1. Right guys finnaly got back to building my cnc router, gantry is 50" wide and made of 2x6" box alloy and the sides are 20mm thick plate the table is 6ft long and i intend on machining wood plastic and alloy. i have not yet got any motors for this size table and i was going to purchase some of gary's finest ballscrew pretty soon. BUT... im still unsure what pitch to get as i want to have good "nippy" but accurate control over the movement. i have decided to use 25mm thick screw on the X & Y but i could really do with a second or third oppinion on what pitch and motors to get.

    I could always add belt drive to the ends instead of direct this might give me some more flexibility..

    What do you guys think...

    Last edited by AdCNC; 05-01-2010 at 07:54 PM.

  2. #2
    What sort of speed are you after? You'd need to go pretty thick for that length if it's going to be fast and not whip (25mm at least).

    I'm running 1500mm lengths of 25x25, giving me about 18m/min, and with 400 steps per revolution, accuracy is 0.0625mm. But I've also got some pretty hefty steppers to drive them though...

  3. Yes matey i was thinking around that for my rapids, i will be fully supporting my ballscrew at both ends with some hefty bearings (once i get the ballscrew machined), i will also need some meaty motors any thoughts here? im planning on getting the high voltage drives from zapp also.

  4. #4
    I used the SY85STH146-4208 motors for my machine - they're very torquey. You will definitely need the high voltage drivers. Irving did an excellent tutorial on choosing motors:

    http://www.mycncuk.com/forums/showth...eed-A-tutorial

    When I got mine, it was a case of "as much as I could afford" (after having a brief discussion with Gary about it).

    I also got the previous generation for the driver than the one Zapp's currently offering in their NMEA-34 Kit 2.

  5. hmmm ill try and get my head around all the maths but tbh im not that good with that sort of things. might give gary a buzz tomorrow see what he suggests.

  6. Quote Originally Posted by AdCNC View Post
    hmmm ill try and get my head around all the maths but tbh im not that good with that sort of things. might give gary a buzz tomorrow see what he suggests.
    Use the spreadsheet on post #2 in that thread...it does all the maths for you!

  7. Quote Originally Posted by tribbles View Post
    What sort of speed are you after? You'd need to go pretty thick for that length if it's going to be fast and not whip (25mm at least).

    I'm running 1500mm lengths of 25x25, giving me about 18m/min, and with 400 steps per revolution, accuracy is 0.0625mm. But I've also got some pretty hefty steppers to drive them though...
    Well, im set on going with servo motors all round, 2 on the X ( each screw ) 1 for Y and smaller 1 for Z. im going to use 20x5mm screw for my Z but i am unsure if i will get the accuracy with the X and Y if i use 25x25 for the X and 20x20 for the Y
    i was thinking of using a belt reduction connecting the servos in the regions of 3:1 or perhaps abit higher, What are your thought as servos are fast but need gearing to get torque. As Tribbles said about his accuracy being 0.0625mm could i achieve anything better with servos in conjunction with the pitch of screw.

    Or would it not matter if i went for a finer pitch screw and kept with the servos and still be able to achieve good rapids relying on the high speed of the servos!

    AHHHHH questions questions questioins :(

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