Drive gear coming loose on motor shaft

[scbiomed]

Recently I've been called to repair several chiropractic massage tables. They all have the same problem. The chain drive gear becomes loose on the motor shaft and slides foward. There are two set screws and the shaft is keyed but it does not have any flat spots. Tightening the set screws is only a temporary fix, the gear works loose after a few days. Would grinding flats on the shaft help keep these gears in place. Also the manufactuer has positioned one of the set srews directly over the key. Is that proper?

 

[EMc]

I'm just a visitor, but I have seen a few set screw and key slot setups. First of all, it sounds like the manufacturer made a bad design choice; anything designed to produce vibration should not have set screws. Not that there's much you can do about that, except put in a design change request.
If you can arrange it so that the gear does not ever have to move again, there are a number of adhesives used in the plumbing industry that will probably glue it in place for ever. Or, if the gear does need to move, but only to discrete locations, you could try drilling and cotter pins.

EMc

 

[diamondjim]

I see nothing wrong in drilling a slight indentation
in the shaft for one of the set screws. Ideally, the
second setscrew should be 120 degrees from the one over
the keyway. I think I would try installing them with a
Loctite product on the threads.

 

[GregLocock]

I've seen a grub screw onto the key before , the advantage is that if the grub screw burrs the key then dissassembly is still easy, whereas if the shaft gets burred then it can be hard to pull the gear off. Having one on the key and one on the shaft ruins that theory, of course!

Drilling the spot for the grubscrews is a good idea, but I'd use Loctite to hold both the shaft, and the screws. Loctite is available in a whole range of adhesive qualities - 600 grade is as good as welding, 200 grade is dismantleable.

Cheers

Greg Locock

 

[FINN_imported]

I design vibratory compactors and have used a variety of the LOCTITE products. The ones I use most commonly for securing gears to shafts is LOCTITE 243. It has very good resistance to oils and works with most surfaces. It is also removable, which can be very important to future repair, especially in vibratory equipment.

 

[MikeMilburn]

I agree, Loctite products are a cure but if you want a mechanical fastening instead of chemical, how about drill and a roll pin...Mike