I'm in the process of rebuilding my table top 24" x 36" router that I purchased a year and a half ago from a company which will remain unnamed. The design has two driven screws, one on each side of the gantry, driving the y axis (I refer to the x axis as the axis on the gantry and the y axis as the axis that moves the gantry). From the beginning I had problems with the gantry racking and I eventually decided it was a mechanical problem created by the manufacturer using linear bushings rather than ball bearings on only end supported 1" diameter shafting. Now I'm not so sure. I've replaced the linear motion with Thompson type bearings on fully supported shafting and before I installed the lead screws the gantry moved effortlessly. But when I wired everything back up I had the same problem with racking. What happens is the gantry binds and the motors stall. Pushing the gantry back and forth without the screws in place it's impossible to make it bind. The weird thing is if I remove one of the screws everything works fine. I can run the gantry back and forth at 150in. per minute on just one screw--either one. So the two screws together seem to be fighting each other. They are both Acme 3/4-6 running in delrin nuts. They are within a few thousands of parallel and one has a slight bend but runs fine by itself. My steppers are 156 in-oz Kelings which I realize may be a little underpowered but if one motor can drive the axis at 150in per minute why can two barely move it a 25in per minute without vibration and binding? Any ideas or advice would be dearly appreciated.
Curtis E.