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IndustryArena Forum > Mechanical Engineering > Linear and Rotary Motion > Timing pulley size needed to increase speed of screw
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  1. #1

    Unhappy Timing pulley size needed to increase speed of screw

    Hi, I’m trying to figure out how to increase the speed of my Y axis driven by a ball screw and stepper. I’ll list some of the specs below.

    Machine is currently in use daily.
    -4x8 format router vacuum table

    Y axis ball screw - 25mm dia x 5mm lead x distance between supports is 50” ..I know the 5mm lead is not good but gotta work with it…

    The stepper driving the screw is a 1/8deg nema 23 @ 600oz 4amp

    My problem is it’s Direct drive, I want to move the stepper and use a pulley system to help decrease the steppers rpm and increase the screw. Hopefully keeping torque.

    Currently it is only able to achieve 90ipm, we would be happy with 200ipm if it’s even possible with a pulley/belt setup. I can machine the mounts etc in house so not concerned there. What I can’t seem to figure out is what tooth/size etc pulleys I’ll need to get close to or over that 200ipm.

    Here a few more details on the current setup coming from mach3

    Steps per. - 9973 Yes 9k lol
    Velocity. - 90.
    Acceleration. 20

    Nothing seems right when I do the math, looking for some help finding a suitable pulley size for the stepper and the screw

    Thanks

    Alex

  2. #2
    Community Moderator Jim Dawson's Avatar
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    Re: Timing pulley size needed to increase speed of screw

    2.2:1 ratio would give you 200 IPM at your current stepper RPM. So any pulley combination that would give you somewhere around that ratio would reach that goal. Just set the steps per to match the new ratio.

    Now the question: Does the stepper have enough torque to drive the system at that speed? I don't know. In general a NEMA 23 sounds a bit light for the task, but I tend to over power axis drives, you can always turn them down a bit. The torque of a stepper motor drops off rapidly as the RPM increases, so keeping it in the lower end of it's RPM range is better.

    Given that this is a machine in commercial use, I would be tempted to repower it with AC servo motors, maybe in the 400W to 750W range, and be completely done with the problem. Yes, it will cost a bit more, but the increase in productivity will make up for it in the long run.
    Jim Dawson
    Sandy, Oregon, USA

  3. #3
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    Re: Timing pulley size needed to increase speed of screw

    I think that's working out at around 460rpm atm at the stepper at 90ipm.
    I would go with an AC servo 750w-1kw that has 1500-3000rpm.

    I get 600rpm on my mill using 60V to run my nema23's (566oz).

    If you belted it 2:1 you would likely half the existing torque (1 rev of stepper = 2 rev of screw).

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