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  1. #81
    Community Moderator Al_The_Man's Avatar
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    Quote Originally Posted by Zappautomation View Post
    Adding a belt and pulley or any gearing will reduce the amount of power you will be getting at the load.
    Gearing has losses so if the efficiency of your gearing is 90% then you will loose 10% of the input power to heat.
    .
    I am not sure I follow this? The torque will increase by the ratio of reduction, e.g. for 2:1 your torque will double, even if you lose 10% in efficiency, your torque has increased to almost double, besides that your load to motor inertia ratio will will be reduced by the square of the reduction, for 2:1 this will be reduced by 4.
    The industry recommended target for this is 10:1 or less.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
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    im talking about actual power, and any gearing will reduce the actual power.
    Inertia also needs to me considered, but it is better to use a larger motor with a higher inertia than to use gearing to get the inertial mismatch within the 10:1.
    The use of gearing is personal preference only, i prefer not to use it if i don’t have to.



    Quote Originally Posted by Al_The_Man View Post
    I am not sure I follow this? The torque will increase by the ratio of reduction, e.g. for 2:1 your torque will double, even if you lose 10% in efficiency, your torque has increased to almost double, besides that your load to motor inertia ratio will will be reduced by the square of the reduction, for 2:1 this will be reduced by 4.
    The industry recommended target for this is 10:1 or less.
    Al.


    Zapp Automation Ltd
    www.slidesandballscrews.com


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    Hi,
    my machine is 1x1.5 so is it ok to put 1 ballscrew in the middle of the axis and this move the 25kg gantry in 1500mm length? This link includes calculators and here you can calculate the critical speed of the gantry..so given the 16mm ballscrew diameter in 1500mm length with end fixity=D, we take 1917RPM...
    I'll be happy with ~400IPM rapids and ~200-250IPM cutting speed in wood...
    What are your thoughts on this?

    Thanks,
    Kostas



  4. #84
    Community Moderator Al_The_Man's Avatar
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    Here is an excellent reference by SKF.
    http://www.divshare.com/download/8629204-fa4
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


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    Thanks a lot,

    Great article !!!!!



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    nice article



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    Default hallo

    hallo



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    phwoar! i read all that!

    is that there "warner red label" a 2 start thread? me sees two return tubes and the pitch is waaaay steep for the depth.

    which raises an interesting point...do the balls recirculate on the same track or keep crossing over in a multi start system?



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    Great write up!

    Thanks!

    JGRO Complete - G540, 380oz Nema23s, 1/2-10 ACME, 30"x14", Craftsman router
    Joes 4x4 R&P in progress


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    newbie questions:
    i note that many of the items on ebay are described as having "signs of cosmetic wear"... is it a false economy to buy used ball screws for precision CNC applications?

    are there any nuts to stay away from with the THK ground ball screws? i've had a hard time correlating markings i see in the item images with listings in the THK catalog (THK KX 80376, for example).

    are the differences between BIF, DIK, BTK, etc. important to the performance of the unit or is it just a different nuts/seals?

    lastly, how much of the shaft needs to protrude from the fixed end for attaching to the motor?

    thanks!



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    Quote Originally Posted by beaker152 View Post
    newbie questions:
    i note that many of the items on ebay are described as having "signs of cosmetic wear"... is it a false economy to buy used ball screws for precision CNC applications?

    are there any nuts to stay away from with the THK ground ball screws? i've had a hard time correlating markings i see in the item images with listings in the THK catalog (THK KX 80376, for example).

    are the differences between BIF, DIK, BTK, etc. important to the performance of the unit or is it just a different nuts/seals?

    lastly, how much of the shaft needs to protrude from the fixed end for attaching to the motor?

    thanks!
    BIF : Offset preload
    DIK: Offset preload, slim design
    DIR: Rotary nut
    BNFN: Double nut preloaded
    DKN: Doubel nut preloaded, slim design
    BLW: Large lead (1x screw diameter), preloaded
    BNF: Single ball race
    BNT: Square nut
    DK: Slim version of BNF
    MDK: Miniature
    BLK: Large elad, no preload
    WGF: Super Lead (1.5x-3x screw diameter)
    BLR: Large lead rotary nut

    These are all precision ground ballscrws....



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    Quote Originally Posted by louieatienza View Post
    BIF : Offset preload
    DIK: Offset preload, slim design
    DIR: Rotary nut
    BNFN: Double nut preloaded
    DKN: Doubel nut preloaded, slim design
    BLW: Large lead (1x screw diameter), preloaded
    BNF: Single ball race
    BNT: Square nut
    DK: Slim version of BNF
    MDK: Miniature
    BLK: Large elad, no preload
    WGF: Super Lead (1.5x-3x screw diameter)
    BLR: Large lead rotary nut

    These are all precision ground ballscrws....
    To add on: A couple of the screw models (e.g., BNT, IIRC) are available as both a rolled and as a ground screw. Just knowing the product line of the screw may not be enough to determine rolled vs. ground (and a seller may not know the difference).



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    Quote Originally Posted by Bear5k View Post
    To add on: A couple of the screw models (e.g., BNT, IIRC) are available as both a rolled and as a ground screw. Just knowing the product line of the screw may not be enough to determine rolled vs. ground (and a seller may not know the difference).
    Yes true... You must do your homework as well. One seller even has videos on his auctions showing the ballscrews' movenment, which helps. Check Swede's first post here for pics; there's good info there. Look for package markings or markings on the nut that say C0, C1, C3, C5; good chance they're ground, though I saw some rolled ballscrews that claimed to have C5 accuracy. After looking at a few auctions, it should be pretty easy to determine which is which.

    I've been fortunate to find ground ballscrews in their original packaging, still sealed, and I guess that's the best way to insure you're getting something that works right. Of course that's no guarantee and there's always a small risk involved with online purchasing. But the more you look, the better you get at spotting the good stuff. Particuarly with the THK stuff, the rolled ballscrew nuts look very sumilar to the ground ballscrew nuts..



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

    Ive looked at the prices at they are way too steep for me at this time. Having a budget of about $300, Im looking for what would be the next best thing. Is it possible to find a ACME anti-backlash ballscrew with somewhere between C7-C5?



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    typo
    Quote Originally Posted by UserJ View Post
    Ive looked at the prices at they are way too steep for me at this time. Having a budget of about $300, Im looking for what would be the next best thing. Is it possible to find a ACME anti-backlash ballscrew with somewhere between C7-C5?
    u shud be able to get c7 with good rolled screw. depending on length, dia, etc, u may buy it for that price. list this info if u want more info.... pm me with the details if u want a quote from ballscrews.com (thomson or bs&a).

    Last edited by mike_Kilroy; 09-06-2011 at 07:42 PM. Reason: typo


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    Hi, I was under the impression that in order to obtain "zero backlash", it required a double nut. Nonetheless, I have seen a variety of ballscrews listed on automationoverstock that are single nut, double nut, and a range of screw specs from C2 to C7, all claiming "zero backlash" nuts.

    1) Am I confusing ball screws with other types of screws that need a double nut for zero backlash ?

    2) Surely, a C2 ballscrew has less backlash that a C7, even if they are both called out as zero backlash nut types ? I guess then it is a question of spec / price for new one, but in the NOS market, that gets distorted a bit.

    3) I assume that the NSKs with "zero backlash" are better than the hiwins with an "anti backlash" nut ?

    Thanks

    Harry



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    Smile

    The ball-nut doesn't have to be double to be zero-backlash. The best way to find out about one particular type of ball-screw, is to look up the speck-sheet. It usually says how the pre-load is achieved. Usually it seems to be achieved by oversized balls, or by grinding the ball-nut a special way (maybe you could say that there is two nuts in one nut?! (hehe). Thus no double nut is needed. A C2 ball-screw does not have to have less backlash than a c7, but yes I guess it's true, since they probably don't sell a c2 ball-screw without pre-load. I have not seen any though.
    I would bet on NSK's, but then again I have never used Hiwin. I don't think I will even buy a new c2 screw though.



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    I'm not an expert on this, but...

    As far as removing backlash, it can also be done by offsetting one of the ball races as well.

    The accuracy grade has more to do with the lead accuracy of the screw. I don't think swapping ballnuts or bbs out would change that, just the amount of preload.

    A C2 screw is an amazing piece of machined work, but it means nothing if the rest of your machined is not built to anywhere close to that tolerance!



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    Thanks, of course a C2 grade is far beyond my needs, it just happens to be one of the options in the "new old stock" section, so the price is higher than C7 hiwins, but no so high that it is crazy.

    That being said, I can make one of the C7 rolled hiwins for 1/2 the price, but none of this stuff is really "cheap" so it is a question of doing it once vs twice.



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    If you're not sure if you can take the lead accuracy of a c7 screw, and the price for the c2 one is not a deal-breaker, I would probably say that you got it right. It's better to pay a bit more and be sure, then to try and see if it works. It never seems to work to well with CNC. (At least not in my experience, as little as I have.)
    To even be able to have any use of c2 accuracy, you would need some fancy machinery though. But even if you don't It'll probably beat the c7 one, as long as you have the right support bearings and such.



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