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    Making electric motor variable speed for bowl lathe

    I'm working on a homemade bowl lathe, and instead of having a 4-pully step for the speed control I was wondering on how to just make the motor variable speed, maybe with a light switch dimmer sort of deal. Any suggestions?

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    Re: Making electric motor variable speed for bowl lathe

    If you are using a single phase induction motor for a motor, then no, you may not use a light dimmer (or any other speed controller really).

    To have electronically variable speed you will either need a universal/dc motor with PWM speed controller or a 3-phase inverter-duty induction motor with a variable-frequency inverter to control its speed.

    Induction motors are phase-locked to their drive frequency (60Hz in the US) and will always try to maintain their targeted RPM (typically 1800 or 3600RPM nominal). Aside from the fact that the inductive nature of such a motor would very likely destroy a light dimmer in short order, all a dimmer would do is increase slip under load which might initially seem like speed control until you realize that increasing slip really means a highly unpredictable RPM since the RPM will vary constantly depending upon the load... and not whatever "speed" setting you may have intended to dial in.

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    Sounds like a cool project. Make sure to post pictures .
    Most large variable speed lathes use both pulleys and motor speed control. This is because at low RPM VFD's driving 3 phase motors deliver very little power. They are aproximately constant torque. So if a 1800rpm motor provides 3hp then at 180 rpm you only get .3 hp and the lathe would stall too easily. At low speed you need gear (pully) reduction to let the motor run fast enough to provide sufficient driving power. I suggest googling to see the gear ratios on the powermatic 4224 or 3520b to see what to aim for.
    Good luck!
    Salem

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    Re: Making electric motor variable speed for bowl lathe

    Maybe a fully Variable belt design? I've seen designs for a cone-like design on other applications. Definitely pics!
    -Zach

    Reinventing the Wheel....One 800mg Ibuprofen at a time!

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    I have a Reeves drive lathe (Jet 1236). I have never seen a wood reeves drive lathe that turns slow enough for bowls.

    I would much prefer stepped pulleys and a VFD / 3 phase motor.
    Salem

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    Re: Making electric motor variable speed for bowl lathe

    My lathe is set up with stepped pulleys and a VFD/3 ph motor. We have the minimum run set at 30% and the motor is 1750 rpm. So on a 1/1 pulley set the min rpm is 525 and at 3/1 I can get down to 175 RPM which is good for medium bowls. If you are turning very large bowls you may need to go to a 6/1 pulley set to get slow enough, by very large I mean 36 inch diameter bowls.
    Most people who are into preparedness, didn't get there because it makes sense. They got there because they suffered and chose not to suffer again.

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    Re: Making electric motor variable speed for bowl lathe

    Quote Originally Posted by eyekode View Post
    at low RPM VFD's driving 3 phase motors deliver very little power. They are aproximately constant torque. So if a 1800rpm motor provides 3hp then at 180 rpm you only get .3 hp and the lathe would stall too easily.
    Interesting. Do you know what the torque calculation is like for the smaller DC VS lathes?

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    Re: Making electric motor variable speed for bowl lathe

    Thanks for all ya'lls help, I will definitely consider all of this. I was cruising around on CL and came up with the idea why couldn't I take a motor off something cheap, like an old treadmill, or something of that nature with a variable speed 1-2 hp motor in it that can handle heavy loads (sometimes VERY heavy). I know this opens up a whole new set of doors... but any suggestions? or is this a huge shot in the dark?

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    Re: Making electric motor variable speed for bowl lathe

    if you want to turn big bowls - very heavy then i suggest at least a 3 hp motor and 5 hp would be much better.
    Most people who are into preparedness, didn't get there because it makes sense. They got there because they suffered and chose not to suffer again.

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    Re: Making electric motor variable speed for bowl lathe

    Quote Originally Posted by dustin510 View Post
    Thanks for all ya'lls help, I will definitely consider all of this. I was cruising around on CL and came up with the idea why couldn't I take a motor off something cheap, like an old treadmill, or something of that nature with a variable speed 1-2 hp motor in it that can handle heavy loads (sometimes VERY heavy). I know this opens up a whole new set of doors... but any suggestions? or is this a huge shot in the dark?
    My (possibly incorrect) recollection is that most treadmills do use DC motors for their main drive-train. Such a motor would be suitable for a lathe, though I could not begin to say how it would compare with a traditional induction motor of some arbitrary size -- I really have not used lathes so I would be uncomfortable offering advice in that respect.

    If the motor has a built-in tachometer and such is combined with a suitable after market PWM controller that can make use of that tachometer, then it can potentially deliver near full power even at fairly low speeds because the tachometer will provide the controller with absolute feedback on actual drive speed (this is particularly true for tachometers with a fine feedback pitch), which the speed controller can then react to in real time to try and maintain the desired RPM even under widely varying load (literally up to full power -- even at low speed -- if that is what it takes to maintain the desired RPMs). Only when the motor is overloaded at a particular speed would its speed regulation suffer.

    However, to roll your own custom setup with an aftermarket speed controller and make it work with a motor you just happen to have on hand (as opposed to a purpose-chosen motor) will require that you have a good bit of electrical and/or microcontroller or speed-controller configuration experience. You might find a ready made solution, but I would not count on it unless you start out choosing each of your components to match a known workable solution package (you never know what info you may come across on the 'net).

    Whatever adventure you may decide to embark on, we all wish you the best and look forward to hearing back from you with regards to your progress should you choose to pursue such. Just because something may not be easy or trivial does not necessarily mean it is not worth trying if you enjoy the challenge and are not afraid of possible failure -- sometimes knowledge and experience truly are their own reward.

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    I wish Jim (froglips) would chime in as I believe he made a lathe with his father. Where is that guy???

    Anyway I have heard of people scavenging treadmill motors and doing cool things with them. But I suspect it will not have the power to make a decent bowl lathe. You can look at the electrical specifications on the treadmill if it is not close to 15A you know it will not even be close to strong enough. Even some 16" lathes (which is not large for a bowl lathe) move up to 220v.
    Salem

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