Gage blocks

R

rstreich

Guest
It seems I need a set of gage blocks. My caliper and micrometer seem to disagree about everything by about .001 and I'd like to know which is right and send the errant one off for service.

The only problem is there are about 870 different varieties of them. Anybody got a recommendation? I'm not cutting anything other than case necks with these tools, so I don't need to spend several hundred bucks, but I'd like to be reasonably accurate.
 
Even if you get a sett of gage blocks the blocks will vary in size according to the temperature they are at.
So any setting of a mic with a gage block is only good if the gage block is correct at that temperature when you set it.
So the problem is that at what temp is the gage block correct for its stated size?
If you can buy a sett of blocks that state at what temp they are spot on then you have a place to start.
Get the blocks to the right temp and set your mic.
The average electronic calipers are not as accurate as a good quality .0001 micrometer and the slightest angle of the jaws accross the work will give a different result with calipers.
I use a Starret .0001 mic to measure neck turning diameter and find it better than electronic calipers but some will dissagree I'm sure.
Everthing expands and contracts with temp changes.
Consistancy from neck to neck is more important than knowing the actual diameter perfectly.
Because you have some neck to chamber clearance any tiny change of the neck diameter will not hurt anything as long as all the cases in a batch are the same diameter and thickness.
You don't really need a full sett of blocks. Just buy a single gage block that is close to the actual size of the neck diameter and sett the mic with that.
That way you will be making it more accurate close to the desired size you need to measure. Temp not withstanding.
http://www.mitutoyo.com/TerminalMerchandisingGroup.aspx?group=1664
 
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Gage Blocks

rstreich
You don't need gage blocks.Just get you a set of mic standards.0-1" 1-2" 2-3'
Your mic's and your dial caliper are calibratied to +/- one division.
Example: if you have a set of mic's that read in .0001 than using a standard of .500 you could have a reading of .5001 or .4999 and the mic would still be within it's calibration limits.You can get mic standards from starrett,or mitutoyo.Good luck.
Russ
 
Purchase a pin gage that's somewhere in the neighborhood of the necks you're working with. From MSC or McMaster, you should be able to get a USA one for $1.50-$3.00.

They only come in + or -, so there's no such thing as a "right on". It'll be plenty close enough for your instruments though.
 
J. Valentine: The thermal expansion of the gage blocks and tolerances for each of the standards is what was making the choice difficult. Just how much would the steel blocks expand/contract over a 20-degree temp range?

Metrologists: I went digging through MSC and Enco for standards. The entries in catalogs are a real pain. They don't even list dimensions for most of them.

4Mesh: The pin gage is a good idea as I was thinking about getting a set anyway (if I just bought one it'd be about 30 seconds before I managed to lose it). The only concern I have is how difficult it would be to get a good measurement on one. I haven't seen one, but I imagine they'd have a rounded or even pointed end on them.
 
The thermal expansion of the gage blocks and tolerances for each of the standards is what was making the choice difficult. Just how much would the steel blocks expand/contract over a 20-degree temp range?
Click to expand...

You don't have anything sensitive enough to measure the difference ;) If it was an issue and money was no object you could always buy carbide gage blocks.

Majority of people using mikes can't measure within .0002" repeatedly. It's all in the feel.
 
I always thought that gage blocks had a very similar coefficient of thermal expansion to the steel in micrometers, so it could be ignored in normal shop situations. It surely is not a factor in the range of case necks that we are concerned with here.
A set of .250 to .499 (minus) pins is pretty cheap and very useful in precision reloading.
I would not use calipers for anything requiring the accuracy that we want when neck turning or fitting necks to chambers. They are fine for cartridge length or measuring over a chamber gage but still requires skillful use.
 
Gage Blocks

rstreich,
I'm not trying to crap on your project,But your way overboard here.Go with the gage pin.Ask for a size close to what you working on.Order a X tolerance.
That would have a .000040 tolerance.The tolerance would be +.00004 if it is a go pin or -.00004 if it is a nogo pin.You could order a master set pin that would have a tolerance of +/-.00002.If it is a steel pin and your worried about heat, the Expansion Coefficient would be .00000639 per inch, per degree F. What I'm trying to tell you is Don't worry about it.Just have some fun:p
Russ
 
Jay

Once had a millwright tell me a bearing diameter on a ballscrew off a CNC milling machine was .0003" oversized. He was positive, he measured it with a digital caliper. Ya, that went over REAL well. :D
 
You can also

get Croblox, tungsten carbide, or ceramic Cera blocks. The Croblox can be found in .05, .1, & .5 in size. The Croblox and cera are not temperature sensitive.
 
ReStreich-

You probably have figured it out by now, use the guage pin diameter to check your mics/caliper, not length. Pointed or square end wouldn't matter.
Close does matter, especially arm pits.

Steve Moore
 
In the original post he said he was using the tools to measure case necks............so the mic can just be zeroed on itself. Close the faces against a clean piece of paper and slide the paper out to clean the faces. Close the tool with moderate pressure (forget the ratchet or friction stop), and check for zero & adjust the sleeve as necessary. As long as the mic isn't a total piece of trash it should be more accuate over a case neck than you can discern.......I wouldn't worry about checking it over a gage block or pin.

Keep in mind that you're measuring conditions (round, soft part) can easily cause you to measure small. Try to use a light but sure feel.

-Dave-:)
 
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