Crazy band saw motor idea?

[Pirate]

After reading a post on increasing band saw motor hp, I had a thought.
I have a stash of 1/2 - 1 hp motors.
Would there be a problem, if I put a double pulley on the motor on the saw, and belted an additional motor to it? Making a 2 motor saw.
Not sure if motors run at the exact rated speed.

[Splinter Puller]

One thing I can think of is the amp loading of having them both start at the same time. It would be interesting to see.

[TDKPE]

Someone here did that. I don't remember the details, but he used one motor for most work, and fired up the second one for resawing and such. It just spun when not energized. Or he clutched it by slackening the belt. I don't recall the details now.

Synchronous speed is 1800 rpm, and unloaded speed with be only a few rpm less than that (it can never be synchronous if it's driving itself). They will slow down a few percent from unloaded to full-load speed in proportion to the load, so even if they're a few rpm off, it won't make much difference unless one of them is a specialty motor, which you're not likely to have with small single-phase general-purpose motors.

[thewizzard]

Could it be done, sure Why waste the time, money, and effort developing a Rube Goldberg machine that already has a better solution. Use a properly sized motor

[Pirate]

Waste of time, vs. money.
Of course a new motor would be best.
Time involved would be very little to mount a motor. If someone had a spare motor, but didn't want to buy a big motor, it would be a simple way to do it. (Simple for some people)
I like the idea of energizing the 2nd motor just for heavy cutting. Don't see any reason to clutch it. Let it spin.



Could it be done, sure Why waste the time, money, and effort developing a Rube Goldberg machine that already has a better solution. Use a properly sized motor

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[stav]

Your question reminded me of this

[Pirate]

Change the driven pulley to a sprocket and that would work. Variable speed also!

stav said:

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Your question reminded me of this

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[TDKPE]

If you want to do that, get a two-groove sheave from Surplus Center, with a pitch diameter the same as the OD of the original motor sheave (or about .15" smaller, which is really where the PD is anyway for most 1/2" belts), or close to that at least. Go larger rather than smaller if you have to. Also buy the same cast iron sheave in a single groove version for the secondary motor. That way the PDs are exactly the same for the belt that connects the two motors. The backup motor drives through one of the grooves of the main motor, and the other groove drives the arbor.

Watch the pitch diameters of those sheaves, as they're grooved for both A and B size belts. A belts, like 4L belts, are 1/2" across, and is what the saw has now. But it will sit deep in the groove, so the PD is smaller with the smaller belt (which is why they show two PDs for the two belt sizes they're designed for), and that's what you want to match, or shoot for at least. OD means nothing here.

You could run a longer belt over both motor sheaves, I suppose, but it would only be turning about 90 degrees over the sheaves assuming they're side by side, and slippage may be a problem.

[kurt18947]

When running single motor, how much of the operating motor's output would go to spin the non-operating motor, I wonder.

[TDKPE]

Easy enough to estimate. Run the main motor with no belts, and take a current reading. Connect the belt to the aux motor (no belt to the saw), and do it again. Plug the numbers into (BLA-NLA)/(FLA-NLA)xHP where FLA=full-load current (nameplate), NLA=no-load current, and BLA=belt-load current, and HP=nameplate shaft power rating.

Efficiency and power factor will both be very low at just belt load (and internal wind and bearing losses in the aux motor), but the current will be more or less proportional to shaft load anyway, at least close enough for this sort of thing.

The belt will probably be the biggest loss, depending on tension.