Lathe Motor Replacement Conundrum

[N Hurst]

I was gifted a basic ("Professional Woodworker" brand) lathe with a dead 3/4 horse motor. I have an old Dayton 3/4 horse motor (which is much bigger and heavier than the one in the lathe) which I'd like to use for the lathe, but the spindle on the "new" replacement motor is maybe 1/16" too large for the pulley from the dead motor.

How should I go about getting the pulley on the motor? Should I crank up the motor and just use sandpaper on the spindle until the pulley fits or what? I'm hesitant to try to drill out the pulley because I don't want to make the hole off center and ruin a mostly irreplaceable part.

Also, since the "new" motor is so much larger than the dead one, I have to relocate the motor to below the lathe's motor enclosure... would one of those link belts be a good option for connecting the pulleys or should I just go to an auto parts store and try to find an appropriate size belt there?

Thanks! Nathan

[dpb]

N Hurst wrote: ...

Purchase a pulley of the proper diameter and bore.

Did the original motor run at the same rpm as the replacment?

...

Either way would work...

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[N Hurst]

Any recommendations on where to go for one?

Rather than a flat side section on the spindle like most motors I've seen, my motor has a notch cut out of the spindle in which a small square metal peg was inserted.

I have no idea. There is no plate of any kind on the original motor, and aftermarket support of this brand of machine appears to be pretty slim. The replacement is a 1750rpm, and I'm pretty sure a machine of this level wouldn't spin at the 3000rpm mark.

[N Hurst]

I hate to double post, but I found someone with a Craigslist ad for the same lathe I picked up:

[Tom Veatch]

(my preferred online "go to") (my preferred local "go to") do a Google search for "sheave" any your city location and it may bring up some local outlets.

A square key fits in the notch and mates with a similar notch in the sheave to prevent the sheave spinning on the shaft. If you check the motor dataplate, find the frame size, and compare it to the entries in a NEMA frame chart, it will give you the diameter of the shaft and the dimensions of the notch. Or, since the key slots are standardized based on the shaft diameter, you can just get one that matches from the same place you get the sheave.

For example a motor with a NEMA 56 frame has a 5/8 dia shaft which takes a 3/16 square key. See for example:

Any keyed sheave/pulley fitting that shaft would also have a 3/16 keyway. Here's an example

the description and specs indicate that the sheave has a keyway.

A 12" length of 3/16 keystock from Grainger is about 95 cents if you want to cut your own.

Tom Veatch Wichita, KS USA

[dpb]

Local hardware for a start, motor shops and/or auto parts places and other industrial distributors.

There's always the online route of McMaster-Carr, Grainger, et al, but ordinary items like this shouldn't be any problem locally.

That's typical keyed way -- more than likely 3/16". Key stock or precut keys are a dime at the hardware store or may well come w/ the pulley.

...

That's why I asked -- if you had a common 3450 rpm motor, I was betting the original was likely 1725.

[N Hurst]

The only 4 step pulleys I can find have minimum sizes ranging from

1/4" larger than the original at the smallest step to 1/2" larger at the largest step. I know that will yield a higher overall rotation speed, but does anyone out there think it will be any more dangerous than otherwise?

Also, after measuring, I discovered that the original pulley bore is

1.5cm! I'm glad I came here for help, because I hadn't even thought about this thing being metric! The pulley steps on the original are 4, 5, 6, and 7 cm, and the replacement ones will be 1-3/4", 2-1/4", 2-3/4", and 3-1/4".

-Nathan

[dpb]

The speed difference will be the ratio of the diameters--I didn't do 'em all, but the first is roughly 11%; I wouldn't worry at that difference.

The other choice still, of course, is to get the existing pulley rebored at a machine shop--depending on whether you have a local kind-hearted retiree w/ a shop in his basement you might get it done pretty inexpensively; commercial shops tend to be pretty pricey.

--

[Tom Veatch]

You'll probably be OK. The important thing is the Pitch Diameter for the belt section you'll be using and that's not obvious from the OD. It depends on where the belt rides in the groove.

You sure about the 1.5 cm measurement? The closest I see to that in the IEC frame charts is a 71 frame with a 14 mm shaft.

Tom Veatch Wichita, KS USA

[Leon]

Have you looked into having the old motor repaired?

[N Hurst]

No, I haven't. I'm not sure it would be worth it. It's not a very impressive specimen, and I think it would probably cost me more than $20 to have repaired, which is what a new belt and pulley would cost me.

Here's a photo of the old motor and the "new" one, side by side:

tells me that the 3/4 hp I'd get from the Dayton brand motor would be better than the 3/4 hp the unbranded one would give me.

I was under the impression that small motor repair was generally a comparatively expensive proposition. If I'm going to be out around $20, wouldn't it be better to have a more robust motor driving things than repair something that's already broken down once?

And to Tom:

I'm not 100% sure on my measurements. I've been using the "inside the house" tape measure, which sometimes doubles as a toy for my 2 year old son, so you're most likely right in that it's 14mm. I would hope the motor would have that information on it, but I'm learning to not expect too much from these cheap imports. :-)

-Nathan