Sunday, March 29, 2015

Threaded Pot

Some things seem simple but take a whole lot of time.  Threading the new on-board potentiometer was one of them.  After deliberating with Nancy we decided that a max speed of 3 mph is good for the on-board control.  The new 1K pot is larger in diameter than the old one.  I had to drill out the SBT frame for it to fit.  I also had to thread the shaft of the pot to 1/4-28 for the wheel.   For hours I tried everything but the die was not catching it would just spin on the ground down champher I had made.  Finally after a nap I remembered something Robb asked, was it a split or solid die?  Well it was solid, I split it, first by removing all the teeth on my hack saw, then with a dremel.  I now had an open die.  Sure enough It was working great, cutting at 28tpi and an oversized shaft first try.   Holding the tip of the potentiometer in a vice grip, and then the bench vice I was able to cut enough threads to mount the wheel in the right spot.
 It did take chasing the threads a few (about an hour) dozen times to get the diameter down to the size needed for the threaded wheel to fit.  It is hand tight until the last three threads, then it has to be worked with a tool.   Tomorrow I will cut off the extra pot length and start wiring the machine.

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