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  1. #51
    yes thanks Jonathan I saw that thread, very interesting and those stepper mounts looked very nice.

    Am I right in thinking the advantage of the rotating ballnut is gained on lengths over 100cm?

  2. #52
    Quote Originally Posted by mocha View Post
    yes thanks Jonathan I saw that thread, very interesting and those stepper mounts looked very nice.
    Thank you... if you've not got the kit to make them yourself then I can make them for you. Let me know if you're interested and I'll work out the price for what you need.

    Quote Originally Posted by mocha View Post
    Am I right in thinking the advantage of the rotating ballnut is gained on lengths over 100cm?
    The simple answer is it depends. If it's a small diameter screw, or you want a very high feedrate, then yes you'll gain at 1m. See what I put about critical speed in post 39. You do save by not buying the bearing blocks and you can get away without end machining on the screw. This is good since it makes the size/pitch screws that are not on eBay more reasonably priced.
    If it's a 25mm screw then the rotating nut setup I made has the same inertia as about 700mm of the screw, so you wont gain anything below that. The critical speed of a 700mm long 25mm diameter screw is very high anyway, so you wouldn't need to use a rotating nut anyway. I've not worked out the moment of inertia of the 16/20mm version yet.

  3. #53
    GTJim's Avatar
    Lives in Coventry, United Kingdom. Last Activity: 2 Weeks Ago Has been a member for 8-9 years. Has a total post count of 110. Received thanks 3 times, giving thanks to others 20 times.
    I realised the problems with my sketch after I post it, but I had to go out.
    But it has made me think of other approaches to this problem.

    Thank you all for your input as its very much needed.

    I'll be ordering some metal soon so need to get the basic concept right.

    Jim

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