1. #1
    My mk3 cnc machine has just has an upgrade from single to twin X ballscrew. Now that I can jog the machine around it is clear that there is significant run-out from the new ballscrew - it's very bent!

    The runout is enough to cause a kind of cyclic loading on the angular contact bearings which makes the stepper and ballscrew run quite rough. I suspect it was bent in transit from China at it is a 1605 at 1300mm long and arrived in lots of bubble wrap and tape, but no solid box.

    The original X ballscrew is not perfectly straight either but is significantly better. This one was much more expensive and was UK sourced (motioncontrolproducts). I'm guessing it is still China sourced but was sent over in bulk in some kind of crate.

    I've made a few enquiries and found a ballscrew specialist company slightly north of Derby who will straighten them using a 60 ton press to a claimed 0.05mm runout. Cost 45 / ballscrew. My concern is that the straightening could chase the bend into the threaded/plain shaft end. They do offer a grind, plate, re-grind service to cover this but no figure on that.

    So this weekend the worst ballscrew will be sent out for the basic 45 straightening and next weekend I should be able to report back on whether it runs better in the machine.

    Depending upon how this goes I might also send the other one out. I'll report back here with the results as I'm sure I'm not the only one using bent ballscrews.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  2. #2
    Would it not be worth a try at straitening it yourself, If you can't get it right then you could send it off.
    You could roll it along a flat surface to see how far out it is. They don't have to be perfect. ..Clive

  3. #3
    I tried straightening a ballscrew myself once, made a jig with a dial test and everything. Its an art and one I did not have the patience to master, check out some of the youtube videos there are a few out there. Bottom line is you really need to have a good setup with jigs and some way of applying lots of pressure to isolated points on the screw. You could try getting the worst of it out by eye using a flat surface and a vice, it would be an amazing skill to learn and something that would stand you in good stead for repairing and building machines in the future. Most ballscrews come bent shipped from the factory espically if you buy rolled, and I think straighting is considered part of the machining process if done correctly.
    CNC routing and prototyping services www.cncscotland.co.uk


  4. #4
    I have mentioned in a previous post that we used to straighten motor cycle fork legs with a very simple device that can be used to apply force to any particular area. I can't see why the same system would not work for ballscrews. G.

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