'm doing QC on the micrometers, calipers...
Plastic/nylon jaws on the clamp won't wear on the standards.

I would just about bet the Brown & Sharpe is the closest to correct, they have VERY hard measuring faces and are VERY precisely ground.
The internals of Brown & Sharp equipment are built with the very best materials and are very precise.
Unless some idiot has had ahold of them, they are very hard to ruin or knock out of adjustment.

Like I said, you need TWO standards, one 'Short' (within range of measurement) and one 'Long' (within range of measurement to make sure the micrometer/caliper is correct OVER RANGE OF MOTION/MEASUREMENT.

Rods are fine for what 99.9999% of reloaders so, but gauge blocks are a requirement for gunsmith, machinist, etc.

----------------

I can't deal with the 'Close Enough' bunch...

You don't break out a caliper or micrometer for 'Close Enough'.
The display on calipers/micrometers don't say 'Close Enough', 'Relative', or 'Doesn't Matter',
It gives a SPECIFIC READING, and *IF* you know what you are doing and have standards, the reading is specific & accurate.

If 'Close Enough' is what you are looking for out of a Horror Fright caliper with no standards, then why not just bend a coat hanger?
That's 'Close Enough', coat hanger, rock & stick, holding your fingers 'About That' far apart...

The 'Use a feeler gauge' bunch...
You ASSUME The feel gauge is PRECISELY ground (not likely when you pay $8 a set at Horror Freight), and they do ONE check at 0.010" and ASSUME the rest of the scale is correct also...

That's a LOT of making an A** out of U and ME (ASSUME)

Yes, I'm OCD, but when you want something machined correctly, or you want ammo that's PRECISELY sized, you want a little OCD in the mix.
I don't use a yard stick to measure/cut your headspace, and you wouldn't want me to ASSUME it's correct or just stop at 'Close Enough'...

[alamogunr]

This is going in a direction I did not foresee. Thanks to country gent and others. I hope the rest have fun.

[EDG]

You might really be peeved to know that you do not need a standard to properly set up most 0-1 mikes.
Think about it a minute. The zero setting of the mike is set by running the spindle out to touch the anvil.

Of course you can go OCD and check it at a larger dimension but what is your plan if it shows to be off at the second dimension? When the mike is off at one end and not the other it may be due to a sprung frame, excessive lubricant or a miss set thread collar on the female thread.
If you are unable to correct the error the mike can be set up to be accurate in the zone you use the most or the error can be split between each end of the travel. For the most part your 0-1 mike will be dead on end to end when the zero is properly set and there is no need to use a standard. I have more than a dozen 0-1 mikes. Only 1 was bought new and that was in 1969. All these mikes are right on end to end.
The precision of gage blocks for the most part are worthless for everyday checking of an 0-1 mike since it is normally checked at zero. The twenty millionths or so tolerance on the gage block is so much more precise than the resolution of the micrometer it provides no benefit.

Finally if you want to be OCD your gage block is not really known to be accurate unless you have it calibrated on an annual basis. That is the requirement to use the gage block to calibrate any equipment used to accept product sold to the US government or sold under the claim of having an ISO 90001 quality management system or MIL-Q-9858.

This is one of my 'Pet Peeves',

If you have precision measuring equipment, you NEED a 'Standard' to check the accuracy of that measuring equipment...

The 'Standard' here would be a 'Gauge Block', or a Rod, to verify your micrometer/caliper (whatever) isn't lying to you.

https://en.m.wikipedia.org/wiki/Gauge_block

You can buy these blocks by the piece, you don't need to buy the entire set,
And I suggest you buy one from a major manufacturers, like Starrett, Mitutoyo, Brown & Sharpe, etc.

DO NOT over handle these, keep them protected!
Just handling wear or rust will ruin them.

To do this CORRECTLY,
You will need two precise measurements, like 1/4" and 3/4" or 1".
If the micrometer shows correct at 1/4" AND 1", it's most likely correct over it's entire range.

Keep in mind the heat from your hand can skew readings, the standard can expand with heat, so do as little 'Touching' as you can.

Some standards have a plastic or foam insulation on them so the heat from your hand doesn't skew readings.
I use a plastic clamp to hold standards when I'm doing QC on the micrometers, calipers...
Plastic/nylon jaws on the clamp won't wear on the standards.

I would just about bet the Brown & Sharpe is the closest to correct, they have VERY hard measuring faces and are VERY precisely ground.
The internals of Brown & Sharp equipment are built with the very best materials and are very precise.
Unless some idiot has had ahold of them, they are very hard to ruin or knock out of adjustment.

Like I said, you need TWO standards, one 'Short' (within range of measurement) and one 'Long' (within range of measurement to make sure the micrometer/caliper is correct OVER RANGE OF MOTION/MEASUREMENT.

Rods are fine for what 99.9999% of reloaders so, but gauge blocks are a requirement for gunsmith, machinist, etc.

----------------

I can't deal with the 'Close Enough' bunch...

You don't break out a caliper or micrometer for 'Close Enough'.
The display on calipers/micrometers don't say 'Close Enough', 'Relative', or 'Doesn't Matter',
It gives a SPECIFIC READING, and *IF* you know what you are doing and have standards, the reading is specific & accurate.

If 'Close Enough' is what you are looking for out of a Horror Fright caliper with no standards, then why not just bend a coat hanger?
That's 'Close Enough', coat hanger, rock & stick, holding your fingers 'About That' far apart...

The 'Use a feeler gauge' bunch...
You ASSUME The feel gauge is PRECISELY ground (not likely when you pay $8 a set at Horror Freight), and they do ONE check at 0.010" and ASSUME the rest of the scale is correct also...

That's a LOT of making an A** out of U and ME (ASSUME)

Yes, I'm OCD, but when you want something machined correctly, or you want ammo that's PRECISELY sized, you want a little OCD in the mix.
I don't use a yard stick to measure/cut your headspace, and you wouldn't want me to ASSUME it's correct or just stop at 'Close Enough'...