Safe RPM for Chinese ballscrews


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Thread: Safe RPM for Chinese ballscrews

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    Member Biggs427's Avatar
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    Default Safe RPM for Chinese ballscrews

    I have 1000mm and 700mm long 16mm dia and 10mm pitch ballscrews I bought from BST automation.

    Like many, if not all, chinese components, there's not much documentation for that.

    I'm wondering what would be a safe max rpm?

    My rapid speed is 12 000mm / min which is 1200 rpm.

    I assume that I should be ok but since I can't find this information I just wanted to see if other with more experience had an idea.

    Thanks

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    Default Re: Safe RPM for Chinese ballscrews

    As long as the screw doesn't start whipping, it'll be fine.

    Gerry

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    Default Re: Safe RPM for Chinese ballscrews

    I tested it at 1500 RPM and no whip. Higher than that the steppers started to loses step so I dialed it down at 1200 RPM to have a 20% safety margin.


    Thanks Gerry!



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    Default Re: Safe RPM for Chinese ballscrews

    As far as I can figure it depends on how straight the screw is. I agree with what Ger said, if it isn't whipping it's fine.

    I've been watching videos of people with bent ballscrews, and they are whipping at low RPM.

    If you can run a 1000mm screw at 1500 RPM with no whip, then you have a straight screw. For a 16mm diameter rolled screw, you have a root of around 13.7mm according to the spreadsheet I have from Thomson. If you put that in the Nook calculator, which is overly conservative I believe, it gives you 1656 RPM (with end fixity B, and a length of 1000mm).

    But here is a video of running a 1200mm screw at 2000 RPM without whip.



    I think it all depends on how straight the screw is, which depends on the supplier's quality control and perhaps a bit of luck.

    How was your experience with BST automation? What is the quality of the product? I am considering them for my purchase. I was going to go with a popular EBay seller, but then I decided not to because of all the complaints of bent ballscrews, off center machining, and missing ball bearings in the nuts. I'll be using 25mm OD screws.



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    Default Re: Safe RPM for Chinese ballscrews

    Quote Originally Posted by NIC 77 View Post
    ... How was your experience with BST automation? What is the quality of the product? ...
    My experience was good. Their price is a bit higher than some other merchant but I think it is worth the extra money. Their packaging was the best I've had from Chinese merchant. I've ordered my X axis 1000mm screws from them and it arrived fast and as straight as it could get.

    I've made the error of ordering my Y axis 700mm screw from "The Jason August" store. They were ok to deal with; answered mails fast, quick to process the order but the screw arrived bent. 0.050 approx. I had to bring to my dad's shop to straighten it with his press and V blocks.

    I think I did good as the screw is not whipping at 1500rpm but it was a PITA to make it straight.

    The ones from BST, I just checked them with a straight edge and installed them... No fuss, no muss.



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    Default Re: Safe RPM for Chinese ballscrews

    Quote Originally Posted by Biggs427 View Post
    My experience was good. Their price is a bit higher than some other merchant but I think it is worth the extra money. Their packaging was the best I've had from Chinese merchant. I've ordered my X axis 1000mm screws from them and it arrived fast and as straight as it could get.

    I've made the error of ordering my Y axis 700mm screw from "The Jason August" store. They were ok to deal with; answered mails fast, quick to process the order but the screw arrived bent. 0.050 approx. I had to bring to my dad's shop to straighten it with his press and V blocks.

    I think I did good as the screw is not whipping at 1500rpm but it was a PITA to make it straight.

    The ones from BST, I just checked them with a straight edge and installed them... No fuss, no muss.
    That's some good info. Thanks for that. Are these single nut screws? Any backlash? I'm torn at the moment between SFU 2510 from BST Automation or DFU 2510 from Linkcnc, both on Aliexpress.



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    Default Re: Safe RPM for Chinese ballscrews

    All are single nut.

    I measured with a dial indicator and didn't measure any. My dial indicator is precise to 0.0005.



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    Default Re: Safe RPM for Chinese ballscrews

    What you are looking to determine is the critical speed of the screw.

    If you want to eliminate the guesswork go to Nook Industries Engineering Tools and look for the Critical Speed calculator.

    bob



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Safe RPM for Chinese ballscrews

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