Hi, I am in the process of building a SC/TO after consultation with Milowbailey and Peter. I read the notes on building these and decided that I would go ahead and make an all-metal drive shaft for the SC and add a switch for separate heat control as well.
Instead of using a ¼†socket and a full thread bolt, I opted to get a 2†long ¼†drive extension, since that would be a more rigid shaft. I cut it to 1.75†to match the length of the original plastic shaft. I thought it would be only case hardened, since it was just $3, but found that it was fully hardened, a quality move by the Do-It folks, but could not be drilled for a machine screw on the other end. So I annealed it with a propane torch (hold in vise grips, heat until red hot, then allow to slowly cool to room temperature). Once annealed, I was able to drill and thread a hole at the top (#29 drill and 8-32 tap). I drilled it deep enough for the full depth of the tap, but it could be as little as ½†depth.
Per a suggestion on this forum, I wrapped the nylon square drive of the motor in Teflon gas line tape to hold the ¼†drive extension more securely, and to provide a bit more insulation from heat coming down the metal shaft. When the new shaft was installed, it came to the top of the center rise of the pan, just as the old shaft did.
I made new stirring arms by bending two pieces of brass wire at 90°, then shaping the arms to match the profile of the original arms. I had a 3/16†thick large washer that I cut four grooves into, so the bent arms fit in but did not reach the center, leaving room for the installation screw. I sandwiched the brass arms with another, thinner washer, then bolted the stack together with a 1†long 8-32 stainless steel machine screw, washers and nut.
I placed a large thin washer over the center rise hole in the pan to close that opening, then screwed the stirring arm assembly into the threaded hole in the top of the metal shaft. As long as the motor rotates counterclockwise, it should remain seated. If it loosens, I can add a jam nut on the 8-32 machine screw.
When the unit was started, it all rotated OK, and I had an unexpected “featureâ€. Because of my poor brass wire bending skills, each wire follows a slightly different path around the pan, hopefully enhancing bean agitation.
For the switch, I disconnected a female spade connector from the thermostat, which is connected in series to the heating element. I had a length of power cord from a failed leaf blower, and it already had two female spade connectors. I attached one of the power cord female spade connectors to the thermostat. I now had two female spade connectors that needed to be attached. Instead of cutting the wires, I made a short jumper using two male spade connectors. I wrapped all exposed stuff in high temperature electrical tape.
I routed the switch wire through an existing hole in the SC bottom, and drilled a small hole near another existing hole, and used a nylon zip tie as a strain relief. I won’t describe wiring the switch because there are a lot of different types. Powered up and the switch works to turn the heating element on and off and the thermostat is still in the circuit for safety.
Interestingly, except for the small hole I drilled for the strain relief, all original parts are still there undamaged.
I also found that the metal shaft, being a smaller diameter than the plastic shaft, wobbles a bit in the large pan hole. I think I can make a heat resistant spacer to fill that gap. I think I have a phenolic block somewhere...
Now I’m waiting for the TO and temperature sensor to arrive. I will make a sheet metal extender and chaff release when I have exact dimensions on the TO.
Thanks for listening,
RamzyB
