Is there a good way to fit an old gear onto a new motor?

I have an old machine that I would like to give a new motor. The old motor is a century or so old US made 1 hp AC induction motor, the motor I would like to replace it with is a 1.75 hp DC motor from a treadmill. I think I have the electronic controls covered. My next problem is fitting the DC motors shaft to the old gear. The DC motors shaft is slightly smaller than the old AC motors shaft. If I came up with a spacer/sleeve to make up the difference in the shafts diameter would a spacer sleeve hold up to high RPM, and not have balance or other issues? My current goal is to put the new DC motor inside of the AC old motors casting. This would keep the look of the original machine but giving it a variable speed motor. Should I just scratch that idea an do some kind of jackshaft, or just give up and try and come up with replacement AC motor?

Sorry if this is in the wrong section or just a stupid question. Wasn't really sure where to post this, or if this has been covered already.

A 100-yr-old induction motor will not turn fast enough to make balance an issue. The highest possible speed is 3600 RPM, but if it's 100 years old, the speed is probably more like 1800, 1200, or 900 RPM wide open - ignoring induction motor slip. If you make the sleeve ID and OD fit well and make them nice and concentric, you should be fine.

Before you work out how to sleeve up the treadmill motor shaft to match the existing gearbox, think the physics through.

Treadmill motors often develop their (questionable) HP at high RPM, 9000 or so. If your motor turns 9000 and you want 1 3/4 HP at the gearbox you will have to add another reduction to match the speed/torque of the the treadmill motor to the existing gearbox input. Look at the nameplate RPMs. That's where you start.

Motors are pretty much constant torque machines. The full load torque is a rough function of the load current. If you run a 9000 RPM motor at 1800 via a speed control, the delivered HP will be 1.75 X 1800 / 9000 = 0.35 HP. Can you live with that?

Motor fans are usually designed to work most efficiently at rated RPM and become less effective at lower RPM. I don't know what your machine does but if it has a high duty cycle, the motor if run at 1/5 rated RPM may turn too slow to cool itself.

thermite said:

Yes.



Your 100 year-old AC motor can probably be rewound. If it even needs that, rather than just a good cleaning, new leads, re-varnishing, and new bearings. A comparable 1 HP AC motor is not hard to find.


Bill

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plus one

The older motors are a damn site heavier duty motor compared to newer ones of similar hp rating. They can take more load and don't build up the heat.

Are you just wanting to make the older motor run at different speeds?

Have you checked this out?
Compact Micro AC Drive<BR>1/4 to 3hp, Single or 3 phase <BR>Hitachi NES1 Series | Search All AC Drives | Marshall Wolf Automation, Inc.

alonzo83 said:

plus one

The older motors are a damn site heavier duty motor compared to newer ones of similar hp rating. They can take more load and don't build up the heat.

Are you just wanting to make the older motor run at different speeds?

Have you checked this out?
Compact Micro AC Drive<BR>1/4 to 3hp, Single or 3 phase <BR>Hitachi NES1 Series | Search All AC Drives | Marshall Wolf Automation, Inc.

Click to expand...

The motor is for a bandsaw primarily for cutting patterns in wood. Ideally I would just keep the old motor going. But the variable speed idea might come in handy for cutting metal with a different blade and a cooling system (the saws were geared for wood, metal cutting or animal bones depending on what the original buyer wanted). The old motors housing is cast into the saw partially, and the motor is missing everything aside from the coils and the castings. It is repulsion start, or was so tracking down the antique starting mechanism is going to be something of a chore if not impossible.

Thanks for all the replies, and for some more options to consider than the treadmill motor.