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Fitting large-bore mandrel to a smaller bore motor?

I have a nicer old motor and one of those tapered-threaded mandrels for cotton buffs, and I need a buffer. The motor shaft is smaller than the hole in the mandrel. I can turn a "bush" to fit between them.

The motor shaft has a flat, and the mandrel two setscrews. Do I

a) drill, thread, and setscrew the bush to the shaft, then setscrew the mandrel to the bush;

b) drill and pin the bush & shaft, then as a); or

c) insert the bush and lock it with one setscrew, mark the centre of the other setscrew hole, swap setscrews and repeat, take the bush out and drill clearance holes so the setscrews bear on the shaft; or

d) do something else?

a) might be tricky as the bush wall is likley to be 1/8 or so. b) is the way I'm leaning - the pin will be retained by the mandrel. c) has the advantage of complete removability, and I might want the motor for something else.

Reply to
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I would do something like C. Maybe just make the bushing, measure the distance between the two setscrew holes, and drill two holes in the bushing the correct distance apart. The holes can have generous clearances so the bushing can still work even if the holes are not exactly the right distance apart.

Dan

Reply to
dcaster

Hey ,

Well "nicer old motor " or not, with your comments that the "bushing" will be made to accommodate a shaft about 1/4" diameter smaller, and that is already weakened slightly by having a flat, one thing to consider is whether the smaller shaft can take the same forces as the buffing mandrel was designed for. It is quite amazing to see a shaft unsecured make a severe bend when it starts to "whip" due to applied forces beyond its limits.

Take care.

Brian Lawson, Bothwell, Ontario.

Reply to
Brian Lawson

I would do (c). The setscrews will transmit torque from shaft flat to mandrel. All the bush need do is keep mandrel and shaft concentric. It could have considerably less than 1/8" wall thickness with no problem.

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Reply to
Don Foreman

========== Always try the easy/simple solution first.

You are going to use this for buffing, so run-out is not critical.

Try making a bushing, split one side with a hacksaw, and install with the split at 90 degrees to the set screws, with the set screws *NOT* over the flat on the motor shaft. Tighten to a reasonable torque, install a buffing wheel and have a go.

More than likely this will be more than adequate for the typical home/hobby shop.

Unka' George [George McDuffee]

------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?

Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625).

Reply to
F. George McDuffee

My preference would be to mount pillow blocks and fullsize shaft for the mandrel, and offset the motor with a pulley where it won't interfere. That way, you can have a left and right mandrel (two buffers or buffer and a fine wire wheel), and can update the motor power or change the rotation speed (by choosing different pulleys) or direction.

The buffer wheels are replaceable, so should the motor be.

Reply to
whit3rd

Given the wall thickness of the bush, I would suggest (c) is the best bet. This is assuming that the two setscrews on the mandrel are in a straight line, instead of set at different angles around the mandrel. (You don't want a setscrew tightening onto any area of the motor shaft other than the flat, or the burrs raised may prevent disassembly. You probably should get somewhat longer setscrews to keep enough threads in the threaded section of the mandrel.

Good Luck, DoN.

Reply to
DoN. Nichols

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