Set screw holes to act as keyways

[asid61]

Is it possible to drill short close clearance blind holes through a shaft to allow a set screw to go through? This way the set screw can act as a key instead of a set screw.
Sort of like the way the dogs in WCP dog shifters are, but the screw only goes partway through the diameter shaft; that way, it can still clamp onto something.
Round shaft, not hex.

[nathannfm]

If I understand you correctly you would be putting the set screw in shear as some of it would be threaded into the shaft and some of it would be threaded into the component. I would say this is probably not best practice but depending on the application it could work. If possible I would drill the hole all the way through the shaft and out the other side of the component and use the entire length, this will at least give you 2 shear points instead of 1. It would also help you tap the hole as it can be difficult to properly tap a very shallow blind hole. Also, if possible I would also recommend using a pin in said through hole instead of a set screw as the threads on screws act as stress risers when put in shear like this.

[asid61]

Originally Posted by nathannfm

If I understand you correctly you would be putting the set screw in shear as some of it would be threaded into the shaft and some of it would be threaded into the component. I would say this is probably not best practice but depending on the application it could work. If possible I would drill the hole all the way through the shaft and out the other side of the component and use the entire length, this will at least give you 2 shear points instead of 1. It would also help you tap the hole as it can be difficult to properly tap a very shallow blind hole. Also, if possible I would also recommend using a pin in said through hole instead of a set screw as the threads on screws act as stress risers when put in shear like this.

Thank you! That information is very helpful.
I would use a shear pin, but I don't want to deal with getting them in; apparently it's very tricky.

I ask because SDP-SI sells pulleys with set screws on them, and I can't really key the shaft and the pulley easily. The easist way to do it would be to leave the pulley threaded and just drill a bit into the shaft. That way the set screw still stis okay.

It doesn't look like it'll be a problem because I decided to go with gears anyway, but I might need this for future stuff.

[Mr V]

tighten the set screw down hard where you want the pulley remove it and look for the witness mark. You can then drill a divot of just file a flat to increase the locking power. Depending on the shaft and set screw sizes drilling all the way through could compromise shaft strength.

[MrForbes]

You can get away with a set screw to keep a pulley on a shaft, in a low stress application, such as a continuously rotation situation (think fan blade). Using it in a situation where the load is reversed often, such as in just about any mechanism we put on a robot, will result in bad things happening, since you won't be able to keep the screw tight.

[Jared]

If you have the machining resources, use a roll pin. It'll be much stronger.

[Cory]

The method you're considering is going to be subpar for just about any FRC purposes. The screw is going to be very weak to start with relative to a pin/keyway and will be in single shear. with the dog screw you at least have double shear.

Roll/shear pins are pretty easy to install. You could also look into a trantorque, if you have a large enough ID and have no means of creating a keyway and don't want to drill through the shaft.

[DampRobot]

100 has done this before and it did work. However, like other posters have said, this is a bad idea for anything that will see significant torque.

[philso]

If you ever have to change your pulley or your motor, it is going to be very difficult to get a new hole drilled that matches the part you are not changing. You may as well change both the motor and pulley as a matched pair.

[asid61]

So it looks like roll pins are the preferred method. Not a huge problem, but I've read they snap when pressing.
In the future I'm going to have to press a few roll pins to try it out.

[Dad1279]

After a few issues I bought a broach to put keyway in hubs/pulleys. Now we use hex shaft whenever possible.