Re: [CAD_CAM_EDM_DRO] How does one adjust Ballscrews on a Bridgeport

Stephen Wille Padnos <spadnos@...> wrote:

they
feel "springy". If I lock the table and push the handwheel, it turns a
little (around 8-10 mils, according to the dials). If I let go, it will
spring back to where it started. It gets harder to push (like a
spring), until eventually I overcome the table lock friction, and the
table moves.

Steve, Thats deflection, not backlash. Backlash would display a deadspot of resistance in the handcrank. If it has gradually rising resistance in both directions axially on a locked table that is definitely deflection. Tightening the nut on the handcrank has no effect on backlash its merely to hold the handcrank hub against the outer bearing and keep the handle on, all the backlash adjustment is attained between the two endplates. The mills that I've had and seen apart, the ballscrew take-up was accomplished via shims in between the shoulder on the end of the screw and the bearings in the endplates. Less than massive ballnut cross-blocks relatively thin end plates at right angles with considerable moment and small but measurable torsional twisting of the screw are the probable suspects. Each one gives a little appears to be alot. I wouldnt even toil with it and proceed on with the retrofit. Remember, these are converted manual machines and we can't expect the same results we would
enjoy from a Mazak or Fadal. The best test for backlash is a dial indicator mounted in the spindle or on the quill and check the movement of the table in relation to the handwheel. I'm guessing its going to be within a thou under a no-load transistion. If it isn't then start shimming bearings. If the ballnut is worn and producing backlash many of the control softwares like Mach2 have a settable backlash compensation value available for each axis.

Ron




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