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rotate
06-25-2009, 02:29 AM
I have a DC motor that I'd like to use to replace the AC motor on my small lathe. I believe it came off an electric caddy which is power by 12V battery. The problem is that the shaft coming out of the motor is stubby. I need the shaft to be 20mm in diameter and a great deal longer. The original shaft is 8mm in diameter. What would be the best way to extend the shaft? I'd like to avoid welding or brazing.

Also, based on the size of the motor, what would you say is the maximum power that this motor can produce? I'm think somwhere around 1/4 hp. Unfortunately, there's no name plate on the motor.

http://i7.photobucket.com/albums/y287/rotate85/DSC01416.jpg


http://i7.photobucket.com/albums/y287/rotate85/DSC01417.jpg

John Stevenson
06-25-2009, 04:40 AM
Look for another motor, that one is too much work / hassle to bother with if you don't have to.

.

Circlip
06-25-2009, 08:39 AM
Clear, succinct and a blind alley Sir John. We could have had 19 pages, 125 postings and 15 hijacks out of this one, Cheers :D

Regards Ian.

rotate
06-25-2009, 12:28 PM
Look for another motor, that one is too much work / hassle to bother with if you don't have to.

.

Sir John, I agree, however the nature of this hobby is sometime to take the most circuitous route possible :D. I have to learn when to walk away from something so that my time can be spent on something more productive or entertaining. Sometime it gets personal, which means that I'll end up spending $$$ on tools just to fix something that's only $.

Just for fun, if you did have to do this, how would you do it? Would you remove the rotor and then modify the shaft? How about 20mm shaft with 8mm bore and then use a setscrew to hold it? Will it hold?

jbacc
06-25-2009, 12:43 PM
Sir John, I agree, however the nature of this hobby is sometime to take the most circuitous route possible :D. I have to learn when to walk away from something so that my time can be spent on something more productive or entertaining. Sometime it gets personal, which means that I'll end up spending $$$ on tools just to fix something that's only $.

Just for fun, if you did have to do this, how would you do it? Would you remove the rotor and then modify the shaft? How about 20mm shaft with 8mm bore and then use a setscrew to hold it? Will it hold?

In my completely humble and uninformed opinion :-), I would go the route of 20mm shaft with 8mm bore and a set screw.

Good luck.

Joe...

lakeside53
06-25-2009, 12:44 PM
I don't see enough protrusion to have an unsupported extention. If you can have a pilot bearing on the end of the extention, and mount the motor and bearing in a common bracket, then maybe the set screw idea would work.


I'm sure Sir Jon will have a dozen other methods... but.. one way...

Dissasemble the motor. Bore the shaft to say 6mm (as true as you can) for a couple of inches, make an oversize "extention", light knurl on the insert end, press it in with red loctite or epoxy (tiny amount..). Turn the oversized extention to size and true between centers.

Painfull on a small motor... and 6mm to 20mm is a lot.. and I still think you'd need a pilot bearing.

winchman
06-25-2009, 03:03 PM
Make the shaft extension hollow except for the end that fits on the stub shaft. Bore it out just enough to clear a broach that'll give you a tight slip fit. Support the other end of the extension with a bearing, possible a needle bearing on the ID of the extension.

Is that circuitous enough?

Roger

Circlip
06-25-2009, 03:11 PM
Thought about the torque requirements of whatever you're trying to drive and what the remaints of the shaft is capable of delivering???

For a 20mm dia shaft, Sir John got it in one.

Regards Ian.

David Powell
06-25-2009, 06:29 PM
At the last Tsme meeting i tried to sell my home made dividing device for 5$ but no one wanted it, so it came home. The basis of it is two four bolt self aligning flange mount bearing blocks. As your motor has four mounting bolts it occurs to me that you could use a suitably sized unit to simply bolt on about an inch or so away from the motor, make a shaft of such a size to fit the bearing and fit over the stubshaft with a set screw and having a tailpiece of the size you need. and there you are. My bearings are quite large apparently 1" bore. and the hole spacing is 2 3/4" roughly. if my bearings are any use I will deliver in return for a cuppa, regards Dave Powell.

Quetico Bob
06-25-2009, 06:50 PM
Think David is spot on, too bad you couldn’t make the extension and pulley as one piece. But that would get complicated for locking to original shaft. Sounds like a fun project to use some creativity on.:)
Cheers, Bob

gda
06-25-2009, 09:12 PM
It depends on what you are going to mount on the extended shaft. Is it just a pulley and will see a radial load? Or to a well supported jack-shaft.

For something that small I'd slap on a clamp style ridgid shaft coupling

http://images.machinedesign.com/images/archive/prods0700jpg_00000034411.jpg

If you need to you can add a bearing support on the other end of the stub shaft. You will have to fuss with the alignment so not to but undue load on the bearings through mis-alignment.

Chester
06-27-2009, 11:33 PM
I'd make a bearing jackshaft to piggyback that motor. Drive it on the stubshaft end and mount your lathe pulley on the other end, that way you would have your bearings in between the pulleys. You have mounting bolts already on the stub shaft end and could make up a bracket for the other end that would accomodate the bearing as well as a foot for motor mounting. That new bracket could even be held on with a hose clamp if necessary.

gearedloco
06-28-2009, 03:00 AM
I don't see enough protrusion to have an unsupported extention. If you can have a pilot bearing on the end of the extention, and mount the motor and bearing in a common bracket, then maybe the set screw idea would work.


I'm sure Sir Jon will have a dozen other methods... but.. one way...

Dissasemble the motor. Bore the shaft to say 6mm (as true as you can) for a couple of inches, make an oversize "extention", light knurl on the insert end, press it in with red loctite or epoxy (tiny amount..). Turn the oversized extention to size and true between centers.

Painfull on a small motor... and 6mm to 20mm is a lot.. and I still think you'd need a pilot bearing.

I'd be reluctant to disassemble the motor. From the size, I'd guess it's a permanent magnet motor. Depending on what the magnets are made of, removing the armature could cause them to loose a significant amount of their magnetism. This would, for all practical purposes, turn the motor into a poorly shaped door stop. FWIT

-bill