Posted by Ken Leung at 1/26/2001 12:31 AM EST
Student on team #192, Gunn Robotics Team, from Henry M. Gunn Senior High School.
In Reply to: Re: i repeat the "i am a ninny" phrase...
Posted by Brett on 1/25/2001 11:27 PM EST:
: I don't think the coupler has any set screws... (none that I would consider set screws) It's threaded and has 4 screws along the side to clamp it down over the drive shaft and whatever you're driving, as a compression type fitting rather than set screwing.
Ok, so the drill motor coupling can be seen as two part: the first half attaching to the output shaft of the drill motor gear assembly, and the second half attaching to a 3/8" shaft. Both halves each have two #6-32 UNC-28 set screws on the side for tightening the whole coulping so it will grip harder on the drill output shaft as well as the 3/8" shaft.
Now the difference between the two halves is that:
the first half (for drill motor gear assembly) is threaded internally so it can be screwed on, with a 1/16" hole on the side for a spring pin to prevent the coupling from unscrewing.
the second half (for a 3/8" shaft) is smooth internally (not threaded), NO 1/16" hole on the side, and a 1/8" keyway so you can make a identical keyway on a 3/8" shaft and use keystock to lock that shaft with the coupling.
Now, what Andy suggested is a modification on the first half, where you use a lock washer to grip the coupling tightly on the motor output shaft (same way lock washers lock nuts on a bolt), and enlarge the 1/16" pin hole, tap the hole, and use a #8-32 screw (which to my knowledge we count that as set screw) instead of a pin to prevent the coupling from unscrewing. Since the lock washer is always locking the coupling pretty hard, there won't be as much stress on the #8-32 screw, therefore it worked nicely.
As for the other half, I am not sure how strong are the two #6-32 UNC-28 set screw on the side, but on theory they can be tighten so the 3/8" shaft won't slip out, while the key prevents that 3/8" shaft from spinning freely. But you would want to support both side of that 3/8" shaft anyway because of the side load if you are putting a sprocket on it to drive a drive train. In the process of supporting the shaft on both side and/or mounting a sprocket on the shaft you can figure out a way of making sure that shaft won't slide out of the motor coupling...