Thursday, December 31, 2009
McWire Motor Coupling
The basic McWire cartesian structure has been built. The last step was to couple the drive screws to the motors. I was undecided on the way to do this. The stepper motors I have a D shaft. I was a little concerned about using the suggested aquarium tubing with them. I was in the hardware store on my way to find some tubing and I came across the PEX pipe. It's a semi rigid plastic pipe. It was cheap and very sturdy. It's even rated for hot potable water so I though i would give it a try. I meant to pick up some tubing as well as a fall back incase this didn’t work but, I was so focused on making the PEX pipe work, I forgot.
It's 3/8" OD and ID about 7/32". At first, I tried to slide it on the the motor shaft with a good amount of pressure but it was a no go. The motor shaft diameter is a 1/4" so I drilled it out to 15/64" and tried it again. No joy there either. Then I tried a 1/4"drill. Finally the motor shaft slid in - but not without a significant amount of pressure.
On the final assembly I kept the jam nuts on the rod to help get the pipe off if ever I need too.
I discovered another place a spacer is needed. When I attached the coupling nut using the 1/2" conduit strap to the X and Y platforms, the added assembly was running into the end support. I lowered the end support from the rails with 1/4" of PEX pipe for a spacer. This was only a problem on the X and Y as the Z coupling nut assembly is not at the end of the platform.
Another option was to take off the end support completely as it seems it's only function is to hold the opto-endstop and I think that could be done in a different fashion. For now I will leave it.