lathe problem

[Timewarp]

Well i went to use my lathe today, turned it on and hear terrible vibration coming from the motor??

The lathe is a 11x26, my first, and my machining eduction is limited to this board and some books. The picture shown is the drive motor on the bottom, driving an intermediate pulley with a toothed belt. When I turn the pulley by hand, every few revolutions the belt will tighten and almost bind. It seems to do this whether or not the belt is tight or loose. With the belt off the motor runs fine (no Load) and the pulley turns ok. the belt looks ok.
The binding under power is what is causing the vibration. Pulleys look aligned ok.
Has someone else been here?
Paul L

[Mike Burdick]

Okay, I’m going to ask the obvious question: Does the spacing in the belt cogs match EXACTLY the ones in the pulleys? Check both pulleys. If they don’t, then the cogs will ride up on the pulley and cause it to tighten and loosen as it turns. Depending on the error, it may take several revolutions to pull out.

By the way, what is the Brand name of your lathe? Not that it matters...I'm just curious.

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[This message has been edited by Mike Burdick (edited 02-03-2005).]

[Doc Nickel]

That looks a great deal like the drive end of my old Grizzly 9" x 19". I had a problem with the motor pulley coming loose on the shaft and walking one way or t'other. This caused the itty-bitty Vee-belt to twist and eventually break.

Check the setscrew and/or key on the motor pulley, and double-check the alignment, Use a visual aid like a ruler or flatbar, not just a Mark 1 Mod 0 eyeball. Mine "looked" okay the two or three times I fiddled with it.

Doc.

[Timewarp]

Mike, It does feel like the cogs on the belt are riding up on the pulley, Can this be possible? I'll have a closer look at the cogs. It used to run just fine!
I had a similar problem with a small crane last summer. The starter bendix gear almost fit perfectly with the ring gear on the flywheel- but not quite. I must have taken the starter off and put it back on 20 times on my back in the rain before I figured it out. I'm a slow learner, but stubborn!
The lathe is from Modern tool (Edmonton?) It's the only one I've used, not a Cadillac but fun and useful.

[C9]

If the pulley setscrew is working loose, a good cure is to stack another setscrew on top of the first one after the first one is properly torqued.

Most times the pulley setscrew threads are deep enough to take two setscrews.
I like doing it this way better than using a thread locking compound.

[Rex]

Sounds like the belt may be stretched in one section. Order a couple of belts, one being a spare.

[lynnl]

Your statement "....When I turn the pulley by hand, every few revolutions the belt will tighten and almost bind. It seems to do this whether or not the belt is tight or loose. .."

Do you mean 'every few' revs of the pulleys or of the belt?

d'ya suppose a few of the cogs could be partially detached from the belt backing, so that they sometimes shift outta position?

I once had a motorized Rockwell table saw that was driven by a small (about 5" id.) cog belt. It would occasionally have that problem when small chips got caught up between belt and the cogged pulley. Tho with that one it would usually tear the belt since it was so small and tight.

With a metal lathe I'd think metal chips could very likely get in there and do some belt damage.

[This message has been edited by lynnl (edited 02-03-2005).]

[Elninio]

Somethings probably loose, or not inline?

[Elninio]

Also did this happen overnight>?

[wierdscience]

XL timing belts have been known to break internally.It may be as simple as changing the belt.

[nheng]

Timewarp, I've got a dumb question. Shouldn't that black tensioning roller be roughly 180 degrees from where it is now, applying pressure against the timing belt from the right side as we look at it ??
Den

[flange]

Quick question if you take the belt off does the motor turn freely? Sometimes if a motor has a high side load/belt pull the bearings will fail. If the motor is one that uses bushings rather than bearings they can actually wear to the point of the armature hitting the stator.Much noise and vibration.

[Timewarp]

OK guys, thanks for your help. I went down to the shop after "work" and got it figured out, feel a little dumb though.
Alignment problem. The motor pulley has side walls that are a very tight fit to the belt. any misalignment and the belt wants to walk up the sides.Also the side of the belt is getting a tiny bit frayed, so I'll have to get a replacement. Nice to be making chips again.
Paul