Frustrated with bent Y axis lead screws on SX2.

I was having problems with the Y axis binding and back lash. After some work I figured out the lead screw was bent or not concentric. You could see the far end move almost 1/8” as it turned. This was with both the stock retainer and my home made bearing block. If you tightened down the acme nut the axis would bind, bad.

I finally ordered a replacement lead screw and nut, 20 tpi from LMS. I went to put them in and the opposite end also moves as it rotates but less than 1/2 what the original one did. So I play around and finally get some compromise where the acme nut is tight in its mount and the stepper does not stall BUT the whole table rocks as it turns! If I tighten the jibs down enough to take that movement out the stepper stalls.

So the problem still seams to be the lead screw and bearing surfaces are not concentric. Is this a common problem? I have done some google searching but have not seen any direct complaints about this machine. Is there some way to design a bearing mount to compensate for the problem with out increasing back lash? Maybe find some one with a lathe that would let me true up the shaft and then buy new bearings and pulley?
Y axis rocking - YouTube

Thank you.

All the chinese mills we buy are called "kit mills" or lathes for a reason.
Something needs to be done to all of them. Some more than other. Sometimes people can live with what ever problems there having. Some cant.
Ive read plenty of people who had to regrind scrape cut the dove tails off in replacement for linear ways.
What ever you do . Do it right and make sure you do it perfect.
I would consider ball screws and new mounts .

I have contemplated ball screws. I even have an extra one here so I may try to machine it to work. I am just frustrated that even the replacement is messed up.

I dont think its the lead screw . I think its the casting. Chances of you getting 2 in a row a slim to none. Ballscrews will allow you to use your own mounts and not the ones supplied.

The rocking goes away if I losen the leadscrew nut under the table. The table slides good on its own. Also if I mount the screw in a known good chuck the other end of the screw moves out of round.

I also talked to LMS and they offered to send me another screw. Very upstanding place to deal with.

I hope thats the case . Its an easy fix. I just dont think it would be .
BUT know if the new screw doesn't fix the problem its clearly not the lead screw.
Were do you live . Im sure any one on the boards close by would be willing to help you. I would .

I live in Las Vegas. I am working long days this week and will have time this weekend to take some video showing in detail the problem. I will also take some measurements.

I live in CT maybe some one from NV would chime in.

Should be able to find a volunteer that is going to Vegas!

It would be cool for a fellow CNCzone member to stop by. Even if it was just to BS about stuff.

I think I have the problem solved. I was working on taking some video of the old and new lead screws. After shooting the original lead screw I started to take the new one out of the machine. Just for the heck of it I gave it one more shot at alingning it.

First I moved the table as close to the bearings as I could. Then I losed the lead screw nut so it could float. Next I snuged up the gibs. Rocking the lead screw back and forth I found what felt like the center of the rocking motion and snuged up the lead screw nut under the table. Moved the table manual and it felt pretty good. Once the drive belt was back on I ran it under power. One more minor gib adjustment and all was well.

Here is a video of the table zipping around at 60 ipm. I CAN stall the steppers at 60 if I push really hard. At 20 ipm they will pushe me or the bench around the floor. The table feels solid enough for my intended uses. Minimal back lash or movement in the gibs.

mill moving 60ipm - YouTube

The original lead screw is bad and the replacement was much better yet not perfect. I think finding the correct alignment procedure was the key. I also think there was some luck in hitting the right spot. LMS was exelent in there suport as well. Even with out me directly asking they have another lead screw on the way! I am happy with the machine as is so I think I will just returne the latest one.

Good work. Glad you got it sorted out.