keyed pulley attachment

[revwarguy]

Hello,

I am trying to mount a pulley on a motor shaft. The shaft is keyed, as is the pulley, but there are no set screws on the pulley, and not likely to be any anytime soon.

The keys are 3/16 and I have a key of that dimension. The key taps snugly into place on the motor shaft, but the pulley easily slips on and off of the shaft with the key in place.

I do not need to remove the pulley very often, if at all, but I would rather not locktite it or epoxy it. I am thinking of making some shims the size of the key, using aluminum foil for instance, that would be placed under the key in the motor shaft, raising the key enough to make a tight, almost press fit.

Is that how you would do it? Any better idea?

Thanks in advance,

 

[DMS]

I think that the foil will loosen up after a while. If it were me, I'd see about adding set screws to the pulley. If that option was out, I'd look at a temporary loctite (blue).

Does the torque on this shaft reverse? Just asking because things are more apt to wiggle loose if that is the case. If your only goal is to keep the pulley from sliding around, perhaps a couple shaft collars, one on either end of the pulley, with setscrews?

 

[tkingmo]

Or, if there is sufficient room on the shaft put a set collar before and after the pulley to hold it in place.

 

[Terrywerm]

It sounds to me like you may have a pulley intended for use with a tapered or "gib head" key. They are commonly found on some farm machinery and use a key that looks like this: Contrary to what one might think, they do not loosen up very easily, but make sure that you have good guards over them - they will grab and wind up anything that comes within their reach!

 

[revwarguy]

Thanks for the responses. I don't have any drills or taps long enough to go into the vee of the pulley, and don't really want to invest some if I can help it.

The pulley I did indeed get at a tractor supply store. Is the gib key you showed in the image wedged shaped? I will not be reversing direction, and I can't used a collar because the shaft does not extend past the edge of the pulley. I only need to keep the pulley from working off the end of the shaft, even though the main force will be in the other direction (to keep it on, not off).

I will try to look for a gib head key, I guess. Maybe carefully file some of the round to a wedge shape on a Woodruff key?

 

[eightball]

I have knurled keyed surfaces before I would grind A key to fit flush with the shaft with a radius close to the shaft. Dosent have to be perfect I drill and tap a couple of holes in the key so I can use jackbolts for removal

 

[Terrywerm]

Thanks for the responses. I don't have any drills or taps long enough to go into the vee of the pulley, and don't really want to invest some if I can help it. The pulley I did indeed get at a tractor supply store. Is the key you showed in the image wedged shaped? I will not be reversing direction, and I can't used a collar because the shaft does not extend past the edge of the pulley. I only need to keep the pulley from working off the end of the shaft, even though the main force will be in the other direction (to keep it on, not off).

I will try to look for a gib head key, I guess.

Yes, they are wedge shaped, or to put it another way, they have a slight taper to them. They also work best in cases where there is a spacer sleeve on the shaft to keep the pulley a preset distance from the shaft bearing. This way when you drive the key in the pulley placement does not change. It can be a real challenge to get them right when the pulley is floating on the shaft! Of course, the other challenge is when you want to remove the key, especially if there is no room to work. They are really designed for speedy assembly such as in a factory and I've never seen a pulley designed for a gib head key as an aftermarket replacement, only as OEM parts. They are always cast iron or cast steel, never aluminum, and are not designed to be removed very often. If I had my choice when purchasing a pulley, if it is for anything other than fractional horsepower, I would purchase one that uses a split taper bushing such as Browning's QD series. Put them together with some anti-seize and you can get them apart whenever you need to.




Your best bet at finding a gib head key would be an implement dealer. I know for fact that they use a bunch of them on John Deere, Hesston, and CaseIH round balers (don't ask how I know!) but they are in the 5/16" and 3/8" sizes.

Removal is accomplished using a wedge that you drive in between the pulley hub and the head of the key. In most cases it is necessary to make the wedge to fit the specific application. You start by driving the wedge in with a hammer, keeping an eye out to make sure that the wedge does not start creeping up. Hammer it back down if necessary, then keep tapping and don't try hammering on the pulley as it will do you no good. After a bit, the key will begin to move slightly; keep going and you will soon see the key and the pulley coming apart from one another. Once it is loose you can pull the key out and slide the pulley off of the shaft.

One last thought: Did you by chance happen to purchase a pulley that missed a step in the manufacturing process, namely that of drilling and tapping for a setscrew? If that pulley is for a 3/4" shaft (you did say 3/16" key, right?) and it is a generic pulley purchased at TSC or a similar store, I would be willing to bet that it is supposed to have a set screw in it. Pulleys for gib head keys are almost non-existent in the generic parts world.

 

[revwarguy]

I have knurled keyed surfaces before

That's an interesting idea - knurling would make the key "swell", probably enough to cause a good fit. Not sure how I'd knurl a 3/4 inch by 3/16 inch square key, though.

Wow, thanks for the detailed response, Terry. The pulley is black and machined, not stamped or cast. It is 3 inch diameter for a 5/8 shaft and a 3/16 key. You have me wondering if I got "lucky" and picked one up that slipped pass the set screw station.

 

[Terrywerm]

You are most welcome! I am thinking that you may be correct on that assumption. It might be worth making a return trip to the store to see if the others are like that or if they are correct and have setscrews in them. If the others have setscrews, you could probably exchange the apparently defective one for a good and proper one, and that route may be easier than finding a gib head key in that size, or knurling a regular key.

One other possibility exists. Some riding lawn mower decks use a pulley on the top of the spindle where the spindle has a stepped shaft and the pulley is held on by a nut on the threaded end of the shaft. Many times stores like TSC, Theisen's, Blain's, and other Fleet and Farm stores will carry a line of replacement pulleys and spindles for those mower decks. Could it be that you got your hands on one of them? No setscrew would be necessary for a pulley held on a spindle by a nut.

 

[12bolts]

... I don't have any drills or taps long enough to go into the vee of the pulley, and don't really want to invest some if I can help it......

A long series drill bit in the appropriate size will only cost a couple of dollars.
You can make an extended tap by getting a piece of steel tubing with the internal hole close to the size of the square tap end and form it around the tap. You now have a tap that will reach into awkward spots and can be turned with pliers or vicegrips. Hard to keep straight but will do the job in a pinch. i once tapped a 3/16 thread into a windmill part with a 2ft long piece of tubing.

Cheers Phil