[rs4race]

Hey all so from the internet searching I did I found reccomended 0.126" up to 0.128" balls to replace. I ordered up some 0.126" bearings on ebay and they came in yesterday. My z-axis is relatively easy to access so I gave that a shot this morning. I installed one set (each ballnut has 3 sets of 17) and it was way too tight. So I took them back out and measured them. they ranged between 0.126" and 0.1255" (yeah I measured all 100 more than once.) I had enough to try a set of 0.1255" balls but they were still much too tight.

Before I reassembled I measured the stock BB's they were 0.1245". I was thinking about ordering some 0.125" BB's but saw there were alot of other options in between (0.1248" for example). I'm curious, of the people who have done oversized BB's how much oversize did you go? My backlash is about 0.0045" on each axis.

[rs4race]

No replies... So I ordered 0.1255in and 0.1250in. Both fit in the z-ball nut but the 0.1255 seemed like it had a bit of drag. The 0.1250 felt smooth so I installed those I havent had a chance to test the backlash change yet. If its still above 1 thou I'm going to try the 0.1255in balls. My goal originally was a half thou or less, but I think that 1 thou is going to be really good for backlash. I will post my results after I test.

[arizonavideo]

A little drag is normal and perhaps best. You need to test the drag with the plastic seals out. The screw makes less drag under load.

The .1255" sound like the proper choice. The screws can give less than half thou no problem.

[rs4race]

Thanks for the reply.

I just got back in from the garage and started with the z-axis. I took your advice and tried the 0.1255in balls in the z-axis. It was still too tight and didn't shrink the backlash. It limited the max speed also so I took them out and put the 0.125in balls back in. I also double checked the preload on the thrust bearings. The backlash is at about 2.5 thousands now. I noticed some play in the coupler which may take that out. If that doesnt take out a significant amount of backlash does anyone have any other areas that might cause the backlash? Also I pushed up on the head and there was quite a bit of deflection about 6 thousandths, I tightened up the gibs and it went down to about 1.5 thousandths. Is this normal?

The x-axis started at 4 thousands backlash and fit the 0.1255 in balls nicely. After re-install the backlash went down to about 1.5 thousands.

The y-axis is already at 1.5 thousandths so Im thinking about leaving it there. If I want to swap the balls out there is a lot of dissasembly due to the motor being mounted on the rear and the long ball screw.

[arizonavideo]

Have you checked the Gib strip on the Z?

You need to blue it and run it up and down and shim or grind or cut to get a good fit. Also check the general fit of the slide. Often times it is the slide rocking before it moves that gives backlash.

You can grind the bottom end of the ball screw so it is smooth and flat so you can get a good reading from a indicator to check the support bearings when under load.

The seals on the ball screws often give a false tightness feel when the ball are still loose.

The 575 oz motors give really good power with a 50V supply up to about 800 RPM. After that the power drops off like a rock. That is 160 IPM wit a 5 TPI screw. If you get good performance to 150 inches then that would be OK for a new still stiff system. Everything will break in as you get time on the machine.

I have seen many get 300 IPM but often that is with loose screws and Gibs. The motors are making around 120 oz at that speed.

[rs4race]

I did test without the seals. The too tight was the bearings for sure. I have seen a few mentions that the z axis ways are ground poorly. Is the test your suggesting to color the gib run it and it should wear off the color on high spots? Then I lap the high spots?