Treadmill/Variac controller

I am building 6" lathe in my spare time and intended to use treadmill dc motor. My thought was I would gear the motor to raise the rpm to a stronger torque band at a lower spindle speed, something like a high stall race torque converter in a race car.????? Yes/No?
 
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Hi Charles , to answer your question , yes . My thought is just like yours , gear the motor so that it is at a higher RPM turning a counter shaft at a slower RPM , giving you more torque at your spindle . Reading RJ's posts that is what he is doing , plus a lot of other stuff .
 
Take note of the other limitations. These DC motor can spin at some really high speeds. . . much to high for a machine in most cases, but they do have limitations. What you're adding at the low end, you will be taking from the high.
 
I am using the stock 602 pulley arrangement. In the low/low configuration, the pulleys provide an 11.5:1 reduction in speed. In the med/low configuration, it is 5.75:1. The OEM motor is a 1725 rpm while most treadmill motors are over 3,000 rpm so there is an additional 2:1 speed increase that needs to be addressed as well. Pulleys will do the job but in order to keep the driven pulley a manageable size, the drive pulley must be fairly small in diameter which leads to the possibility of belt slippage. A solution would be to use gear belts rather than v belts.

I am finding that an overall speed reduction of 5.75:1 from my 4090 rpm motor plus the controller with feedback meets 99% of my requirements, giving me an operating range from 10 rpm to 800 rpm ( I limited the maximum motor rpm). If I require a higher speed, a belt change can get me to over 6,000 rpm if I were crazy enough to do so. From a practical standpoint, I could work nicely with two pulley settings, the 5.75 and 1.44 speed reductions giving me an operating range from 10 to 3200rpm.
 
Now that I think about it I should simply use 1/2 HP AC motor and save the DC treadmill motor for some other project.
 
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If you elect to use a single phase induction motor, you will want a larger selection of pulleys and/or gears to effectively cover the required spindle speeds. Not impossible; it's been done that way for well over a hundred years. Unless you have source of pulleys and gears, buying new will be a significant expense. Speed selection via mechanical means would probably require some six to ten different settings. A variable speed drive can cut that down to one or two.

I would suggest considering gear belt pulleys rather than v belt. Yo will get much more torque for a given sized pulley. In my case, the 602 already uses a gear belt for the initial speed reduction but final drive to the spindle is a 3L belt. This effectively limits the maximum torque to the spindle to around 10 lb-ft. A gear belt can transfer much greater torque with smaller pulley size and belt tension, resulting in less wear and tear on the bearings.
 
Thanks very much for your reply and advice of which I am going to make use of. I will go with the gear belt system. This lathe that I am making is in it's infancy. For the spindle I have some 2" deflector sheave shafting that I will make use of and double row thrust ball bearings for the spindle. I will bore a 1 5/8" through hole in the spindle shaft. I'll post my progress after the holidays. Thanks again and have a relaxing happy Christmas.
 
Charles , what is your lathe ? Will you be running a countershaft ? RJ , what is a 602 ? The mill I want to convert has a big pully on the spindle that is approximately a 6" dia . I don't have the pully that will go on the countershaft . But like RJ says don't have it to small or it will slip . RJ with my spindle pully at 6" and my countershaft pully at say 3" what size pully would you recommend for the other side of the countershaft (the big one)(I have room to go big) and the primary pully on the motor ?
Thanks , Mark .
 
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Charles , what is your lathe ? Will you be running a countershaft ? RJ , what is a 602 ? The mill I want to convert has a big pully on the spindle that is approximately a 6" dia . I don't have the pully that will go on the countershaft . But like RJ says don't have it to small or it will slip . RJ with my spindle pully at 6" and my countershaft pully at say 3" what size pully would you recommend for the other side of the countershaft (the big one)(I have room to go big) and the primary pully on the motor ?
Thanks , Mark .
Click to expand...
602 = Grizzly G0602. Sorry, I comment so much about it that I just use the abbreviation.
 
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