Sk3 keyway for pulley

has anyone successfully ground a keyway into the sk3 shaft? i have a pully i would really like to use but it only has the grub screws where the belt runs and im not sure if those two alone would be enough to hold it from slipping.

one of my ideas is to grind/file a flat spot onto the shaft (only a mm or so deep) for one grub screw to grab onto but i would rather bring it up and see what you guys thought.

thank you in advanced!

Yep gotta do that. Flat spots for all grub screws.

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well im glad to hear im not the only one with that idea, and that others have done it successfully. only thing is if you did 2 how would you keep it centered? i figured just do one flat spot that way you could tighten that screw first to center the shaft then use the other for extra tension.

i guess if you did the flat spots small enough (just the width of the screw) it would still self-center.

why are people even bothering with keyways?

because im not sure if it will slip or not on the shaft with the 2 small grup screws in the teeth.

It will not slip…make sure to blue loctite the grub screws…

Because they are fifty times better than a grubscrew? When I hit the brakes, I want to know there is a piece of metal that I’m pushing against, not some cheesoid shitty grubscrew where if it slips, I might not have brakes.


You dont need either with retaining compound. Baffles me people are still using mechanical retaining methods.

Baffles me anyone would trust a non-mechanical retaining method. Maybe I value my body more than normal?


uh… wouldn’t a screw count as mechanical retention?

im gona try it with just the simple grub screws and see what happens with a torture test on a open straight road and see what happens

Not if it can rotate and back-out

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green loctite.

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AXCC408B (9)-05


It will slip. Flat spots for grub screws on pulleys without a keyway. It’s just standard protocol. Always loctite grub screws. And give the loctite at least 24 hours.

Trying to stress test with no flat spots is silly. If it slips, no brakes.

If you’re against it, others have had good experiences with loctite for shafts/pulleys. I’ve never used it in fear of damaging the pulley trying to remove it.

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Noob question… what is a keyway?

It’s a 3mm notch in the axle coming out of a motor – and a 3mm notch on the inside of a pulley

You put a key (photo above) in the notch and it locks the pulley from rotating or slipping on the round shaft

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Once I cut a keyway into an sk3 shaft w a Dremel tool. I wouldn’t do that again. It’s really hard to cut a keyway by hand. File a flat spot and loctite the grub screws. It’s what most do and it works.


yeah on my first motor i tried to cut a keyway aswell…it was just mess… i tend to flatspot and grubscrew

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What I did for the 3 sk3’s that I’ve used now in my builds. Grind a flat spot for the grub screws (2-4 per pulley) and also put loads of loctite on the shaft. Super. Tight.