Set screws to secure the position of a collar on a shaft accurately and securely

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dansawyer

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The project involves securely and accurately mounting an aluminum collar on a 5/8 inch steel shaft. I have the collar turned to within 15 thou, concentric to the shaft, of the final value and before I perform the finishing turning. The objective is 1 thou TIR between the shaft and the . There will not be significant force on the collar once assembled.
The collar will be turned to 1.200 inches. It will be 1.25 inches long. There is currently one set screw drilled and tapped.
My question is for maximum precision and stability should there be two set screws along the axis. Or should there be 4 set screws in pairs of 2 along the axis and the pairs at 90 degrees to each other.
The parts will have to be machined prior to assembly, however once assembled they will not need to be disassembled.
I am asking now because if more set screws are needed then they should be machined before the finishing pass.
 
The fit of the shaft to the collar will determine the accuracy. One teensy setscrew will do as long as there isn't a lot of heat, vibration, shock, nuclear detonation, etc. but I suspect you'll have a bit of that- put two screws at 90 degrees to each other in that case
If you really want it to stay on use Loctite also, or even epoxy
-Mark
 
i have seen more precision shaft collars with a single set screw hole, than any other design.
the collars and shafts usually have less than .002" clearance between
 
Drill and tap one set scree. when you get the collar in place use the tap drill to dimple the shaft, then use two set screws half the length of the wall thickness. put the first screw in and tighten and lock it down with the second screw.
 
Machine collar for slight interference fit.
Heat collar, cool shaft; install at proper position.
Indicate shaft in 4-jaw and perform final machining of collar.
Drill and tap into both collar and shaft itself.
If you have room put locking set screw on top of holding set screw.

This puts the set screw in pure shear.
 
Thank you all, those are clear and helpful answers. I may redo the project just to follow advice and avoid the mistakes I made.
It is too late for the interference fit, however the machining on the shaft went very well. Measurements on the lathe are indicating everything is within tolerance.
 
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To me it would seem that a set screw on an aluminum collar could cause the collar to bulge from the side load.
A roll pin and some Locktite would be strong and eliminate any out of balance vibrations.
 
I'd position the collar in place, then drill and ream an undersized hole for a dowel pin.

Shootymacshootface has a very good idea. If you search under my name and Massey tractor, you'll find a POTD post by me where I repaired a starter. The Bendix is attached to the armature shaft with a roll spring pin. It's how it's done in industry.

Bruce
 
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