So we all have some tool for measuring our boolits to make sure of this or that but what kind of gauge should be used to calibrate our micrometers and calipers to make sure they are in spec?
So we all have some tool for measuring our boolits to make sure of this or that but what kind of gauge should be used to calibrate our micrometers and calipers to make sure they are in spec?
I close them, set to zero, and measure away....
I too just check for "zero", gently. I've been using micrometers off and on since 1968 and rarely found a need to check against "go blocks" (when I was working in a machine shop measuring to .0005" I dropped a mike and needed to check it ). Since I don't use my mikes like a c-clamp I've never had any good micrometers loose accuracy...
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I check zero then check a 224 and a 308 match grade bullet. I keep the "gauge" bullets forever. This will not tell me if the instrument is dead on accurate but it will tell me if it has changed.
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You can buy standards to set them by. If the micrometer is in good shape, clean the faces of the checking surfaces, gently "zero" them out and adjust if needed. A small spanner wrench is required.
Have a blessed day,
Leon
Typically when calibrating a o-1" mic you would make the adjustment by closing the mic and making the adjustment.
If you are measuring stuff that is closer to 1" then using a 1" standard would be more accurate.
Older micrometers do vary sometimes. Newer quality ones ,,, not so much. Pretty much anything is going to be accurate enough for measuring boolits.
Randy
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On 0-1 mics closing to your feel is the prescribed method of checking to see if they are zeroed. On bigger a standard or Jo Block is used same with calipers. We also had to once a year check micks at .025 increments, this showed any anvil wear on the insterments. Calipers were checked thru their range every inch. They were also checked back of jaws and front of jaws for wear. ( the narrow Knife edges wear faster than the backs wider surfaces. ID jaws were checked in rings. The depth measuring surfaces of the jaws were done with Jo blocks same as the depth rod. In the shop measuring tools were checked before use. My 4', 5' and 6' mics went months not being needed. The0-1" and 2" were daily as were the 6" calipers. the 24" calipers again might be in the box for several months between uses. ANother thin is to clean the measuring faces before use and setting.
I worked as a quality manager for a couple of very big companies before retiring. One of my responsibilities during my career was to supervise several metrology labs where there were literally thousands of gages that were in the system. In my experience, it would be rare to find a new set of gages that weren't accurate unless they had been dropped or damaged. Even the cheaper foreign stuff was fairly accurate. The correct way in a manufacturing organization would be to check the gage against known standards (gage blocks, etc) over a range of measurements within the gages design. For actual real world use, setting them to zero by gently wiping and closing them and adjusting to zero will suffice for any needs in the shooting world.
For low usage 0 to 1 mics zeroing at closed is adequate for most applications. When trying to get max accuracy using a gage pin or gage block the same size as you measuring. For over 1" mic standards or gage blocks.
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In a shop I would use a 1.0000" gauge block to verify it at 1", and a 0.1000" block at the low end. If it is correct at zero or with feeler gauges, then that should be good enough for measuring bullets.
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Last edited by jimkim; 10-13-2017 at 04:16 AM.
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It is very rare to need a test standard for something like a 0 - 1in. micrometer. Checking that it reads zero when it is closed down to zero should be fine. I have a larger micrometer with an interchangeable anvil to measure down to zero, and the same applies. The need for a standard comes in with 2 - 3in. and larger, which can't be closed down to zero.
In theory you could just keep a small piece of, say, nominal 1in. ground flat stock which you have measured when the micrometer was new and trusted, marked with the measurement if it was a thousandth or two over or under. But a proper test standard has convex ends, just as if it had been made by drilling through a sphere with a long, thin holesaw. That way it is accurate if it is rocked slightly out of alignment with the axis of the threads, and more important, it is less vulnerable to specs of dust distorting the measurement.
The common mistake in checking a mic or vernier is to close it tight or try to use it as a vice in checking something. I was a quality control supervisor for a while and I had a class for new quality control inspectors to teach them the proper use of their mics and calipers. Once taught none of them mishandled their equipment.
My experience with the "older mics" was I never had a problem with them either since they were made very well probably better than some of the suff out there today. I grew up with the old style mics and calipers instead of the direct read out ones.
I will check my calipers with my mic to see if the jaws are all good.
Especially the inside diameter end.
Now to really get proper measurements then your tools and test piece should be the same temp. 25 c and all that.
In reality if measure something with a mic I will use the same tool to measure my component.
That way if my tool is a poofteen out then the work will be also ...but they will have the desired fit.
Don't forget its all about feel and a old mic used to measure cutting tools all day with scores in the anvils will feel a lot different than polished surfaces.
My 2 cents worth.
Now that we've covered what not to do I'll touch on the checking part. Its already been mentioned that there are go gauges precision ground blocks. In addition there are also pin gauges that are specific diameters that can be used to check. I wouldn't try to use for example steel or aluminum in different gauges because the tolerance isn't tight enough to use.
To clean the jaws on calipers or mic's close them lightly on a clean sheet of paper and pull the paper thru the jaws.
Certified pin gages - your choice plus or minus Tolerance: 0.0002"So we all have some tool for measuring our boolits to make sure of this or that but what kind of gauge should be used to calibrate our micrometers and calipers to make sure they are in spec?
Even my Harbor Freight calipers are with tolerance ...
Regards
John
Standards are pretty easy to get, a lot of micrometers ship with a standard included with the mic. You use the standard to set the mic to the exact length of the standard and this calibrates the mic. I do things a little differently, I like to calibrate the mic as near as I can to the diameter I am going to be using it the most. I have to take a lot of 45 caliber measurements just from the volume of 45 caliber barrels and cylinders I get in for throating so I like to zero my mic at .4520" and call it good.
Last edited by DougGuy; 10-13-2017 at 03:20 PM.
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Use a gage pin close to the diameter of the work you most frequently measure. A .452" Z minus pin is actually .4518" where a ZZ minus is .45198" so your mic should be one that reads in .0001" for cylinder, barrel, and boolit work and it should read pretty close to what the pin diameter is when mic'ing a gage pin.
My parkinsonism that controls walking and balance has made me unable to work in the shop. VOTE RED * PRAY OFTEN You are welcome to message me here or send email to xlordsguitars@gmail.com.
Gage pins are a good choice for a mike standard since they're also a needed tool for checking hole sizes and cylinder alignment and timing.
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