What is the best way to mount a pulley on a smooth shaft?

Lon Aguiar

Lon Aguiar

Joined
May 23, 2007
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I am setting up my KMG for variable speed and I picked up a new Leeson 1.5 hp 3ph motor on eBay for dirt cheap. Only problem is that the shaft has no keyway. It is a pump motor with a 5/8" shaft that is threaded on the end. I'm trying to figure out the best way to mount a pulley on the motor. Here are the option I'm considering.

1) Use a fixed bore pulley. Drill a dimple in the shaft and just use the set screw.

2) See if a a motor or machine shop can mill a keyway in the shaft.

3) Use a pulley that uses a tapered bushing to mount to the shaft. I was looking at the QD and split taper bushings and pulleys. They clamp to the shaft and also use a key. I am just not sure if if the bushing will clamp to the shaft tight enough by itself (no key) so it won't spin.

4)Use a keyless bushing like a Trantorque. These don't need a key but I can't seem to find a pulley to use with it. I'm not sure if a regular pulley(with a keyway and set screw) will work.

Any ideas what would work best?

BTW, when in looking into the Leeson motor I found out that all of their 3 phase motors over 1 hp are inverter rated.

Thanks!
Lon
 
said:
1) Use a fixed bore pulley. Drill a dimple in the shaft and just use the set screw.
Click to expand...

You can file a flat easier than drilling a "dimple". That is working for me on my clone
 
I personally would have a keyway put into the shaft. Other options will work, but if the pulley is already made for a key, that is how it was designed to be affixed to a shaft. The keyway will result in a decreased chance of problems down the road. Just my opinion.
 
A keyway is not any problem to add. Get an 1/8 flat wheel burr for your dremmel or die grinder and cut a slot. Widen it slowly until it is almost 1/4". Switch to a 1/4" wheel burr and finish off the keyway. It should take about 5 minutes to do this. The two burrs will cost very little. If possible, get carbide burrs. ( use different width burrs to fit the keyway on your pulley).
Stacy
 
Adding a keyway would be the "proper" solution to the problem.

However, you might double-check that motor; a pump duty motor, especially one without a keyway on the shaft, may not have the proper bearings for a side load. (IE, the belt tension pulling the shaft to one side.)

It's bearings will be optimized for axial loads- in line with the motor shaft.

You shouldn't have a problem, but it is an issue you should look at. Wouldn't want to go through the time and effort only to use a motor that'll develop bearing problems in less than a year...

Do NOT just drill a dimple for a setscrew; all the torque will be focused on that setscrew, and it WILL strip under even light to moderate loads.

Tarantorques and similar shaft-clamping systems work fine- the TT can hold an enormous load, the BattleBots guys use them for drives and weapon shafts a lot, and some of them use 15HP motors overvolted to 20+HP - but they're also somewhat expensive, and often tough to find a "conventional" V-belt type pulley.

Doc.
 
Stacy,

I thought about trying something like that but was afraid I would mess it up. I was going to get a solid shaft coupler and grind away the area over the keyway, slide the coupler over the shaft, clamp it down and use the exposed keyway in the coupler as a file guide. I think the keyway is the way to go. I'm not really keen on using just the set screw to hold the pulley in place.

Thanks,

Lon
 
Doc,

I've ruled out the set screw only option. Going with the keyway.

These are the bearing specs from the Leeson website on this motor.

Bearings:
203 Double-sealed ball bearing, shaft-end; 203
Double-shielded ball bearing, switch-end. Shaft-end
bearing is locked to limit axial movement of the shaft.

Not sure if this is o.k. or not. They make a single phase version with a keyed shaft that uses the same bearings. The motor is brand new and it was only $30 so it's not the end of the world if the bearings go at some point.

Thanks for the help,

Lon
 
Being a Leeson (good American brand) you're probably okay.

I've seen some no-name or unbranded motors (I don't think "Whirlpool" makes their own motors :D ) that only had bushings in the pump end, or ball bearings, but noticibly undersized (since they really only need to guide the shaft, not necessarily support it against major side loads.)

The "bearing locked" part just means there's a step or snap ring on the shaft that keeps the shaft from walking forward or back (more than a few thou, anyway.)

I think you'll find that accurately filing a keyway will prove difficult, even with a coupler as a guide. You might call a local machine shop and have the slot milled. It'd be pretty easy to get the keyway out of whack or add stress risers to the shaft, if cut by hand. (But then, I have three machines in the shop I could do it on... your mileage may vary. :D )

Doc.
 
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