Variable Speed Forwad/Reverse DC Lathe Motor?

Discussion in 'The Projects Forum' started by Sardis, May 4, 2015.

  1. Sardis

    Thread Starter New Member

    May 4, 2015
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    *Background info:
    Hi, I am a machinist and I wanted to convert my lathe to variable speed. I Have been researching the idea and have come to some conclusions about what I need, but I do not have a full knowledge of how to do it.

    I have obtained a broken treadmill and confirmed the motor works and is in good condition. (Pictures below)
    -Treadmill motor- DC 90V, 15A, motor with 4800 rmp.
    -current lathe motor-AC 110V, 11A, 1680 rpm motor.
    I am planning on using the belt system to keep the max rpm under 1700.
    It is mandatory that I be able to reverse the motor.

    This is a list of thing I think I need: Bridge Rectifier, ON-OFF-ON switch, Variable speed switch (Link).
    I did my best to make a circuit diagram of what I was thinking (Below).

    *Questions:
    1- Am I not incorporating some part that I need?
    2- Should I put the on-off-on switch in region 1 or region 2? (diagram)
    3- Is the bridge rectifier positive/negative specific?
    4- If the rectifier is positive/negative specific is there anything I have to do different to be able to place the switch in region 2? (On DC Current)
    5- Is there another type of hardware to use instead of the harbor freight router speed controller?
    6- Do I need to take into account any other factors?

    Thanks for your help!

    111111111111111111111.jpg 22222222.jpg
    lathe.png
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You may get away with doing it that method, but it is a little crude and does not give you the control of a DC controller such as made by KB/Baldor etc, these are readily available on ebay.
    The offer the ability to set accel decel etc as well as inhibit terminals for reversing and resetting the drive when you do so, as you should not reverse these motors under power.
    Max.
     
  3. tcmtech

    Well-Known Member

    Nov 4, 2013
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    On a bare minimum of parts your circuit should work but the speed regulation under variable loads will likely be a bit poor.
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    BTW do not run it in as a spindle motor without removing the flywheel first.
    You need to determine whether LH or RH thread.
    Max.
     
  5. Sardis

    Thread Starter New Member

    May 4, 2015
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    When it comes to lathe turning speed its important to be able to keep a constant speed but not as important (at least for my purposes) to duplicate the same speed. So I don't need "fine" speed selection. What I want is a setup that lets me run constant unyielding speed from 100-1700 rpm while turning against the friction/pressure of the tool.

    I will not need to reverse the motor under power. I quickly looked on ebay and I don't really want to spend all that much if I don't have to. Is there a other brand? This hardware will be eventually exposed to oil though not regularly or in great quantities. I want to keep it as simple and expendable as possible just in case.

    If you were coming at this project what would be your plan?

    I will be removing the flywheel.

    Thanks for the quick responses!
     
  6. Sardis

    Thread Starter New Member

    May 4, 2015
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    Also tcmtech wht do you mean "speed regulation under variable loads will likely be a bit poor"? Are you saying it will tend to want to jump from speed to speed when I am selecting? If so that's fine as long as I can still get the "jumps" to be in like 100 rpm jumps.

    And if I do "my" setup I'm still not sure about questions 3 and 4. Thanks!
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    A bridge rectifier has 4 terminals, 2 are AC in and + and - out, very simple.
    Just the polarity determines the direction of rotation, so just reverse if needed.
    Simple applications result in simple results, you have to apply the type of drive to achieve the results you require, for something like spindle control, I use the KB type, but even then there is the cheap version, which is SCR bridge type, or PWM which is superior, but more $$$.
    It depend on your end objective, how much you spend.'
    That is a nice motor, BTW, one of the better TM motors.
    Max.
     
  8. BillB3857

    Senior Member

    Feb 28, 2009
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    Looking at your drawing, you need to put the bridge after the speed control and the DPDT switch between the bridge and the motor. The + and - of the bridge will go to the switch and the AC terminals will go to the speed control. The way it is drawn will not work.
     
  9. Sardis

    Thread Starter New Member

    May 4, 2015
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    Will something like this work better? (link) I would not need a rectifier with this right? Then run the "motor out" wires through the on-off-on switch for reverse, then to the motor?

    You all can probably tell but I have no idea what I am doing. If anyone has a link to hardware around 50 or less they could link I would love to see it.
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    That is for less than 120w motors, yours is way above that.
    Max.
     
  11. BillB3857

    Senior Member

    Feb 28, 2009
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    You need to check the wattage of the motor you have and the drive you have linked to. Very large mis-match. 1350 watts for your otor vs 120Watts for the drive you linked to.
     
  12. Sardis

    Thread Starter New Member

    May 4, 2015
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    Lol that would make things difficult! sorry

    I'm typing "90v 15a dc controller" into ebay with a $75 cap and getting virtually 2 items repeated. 1 Link, 2 Link
    I'm missing something, but would one of those suffice?
     
  13. BillB3857

    Senior Member

    Feb 28, 2009
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    Do you already have a 90V DC supply that can deliver 15A? Both drives you have linked to need that.
     
  14. tcmtech

    Well-Known Member

    Nov 4, 2013
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    I am saying that as your torque demands change your RPMs will go up and down some from where ever you set it at.
     
  15. BillB3857

    Senior Member

    Feb 28, 2009
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  16. Sardis

    Thread Starter New Member

    May 4, 2015
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    Looks awesome Bill, but I would be able to buy 3-6 used treadmills of CR for that... I would have used the electronics from the one I have but it was broken. So that's the reason I'm trying to keep it under 50ish. You all are a great help! Thanks for all the time your spending!
     
  17. BillB3857

    Senior Member

    Feb 28, 2009
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    An old saying goes like this.... "If ya gonna play, ya gonna pay!?" Do you need speeds that are between the geared speeds?
     
  18. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The KB drives are plentiful on ebay e.g. 331507261203
    Max.
     
  19. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Do you not have the speed control board that went with the treadmill?
    Here's a brand new KBCC-225 drive under your $75 cap. The KB drive is a medium-featured legit DC drive with load regulation (+/-1%) via armature feedback. You can expect smooth consistent running speed whether you're hogging into your workpiece or free-spinning. With your rectified router speed control, you can expect stalling at low speeds and severe bog-down at higher speeds.
     
  20. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Did you just steal that right out from under me while I was typing? I think you did, you one-upper. tisk tisk. ;)
     
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