Thanks! Hopefully it takes you less time. Figuring out how to make the blade took lots of trial and error.
I was lucky if I could get a month out of a battery, so like you, I've had to keep the battery out when not using the caliper.
Digital Caliper Battery Cov...View Instructable »
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You probably would need to. I image things like dirt and sand would be a bit too abrasive and would possibly wear away at the strings of your instrument.
Good comment. I already had the chuck so I took it to the store and found the correct bolt through trial-and-error. What you said is useful info for anybody wanting to start the project from scratch.
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There's actually a sub-field of mining called "electrowinning" which focuses on extraction of metals from solutions via electrolysis. They typically use CuSO4 instead of HCl. You may also want to look into copper plating with CuCl2, there may be a way to add brighteners (not sure what exactly) that would allow the copper to form as a solid mass on the electrodes rather than as loosely adhered powder. There's actually a great book by Lowenheim from the 1978 called "Electroplating" which is voluminous about the process in general.