The ability to measure

[Webster]

The guy on U tube says since the metric people didn't go to the moon, and we did stick with SAE.

I remember when the world changed to mettric and we didn't, the justification was that all our machinery was SAE and it would cost trillions to change. Funny everyone else didn't have a problem changing. A good friend of mine was a draftsman at the Main Battle Tank Plant near the Cleveland airport about 1970. The tank was a joint project with Germany. The Germans made parts with metric blueprints and we had SAE blueprints for the same tank. Lots of fun making parts to both specs. Are we still the only SAE country in the world?

 

[Rocketvapor]

American industry just had an aversion the Metric System.
Old hands measuring parts found it confusing. We had people using the four place 39.37 conversion, even in our Metrology Lab. We had to revise 100's of cal procedures to use the 'Defined' conversion of 2.54.
NIST and other gov agencies actually had to calculate inch based measurements from Metric Standards to calibrate precision instruments back 20 to 30 years ago.
The HP Laser Interferometer was a big plus for linear measurements.

We find that in other Metric measurements, like scales that are a little more accurate in gram mode over grain mode. or Mil vs MOA discussions.

Since I like my new cheapo caliper (inch) I ordered a Metric version with a 0.02 mm dial division.
I'll leave it to others to calculate if that is better than 0.001" resolution

 

[dgeesaman]

I just push the in/mm button on my digital measuring tools. It’s a heck of a lot faster than reading a manual tool and performing a calculation, or buying metric manual tools.

Also I know the definition is to divide mm by 25.4 to get inches. The .003937xxx conversion is irrational in every sense of the word.

 

[Rocketvapor]

Sometimes resolution, Metric or Inch is limited to the Liquid Crystal Display, or internal measurement methods and rounding.
Inch mode resolution vs Metric mode resolution.
For example, my iGaging Speed Mic has 0.00005 inch resolution but has 0.001mm resolution in metric mode.
Even the A&D FX120 is a little better in gram mode.

 

[jackieschmidt]

As I said, I use “tenth” micrometers in my bullet making, but more for comparison. I have “master bullets and seated cores” that I know are correct, and I make sure each lot is exactly like those.

I didn’t mention it in my previous post, but when turning necks, I to measure to the “tenth“ with my ball micrometer. But even then it is a comparison. I have a case that is exactly the thickness I want, and duplicate that thickness each time.

By using comparative measuring, I don’t have to worry about other variables that much.

Since I do own a fairly large industrial machine shop, I do a lot of measuring, and am realistic about what is required for each individule job. I my shooting endeavors, by far the most precise measurements are in my bullet making.

 

[hogpatrol]

In my CMM room days measuring car bodies and parts, we measured in microns, defined as if you had dog poop on your hand and could still smell it after scrubbing, that was one micron.

 

[jackieschmidt]

I remember when the world changed to mettric and we didn't, the justification was that all our machinery was SAE and it would cost trillions to change. Funny everyone else didn't have a problem changing. A good friend of mine was a draftsman at the Main Battle Tank Plant near the Cleveland airport about 1970. The tank was a joint project with Germany. The Germans made parts with metric blueprints and we had SAE blueprints for the same tank. Lots of fun making parts to both specs. Are we still the only SAE country in the world?

In our Shop, The only time we have trouble with metric is with threads. All of our lathes have imperial lead screws, so when cutting metric threads, we have to leave the half nut engaged and reverse the lathe.

We do get prints that are dimensioned in metric, you simply have to convert.

Heck, I just use my IPad to do quick conversions.

 

[jackieschmidt]

In my CMM room days measuring car bodies and parts, we measured in microns, defined as if you had dog poop on your hand and could still smell it after scrubbing, that was one micron.

 

[hogpatrol]

In our Shop, The only time we have trouble with metric is with threads. All of our lathes have imperial lad screws, so when Cutting metric threads, we have to leave the half nut engaged and reverse the lathe.

We do get prints that are dimensioned in metric, you simply have to convert.

Heck, I just use my IPad.

Ran a few Polish lathes that one would have thought you could do metric conventionally but yeah, threading up to a shoulder, no brake, you had to be fast on the draw, back off then reverse. I've had a couple miscues where the brain and hands weren't working in sync.

 

[NZ_Fclass]

Having owned a caliper from the Shanghai Optical and Dishwasher Collective (SHODCO), makers of the Shining Deer 4x riflescope, I can attest that a Mutitoyo is money well spent. Whether it has 3 or 4 digits east of the decimal point, the measurement quality and repeatability is worth every cent.

 

[jackieschmidt]

Wow, you make bullets, I am impressed!

I can’t be certain if you are being facetious, , but if not, there are multitudes of Short Range Benchrest Shooters that have excellent bullet making equipment and make excellent bullets.

 

[357Mag]

I was reading a post on the forum the other day and was impressed with the posters ability to measure to .0001. I thought to myself Holy crap he must have some very accurate measuring tools. There was a picture included and the dial indicator was in the picture. I thought to myself I want one of those that goes to the 4th decimal point, and right now. So I blew up the picture as large as my computer would allow to get the model number, and to my surprise the manufacturer of the indicator had printed right on the face of the indicator that it was only capable of .001, or 3 decimal points of accuracy not 4 so how does this poster get the extra accuracy he is claiming? Is there some dial indicator guru like SParker with scales that fixes them, or something I don't understand? Please help I want the .0001 so I can make the best ammo I possibly can.

Howdy !

Back,when I was an aircraft mechanic working in the Hydraulic Shop at the local Air National Guard, we were tasked to measure F-16 Main landing gear “ drag braces.
We were required by the applicable tech order to make length measurement on a
“ calibrated “ machined piece of steel plate… that featured 2 vertical steel pins set for an allowed spacing distance. For the desired level of accuracy and precision in measurement, the Air Force set a certain level of “ flatness “ the top surface of the plate had to maintain, and could not exceed. The limit was called out within some ten thousandths of an inch over the entire length of the plate.

The Air Force’ regional Precision Measurement Equipment Lab would not ok periodic
re-inspection and re-certification of the test jig as approved for use, unless the specified flatness level of the base plate’s top surface was within AF established spec.
How do you “ calibrate “ ( Air Force PMEL description ) a flat steel plate ?!?

You uniform the surface by a performing an intricate machining/polishing of the surface
to get the plate back into spec..and THEN send it to the PMEL lab for re-certification.
To maintain the specified tolerance on “ flatness “, the machine processes had to be performed in a room within an allowable limited temp span. The kicker…. a-soon-as the machined plate left the temp controlled room, the temperature swing was enough to once again put the plate “ out of spec “. Temperature change had effect of the metal down to 10 thousandths of an Inch level. The PMEL lab was some 2hr away from our base, and the jig was treated to a covered pickup truck ride… both ways.

Best we could do was find out what temp the PMEL lab was maintained at, and pass that info on to the machine shop… ostensibly for them to duplicate that temp while they worked on the steel plate. Once PMEL ok’d the jig for use ( certified as calibrated ), best we could do once it made it back to our Base’s Hydraulic Shop; was to make the critical drag brace measurement only when we first had the shop set to the same room temp as the machine shop used.
And, when the fixture once again came up for “ cal “, we did the whole goat rope all over again.

My point:
Don’t….. Ah Say…. DON’T drive measurements down to the .0001 level IF you don’t have to.
That way lies madness.


With regards,
357Mag

 

[jobhopper66]

I can’t be certain if you are being facetious, , but if not, there are multitudes of Short Range Benchrest Shooters that have excellent bullet making equipment and make excellent bullets.

I thought it was a fairly well known secret that you made bullets.

 

[K22]

I can’t be certain if you are being facetious, , but if not, there are multitudes of Short Range Benchrest Shooters that have excellent bullet making equipment and make excellent bullets.

I was not being facetious; I am impressed with anyone hobbyist that can make bullets especially benchrest quality. I assumed, maybe incorrectly, you were referring to jacketed bullets.

PS The only bullet making experience I have is many years ago, a friend cast lead pistol bullets and I helped in the process receiving a share of the production. This was a fairly straight forward process.

 

[AlNyhus]

I was not being facetious; I am impressed with anyone hobbyist that can make bullets especially benchrest quality. I assumed, maybe incorrectly, you were referring to jacketed bullets.

There's a fair number of competitors on this site that make their own jacketed bullets. -Al

Time to make the donuts....

Like the old Dunkin' Donuts commercial....time to make the bullets. A colander full of washed cores, rinsed and ready to dry: Then rolled on a big slurp up towel: Spread out to dry on a beach towel. Tomorrow, they'll get stuffed into jackets. Good shootin' :) -Al

forum.accurateshooter.com

 

[Old Navy]

Any variable that you can eliminate, should help on target.
Being able to measure better than 0.001" while a little anal takes that measurement out of question.
Many throw money at it.
But refuse to take the time to sort primers.
Time is too expensive.

Time is cheap at my age. And I know you know that that last number will vary with room temp alone.

 

[Rocketvapor]

"that last number will vary with room temp alone."

HOW MUCH WILL IT VARY?
Tell us.
You can CALCULATE temperature coefficients of the metals involved and COMPENSATE if really anal
True size of bullet and instrument @ 68F compared to as measured @ a room temperature of 75F.
Most of the cross section of a bullet is lead (about 15-16 ppm/degree F)
For a 0.308" bullet, the diameter would be about 5 microinches per degree F larger,
or about 0.000035" @ 75F than @ 68F
BUT, the caliper/micrometer would have grown also making the error LESS.
Part and instrument @ DIFFERENT temperatures might be a bigger issue than everything @ "Room" temperature.

Calculate the error of a brass .308 case length and micrometer with both at 75 or even 95F and post your results.
People refer to "Lab Environment" and YES it matters.
For high precision lab measurements and calibration of really precise instruments.
Using the HP Laser Interferometer out of the lab required measuring and compensating (via software) the speed of light in the air environment.
Nice thing is that when you have a temperature correction, it will also work next Wednesday.
Write it down so you don't forget it or put it into a PROCEDURE.
Don't we have some machinists that had to make precision parts out on a comfortable shop floor and send them in to the QC in a temperature controlled room?

How many bench rest shooters HOPE for an inch at 600yds?
That's about 1 inch over 600yds (1/21600).

This shop floor was NOT kept at 68F.

to make this somewhat precise object that needed to bolt up to other precise objects made in different shops and joined in another.

 

[Old Navy]

I knew as soon as I posted that I made a huge mistake.

 

[Dgd6mm]

I truly like reading stuff from you smart fellers.
Thank you for the great detail.