I think I need to make one point clear from my previous post. The ball bearings are still taking all thrust loads present. The thrust bearings (fancy name for washers) are there to spread the load evenly and transfer it to the center race of the ball bearing. I looked for washers with very accurate center holes and found them in the form of thrust bearings. I even considered making my own washers as precision washers are hard to find in small quantities. Thrust washers are not hard to find in small quantities. The thrust washer also protects the bearing seals from the damage seen on the first set of bearings. And lastly, there is one more surface for rotation when it happens.
The best thing I did was my own machining of the ends of the screws. I now know for sure that the thrust faces are smooth and true. The scratches on the first bearings really bothered me how they got there. They were not there when the bearings were new. I now have a 1/16 inch thickness of protective leaded bearing bronze between the screw steel and the ball bearing shields on both ends of the screws.
The proof is the Y screws are now running much smoother and even faster. The “clean up” did what I thought it would do.
The strange thing is when I do something like this, I sort of get a “high” from having solved a problem. Drugs are a lazy persons way to a high. Much better to gain euphoria the old fashion way, earn it! 🙂
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.
I received the thrust washers for the HB2 yesterday. Great quality and FLAT washer type bearings. I am so used to seeing and using stamped washers with a crown and rounded edges and imperfect holes, it is a simple pleasure to see a perfect square edge. Why do I feel good about such a simple part? I guess it is just the precision of a well made part and the machinist in me.