[FTC]: Wormgear and set screws

[Sasha]

We are using a tetrix wormgear to rotate a robot arm. This provides the necessary torque, but after some time on the field, the set screws in the wormgear get slightly loose, allowing the axle some "play". Not too much - maybe 10 degrees rotation - but with the arm being about 11 inches long,it becomes significant.

Anyone knows of a better way to clamp the axle in the wormgear (other than regularly retightening the set screws, or using threadlocker)? We were even thinking of drilling some small indentations in the flat of the axle, to accept the set screws, but it might weaken the axle too much. Or maybe someone can suggest an alternative wormgear box, which would be small and fit the tetrix motor shaft?

[MattRain]

One of my teams has an axle that bares the whole load of their lift. They have taken the axle, cut out a flat section, and then drilled about a 1/3 or 1/4 down, allowing the set screw to set into. They plan on tapping two more holes into the hub to help as well. From all the practice, they still haven't had any problem with the axle. (They snapped a steel cable in half, not budging the set screw a bit.(That problem has been fixed. ))

[wgardner]

Originally Posted by Sasha

Anyone knows of a better way to clamp the axle in the wormgear (other than regularly retightening the set screws, or using threadlocker)?

I would think that the threadlocker/loctite would be an effective and simple solution. Is there a reason why you think you shouldn't use threadlocker?

[Sasha]

Originally Posted by wgardner

I would think that the threadlocker/loctite would be an effective and simple solution. Is there a reason why you think you shouldn't use threadlocker?

We were not sure how efficient it is and wanted to explore other options.

[wgardner]

Originally Posted by Sasha

We were not sure how efficient it is and wanted to explore other options.

We've had good luck with threadlocker. It's cheap and easy to test.

There are also threadlocking set screws that have a blob of stuff on them that locks the thread sort of like the way nylock nuts do. You could try these too (if they have the size for the worm gears).

http://www.mcmaster.com/#set-screws/=vcj3r2
(scroll down on the left side and click on "thread-locking" under "features")

[DavisDad]

Originally Posted by Sasha

We were not sure how efficient it is and wanted to explore other options.

Thread locker is an excellent product for preventing fasteners from loosening, but has limits. If your set screw is loosening because of wear on the mating surface (e.g.: set screw digs into a round shaft and make a grove) thread locker will not solve the slipping problem. It doesn't take much of a flat on the shaft to prevent slipping. We always use thread locker on setscrews.

Also, have you seen the different types of setscrews? See the McMaster page:

http://www.mcmaster.com/#set-screws/=ve2e3b

I like the "extended dog" type with a shallow hole drilled on the shaft. It's bulletproof and on assembly, you can easily feel and see that the setscrew is seated; you can see by the depth of the tightened setscrew that it is engaged correctly.

[Al Skierkiewicz]

As a caveat on using threadlocker, do not allow it to migrate to polycarbonate on your robot. It cause a condition called "crazing" that eventually weakens and destroys the poly. A small flat spot on the shaft is a good method to use. It also makes dis-assembly easier.