[Adamj12b]

I am trying to retrofit my knee mill by replacing the old worn out screws with new ball-screws and ball nuts. I turned the end of the Y axis screw down to the same dimensions as the stock one, but when I tried installing it wit would wobble when turning. At first it wobbled almost 1/2". I then tried adding some material with the welder to create a shoulder to ride on the bearing race. This helped a little but not much. We later discovered that the threads weren't perfectly straight on the screw, because we had to use a die to make them, because the auto-feed on the lathe is broken. So, I cut the screw back some more, cut the old threads off and redid them. This time we used the tailstock to push the die and keep it straight. This seemed to work very well. I then tried it again, but it still wobbled. We then tried adding material again with the welder to create the larger shoulder again. This time we filled the gap in the threads and went around an extra time to make the shoulder taller. This seemed to help even more but still not perfect. I then cut the back of the nut on the lathe to make it perfectly perpendicular to the screw. Also helped a little but still not perfect. So now I am stuck and dont know what to do.

Is there anything I can do to make this screw work? Or should I buy another and bring it to the local machine shop?

Using a dial indicator on the threads of the screw, I measured the High and low spots in the screw. At the low the dial read .0085" and at the high it read .048", diving a difference of .0395" out of wack.

Anybody have any ideas?

-Adam

Picture 1: Screw with Weld before being re-turned
Picture 2: Screw after being re-turned
Picture 3: Dial Indicator showing low position
Picture 4: Dial Indicator Showing High Position
Picture 5: Dial Indicator Setup
Picture 6: Back of bearing mount with shoulder on inner race
Picture 7: Front of bearing mount with nut on inner race