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  1. #21
    Quote Originally Posted by diy-john View Post
    latest draft -version for X -screw is here
    The X screw is best held in tension, suggest you put a thread and one bearing at either end.

    I have found 31pcs of the 12mm Belleville washers I used...
    www.bellevillesprings.com pn: D2812215

    You are welcome to half a dozen, just shout.

  2. #22
    Was going to mention adding the second thread for tensioning but for some reason I thought that drawing was for the Y-screw...oops. I've got a thread on both ends of my router X-axis screws for the same reason.

    Do you reckon the D2812215 Belleville washers would be suitable for preloading RM1204 ballnuts? The screw I have here is actually 11.60mm diameter so it's going to close... Apparently 10-15% of static thrust rating is a good compromise for preload, so 1KN. I probably need a lower spring constant for that as such a small deflection will be hard to measure.

  3. #23
    Quote Originally Posted by Jonathan View Post
    Do you reckon the D2812215 Belleville washers would be suitable for preloading RM1204 ballnuts?

    I used them with 1204's on my Roland mill at considerably lower pre-load than on the Warco. I don't go above 5mm tooling on that.

    Works okay, but agree a lighter section washer would be easier to adjust and give you more take up.

  4. Looking at the drawing is seems over complicated.
    If you want zero backlash and don't want any movement on the support bearing just go for a good quality FK12, the gten R1605 ballscrew and the R1605T3-FDID-P1

    This is the link to the datasheet for the FDI and FDU type ballnuts and it is 34mm between the flats, so it is actually 6mm difference.
    http://www.zappautomation.co.uk%2Fpd...%2FFDU-FDI.pdf

    The ballnut is already pre loaded for zero backlash and has been tested on the screw.

    you will need ti install chinese fonts in acrobat.

  5. #25
    Quote Originally Posted by Gary View Post
    The ballnut is already pre loaded for zero backlash and has been tested on the screw.

    That looks interesting, is it shimmed or does it have springs? The data sheet is vague.

  6. No its a spacer between the two nuts.
    I dont know of any commercial double ballnuts that use a spring.
    All the manufactures i have worked with use a spacer to pre load the double ballnut, and there are reasons for this.







    Quote Originally Posted by Robin Hewitt View Post
    That looks interesting, is it shimmed or does it have springs? The data sheet is vague.

  7. #27
    Quote Originally Posted by Gary View Post
    All the manufactures i have worked with use a spacer to pre load the double ballnut, and there are reasons for this.
    Good point, I forgot to mention that John will need to leave room to fit an oil pipe to the nut. I use 4mm OD nylon tube and standard push fittings which are a bit sticky out and it will drip

  8. #28
    Quote Originally Posted by Jonathan View Post
    I can machine the ballscrew as you've drawn it for 15 plus postage.
    Wow, cool Jonathan. Can't go wrong with that. Thanks!

    Quote Originally Posted by Robin Hewitt View Post
    www.bellevillesprings.com pn: D2812215

    You are welcome to half a dozen, just shout.
    Robin, yes please, need those.

    Quote Originally Posted by Robin Hewitt View Post
    suggest you put a thread and one bearing at either end.
    Made another draft of X-axis screw. Please is this any good now?
    - added a thread to the other end. And also a similar "structure, a fixed mount" for the ballscrew. So there are now two such mounts, one at either end of the screw.
    - there are two (2) screws in picture below, but it is the same one single screw.
    -- The other one just highlights, what components would fit, and where. Like hand-wheel, pulley, shims, Belleville washers.

    Click image for larger version. 

Name:	draft-x-screw-2012-03-15.png 
Views:	240 
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ID:	5483

    Not sure about the dynamics, kind of figured out, that with this setup, the Belleville -washers + half nuts at either end of the screw ---> would tension the screw sort of around either end fixed mounts. Please correct if you think one has mis-understood the principle.


    Quote Originally Posted by Gary View Post
    This is the link to the datasheet for the FDI and FDU type ballnuts and it is 34mm between the flats, so it is actually 6mm difference.
    http://www.zappautomation.co.uk%2Fpdf%2FBallscrews%2FFDU-FDI.pdf

    Gary, the 34mm height ballnut gets me off the hook. Thanks for pointing out these alternatives. Will speak to you about other components.


    Thanks!

  9. #29
    Robin - thank's for confirming that about the washers. I'll order some 'lighter' ones (http://www.leespring.com/uk_product_...ype=W&subType=)

    Quote Originally Posted by diy-john View Post
    Wow, cool Jonathan. Can't go wrong with that. Thanks!
    :) Discuss details when the design's ready.

    To put the screw in tension you don't want to have pairs of angular contact bearings at both ends, as that fixes both. You need a pair of angular contact bearings at one end, and a standard deep groove bearing plus Belleville washers and thrust bearing at the other end to provide contact force for the tension. If both ends were fixed rigidly with angular contact bearings the tension in the screw would depend on the relative spacing of the bearing blocks and the length of the screw between them, so there's no way to set it.

    By 'standard washer' I assume you mean an accurately machined washer with parallel faces. You don't need a washer between the ballscrew end and angular contact bearing as the bearing is most accurate resting on the machined shoulder on the screw.

  10. #30
    That looks horrible. I'm obviously not explaining this at all well.

    To put the screw in tension you just need one angular contact bearing at either end. The Bellevilles try to stretch the entire screw end to end. Adding more bearings just gives you an alignment nightmare. There is hardly any side loading on the screw to worry about, so don't worry. I used one bearing at either end of my overlength X screw and it was fine and dandy.

    I used a pair of bearings at the handle end of my Y screw simply because I couldn't fit any bearings at all on the far end.

    Not a problem for the X so I put one bearing at either end.

    The whole she-bang should be sloppy, right up to the moment you tighten down on the Belleville's.

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