bent RM1610 Chinese ballscrews

Hi,

I am making a CNC pick and place machine as the senior project of my engineering coursework.

There is a very limited budget so I ordered RM1610 ballscrews from linearmotionbearings2008 on ebay, about 3 feet long pre machined.

Both screws are bent. They appear to have just a single bend very close to the center of the screw, one is about 200 thou and one is around 100 thou.

It causes enough binding that the stepper motor will skip steps.

Any advice on straitening them?

Due to time constraints I don't have time to wait for replacement screws and would not have money to buy better local screws.

Thank you...

I have seen videos on how they're straightened in a "real" shop, but can't seem to find them now. If you can accurately find the bend, I'd mark it, then hold the screw in a couple of v-blocks a couple inches away from the bend, then use a press (small strokes, re-check regularly!) to try to reverse the bend.

If the bend is really bad, it might have also stretched the screw slightly.. Depending on what kind of precision you're going for, that may not be a big deal, though :)

Good luck..

I have access to a regular shop press but nothing fancy.

My dad is suggesting basically the same thing.. He says roll it on a piece of glass, mark the highest spot with a pen, then setup 3 v blocks one under the bend and 2 within 4 inches of the bend, but the outer 2 shim up starting with 1/32th of an inch then press down till its touching all 3 blocks check again, make the shims bigger as necessary and repeat the process. That way I really cant make it any worst.

Does this make sense?

I straightened a 1605 ballscrew tonight (only about .050 out) by rolling it on a granite surface plate, marking the high spot, then clamping it in a brass lined vise and just tugging on the ends. It took me 3-4 tugging sessions to get it within .005, which is as close as I cared to get it.

Thanks for the reply.. What do you mean tugging ?

You mean just putting a bending load on the screw, or something else. Are you straitening it with clamping force from the vice?

So using a press I managed to get the screw to about 30 thou... the bend is still noticeable when spun between the bearing blocks so I will keep going and aim for 10 thou.

I literally just clamped on the high spot, then placed my hands about 8" on either side and threw my body weight backwards. Its tough stuff though, it doesn't bend easily. It probably moved only .010 each time I did it.