garageFab.cc

After replacing Home Depot leadscrews and finishing the assembly of the mini router, I ran an initial endurance test. The test consisted of drawing 1/4" grid on 8"x10.5" rectangle, rapid repositioning, then drawing 64 concentric circles with 1/16" spacing in the middle of the rectangle. The feedrate was set to 17 IPM (~7mm/s) while rapid movement was set to 20 IPM - not really rapid, but it was the fastest considering that motors stalled at 25 IPM. At 17 IPM the test was going to take some 1 hr 30 min or so. It ran for an hour - the Y axis stalled about halfway through the concentric circles. The rapid repositioning also didn't work too well since the circles were shifted relative to the grid in both X and Y - I have not yet figured out by how much exactly.

The video is 16x realtime. Y axis stall happens in the very end at 4:20.

Audible chatter in the video is some of the leadscrews knocking - I think this is due to the design of the shaft mounts, allowing some lateral play of the bearing. I wonder how much this knocking contributes to stalling and skipped steps. I sketched a new shaft mount design and one of the next things I want to do is mill new shaft mounts from plastiс and try them. I also wonder if the leadscrew whip is a problem - 20 IPM works out to be 400 RPM on 20TPI thread.

The biggest problem though is the measly feedrate, especially for 11"x8.5" work area. Using 16TPI ACME screw is not going to make it much faster. I did see on Mcmaster some 1/4" multistart ACME screws with 1/4" distance per turn (equivalent to 4TPI on single start). If stepper can do 200 RPM with them, the feedrate will be 50 IPM; but these screws are pricey - $60 for 6ft. One thing I want to try is a flywheel on the stepper shaft, maybe it will boost the max feedrate, even if at the expense of acceleration.