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View Full Version : how to figure out the missing step pulley

jh
04-23-2009, 07:47 PM
I have a drill press I'm trying to repair that did not have the drive step pulley. It needs about 7 steps IFIRC to match the driven side. How do I go about figuring out what pulley I need ? Thanks James Helmuth

The Artful Bodger
04-23-2009, 08:07 PM
Is one not a replica of the other?

Andrew_D
04-23-2009, 08:31 PM
Is one not a replica of the other?

Maybe...maybe not... I have a 20 year old Tawain drill press with an intermediate step pulley. The spindle is 5 step, intermediate is 5 step, but the motor is only 4 step.

But since the OP didn't specify an intermediate pulley, then yes I would agree...if there is no intermediate, then I would make the spindle and motor pulleys match.

Andrew

Frank Ford
04-24-2009, 12:39 AM
In my limited experience, stepped pulleys mate up with various combinations of other stepped pulleys. I'd start by goofing around with the drive ratios to come up with the appropriate speed range.

Once you have the general sense of that, then it's just elementary geometry to figure out the steps. After all, the same belt has to fit on each step, so you can work out the appropriate differential of diameter/circumference to achieve that.

It may well be that the mating pulley is the inverted form of the other. In the case of my little turret lathe, it worked out differently.

Ian B
04-24-2009, 09:10 AM
Sounds like it's the driver (motor) pulley that's missing. The pulleys don't need to be identical - there's a good case for making the driven pulley steps larger than their corresponding driver steps, to give an overall reduction.

If placed side by side on a flat surface, axes parallel, one 'pointing up' and the other 'pointing down', each of the steps should touch. The sum of the diameters of the steps should be equal, eg. 2" driving a 6", 3" driving a 5", 4" driving a 4" etc. This keeps the belt at about the same tension, whichever step it's used on.

Ian