Should Set Screw Press on Key or Shaft?
Should Set Screw Press on Key or Shaft?
Today I noticed that the drive pulley on my lathe motor had shifted axially. The pulley and the shaft are slotted to accept a square key, and the pulley has a set screw hole that's aligned with the key slot.
Depending on where the key is positioned, the set screw could press on the key itself, or it could press directly on the shaft at the bottom of the key slot. Both the key and the shaft have marks on them from the set screw, so apparently it has been set up both ways in the past.
Which is correct?
-- Russell Mac
Depending on where the key is positioned, the set screw could press on the key itself, or it could press directly on the shaft at the bottom of the key slot. Both the key and the shaft have marks on them from the set screw, so apparently it has been set up both ways in the past.
Which is correct?
-- Russell Mac
Re: Should Set Screw Press on Key or Shaft?
I'd be inclined to suggest that the ultimate is to use a key and let the set screw bear on the top. My rationale for that opinion is based on the notion that a heavy load would most likely overwhelm a setscrew that penetrates the key slot, damaging the slot in which it resides. A key would not allow the movement.
H
H
Wise people talk because they have something to say. Fools talk because they have to say something.
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Re: Should Set Screw Press on Key or Shaft?
Do you mean that the key is present but short and the pulley can be positioned so that the setscrew misses it and goes into the slot instead? That will result in the key being slightly loose in the slots. The setscrew will have to carry all the load with the result Harold describes. It will inevitiably work loose, allowing axial movement. The setscrew's job is lock the key into position. The key's job is to transfer the torque.
Install a longer key.
Install a longer key.
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Re: Should Set Screw Press on Key or Shaft?
Are you using a key that is as long as the slot?
Gregg
Just let go of it, it will eventually unplug itself.
Just let go of it, it will eventually unplug itself.
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Re: Should Set Screw Press on Key or Shaft?
The key and the keyway in the shaft should be as long as the keyway in the pulley and the set screw should bear on the key.
Ted
Ted
Some people raise the IQ of the room when they enter.........others when they leave.
Re: Should Set Screw Press on Key or Shaft?
Thanks to all for the replies. It's good that everyone agrees!
Regardless, it sounds like a longer key is in order, with the set screw holding it in place. I can do that.
Thanks again.
-- Russell Mac
Yes, except it's the key that can be moved around. (The motor pulley needs to line up with the pully it's driving.)John Hasler wrote: ↑Mon Apr 19, 2021 7:32 am Do you mean that the key is present but short and the pulley can be positioned so that the setscrew misses it and goes into the slot instead?
Regardless, it sounds like a longer key is in order, with the set screw holding it in place. I can do that.
Thanks again.
-- Russell Mac
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Re: Should Set Screw Press on Key or Shaft?
I would have the setscrew bear on the key when possible, to avoid damage to the shaft.
Epilog: Should Set Screw Press on Key or Shaft?
Well, well. This problem was more interesting than it seemed at first. As the picture shows, the set screw was farther away from the end of the motor shaft than the end of the slot in the shaft for the key. So there was no way for the set screw to bear on the key. I'm guessing the lathe's history must include a motor replacement somewhere along the way.
Anyway, I made it all better by just turning the pulley around so the set screw is near the end of the shaft.
-- Russell Mac
Anyway, I made it all better by just turning the pulley around so the set screw is near the end of the shaft.
-- Russell Mac
Re: Should Set Screw Press on Key or Shaft?
That will throw your speeds completely off and I can't see how the belt would fit any more.
Re: Should Set Screw Press on Key or Shaft?
Shouldn't be a problem if the opposing pulley is also inverted.
H
H
Wise people talk because they have something to say. Fools talk because they have to say something.
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Re: Should Set Screw Press on Key or Shaft?
I assume Rmac is only using one of the pulleys.
Otherwise he would have used a different solution.
Otherwise he would have used a different solution.
Re: Should Set Screw Press on Key or Shaft?
What Harold said. I flipped both pulleys.
-- Russell Mac
-- Russell Mac