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Tool More information on cheap digital calipers

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Dabbler

Dabbler

ersatz engineer
Testing cheap digital calipers versus Mitutoyo ones. This guy uses cheap calipers a ,lot, but also has a Mitutoyo digital set for more exacting work

TLDR:
1) cheap calipers show inaccurate readings as the battery voltage drops below 1.4V from the nominal 1.5V (or 1.61 for very fresh SR batteries)
2) the brand he tested draws 25 microamps while on, and 20 microamps while off. A Mit draws 5 microamps while on and 1 microamp while off.

- this is just one test suite, but something to think about...

 
Here is something I just learned about a weird failure mode for cheap calipers. We sometimes have repair bushings made. They are turned then plated (Cadmium?) after they are the correct size. Supposedly the plating process leaves some sort of residual magnetism in the bushings. Cheap calipers give weird and inconsistent readings making it impossible to measure the final size of the bushing.

My Mitutoyo calipers are 100% rock solid when measuring the exact same bushing. Trying two different sets of cheap calipers gave the same inconsistent readings when measuring. Putting in a new battery gave the same results.
 
I was measuring some some fixtures that had magnets in them. Never again. Once the jaws or anvils become magnetized they attract micro swarf & become useless for measuring the other 99.99% of the time & can lead to machining screw ups. My cheapo demagnetizer didn't work too well. I'm sure there is a way around it, stronger demagnetizer, or even composite based tools if one can justify it. But I now keep my measuring tools far away from magnets.
 
Most long term machinists avoid magnets anywhere in the shop (except for swithable mag bases -- contradiction isn't it?), The arguments vary, but they amount to attracting shavings at the wrong times, hard to keep clean, magnetizing other tools, etc.

I think it is wise to use magnets *very sparingly*. I don't think they can be avoided.

Even Tom Lipton, who in his early videos criticized magnets several times, put a magnet in his lathe height standard.
 
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