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

pdentrem

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I was given a tool cabinet and assorted stuff for helping an elderly gentleman move and downsize. In the mixed stuff is a depth mic that either his dad or himself had. It had been set aside and the rod was lightly seized. I applied light penetrating oil and finally got it to move. There was lots of light rust inside the spindle and in the hole that the rod passes through as well as the rod. I ended taking it apart completely. In resetting the rod my question how to calibrate? As per the photo it comes with 6 rods in total and I hope that the 5 long ones are correct. The shortest one was in the mic and I removed the pinch nut to clean and lube before attempting the reinstall. I will take it in to work and use some gauge blocks, but here at home I am getting some differences in readings. Mind I am using a dial vernier caliper. When I set the mic to 1" and the vernier agrees, I run the mic back to zero I see that the rod is actually slightly inside the anvil by about 0.003". Am I missing something?
Pierre

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The biggest trouble with depth mics is getting a reliable, consistent reading. The issue is that the base can lift up slightly before the ratchet clicks. The base needs to be held down quite firmly to avoid a bad reading, or must be used without the ratchet with the spindle only touched down lightly on the work. First get reliably consistent readings, then calibrate to match them.
 
Shardlows was VERY good equipment, they specialised in drop forgings, and made the crankshafts for the Merlin engines. based in Sheffield, Yorkshire UK.
 
Shardlows was VERY good equipment, they specialised in drop forgings, and made the crankshafts for the Merlin engines. based in Sheffield, Yorkshire UK.


That is very nice to know. I am an aircraft buff and I love this kind of stuff!
Pierre
 
Shardlows was VERY good equipment, they specialised in drop forgings, and made the crankshafts for the Merlin engines. based in Sheffield, Yorkshire UK.
Love the sound of the Merlin's . Watched a Utube video of a guy rebuilding one and the first firing after restortion.
 
Any gauge that relies on slender threaded rod adjustment is prone to tampering and misuse. I've seen many bent rods. I've found that trying to adjust the rods to correct errors is very difficult and time consuming.
 
Love the sound of the Merlin's . Watched a Utube video of a guy rebuilding one and the first firing after restortion.

Also I get goose bumps when the scene near the beginning of 12 O'clock High, where Dean Jagger's character is standing on one of the hard stands and you hear a radial engine starting to crank over and start up.
Pierre
 
Any gauge that relies on slender threaded rod adjustment is prone to tampering and misuse. I've seen many bent rods. I've found that trying to adjust the rods to correct errors is very difficult and time consuming.
Amen to that!
 
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