Hello everyone.
I'm trying to set up a dc variable speed motor on my model 9c SB. Here is the dilemma I have, can I just set up a motor without using existing pulley system? What I mean is can I just use one belt from motor to the chuck shaft or using pulley (2 belts) is a must?
My current motor is 1/4 hp and new DC motor is 1.5HP, so I think I will have enough torque, maybe?
You can try it, as it won't cost you more than a small flat belt pulley to put on the dc motor, so you can run the flat belt
right to the motor. Oh, and a means to tension the belt of course.
You'll probably find it does not work well, predicted by looking at the relative sizes of the motor pulley you are using
right now, vs the size of the large diameter pulley on your countershaft assembly. Figure out the speed reduction from
that setup, and then figure out how fast the spindle wants to be going, based on the motor speed and that reduction,
figuring the countershaft speed is about the same as the spindle speed. On the center set of cone pulley steps, it's more
or less one-to-one.
You'll find that you probably need to restrict your dc motor to less than 1/4 speed to make it all work out, even with
a pretty small dc motor pulley. Also be aware that flat leather belts don't like to be driven by really small pulleys,
you'll find a fair amount of slippage there.
In my case I deleted the countershaft from a small milling machine, but most of the speed reduction was betwen the
pulley on the countershaft and the pulley on the spindle. Truly the countershaft eats a lot of power that is better off
delivered to the cutting tool. In my case I used a four pole 3 phase motor and can run it between 10 percent of nameplate
speed, and 150 percent.
Jim