measuring wall thickness

[nilebartram]

I did a search and it did not answer my question.. I have 3 Mitutoyo micrometers. I get different reading from the three. They all zero perfectly. I am trying to get a .011" wall thickness. One micrometer is .0123, two is .013, last is .0115. One micrometer is a ball type, the others are the one with inter changeable stem. I should mention. I do micrometer hold . Can you please advise. nilebartram

 

[Dusty Stevens]

It takes years of practice and the correct hold as to not heat up the mic. The speed at which you close the anvil even matters. Best way to learn is to get a good standard like a certified .250/.500 gage block and practice. In the meantime you can get an indicating mic and let it close itself to maybe get a more consistent reading. Another method would be to seat a bullet and measure the outside with your calipers. As long as youre using a good turning tool thatll be just fine, theres no need to measure to the tenths all you need is enough clearance. A weighted mic stand will help if you still want to use a mic. If you hold it by hand this is the most consistent hold pictured here

 

[Jager]

Bear in mind that neck thickness is not going to be perfectly consistent around the circumference of the case neck. If, for instance, you mic the neck at one spot... then rotate the neck 90 degrees and take another reading... then rotate another 90 degrees for a third reading... and finally rotate one more 90 degrees for a fourth reading... you'll almost certainly see different numbers.

Understanding those samples - min, max, average, and standard deviation - can give great insight into the qualities of a particular piece of brass, a lot of brass, and how different headstamps compare.

Measuring short-neck cartridges also brings its own caution... as measuring slightly too deep into the neck such that the shoulder of the case abuts even an infinitesimal amount into the mic face/anvil intersection will throw the measurement off.

Mitutoyo makes good stuff. Use the one with the ball.

 

[LHSmith]

Best solution for me was to simply buy a micrometer stand.

 

[dgeesaman]

Do they measure the same on a flat shim or feeler gauge?

Are they the same diameter on the inside ball?

One thing is sure: using a pin style stem means that any distortion in the neck wall will show a larger reading. A ball stem will touch at a point and largely ignore geometric imperfections.

what you need is a good indication of which will give you a good loaded round diameter. I would take one piece, skim to 90% cleanup, mic it with all three neck mics, then mic a bullet to the .0001 and seat it and measure the finished neck. Now you can assess which is giving you the most indicative measurement.

 

[David Christian]

I like Dusty’s method. Measure the total diameter of a seated bullet then subtract the bullet diameter. I also gently turn the round while measuring to see the variability all the way around.

 

[geo.ulrich]

or setup a pin with an indicator takes all the "feel" out of it

 

[Fred B.]

Make sure you are measuring on same line (distance from shoulder) with all mics.
neck wall can vary from mouth to shoulder.

 

[mikecr]

I get different reading from the three.

I would help if you told us what the readings are.
Is it thickness at same datums? Variance around necks?
And having different anvils doesn't help with comparison.

Forget a pin anvil for this. You need a point/ball contact

 

[nilebartram]

I am forming a 20 vartarg with .223 brass. It is a winter project. Some people think I am nuts, but 221 fireball is getting harder to find. I have 221 fireball brass and I have to turn it also. So I am learning to turn on the .223 brass. My chamber is .226, so I figure my brass has to be turn to .011, the bullet is .204, equals .226. I thought the expander will help uniform the brass. I do notice when I turn the neck and measure you get a different reading. When I think I have turn the brass and measure the neck and it is .011 and I seat a bullet in the empty brass, it measures .228, so the neck must be really .012. Really frustrating.

 

[Arky]

If your chamber is .226 a loaded round should be a MAXIMUM .224

 

[JEFFPPC]

Measuring the neck wall is to me just the beginning step. I seat the bullet I intend to use, the loaded round at the neck measured with a micrometer in relationship to the neck clearance is what I go by.

 

[Dusty Stevens]

For now just forget measuring wall thickness or what a bullet measures. Measure simply over a loaded round and give yourself clearance. You dont need to measure to the tenth right now just use calipers and get clearance. No math involved except figuring out which bushings to buy. If a loaded round doesnt fit your standards, adjust the tool, turn another one and measure again. It makes absolutely zero difference if your neck is .011 or .0113

 

[liljoe]

I have a mic just like that. It zeros fine but the larger it measures the more error it reads. I used a set of gauge blocks to check it one day. At 010" it is off about 0005", at 050" its over 001" off.

You need a good gauge block to check it with like Dusty said.

Joe

 

[mikecr]

In early life I've used cheap tools, harbor freight & stuff,, but have never seen calipers off by a full thou, much less a micrometer. This is likely a measuring method issue.

 

[Ranger007]

It takes years of practice and the correct hold as to not heat up the mic. The speed at which you close the anvil even matters. Best way to learn is to get a good standard like a certified .250/.500 gage block and practice. In the meantime you can get an indicating mic and let it close itself to maybe get a more consistent reading. Another method would be to seat a bullet and measure the outside with your calipers. As long as youre using a good turning tool thatll be just fine, theres no need to measure to the tenths all you need is enough clearance. A weighted mic stand will help if you still want to use a mic. If you hold it by hand this is the most consistent hold pictured hereView attachment 1228433

Dusty you might want to moisturize too, just saying. lol lol

 

[Dusty Stevens]

Dusty you might want to moisturize too, just saying. lol lol

Too much carb cleaner man. Winter is hell on my hands

 

[Ranger007]

Too much carb cleaner man. Winter is hell on my hands

I get you brother I can relate. I wear gloves and it works for me and tend to go through quite a few but oh well.

 

[jackieschmidt]

Keep in mind, when using a ball micrometer with a flat spindle, such as the Mitutoyo shown in post #3, the large area being contacted by the flat spindle can have an affect on the actual measurement. This is less true with a properly turned neck, but there are all sorts of irregularities in the OD of a factory neck that can throw you off. Keep in mind, we are dealing with increments of less than .001 inch.

Since you are trying to measure one spot, I modified this old set of tubing mic’s so the spindle and anvil just contact one small spot. I get more consistent readings in smaller diameters. than I do with my regular ball mics.

 

[mikecr]

Whether you turn down a spindle or not, you still need a ball anvil for neck measure -because necks taper in thickness. The spindle area only serves to push the neck against the ball.
For those with neck mics, their anvils are adjustable and contact with spindle can be set to sneak right into solid donut measurements, without modifying spindles.

Also, since necks are tapered in thickness, to obtain radial thickness variance you need a case mouth stop to set the contact datum.