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  1. #21
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 2 Hours Ago Has been a member for 8-9 years. Has a total post count of 1,490. Received thanks 158 times, giving thanks to others 5 times.
    Opposite way!
    You want to decrease speed of the ballscrew in relation to the stepper, so you get more torque at the screw. Somewhere around a 2:1 ratio would be a good starting point.

    Try running some figures through the spreadsheet to see what kind of speeds you can get with different ratios, while still having usable torque to handle the cutting forces.
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

  2. #22
    JAZZCNC's Avatar
    Lives in wakefield, United Kingdom. Last Activity: 10 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 5-6 years. Has a total post count of 5,796. Received thanks 901 times, giving thanks to others 36 times.
    Quote Originally Posted by Agathon View Post
    If I go for conventional steppers I'll go with the AM822 drivers, but what size motor? The old steppers have a surprisingly small shaft (3/8") so Nema34s with 14mm shaft are a bit of nuisance. I see Nema23 3Nm motors with 10mm shafts - http://r.ebay.com/KuT9Ez - Are these big enough though?
    Ok well first need to check if the machine is fitted with Ballscrews not just lead screws which you are calling Ballscrews.?

    If ballscrews then 3 or 4Nm Nema 23 motors will probably work. I've fitted loads of Both 3 & 4nm motors and to be honest see very little difference between them in performance terms so wouldn't stress over which to use. The Key is buying ones with Low inductance. No higher than 4mh ideally closer to 3mh.
    These are better motor and will fit your needs.
    https://www.cnc4you.co.uk/Stepper-Mo...H401-03-Nema23

    If you speak to them Don't Let them Bullshit you into believeing there drives are as good or better than Leadshine AM or EM they are not.!

  3. #23
    Quote Originally Posted by m_c View Post
    Opposite way!
    You want to decrease speed of the ballscrew in relation to the stepper, so you get more torque at the screw. Somewhere around a 2:1 ratio would be a good starting point.

    Try running some figures through the spreadsheet to see what kind of speeds you can get with different ratios, while still having usable torque to handle the cutting forces.
    OK, that's certainly how I would have dealt with torque issues with a conventional motor, but I thought the whole point was that torque went down as speed increases. I see that gearing down, by say 1:2 would give twice the torque, but getting the speed up to 1800 mm/min (900rpm for the motor) for rapids will mean that the motor is well outside it's optimum torque region. Or is it the case that in practice this wouldn't be an issue?

  4. #24
    JAZZCNC's Avatar
    Lives in wakefield, United Kingdom. Last Activity: 10 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 5-6 years. Has a total post count of 5,796. Received thanks 901 times, giving thanks to others 36 times.
    This maybe your Lucky day my friend.?

    Just remembered somewhere in box I've got some motors and sure enough there was.!! And guess what they are 2 x Brand New 34's with 10mm shaft 8 wire motors model number FL86STH65-2808A-H. Think about 3.5Nm but would need to dig out motor data sheet.

    Also got another 34 4 wire motor with 12mm shaft which is around 4Nm I think. SY85STH65-5904B.

    Drop me PM if your interested.

  5. #25
    Quote Originally Posted by JAZZCNC View Post
    Ok well first need to check if the machine is fitted with Ballscrews not just lead screws which you are calling Ballscrews.?

    If ballscrews then 3 or 4Nm Nema 23 motors will probably work. I've fitted loads of Both 3 & 4nm motors and to be honest see very little difference between them in performance terms so wouldn't stress over which to use. The Key is buying ones with Low inductance. No higher than 4mh ideally closer to 3mh.
    These are better motor and will fit your needs.
    https://www.cnc4you.co.uk/Stepper-Mo...H401-03-Nema23

    If you speak to them Don't Let them Bullshit you into believeing there drives are as good or better than Leadshine AM or EM they are not.!
    Yes, definitely ball-screws. This is a very high-class bit of kit and would have cost many tens of thousands when new in 1980. The slides are conventional dovetails but have low friction inserts and are automatically pressure lubricated.

    Thanks for the link and recommendation - will look into it.

    Sorry to keep harping on about closed loop, but what do you think about using the Leadshine Nema23 kits?

  6. #26
    Quote Originally Posted by JAZZCNC View Post
    This maybe your Lucky day my friend.?

    Just remembered somewhere in box I've got some motors and sure enough there was.!! And guess what they are 2 x Brand New 34's with 10mm shaft 8 wire motors model number FL86STH65-2808A-H. Think about 3.5Nm but would need to dig out motor data sheet.

    Also got another 34 4 wire motor with 12mm shaft which is around 4Nm I think. SY85STH65-5904B.

    Drop me PM if your interested.

    Great, I'll pm you.

  7. #27
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 2 Hours Ago Has been a member for 8-9 years. Has a total post count of 1,490. Received thanks 158 times, giving thanks to others 5 times.
    Quote Originally Posted by Agathon View Post
    OK, that's certainly how I would have dealt with torque issues with a conventional motor, but I thought the whole point was that torque went down as speed increases. I see that gearing down, by say 1:2 would give twice the torque, but getting the speed up to 1800 mm/min (900rpm for the motor) for rapids will mean that the motor is well outside it's optimum torque region. Or is it the case that in practice this wouldn't be an issue?
    I'm about to head out, so this is a very brief explanation.
    Generally smaller motors the torque doesn't drop off as quick, especially on relatively lower voltage power supplies. Larger motors can maintain a similar torque drop, however you're into high voltage drivers, which carry an additional cost. So you can quite often get better performance from a smaller motor spun faster from a lower voltage, than you can with a large motor run from a less than ideal voltage.

    And that is probably as clear as mud, but I've got to go!
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

  8. #28
    Quote Originally Posted by m_c View Post
    I'm about to head out, so this is a very brief explanation.
    Generally smaller motors the torque doesn't drop off as quick, especially on relatively lower voltage power supplies. Larger motors can maintain a similar torque drop, however you're into high voltage drivers, which carry an additional cost. So you can quite often get better performance from a smaller motor spun faster from a lower voltage, than you can with a large motor run from a less than ideal voltage.

    And that is probably as clear as mud, but I've got to go!
    Thanks again - I think I get it. I thought I was good on electrics and motors until I started reading up on steppers!

  9. #29
    JAZZCNC's Avatar
    Lives in wakefield, United Kingdom. Last Activity: 10 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 5-6 years. Has a total post count of 5,796. Received thanks 901 times, giving thanks to others 36 times.
    Quote Originally Posted by Agathon View Post
    Sorry to keep harping on about closed loop, but what do you think about using the Leadshine Nema23 kits?
    The 2Nm won't be enough IMO.

    This machine sounds too nice to be skimping on motor so don't spoil it just for sake of feature that won't give anything more than well setup Stepper would.

    For me it would boil down to 2 options. Conventional steppers with Good drives like AM/EM or Servos. Wouldn't waste money on Closed loop Steppers.

  10. #30
    Quote Originally Posted by JAZZCNC View Post
    The 2Nm won't be enough IMO.

    This machine sounds too nice to be skimping on motor so don't spoil it just for sake of feature that won't give anything more than well setup Stepper would.

    For me it would boil down to 2 options. Conventional steppers with Good drives like AM/EM or Servos. Wouldn't waste money on Closed loop Steppers.
    I certainly don't want to "spoil the ship for a ha'p'orth of tar". Ironically, that's why I was thinking of closed loop. My initial thoughts were to fit Leadshine Nema34 4Nm hybrid servos, but they are only available from China - or at twice the price from the UK. Of course, I'd love to spend hundreds on quality servos, but as a first foray into CNC I need to keep the costs down.

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