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  1. #11
    Quote Originally Posted by russell View Post

    Now to start on the Z axis. I've done some layout drawings and find it is just possible to get a 16 mm ballscrew to fit behind the motor on top of the head so that's the way I'll go. The ballnut has to be mounted rather high up though.
    Hi Russell,
    Can you post a drawing to show what you are trying to do? I don't understand why the Ballnut would have to be placed high up ?
    Are you attaching the stepper on the ballscrew or are you fixing the screw and spinning the nut ?

    Laurent

  2. #12
    Quote Originally Posted by rnr107 View Post
    Can you post a drawing to show what you are trying to do? I don't understand why the Ballnut would have to be placed high up ?
    Are you attaching the stepper on the ballscrew or are you fixing the screw and spinning the nut ?
    Hi Laurent,
    I am attaching the ballscrew to the head and spinning the nut, much as seen on the Hossmachine site here However the SX2+ has very little space behind the motor and the ballnut has to be mounted above the motor height at the top of the Z travel. I will try to post a drawing later.

    Russell.

  3. #13
    Ha.... OK, all clear now! :-) I like it.... very nicely done...

  4. #14
    O.K. some dxf drawing files follow:

    Leadscrew_nuts.dxf
    leadscrew support modified.dxf

    and finally my proposed Z axis layout (provisional):
    z-axis plan.dxf

    To view these download them by right clicking and selecting save link as. Then open them in your favourite CAD program.

    Russell.

  5. #15
    Fixed the X axis backlash problem. Because of the restricted space for the X axis nut the flange on the acetal insert has to be trimmed rather close to the 5/8 in diameter. It was flexing a bit under load so I've backed it up with another plate the same as the one that gives the compression at the other end. I now have lass than 1 thou backlash on both axes with a torque requirement of about 40 oz.in.

    I'll do the same to the Y axis nut to prevent problems under cutting loads.

    Russell.

  6. #16
    My SX2 isn't to hand at the moment, packed away whilst a workshop move is going on.

    However looking at the design of the Z and Hoss's machine is there any reason that the Z screw cannot be mounted to the side in the conventional manner ?
    John S -

  7. #17
    Quote Originally Posted by John S View Post
    However looking at the design of the Z and Hoss's machine is there any reason that the Z screw cannot be mounted to the side in the conventional manner ?
    The only down side of having it on 1 side rather than in the center is that the screw will tend to pull on one side and therefore twist something...
    and may not pull straight. You could fix that by having a linear bearing on a round bar on the other side?

    Laurent

  8. #18
    Laurent,
    I can see your point but in the case of the SX2 where the nut would be very close to the gibs I don't think this will apply, there have been literally thousands of CNC mills built or converted of the Bridgeport type where the nut block is secured to the front of the quill which would have the same effect but in a front to back application instaed of a side to side.

    In fact my big Beaver mill has exactly the same layout on the head and the Y movement is even worse as the ball screw hangs off one side, only the X has a central screw.Click image for larger version. 

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    John S -

  9. #19
    Hi John,
    OK, I beleive you... ;-)
    I like your lubricating system! Nice!

    Laurent

  10. #20
    Quote Originally Posted by John S View Post
    However looking at the design of the Z and Hoss's machine is there any reason that the Z screw cannot be mounted to the side in the conventional manner ?
    I guess you mean something like this.

    Obviously it can be done as many people have done it. However I have the same concerns as Laurent. I have read a number of threads where people have had to add a counterweight to avoid jerky Z movement and I don't want to get caught like that. It seems to be almost universal with the X1 where the leadscrew is behind the column and I guess it is due to the head nodding on the column. It strikes me that the closer the lift is to being in line with the C of G the less the problem will occur. Ideally I would like to mount the ballscrew further forward still but that would involve moving the motor out to the side.

    You are the expert on these machines so I would appreciate your opinion. Perhaps it is not a problem if the gibs are properly adjusted.

    A secondary consideration is the difficulty of keeping the ballscrew clean from swarf at the side. On top it is well clear of any flying chips.

    Russell.

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