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  1. #101
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    The C grade is only the lead accuracy and this pdf will show you what they refer to.
    http://www.zappautomation.co.uk/pdf/...l accuracy.pdf
    Backlash is down to the nut and the best way to get zero backlash is a double ballnut with pre load added.
    there are other ways to get zero backlash like oversized ball but this is not the best way.

    Zapp Automation Ltd
    www.slidesandballscrews.com


  2. #102
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    Yes, it's true the C grading only refers to lead-accuracy, but some people have mentioned it harder to get zero-backlash on c7 screws, because of the relatively large lead-variation compared to C5 or less. For some reason it also seems to hold more true with rolled screws!? This is not my opinion, but something I have read several times here on Cnczone. I have only used mostly C5, so I can't say if this is true or not.
    I'm not sure if Zappautomation refers to my post when he says that oversized balls is not the best way to get zero back-lash, but if that is the case; I was not talking about the DIY approach, but about factory made units from THK and NSK and such. Maybe it's not that common any more, but I think they still use this method in production. If someone know better, then please feel free to jump in.

    I have several new ball-screw of C5 and C3 quality without backlash, and only 2 of them have double nuts. I don't think double nut is better or worse than anything. Double nut tends to be quite a bit longer, but on the other hand they seem to have a bit better load rating. Just for this thread, and just for fun I compared two of mine:
    NSK W2509******* (10mm pitch) (Load rating) Dynamic 11600N Static: 19000N (skewed pitch pre-load)
    THK BNFN 2510A-2.5 (10mm pitch) (Load rating) Dynamic: 15800N Static 33000N (double nut, oversized balls pre-load)
    There is of course more to it than basic load ratings, but it could be fun and it at least gives an indication.
    I don't actually have the THK one, but I have a couple with smaller lead and 5mm pitch.

    Ball-screws are a very interesting subject, something could be talked about for hours. I know I could at least...



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    Hi All,

    I have some ball screw assemblies, out of a Medical Interments Mfg. cnc due to such tight tolerance work, and they are 0.001" or less backlash.

    They are still well coated in grease with no rust or scratches and well protected. These will be excellent for a mill or router project.

    The NSK part numbers are:
    W3206G-91P-C5Z 07H1-0020
    W3206G-91P-C5Z 08H2-0010
    W3204G-127P-C5Z 08H3-0031

    I have no use for them, but if anyone else does, message me and we'll talk.



  4. #104
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    Default Re: Ballscrew Basics

    Nice article.

    I had some issues with ball screws in the past and it was on bearing journal end and a lock nut. If you spend money on angular contact bearings for bearing support, you need to make sure you get the journal machine, usually ground to precise tolerance specified for the angular contact bearings. also, external thread for lock nut will need to be accurate. A lock nut is very critical also since the face of the lock nut will be applying preload to the angular contact bearing sets. Poorly made nut on poor thread will run crooked and will apply uneven pressure to the bearings. If you purchase ball screw support bearing blocks from ball screw manufactures, they will come with a good lock nut as well and all you have to worry about is journal thread being made properly. if you try to machine the screw end, and build your own bearing block and a lock nut, you better know what you are doing. Poor bearing block and lock nut will end up crooking the fixed end of ball screw and the rest of the screw will run crooked. You know when you have poor bearing block ends when you lock up the lock nut and screw runs hard and loosing the lock nut will help smooth out the screw movement. This is because linear bearing is fixing screw nut movement but screw is no longer parallel.


    you can tell rolled ball screw from ground ball screws by looking at the screw shaft. Rolled screw shaft has a channel that runs along the actual ball raceway. it looks like a mini raceway but are just a groove made when materials are pushed in roll process. ground ball screw does not need such channel so there are only one groove that is the ball race way.

    there is a 3rd type of ball screw called whirled ball screw. it does not use grinding so it is cost effective yet it can achieve better accuracy than rolled ball screw.



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    Default Re: OK I cant afford ground ballscrews....what's the next best thing?

    Anyone knows why in general 1605 ballscrews are cheaper than 1204?



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    Quote Originally Posted by JukeBox View Post
    Anyone knows why in general 1605 ballscrews are cheaper than 1204?
    ill hazard a guess that....

    the larger diameter is easier to produce accurately, especially in long lengths.

    the larger nut is easier to machine.

    theyre more common.

    just an idea.

    with so much stuff on hand, one spends more time locating it rather than using it.


  7. #107
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    Default Re: Ballscrew Basics

    Quote Originally Posted by headsmess View Post
    ill hazard a guess that....

    the larger diameter is easier to produce accurately, especially in long lengths.

    the larger nut is easier to machine.

    theyre more common.

    just an idea.
    The second and third statements make sense.

    But why would be larger diameter easier to produce accurately?

    Of course I am referring to rolled ball screws.



  8. #108
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    Default Re: Ballscrew Basics

    Quote Originally Posted by JukeBox View Post
    The second and third statements make sense.

    But why would be larger diameter easier to produce accurately?

    Of course I am referring to ROLLED ball screws.
    i believe the part i put in capitals would explain my train of thought...

    rolling is a deformation process. and ball screws take a LOT of deformation compared to a standard iso threads. depending on the ball size of course.

    a 25mm bar is pretty solid.

    an 8mm bar bends simply by looking at it... there fore the smaller sizes would take more to setup, and make, so as to be up to standards required. more support, more guides, closer tolerances... which then requires a better operator and a better machine... or maybe they have to use less pressure but increase the number of passes? etc.

    think...on the smaller sizes, not only do the rollers produce valleys and crests...but they would also tend to stretch the material axially... i assume...

    now grinding or machining...the forces are far less...

    i could be completely wrong. as i said...its just what im guessing... there could very well be completely different factors at play...maybe the 12mm bar is simply less readily available than the 16mm stuff? or requires less work to straighten BEFORE any other operations are done.


    anyone feel free to correct me...i wouldnt mind knowing the real reasons myself!

    with so much stuff on hand, one spends more time locating it rather than using it.


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    Default Re: Ballscrew Basics

    ahhh, just thought id mention it in this thread than start a new one for such a trivial thing.

    i made end caps and wipers for my ballnuts a while back. just leather washers for the wipers.. they did work but they also reduced one axis' movement by at least 10mm.

    the other month, i suddenly though of what to use. pipecleaners! get the fuzzy ones. wind em in the thread for at least 1.5 full turns, then bend and tie the end over to the nut.

    my previous leather wipers would always let some swarf collect in the crests of the thread, which was slowly making a mess.

    not too mention the difficulty in getting them to wipe rather than get ingested by the screw! very critical on the hole size and the nick required to follow the thread.
    i have tried 1/8 thick o-rings (my ball size) cut and wound on the thread...same deal. they let swarf build on the crests.

    the pipecleaner tends to have fluffy bits here and catch everything.

    on my nuts at least... the ball return has those little tags, which stops the loose end of the pipecleaner going in too far. and one end of the nut has at least four turns of thread unused. (thomson 0.675x0.2")

    just tore the mill down as i now have a surface plate so i can scrape it... and the ballnuts are SPOTLESS inside after chewing up plenty of brass and ally bits.. no more two day cleanout jobs!


    obviously this is really only for the home built things rather than a real machine with decent swarf guards as standard... and when clearance is seriously limited.

    thomson do make proper wiper kits to suit but when one has limited income... and a job that needs doing NOW....

    with so much stuff on hand, one spends more time locating it rather than using it.


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    Default Re: Ballscrew Basics

    I have this 10mm diameter ballscrew with around 3mm pitch, can it be used to replace the leadscrew of the X2 minimill so for CNC conversion?



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    Default Re: Ballscrew Basics

    I cut out 99% of the crap which had been getting on my X-axis rails and ballscrew very simply.
    Ballscrew Basics-6715-jpg
    Stiff bookbinding plastic my wife purchased by the roll. Concertina, and painter's sticky tape.
    But hot chips will melt it ... They haven't yet.
    Replace every ... 12 months?

    Cheers
    Roger



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    Default Re: Ballscrew Basics

    Great article. I know it's kind of an old thread but it answered almost everything I wanted to know about ball screws. I have a question that unless I missed it, I didn't find here.

    I already have one manual lathe and one manual mill. I'm going to buy another lathe and after some time another mill (probably to replace my current ones, not sure yet). They are available with both acme screws or ball screws. I'm going to start with a manual lathe and hopefully turn it to CNC in a while (by doing as little as possible myself and buying as much as possible pre-assembled). I'll use the about 90%-95% manual and 5%-10% CNC. The mill will be about 50% manual/CNC.

    Are there any disadvantages to ball screws on a manual lathe/mill? I think I'll go with acme for the lathe and maybe ball screws for the mill, but not sure. I understand the advantage I'd have with ball screws, but what are the compromises, if there any, when using it manually?

    Thanks



  13. #113
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    Default Re: Ballscrew Basics

    ACME is old technology (really old), and has enormous backlash.
    Ball screws are 'new' technology and can have greater accuracy and zero backlash.
    But ball screws are usually a little bit more expensive.

    If you are considering a future CNC conversion, there is no point in buying the ACME version now. Go ball screw now and be done with it.

    Cheers
    Roger



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    Default Re: OK I cant afford ground ballscrews....what's the next best thing?

    Quote Originally Posted by JukeBox View Post
    Anyone knows why in general 1605 ballscrews are cheaper than 1204?
    Because it is probably the most common metric size... In the same way 5/8" ballscrews are the most common and cheapest Imperial size.



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    Default Re: Ballscrew Basics

    Hi all,
    I need some advice on what ballscrew should I use for my setup:
    static gantry, moving table router. table's size is around 65x100cm, weigths less than 15 kg, but in future should be replaced with heavier deck. Z axis also weights less than 15 kg
    3 nema 23 motors (one per axis) 283oz-in with around 1.8 mH inductance,
    square rails with some noticeable resistance(not because of missalignment, but because of preload)
    drivers: leadshine ma860
    2x 36v/10A PSUs connected in parallel.

    Considering between 1605 and 1610 screw. would be nice to have a faster machine and lost accuracy is not a problem for me. On the other hand I have doubts that 2Nm motor may be too weak for 10 pitch screw. Having in mind that torque will be reduced because of 4x or 8x microstepping I would choose 5mm pitch but it is difficult to evaluate without testing.
    Please share your opinion or personal experience with similar motors and screws.



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    Default Re: Ballscrew Basics

    Hello, I'm looking for a replacement ball screw.. had an issue with mine, there was some internal damage. The actual piece has a Prep brand logo on it, with the designation sfur 02510d, but i can't seem to find a replacement from them. I think it's basically a SFU2510. I use it for our Z axis, and i'm trying to locate a replacement that has a 330mm spiral length (the overall length is about 400 mm) and is already machined on both ends to be fitted into a bearing and a clamp. It seems like there are lots of generic Chinese pieces like this for less than $200, but I can't seem to find one short enough.

    I would appreciate any help or insight on the subject.. boss is riding me to get this replaced.



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    Default Re: Ballscrew Basics

    A lot of LOCAL suppliers will cut to length and machine the ends for you.

    Cheers
    Roger



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    Default Re: Ballscrew Basics

    Do you know if it's rolled or ground? Any tolerance spec on it?



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    Default Re: Ballscrew Basics

    The article says cheap angular contact 7202 bearings for the end of a ballscrew will result in backlash. But SFK 7202's are quite expensive and I can't find SKF's with seals. Also I can't find any info (oddly) on what grade/precision the SKF would be (or for any 7202's).

    What did other people do for these bearings? Have you had problems, do you measure backlash?



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    Default Re: Ballscrew Basics

    ANY single bearing will have backlash. ANY.
    We do not (ever) use a single bearing to support the end of a ball screw. We use double bearings, opposing each other. At the high end we use double angular contact bearings (ACBs) such as 7202, but double deep groove bearing (DGBs) will suffice for many hobbyist machines. In fact, that is the whole point of ACBs: to go in opposition. Don't overload them of course.

    Cheers
    Roger



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