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Thread: General Q about lathe motor control

  1. #1
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    General Q about lathe motor control

    I have a 1754 rpm 115V 6hH ?5.8Amp? motor running my lathe and I want to be able to control the speed.

    DEoes anyone know of an affordable controller or a diagram that I could buy the part at Radio Shack and put it together my self?

    I want to be able to bring the speeds down to 700 or so.

    (Mod, please move if required, thanks)

  2. #2
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    We will let the electronics experts advise on that. It's my understanding this is not a feasible project but the jury will know better.
    For larger projects you probably will want slower than 700. Some kind of pulley arrangement might be what you end up with.

  3. #3
    Julio,

    700 RPM isn't slow enough with out of balanced blanks. On my Jet Mini the low speed is 500 rup and that is way to fast when you first spin up an out of balanced blank. It'll definitely open your eyes and get your heart beating faster.

    100-200 RPMs would be a better low end speed.

    My new lathe goes down to 50 rpm.
    Ken
    ------



  4. #4
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    Julio, putting together a second set of pulleys (jack shaft) is very simple. I did a few web searches and found a good diagram on a SMC members website here. I made mine a little different but it slowed my lathe way down. You can see some pics of my set up here. Nathan Hawkes, a FWW member helped me out by posting some pics of his set up here.

    good luck!
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  5. #5
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    Thanks Jeff and Ken, Jeff; the pictures were great. Now question is pulley ratios.

    Does anyone know of a proprtion formula or a site that would help figure out what pulley sizes I need,

    My set up will lend itself to a nice pair of pillow blocks but I would need the ratios in order to get down to between 500 and 200 as advised here..

    Thanks in advance.

  6. #6
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    Vairiable speed options.

    Here is a quick run down on your PRACTICAL options.

    1) Single phase capacitor start motor. NONE electronically. You can mechanically but you asked about electronic. One of the problems is that the start switch doesn't cut out to till the motor is half speed(??). So if you slow it down then the start circuit cuts in and fried motor.

    2) Universal motor there are speed controls available. I have never used one though.

    3) Install a DC motor and controller. Watch The Surplus Center and sometimes you can find a good deal. There is a guy on EBay that builds and sells these. I have his name but not in front of me. I have done this and it works good.

    4) My Favorite. A 3 phase motor with a VFD. If you shop around and keep asking odds are good you can find a used 3 phase motor dirt cheap if not free. There isn't much of a market in industry for used motors. You can pick up a VFD for $100 if you watch EBay close. Then you have full variable speeds and if you pick up a newer VFD you have options like soft start and stop, remote control switches (hard wired ) and a ton of other options you will never use.
    God grant me the senility to forget the people I never liked anyway,
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  7. #7
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    Jeff covered all the options well. I agree with his recommendation to use a 3 phase motor and VFD. The one thing I wanted to add is that the 3 phase motors you'll buy have a fan to cool them, and are designed to run at rated speed. When you run them at slow speed, the fan is not effective for cooling the motor so if you plan to do a lot of slow speed operation, get a small fan and point it at the motor to keep it cool. Otherwise, the motor can overheat and fail.

    Even though you're running it at a slow speed, the motor is generating about the same heat as when it's running at rated speed.

    Mike
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    Go into the world and do well. But more importantly, go into the world and do good.

  8. #8
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    Julio, here is a link to check on RPM/pulley ratios.

    http://www.owwm.com/Math/ArborRPM.asp
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  9. #9
    Julio...one thing to keep in mind about DC motors and controls. Generally with those, the slower the speed the less the horsepower. So they don't generally work well on large lathes. They'd work fine for small blanks but not too well on larger blanks. My Jet Mini has a dc motor controller and motor. It works for the 10" maximum size blanks but there's a reason PM puts a 3 phase motor, inverter and ac motor controller on their PM3520B.
    Ken
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  10. #10
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    Thanks Ken:

    I guess I am convinced that an electricl solution is impractical.

    Does anyone else have any more pulley configuration solutions?

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