Temperature influence on micrometer readings

[eric n]

How accurate is a 0-1” micrometer outside of a lab?
How much does temperature influence it?

If temp plays a role, why does the brass I turned during a hot summer night last year still measure the same on a mildly cold morning today?

Random thoughts while turning some brass last night...

BTW... I tried some engine assembly lube last night instead of imperial. It worked fantastic and cleaned easily in a sonic cleaner. Using a qtip in the necks for expanding and a dab on the mandrel along with an ice pack for the turner, I was able to hold the best tolerances I ever have.

 

[XTR]

How accurate is a 0-1” micrometer outside of a lab?
How much does temperature influence it?

If temp plays a role, why does the brass I turned during a hot summer night last year still measure the same on a mildly cold morning today?

....

Because the total expansion is a function of the total length, so the expansion of a neck thickness of 0.1% due to a temperature change would be on the order of 0.000012, and you can't measure that. On the other hand a bullet that measures 2.330 CBTO would see a variance of .0023 for that same temperature delta assuming the same expansion rate. That you can measure.

 

[Straightshooter1]

I've asked myself the same questions as I haven't seen any perceptible difference with my micrometer either. I likewise get the measurements. Though I am sure there's a difference, I just don't see that there's enough difference for any concern. It's surely be an issue for much higher tolerances, like what one would see for a jet engines.

BTW: I use a carbide turning mandrel and don't use any lube on it and I get pretty consistent results. When it's a cool environment when turning, the mandrel get's just slightly warm, but cools down during the time I take to burnish the necks with steel wool and then start a new case. If I'm turning cases during the summer when it's a very warm environment, I do have to use some lube (I use Imperial) to make sure the mandrel doesn't get too warm.

 

[billlarson]

From experience i,ll tell you it makes a difference chambering..
bill

 

[Acyr]

A few years ago I was fortunate enough to get a tour of Hondas HPD (Honda Performance Development) This is where they build their IndyCar engines. I got to see each part of the process of building an IndyCar high performance engine from machining to assembly and testing on a dyno. The head of HPD was giving the tour and one thing that I remember most was his explaining how hard it is to maintain accurate measurements when your dealing with ten thousandths of an inch. Minor variations in temperature affect not only the material involved but also the tools that measure it. They had to completely redesign the HVAC system at great expense to combat this.
After seeing the lengths a world class engine program had to go through to consistently and accurately measure in the ten thousandths of an inch I don't believe any of us reloaders or the average machinists can do it. Its not even necessary for what we are trying to achieve. Anytime someone posts measurements to the fourth decimal it is probably not an accurate measurement.
For what we do it just needs to be consistent as possible in weight and measurement whatever that may be.

 

[eric n]

Because the total expansion is a function of the total length, so the expansion of a neck thickness of 0.1% due to a temperature change would be on the order of 0.000012, and you can measure that. On the other hand a bullet that measures 2.330 CBTO would see a variance of .0023 for that same temperature delta assuming the same expansion rate. That you can measure.

Thank you for the explanation. I understand now.

 

[Texas10]

Only by using a standard will you know the answer to your question. If I need to make a precise measurement outside of a temperature and humidity controlled lab, I use the standard to identify the degree of error, and apply that to the measurement taken. If the part is not at the same temperature as the micrometer, there is little hope of obtaining a true measurement.

Does any of this make a significant difference that can be measured on the target? You're a far better marksman than I if you can.

 

[powderbrake]

How accurate is a 0-1” micrometer outside of a lab?
How much does temperature influence it?

If temp plays a role, why does the brass I turned during a hot summer night last year still measure the same on a mildly cold morning today?
.

If you keep the micrometer at the same temp as the object being measured, zero it at that temp, the readings will closely track with changing temp. I say closely track because brass's coefficient of thermal expansion is 11 and steel is 7.2 X 10 (to the -6) in/in/*F. If the temp changed from 70 degrees to 100 degrees, the difference in expansion of a .272 od neck, and the micrometer would be 0.00003. Too small to measure with a .0001 resolution micrometer.

 

[eric n]

If you keep the micrometer at the same temp as the object being measured, zero it at that temp, the readings will closely track with changing temp. I say closely track because brass's coefficient of thermal expansion is 11 and steel is 7.2 X 10 (to the -6) in/in/*F. If the temp changed from 70 degrees to 100 degrees, the difference in expansion of a .272 od neck, and the micrometer would be 0.00003. Too small to measure with a .0001 resolution micrometer.

Is this information in MACHINERY’S HANDBOOK?

 

[chop house]

Minor variations in temperature affect not only the material involved but also the tools that measure it. They had to completely redesign the HVAC system at great expense to combat this.

this is why you don't open the roll-up door at the back of the machine shop.....

 

[Acyr]

this is why you don't open the roll-up door at the back of the machine shop.....

 

[powderbrake]

Is this information in MACHINERY’S HANDBOOK?

I simply googled the expansion coefficients, but it is on page 2193 of the 19th Edition (1973) of Machinery's Handbook

 

[Rustytigwire]

Last employer, jerk to work for but very sharp.
Mild steel 3/4 inch per 100 deg f per hundred feet.
I compared that at some point to machinerys handbook for steel iirc came out close enough.
I cant measure it and sure cant shoot it.
Temp swing distortion behavior:
Mild steel is reasonable. Grows and shrinks predictably.
Stainless gets hot warps every which way takes forever to cool off. Izzat still hot? Dayum!!
Aluminum wont stay hot. Try to heat it falls in your lap.
Life is great!

 

[eric n]

I simply googled the expansion coefficients, but it is on page 2193 of the 19th Edition (1973) of Machinery's Handbook

Ha! You didn’t need to do that but...
Thank you.
I’ll grab a copy and learn something.

 

[Dusty Stevens]

All you gotta do is measure a standard, then put the mic in your pocket for 15mins and do it again. Or if youre a barrel chambering type guy find the deltronic pin that fits snugly into a barrel (holding it in the middle with 2 fingers per procedure of course) then put it in your pocket for 15mins and see if it fits again. Simple tests like this are what machinists use to raise awareness to apprentice machinists.

 

[dave@aDave]

Is this information in MACHINERY’S HANDBOOK?

Machinery's Handbook, 30th edition, pages 596 to 802, Just about everything you want to know. In my case, more than I need.

 

[prwhite]

Dirt, dust and other crap on your measuring tools most likely has more effect on measurements than ambient changes.

 

[Old Navy]

this is why you don't open the roll-up door at the back of the machine shop.....

Worked at a aerospace plant. All of our climate controlled buildings had an air lock. That being two roll up or overhead doors one 20 to 30' back to back. Open one, drive in, close it and then open the other.

 

[Alan Warner]

Yes, temp is everything. We use mitotoyo series510 indicating mics for bullet mfg and when grinding inserts for dies. Setting standards are Deltronic pins and ring gauges that come with certs.
It is common to see deviations from one days end to the next morning of up to .0001. Same thing for the Sunnen bore gages when honing the housings for the dies
Tols on all three series of insert sizes (.7500, .8750 and 1.0625)is +.0001 to .0002 on the hole and -.0001 to -.00015 on the inserts. Gaging is in constant use to maintain a good zero
Can I do it with a handheld mic? Yeah, I can, but it is extremely tedious and not as reliable.
The 510s with very distinct .00005 lines make it easy to see in increments 0f .00001
The mics are held in stands so as to avoid temp saturation from handling.
I use methods as best I can to mitigate temp influence but still find times that
I'm waiting for temps to stabilize
HTH
Alan