I applaud your testing approach. Measure, modify, measure for change. It will pay off. Also try to throw in some stress.
I believe that if you get different results by cutting in different directions, you have backlash (or slop) in the system. This can be caused by any looseness in the leadscrew, leadscrew bearings, linear bearings, structure, etc. You probably will have to tighten it up before it will diminish.
When you cut your squares, also check to make sure that they are square. A larger size would make this more apparent. Check them with a square and also measure the diagonals, they should be the same. Creating level can be done by skim cutting a temporary top.
I don’t have my JGRO anymore, but two things that I worked hard on were the flex of the long pipes, and the leadscrew bearings. I believe that the flex can only be solved with support. Vertical uprights pressing up and in on the pipes will help a lot.
A lot of my backlash was caused by the leadscrew bearings, not the leadscrew nut. With the power off, see if you can move the gantry, etc. You should not be able to.
Leadscrew mounting can help three problems at once: whip, backlash, and motor wear. The trick is to “fix” the screw at the motor end and not let the motor’s bearings take the load while firmly attaching the screw to the frame. It takes 4 nuts, two MDF blocks, and two bearings in a configuration as in the picture. The MDF pieces form a thrust plate. The bearings sit in the recesses and are back to back. The procedure is to loosen the motor coupler, lock the two nuts nearest the motor together, and then tighten the next nut to compress the two bearings together against the thrust plate. Finally tighten the outside nut to lock it all together. Now tighten the motor coupler. Firmly attach this to your machine with nuts.
Steve |