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  1. #1
    dsc's Avatar
    Lives in Lincoln, United Kingdom. Last Activity: 1 Day Ago Has been a member for 5-6 years. Has a total post count of 248. Received thanks 1 times, giving thanks to others 9 times.
    Gents,

    excuse the rather massive thread attack, but I'd rather ask than be sorry later.

    Any reasons why ballnuts are normally mounted inside a housing rather than bolted on top? See attached drawing.

    Click image for larger version. 

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    I've got limited space between the rails, linear bearings and mounting plates and a 1204 ballnut fits nicely with it's 25mm depth. Anything over this, like a 30mm deep housing in order to fit the ballnut inside, will make things bad.

    Second question is for a 10mm ID bearing on a 12mm ballscrew, doable? I know not enough material to hold the bearing in place, so I'm planning to use a circlip to rest the bearing on, again see attached drawing. Stupid?

    Click image for larger version. 

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    Thanks in advance for any advice.

    Regards,
    dsc.

  2. #2
    Quote Originally Posted by dsc View Post
    Gents,

    excuse the rather massive thread attack, but I'd rather ask than be sorry later.

    Any reasons why ballnuts are normally mounted inside a housing rather than bolted on top? See attached drawing.

    Click image for larger version. 

Name:	ballnut.png 
Views:	505 
Size:	7.9 KB 
ID:	9220


    Regards,
    dsc.

    Unless I'm missing something very obvious the two drawing will take up exactly the same space.
    It's the flange that controls how much room you have.
    John S -

  3. #3
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 10 Hours Ago Has been a member for 9-10 years. Has a total post count of 1,831. Received thanks 192 times, giving thanks to others 5 times.
    thanktheidiotwebmasterfortheremoval
    Last edited by m_c; 20-05-2014 at 10:56 PM.

  4. #4
    dsc's Avatar
    Lives in Lincoln, United Kingdom. Last Activity: 1 Day Ago Has been a member for 5-6 years. Has a total post count of 248. Received thanks 1 times, giving thanks to others 9 times.
    John, I should've attached a drawing showing the ballnut, this is something I got from Chai and it shows a flange which is 25mm deep. Perfect for my application, but looking closely at the drawing, you'll see that the 'barrel' of the nut is 24mm, which means there's 0.5mm radius difference between the outside of the round part of the nut and the flange. If I go with a housing that is 25mm deep and bore a 24mm hole in it to fit the ballnut inside, I'll be left with 0.5mm of aluminium on both sides, unless of course I make the housing deeper and I don't really have space for that, which is what triggered my question.

    Click image for larger version. 

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    m_c:

    1) Hmmm, care to expand on why the bolts would be hard to get in?

    2) Sh*te, that's what I was afraid of. I'd happily go with 16mm ballscrew, but the ballnuts for those are 40mm deep, which means there's no way to get it in. Another idea would be a 16mm trapezoidal screw, but again I need nuts which are max 25mm deep. Bearing wise I wouldn't want to go lower than 10mm, as it's flimsy and thin at 10mm anyway (plus manufacturers like SKF / Timken, don't go below 10mm with angular contact bearings which one typical uses for ballscrews).

    Regards,
    dsc.
    Last edited by dsc; 09-07-2013 at 08:47 AM.

  5. #5
    OK got it now. What machine is it for ?
    John S -

  6. #6
    dsc's Avatar
    Lives in Lincoln, United Kingdom. Last Activity: 1 Day Ago Has been a member for 5-6 years. Has a total post count of 248. Received thanks 1 times, giving thanks to others 9 times.
    I'm guessing we're talking loads here? it's a rather non-standard application with a z-axis alone, nothing else, as I need precision positioning in the vertical. Max loads would be maybe 1-5% of the maximum load capacity of the ball screw given to me by Chai (quoted figures where 4kN for static load and 3.5kN for dynamic load). The Z-axis runs on 15mm Hiwin rails, which are a pain in the ass to use, as their profiles are super low, which is why I've got this depth problem.

    Regards,
    dsc.

  7. #7
    Put some gauge plate packers under the hiwin rails to get more clearance ?
    John S -

  8. #8
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 10 Hours Ago Has been a member for 9-10 years. Has a total post count of 1,831. Received thanks 192 times, giving thanks to others 5 times.
    Quote Originally Posted by dsc View Post
    1) Hmmm, care to expand on why the bolts would be hard to get in?
    Look at the drawing, and think about where the bolt head will go with the housing the wrong way around.

  9. #9
    dsc's Avatar
    Lives in Lincoln, United Kingdom. Last Activity: 1 Day Ago Has been a member for 5-6 years. Has a total post count of 248. Received thanks 1 times, giving thanks to others 9 times.
    There's 28mm between the base of the rails and the base of the blocks. 1204 ballbut is 25mm deep, but 1605 is a whooping 40mm, so I'd need 12mm more clearance, it's almost like adding an additional 12mm plate just to get clearance. How do people normally get around this? is it packers / pockets and double plates to get more clearance?

    The bolt head can go from the top on both versions of the housing, it's an M4 bolt and I have 8mm clearance on top for the head. Standard head on a caphead M4 is roughly 7.2mm.

    Regards,
    dsc.

  10. Quote Originally Posted by dsc View Post
    ...

    The bolt head can go from the top on both versions of the housing, it's an M4 bolt and I have 8mm clearance on top for the head. Standard head on a caphead M4 is roughly 7.2mm.

    Regards,
    dsc.
    Standard BS EN ISO 4762 spec caphead for M4 is 6.64 - 7.00mm dia.

    There's 8mm to play with... seems to me there's plenty of room...

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