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  1. #1
    Member De-Evolution's Avatar
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    Question Local Ball screw straightening ??

    Greetings,

    First time posting but I have run into a bit of a pickle and could use some advice, I am in Melbourne eastern suburbs and I need to find a local shop that can straighten a large ball screw (1.8m 32mm dia), I am not sure where to begin looking as the few places I have contacted are not responding. I have one (possibly 3) that need to be done and I think this may be a case where paying a shop is a better solution than half-arsing it myself.

    Any and all advice regarding this would be greatly appreciated.


    Daniel.

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    Default Re: Local Ball screw straightening ??

    Are these new, or used, please tell us the story....



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    Default Re: Local Ball screw straightening ??

    These screws were purchased new a good number of months ago, they are for a DIY cnc machine that I have been slowly building over the last twelve months and only just found the bend while setting up the Y axis. Given the current world situation and my desire to finish this long over due project soon-ish, purchasing a replacement is not an ideal solution.

    I am not sure if the bend was introduced during shipping or manufacture, I have two other screws that I need to remove from the machine to check how straight they are.

    The machine does run with the bend, however it won't do it for more than a few minutes before the motor reaches a torque saturation level and shuts down.

    I am hoping to find recommendations for a local workshop that can straighten them to a reasonable accuracy without costing a lung in the process.

    Cheers.



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    Default Re: Local Ball screw straightening ??

    Hello.

    I´d suggest you first make the numbers and compare cost both of the straightening and the new parts. In my experience the overall cost fixing smail machine parts usually exceeds the cost of new parts. Besides in many cases the warranty you receive from the workshops goes like for 5 seconds or 100 years, whatever happens first.

    Then again if the bend is not totally disabling the axis you could probably try repairing it yourself. If you have two locking supports to place the ballscrew you can turn the nut to the place at the middle of the bend and then add something to push it in the opposite direction for a little more that the required distance to straigten it. This opposite force must be kept applied for some hours. Overnight could be a good choice.

    While this might not fully correct the problem it could reduce it to make it usable enough. You have to check for accuracy in particular in the bent zone as the angle of the part will introduce measuring errors that will not be constant along the whole runpath.

    Good luck.

    Regards.



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    Default Re: Local Ball screw straightening ??

    My thread about some ballscrews I purchased a few years ago is here:

    https://www.cnczone.com/forums/linea...ce-needed.html

    I also tried to find someone local to me who could fix the one that was bent for a reasonable price. If I could have found someone, the seller would have compensated me for it, but I wasn't able to, and the seller sent me a new one free of charge. Good seller, BST Automation.

    For your situation, are these inexpensive C7 varieties from China, or precision ground?

    If they are the inexpensive C7, it might cost more to straighten them than the cost of buying new ones, at least that was my experience, in Canada. Hopefully you can find someone that can help you out.

    In retrospect, there are a number of videos on YouTube of people straitening ballscrews using either a mill or a press, I wonder if I could have fixed it myself? I just had the mini mill and no access to a press at that time...yeah I didn't really have to setup to try it.

    Quote Originally Posted by De-Evolution View Post
    The machine does run with the bend, however it won't do it for more than a few minutes before the motor reaches a torque saturation level and shuts down.
    32mm screws, that's alot of rotational inertia....Are they high lead?



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    Default Re: Local Ball screw straightening ??

    Quote Originally Posted by BBMNet View Post
    This opposite force must be kept applied for some hours. Overnight could be a good choice.
    To bend something made of steel so that it is straight, you need to bend it past it's yield strength (or elastic limit), but less than it's ultimate strength. Leaving it for some hours or overnight will do nothing. Unless there was some process where alot of heat was involved, then maybe. Of course, that would cause other problems.











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    Default Re: Local Ball screw straightening ??

    Hi NIC77,

    These screws were actually purchased from BST Automation as well, 10mm pitch.
    I have watched most of the videos online to do with straightening bent screws, I believe I could jury rig something to try correcting this myself... I am just tired of things going wrong with this build and was hoping I could take the easy way out in this instance.



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    Default Re: Local Ball screw straightening ??

    Well I don't know what to say about that....I didn't see that coming.

    Just one or all 3? still needs to be determined....it's easy to check the other two, decouple the ball nuts from the axis and give them a spin, you will see immediately if they are bent.

    BST had great customer service for me, I don't know what their policy is after several months have passed.

    You said that you noticed this when setting up your Y axis....was it before or after you bolted down your ball nut to the machine? I'm just wondering if a misaligned ball nut could be part of the problem, or not.

    Have you tried spinning the screw with the ball nut decoupled from the axis?



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    Default Re: Local Ball screw straightening ??

    Oh don't get me wrong, Fred from BST was very helpful and the fact this was not found initially is my fault, I have not even tried to contact him regarding this as given how long ago they were delivered it is no longer his problem.

    The axis was stripped completely down to only the ball nut in order to find the bend, given the degree of bend I am seeing I don't think a misalignment could have caused it. The other two screws will be checked in the next couple of evenings.

    If a local shop cannot be found in the following week I will proceed to perform the operation myself, obviously filming it so I have a record of the exact moment the proverbial hits the fan for future reference.



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    Default Re: Local Ball screw straightening ??

    I don't doubt what you're saying. Fred might still help you out with a discount or something, even though so much time has passed. You never know unless you ask.

    I wish you luck, please let us know how it turns out.



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    Default Re: Local Ball screw straightening ??

    Hi Daniel - I have had screws straightened by Linear Techic in Melbourne before. Good people to work with. Regards Peter



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    Default Re: Local Ball screw straightening ??

    Thanks for the info on Linear Technic, after contacting them they appear to be disinclined to attempt straightening as they are Chinese screws. So after all that I guess I am attempting this myself.

    Cheers for the replies all, will be back with an update and some info on my little project in awhile.



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