An Improvement!

I modified the two Y screws on HB2 this evening. I removed the axis screws completely from the machine and chucked them (one at a time) into my Proxxon PD400 lathe. I cut back the 0.250″ diameter shafts at each end an additional 0.063″ – 0.065″ to make space for the 1/16″ thick 1/4″ x 5/8″ hard bronze thrust washers. I also made sure the screw shoulder was absolutely flat to the washer and square to the shaft.

I reassembled all four Y axis ball bearings (new) with a hard bronze thrust bearing (Alloy 932, sae 660) between the shaft and the ball bearing. The flat thrust bearings (McMaster-Carr 7814K11) cost $2.52 each so they were not cheap. I chose them because they are rated to take sudden loads without wear or damage. Exactly what happens in a rapidly and constantly reversing CNC machine.

The improvement in the Y axis operation is amazing! It runs like a totally different machine. I can do 150 IPM rapids (750 RPM) without weird sounds. I don’t trust it that fast so rapids are now set back at 125 FPM (625 RPM). Still louder than the X axis at the same speed but so wonderfully smooth sounding again. 

I’ll take some pictures of the X screw rebuid to show what I did. That change out is next. It will be the same detail as how I did the Y screws. The addition of thrust bearings is certainly worth the slight effort and cost.

I may stop thinking about the motor resonance unless that is what’s limiting me to under 600 rpm. It’s really a non issue as I don’t cut anywhere near those speeds.