[How do I?] Ambrose Shardlow & Co depth mic calibration

http://www.mun.ca/research/resources/ts/qa/cal-ver/TS-0053.pdf

Pick up one of these:
http://www.fowlerprecision.com/Prod...Multi-Function-Check-Standard-53-813-015.html

Or one of these:
http://www.fowlerprecision.com/Products/Setting-Master/538130050.html

If you want to get picky about it. Most people just use gage blocks. It's really nice if you have 2 sets.

These are handy, and not too spendy:
depth-micrometer-masters-dm.jpg
 
True I have the short 1" rod in at the moment, but later it could be any up to 6". So this is good to know. I have been wanting some gauge blocks anyways.
Pierre
 
A quick easy way to calibrate a depth gage is to use a 1-2-3 block that you know is accurate within a tenth or less. Just put the depth rod thru one of the holes against your granite plate or equivalent and calibrate. Good for 1", 2", 3" rod or stack two 1-2-3 blocks together and go up to 6".
 
Adjusting a depth mike barrel to calibrate one rod isn't going to calibrate the mike for other rods. The only way for multiple rod depth mikes ( or internal mikes) is to calibrate each rod in turn by adjusting the rod nuts at the end of each rod. Trying this is needs the patience of a saint !
 
Realistically, most depth measurements are not all that critical. Not that there aren't exceptions to that, to be sure, but there is no practical need, particularly in a hobby shop, to spend all the time to get every rod to zero out within a tenth. If you have the time, and as above, the patience, by all means, go for it. I have a digital Mit that reads in 50 millionths, and it came from the factory very, very close. I have never had to adjust it. I have had it in a clean room environment and it passed. If it ever does get off, I am willing to say that it is the user, or possibly debris in the wrong place. It's really hard to put enough wear on a depth mic to really require much resetting. They need to be checked, but if they are found suddenly to be off, look for why before starting to change things.

But on the other hand, of your set is short a rod or something requires a replacement, you have little choice but to spend some time setting it. But be realistic about it. Think about what you will be using it for and proceed accordingly. For example, I have some spare rods for one of my sets that are ground to a near point, leaving a very small flat on the end, which is original. But since they came from a salvaged mic set, they had to be set for one of my mic bodies. I was content to get them within 0.0005 and be done with it. Now of course, they have to stay with that particular mic, which is a little frustrating at times. After doing a few over the years, it isn't a bad job, unless you want to really set them to zero.
 
Realistically, most depth measurements are not all that critical. Not that there aren't exceptions to that, to be sure, but there is no practical need, particularly in a hobby shop, to spend all the time to get every rod to zero out within a tenth. If you have the time, and as above, the patience, by all means, go for it.
If you just wait until you need the depth mic for a job, you can calibrate it then for the accuracy you need for the job you are doing. That saves a LOT of time calibrating rods you might never actually use, or only need it to be a skinnier pocket ruler for the job at hand...
 
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