Epoxy, glue, loctite gear to shaft. Any chance of working?

I need to get a gear affixed onto a shaft. We have broken two of them trying to press fit it. We do not have anybody to TIG weld it. (The best we can do is flux cored wirefeed, and that becomes questionable). Is there any commercially available product that will bond the gear to the shaft? Both gear and shaft are steel and the diameter of the shaft is 3/8" The gear is in a drive system gearbox. Two small CIMs are geared down 12:45 to this shaft on which the gear in question resides.

We use hex shaft and roto-broach(sp?) our sprockets and gears. If you just want to glue it, I would recommend JB-Weld. It is the omnipotent metal epoxy, and probably available at your local hardware store. If you use enough of it and use it right (I.E. scuff all surfaces and clean them well) it might just work.

Loctite does make a product that will work. It’s called retaining compound and we use it at work for the same thing. On our injection molding robots the gears are glued onto the gearbox shafts with a press fit and the retaining compound. The retaining compound part number is 638. I have my Loctite catalog right here and this is what it says about 638 “A maximum strength retaining compound for use where high dynamic force or cyclic loading is expected. Locks cylindrical assemblies up to .010” diameter clearance. Fixtures in 5 minutes. The shear strength steel/steel is 4500 lbs." The retaining compound is dark green and smells like vinegar. When you’re done putting the gears onto the shafts it smells like you were dying Easter eggs! :smiley:

The primer is #7471 "A solvent based primer that speeds the cure of all Loctite brand anaerobic adhesives and ensures proper cure on inactive metals.

Only a product that our team couldn’t live without, JB Weld! It would work great depending on how much force this gear sees. If it isn’t too hign then it will work. There isn’t any product that will work as a glue under high torques. But JB Weld is the best thing for this situation. We’ve had to JB Weld our wheels together before and it held very well. Best thing is it sets quick

The loctite product mentioned above will work. Metal must be very clean. If the surfaces are polished abraid them a little. Epoxy is less than desirable.

My vote is for the retaining compound, unless you have the room and desire to build up a large fillet of JB Weld on both sides of the shaft. JB Weld is really not intended for this sort of usage; it’s better for static applications.

i’ve used the retaining compound before (green) and it works well. I only used it to secure a set of bearings, and it retained them very well.

I assume you mean the gear broke because the press fit was too tight. You could put the shaft in a drill and use emery paper to gradually reduce shaft diameter until the press fit is not so tight. We had to reduce the kit gearbox output shaft diameter by about .005 inches using this method. You can start with a file if you have to reduce it a lot. We happened to use some abrasive roll material.

Listen to Jay in the post above. Use Loctite 638 or 680. You must have an engineered gap, though. An engineered gap is a gap between the shaft and the hub diameter that you put there on purpose. Take your press fit and reduce it to 0.001" only in the middle. Put gaps (smaller than 3/8" diameter) on each end of the shaft where it contacts the gear. The press fit will pilot the gear and the gap with Lactate will bond it in place. This will work. Reference the Lactate design guides (online). They can help.

-Paul

We figured out a way to key the gear. But thanks for all the comments and suggestions.

I wanted to bump this thread up again to ask a few questions. First, we are trying to fasten a 20 tooth, 1/2" thick, 1.000 PD gear to the big minibike CIM for our transmission. However, the D-shaft eludes any easy way of attaching the gear securely on. Can the gear be fastened to the shaft just by the retaining compound, or is a press fit/retaining compound combination preferable? Any other ideas?

So - we could use milk as a retaining compound? :wink: :wink: