Motor Help !

[Flute Maker]

I have a 1/2 hp....1750 rpm motor on an old Craftsman lathe. The model is 113.12790. It has started getting hot and hums when I turn it on but if I spin the shaft or do a light pull on the belt it comes..The shaft size is 1/2" on...

I have a 1 1/2hp 3450 rpm motor model 818320...The shaft size is 5/8"....I would have to buy a step pulley to fit the 5/8 shaft but would this work ? The step pulleys on the 1/2 hp one begin at 2 in and go on up to to 4 in. It works good and a friend gave it to me so I have nothing in it....What size step pulley should I use to get it to work like the 1/2hp one ?? Thanks !!

Or what do I need to do to the 1/2hp one ??

 

[Sully]

Since the 1.5HP motor runs twice as fast you will need step pulleys that are half as big. It will be tough to find a step pulley with a 5/8" bore with smallest working diameter of 1".

For the 1/2HP motor, it sure sounds like the start cap needs replacing. As to it getting warm, how warm? A motor should be warm but not so hot that you can't leave your hand on the cover for 15-30 seconds. And where is it getting warm? Is it warm all over or just near the ends. If it's just near the ends the bearings could be running dry.

If it were me I would replace the capacitor and bearings.

$0.02

 

[Gotcha6]

You'd be spinning way too many rpms on the spindle to do that. The motor pulley would have to be halved in size to get the equivalent rpm at the spindle, so a 1 - 2" step pulley would be in order and probably not available in a 1/2" v belt configuration. You could put in a second shaft with with pulleys on it to reduce the speed. A 2 & 4" should do it. Lotsa trouble, huh? :confused_ Probably just keep your eyes peeled for a used 1725 rpm motor.

 

[jhreed]

Double the size on the driven pulley. This would make your arbor rpm correct.

 

[Sully]

It might be hard to double the driven pulley if it's in the headstock of a lathe. On my Craftsman lathe, for example, it would be impossible to double the size of the headstock pulleys.

 

[ehpoole]

For the 1/2HP motor, it sure sounds like the start cap needs replacing. As to it getting warm, how warm? A motor should be warm but not so hot that you can't leave your hand on the cover for 15-30 seconds. And where is it getting warm? Is it warm all over or just near the ends. If it's just near the ends the bearings could be running dry.

Just an FYI, if it is getting hot while it is stalled (turned on but not rotating due to a bad starter capacitor), then that would be normal -- when and induction motor is not spinning it is drawing full locked-rotor amperage (and/or overheating the starter coils, if so equipped) at the same time the fan is also not cooling since it, too, is stalled. Once you get it started spinning the motor should function as normal.

If it is just the starter capacitor (and you haven't burned out the starter windings (if equipped) by leaving it stalled), then all the motor likely needs is a new starter capacitor to restore it to normal operation. Just don't leave the motor stalled for more than a few seconds before you give it a startup-spin until you get the capicitor replaced.

You'll likely find that adapting a 3450rpm motor to a 1750 rpm job is simply not worth the effort unless you intend to go all out with variable frequency drives and the like (and the motor you have likely isn't intended for variable frequency drive). It isn't a bad adaptation for single-pulley setups, but in multi-pulley transmissions it is much more easily said than done -- even the belt has a minimum permissible radius that may be greater then the half-sized pully you would need to achieve compatibility.