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  1. #1
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    ballscrew: odd imperial / metric mix

    Hi,

    I picked up a couple of lenghts of ballscrew that I am hoping to use in DIY CNC machine. They had a nominal o/d of about 16mm and a pitch of 5mm. I presumed it was SFU1605 and ordered a couple of chinese ball nuts to fit. They don't !

    They were obviously not just slack but the wrong dimension , so I pulled the balls out and find that they are 3.175mm ie 1/8" . This seemed odd but looking at spec of chinses ballscrew assemblies this is apparently not uncommon. However SFU1605 has an inner track diameter of 12mm.

    Measuring my bar with two balls each side I find 19mm ( 19.05 is 3/4" )

    So it appears that my ballscrew has 1/2" i/d 1/8" balls and 5mm pitch.

    Can anyone help identify this? I've never come across this kind of hybrid before.

    If not I'll have to dump the bar and buy two complete assemblies. Which would be a bummer since I have two 3ft lengths and that will cost a packet..

    TIA. Reg.

  2. #2
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    Re: ballscrew: odd imperial / metric mix

    You could replace the balls with correct diameter (lot cheaper than replacing screws & nuts).
    Current build: http://www.cnczone.com/forums/diy-cnc-router-table-machines/264838-new-machine-desing-quot-cnm13-quot.html

  3. #3
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    Re: ballscrew: odd imperial / metric mix

    Quote Originally Posted by hub View Post
    You could replace the balls with correct diameter (lot cheaper than replacing screws & nuts).
    To know what is "correct" I need to identify what this bar is. So far all I know is 1/2" i/d and 5mm pitch.

    The balls are correct for the ballnut since they came with it. The ballnit is made for 12mm , not 12.7mm. So again I need to identify the bar to get the correct ballnut.

  4. #4
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    Re: ballscrew: odd imperial / metric mix

    Get a few different dimensions.. They're not expensive.
    If you need to go from 12 to 12.7mm then each ball needs to be 0.7/2 = 0.35mm less which is dia 2.825mm as "correct".
    That's a "lot" smaller, not sure about back-lash etc, but might be worth a try..
    Current build: http://www.cnczone.com/forums/diy-cnc-router-table-machines/264838-new-machine-desing-quot-cnm13-quot.html

  5. #5
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    6158

    Re: ballscrew: odd imperial / metric mix

    Hi, if the nuts actually fit on the screws and are just "slack"......that is if they are just a bit loose which gives you lots of end play or backlash, then I think........ and this is only my opinion........ that you could fit a second ball nut to the screw and back one flange against the other to have a perfect anti backlash free ball screw solution.

    Where did you buy just the screw lengths.......haven't seen them listed on EBAY without the whole screw/nut assembly.

    If you give up on the screws, PM me for a price offer as I have a use for them in a ball screw design I'm working on.
    Ian.

  6. #6
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    Re: ballscrew: odd imperial / metric mix

    Sure they're not 1/5" pitch? only 5.08mm so easy to mix up with 5mm. I've got some of those on my mill. Also 5/8" is 15.875mm so pretty close to 16mm.

  7. #7
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    Re: ballscrew: odd imperial / metric mix

    Quote Originally Posted by skrubol View Post
    Sure they're not 1/5" pitch? only 5.08mm so easy to mix up with 5mm. I've got some of those on my mill. Also 5/8" is 15.875mm so pretty close to 16mm.
    No , I have both 5mm and 5 tpi, measuring over ten turns is enought to tell the difference. AFAICT, the chinese use 3/8" balls in their 1605 ballscrews. In any case they do not have sufficient manufacturing accuracy so no two balls screws have the same balls. They obvious practice selection on production and hand choose the ball size that gives the best fit. This is annoying because if you loose one ball during cleaning you can not pinch one from another ball screw. I have a5 ballscrews all with slightly different bearing sizes.

  8. #8
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    Re: ballscrew: odd imperial / metric mix

    Quote Originally Posted by reg.miller View Post
    No , I have both 5mm and 5 tpi, measuring over ten turns is enought to tell the difference. AFAICT, the chinese use 3/8" balls in their 1605 ballscrews. In any case they do not have sufficient manufacturing accuracy so no two balls screws have the same balls. They obvious practice selection on production and hand choose the ball size that gives the best fit. This is annoying because if you loose one ball during cleaning you can not pinch one from another ball screw. I have a5 ballscrews all with slightly different bearing sizes.
    You are correct you can't just add larger balls, it's not going to work, you have to have the correct matching nut

    How they manufacture, and select the Balls is my measurement, they have measuring equipment that measures the Ground or rolled screw, then they Grind the Nuts and measure them also, the balls are fitted from these 2 measurements, it's quite simple

    Normally you would have to know what manufacture made the Ballscrew, to be able to know if it was worth looking for a nut for what you have, are they Ground or Rolled it will have a markings on the od of the screw if it is rolled, like in the snip, if they are rolled they would not be worth doing any thing with, you could machine a plastic nut for them

    If you want your parts measured, you can send them to somewhere like International Ballscrew, if they are worth doing anything with, they would be the best to tell you, there are other Ballscrew repair companies that may be closer to you

    Ball Screw Repair & Ball Screw Rebuild | Precision Spindle & Accessories

    Rolled Screw in snip
    Attached Thumbnails Attached Thumbnails Rolled Ballscrew.PNG  
    Mactec54

  9. #9
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    Re: ballscrew: odd imperial / metric mix

    OK, please note that this was first posted in 2012 !!

    They have the grove as you show for ground bars.

    I did finally manage to identify the ballscrews from some part numbers. They were US manufactured and probably of good quality from medical equipment. The ballnuts are available separately but sadly cost something like 250 bucks a piece. That may be fine if you are charging 250 grand for a medical image scanner or are working on defence contracts with $10k toilet seats but it's out of my budget.

    I had to abandon these screws and settle for brand new chinese junk.
    they have measuring equipment that measures the Ground or rolled screw, then they Grind the Nuts and measure them also, the balls are fitted from these 2 measurements, it's quite simple
    I doubt they get that clever. They have lots of cheap labour and they just test which balls fit, They either lock up; have play or are right.

    I'm sure there a plenty of Chinese graduates who get sequestered into building iPhones and fitting balls into ballscrews. That is why the US has a massive trade deficit. Until US workers accept the same abysmal conditions Chinese goods will be cheaper and there will be a trade deficit.

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