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  1. #51
    Quote Originally Posted by pippin88 View Post
    I like your new machine, though I think hiding the ball screws like that reduces stiffness too much by cutting into the tubes.
    Well that depends on application and what stiffness is required. In this application it doesn't need high stiffness but does require the height. However, I can tell you it's still very stiff.

    I will be building a much larger version that will work the same with lifting gantry but with much more bracing using 10mm wall tubes rather than 5mm used on this.


    Quote Originally Posted by pippin88 View Post
    You can have a single central screw on a lifting gantry machine. The screw moves up and down with the gantry. Nut it attached to the fixed top cross beam. Either rotating but with servo attached to fixed cross beam, or rotating screw with Z servo moving up and down with Z.
    Pros: Single screw (screw mapping, servo tuning, cost). Cons: A bit trickier to implement. Will have screw sticking right up high when Z fully up.
    You could but it will look crap and require you have a high ceiling.
    Also it won't work very well because the gantry could and IMO will definately rack when plunge cutting at the outer edges. Disaster waiting to happen IMO.

    The design I've shown only uses a single motor connected to the screws with belt/pulleys so it's only one extra screw so no big expense in the grand scheme.
    -use common sense, if you lack it, there is no software to help that.

    Email: dean@jazzcnc.co.uk

    Web site: www.jazzcnc.co.uk

  2. #52
    Quote Originally Posted by JAZZCNC View Post
    The design I've shown only uses a single motor connected to the screws with belt/pulleys so it's only one extra screw so no big expense in the grand scheme.
    Was just about to ask whether I have to switch from belts to direct drive. Do I need brakes on the vertical servo's? It's gonna be lifting 150kg after all?

  3. #53
    Quote Originally Posted by hardenum View Post
    Was just about to ask whether I have to switch from belts to direct drive. Do I need brakes on the vertical servo's? It's gonna be lifting 150kg after all?
    You have to design to your own requirements but lifting 150Kg then yes I would go with dual motors with brakes, doesn't need to be servo motors thou, Closed loop steppers will do the job perfectly well enough.
    -use common sense, if you lack it, there is no software to help that.

    Email: dean@jazzcnc.co.uk

    Web site: www.jazzcnc.co.uk

  4. #54
    Retracted.
    Last edited by hardenum; 08-12-2020 at 02:37 PM.

  5. #55
    Quick servo question

    Can I mix and match servo sizes? e.g size 60 for X and size 80 for y etc. ?

  6. #56
    Quote Originally Posted by hardenum View Post
    Quick servo question

    Can I mix and match servo sizes? e.g size 60 for X and size 80 for y etc. ?
    Of course.

  7. #57
    Clive S's Avatar
    Lives in Marple   Stockport, United Kingdom. Last Activity: 16 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 3,323. Received thanks 619 times, giving thanks to others 74 times. Made a monetary donation to the upkeep of the community. Is a beta tester for Machinists Network features. Referred 1 members to the community.
    Quote Originally Posted by hardenum View Post
    Quick servo question

    Can I mix and match servo sizes? e.g size 60 for X and size 80 for y etc. ?
    yes
    ..Clive
    The more you know, The better you know, How little you know

  8. #58
    It's not looking good, the change to new design doubled EG by volume. I'm gonna have to look into doing some FEA to know where I can shave off some material.

    Question

    Are there any handbooks that talk about forces acting on a machine during machining that I can use as a guide?
    Last edited by hardenum; 11-12-2020 at 09:34 PM.

  9. #59
    What do you all think about this setup? Moving the bed to the side(for easier side milling)? I'm not sure if this is a machining center or a grinding or whatever though. By the way that's not a workpiece but the fixture block. Can I mount a workpiece to a vacuum table sideways?





    So who's slapping their forehead?
    Last edited by hardenum; 11-12-2020 at 11:37 PM.

  10. #60
    Quote Originally Posted by JAZZCNC View Post
    Well that depends on application and what stiffness is required. In this application it doesn't need high stiffness but does require the height. However, I can tell you it's still very stiff.

    I will be building a much larger version that will work the same with lifting gantry but with much more bracing using 10mm wall tubes rather than 5mm used on this.
    I can't see how the stiffness loss with a slot is worth it.

    The below shows two identical columns, except one has a slot cut in it. There is 2.36x as much deflection with the slot.
    Click image for larger version. 

Name:	Slot.jpg 
Views:	217 
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ID:	29240

    Bellows don't compromise rigidity.

    Quote Originally Posted by JAZZCNC View Post
    You could but it will look crap and require you have a high ceiling.
    Also it won't work very well because the gantry could and IMO will definately rack when plunge cutting at the outer edges. Disaster waiting to happen IMO.

    The design I've shown only uses a single motor connected to the screws with belt/pulleys so it's only one extra screw so no big expense in the grand scheme.
    Who cares what it looks like?

    High ceiling - maybe. Not that high. Depends on what level the base of the machine sits...

    Racking is a consideration. Depends on width between rails and bearing spacing along the rails.

    I agree, ball screw expense is not the biggest consideration (though starts to get much more when you use high quality bearing blocks etc). I'm thinking about screw mapping and linear encoders - much harder with two screws.
    Belt stretch is a concern for a long enough belt to link those two ball screws.

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