contractor saw belt vibration

[-MIKE-]

Hate to say I told you so, but..... no wait a sec. In this case, love to say I told you so. :-)

[Larry Jaques]

On Sat, 07 Nov 2009 12:12:12 -0600, the infamous dpb scrawled the following:

I think I got 4' of it for $17 from Harbor Fright when I bought mine. I don't think I've spent less than $20 on a belt (serpentine) in the past decade, though. How much are v-belts going for nowadays? Hmm...

35.5" for $11.05? Less than I thought. Still, the lower vibration and ease of use for the link belt makes it a winner in my book, even if the price is $6 higher.

Yeah, variances in machinery quality and style will make a difference.

-- The Smart Person learns from his mistakes. The Wise Person learns from the mistakes of others. And then there are all the rest of us...

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[Christopher Glaeser]

Is it OK to run the motor without belt or load to test the balance of the motor and pulley?

Best, Christopher

[upscale]

Table saw motors are designed to run with a load on them. I'd say that it changes the mechanics of the situation. You might even damage the motor. It's the balance of the motor and pulley running together that you should be concerned with.

[-MIKE-]

Yes. That's a good way to rule out some sort of motor mount problem.

[-MIKE-]

Where did you hear this? I don't think it's a problem.

[krw]

Table saws (real ones anyway ;) use induction motors. Unloaded they'll spin only a few RPM faster than a loaded motor so it's not going to hurt a thing to run it unloaded. The motor doesn't require the load for cooling (as a fan might) so heat isn't an issue either. Go for it.

[Christopher Glaeser]

Thanks. It's running smooth with the new belt, but was curious to observe without the belt.

Best, Christopher

[upscale]

I didn't hear it anywhere and could well be wrong about it. However, tablesaw motors are built to run with saw blades being driven by them putting a load on the motor. It seems sensible that's the optimum condition for them to be running when you're looking to correct any issues. And yes, I have seen and experience a motor that turns and builds speed fine, but stalls when the belt is connected.

You can confirm a car motor runs fine at idle, but I'd prefer my car to be passed under test conditions when the car is actually moving or perhaps on a dynometer when the motor is under stress. Again, that's what seems logical.

[-MIKE-]

I didn't question about any of that, which is why I cut it out of my reply.

You said it might damage the motor. I can't say for certain, but I don't think it would. That's why I asked for more info.

[upscale]

Sure, you could be entirely right. No argument there. My knowledge of electric motors doesn't extend to whether they might have governors for speed or the bearings might be subject to suffering from too much heat that might be generated from a motor running without load.

It's not my motor, so unless someone asked me specifically to find out and that person was a friend, then I'm not going to spend what might take me considerable time to find out. Guess that's a little selfish, but if I acceded to all similar requests, I'd never get anything done for myself.

Makes me think of the guy who has been asked to shorten a metal exterior door. Much of my decision for a job like that, (if I felt I was capable of doing it) would revolve around my relationship with the person who asked me. Unfortunately, there's any number of people, (friends can sometimes fall into that category too) who will take advantage of you every chance they can. For me anyway, close friends fall into the opposite category and treat me well despite my flaws and weaknesses.

[Larry Jaques]

On Sat, 07 Nov 2009 23:13:52 -0500, the infamous [e-mail] scrawled the following:

Hmm, "damage the motor"?!? I doubt 'er.

And how -else- would you discern whether it was the motor/pulley combo or the arbor/blade end which was bad when troubleshooting or tuning, eh? I wouldn't hesitate at all in running any woodworking machine motor alone, with or without a pulley, even.

Unless you have seen warnings on specific combos and can refer us to them, I wouldn't worry Christopher about it. I know of no such warnings on any U.S., Taiwanese, Japanese or Chinese machines from any century.

Thinking back, I do seem to recall some toys with universal motors on them which would blow themselves up with no load, but nothing in the tool area comes to mind.

Got cites?

-- The Smart Person learns from his mistakes. The Wise Person learns from the mistakes of others. And then there are all the rest of us...

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[Larry Jaques]

On Sun, 08 Nov 2009 00:25:06 -0500, the infamous [e-mail] scrawled the following:

Optimal, yes. What is there on a normal motor to destroy? The RPM is self-limiting by design, with 1,725 and 3,450 being the 2 norms.

And what makes you think that they would run any slower (more than 1 percent?) with the blade and belt attached?

Steam and internal combustion engines are the only power plants which really need loads (flywheels, etc.) AFAIK.

There's a whole lot more moving mass changing directions in an auto engine, suh.

-- The Smart Person learns from his mistakes. The Wise Person learns from the mistakes of others. And then there are all the rest of us...

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[krw]

The unloaded limit would be the synchronous speed (1800 or 3600). An induction motor can't turn faster than the AC line feeding it. When loaded fully the motor "slips" to 1725/3450, or whatever is on its plate.

Note that a saw turning a blade is not fully loaded. In fact it takes very little power to just turn the blade. Hogging out a 3/4" wide 2" deep dado in Oak takes a little more.

The flywheel, in this case, is only needed to force rotation to the next cycle, not as a governor. That is, to maintain rotation not to maintain integrity. ;-) A steam (or nuke) power plant and turbine generator are better examples.

A car has a whole lot wider RPM range than a table saw, too.

[Scatter]

That could be the case if the motor was "series wound" as without a load they can just keep getting faster and faster. I don't think any power tools would be purely series wound.

[-MIKE-]

Series wound. Does that mean what I think it means? As opposed to parallel wound? Or something totally different?

[krw]

It means that the armature and field are wired in series.

As opposed to shunt wound.

Motor characteristics:

[-MIKE-]

[Scatter]

Correct, and I forgot to say that it would only apply to DC or universal motors - ones with brushes. Perhaps angle grinders are series wound - I really don't know though (they're probably compound wound instead - sort of a combination of both series and shunt).