How to mount a disc square on a shaft

D

dansawyer

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The project is to mount a round 4 inch diameter disc square on a 1 inch diameter aluminum shaft. The disc is 3/8 of an inch thick. The disc should be centered and square. The outer inch of the disc will be used, however the center 2 inches may be part of the mounting. The shaft can extend through the disc.

I will be machining the disc I had thought about first boring a 1 inch hole. Second, machining a 'collar' about an inch long and 1 3/4 inches in diameter. The disc would be screwed to the collar. The collar would be screwed to the shaft.

The tolerances needed at the edge of the disc is +/- .002.

The primary tool available is a South Bend 9a in fair to better condition. Is this feasible? Is there a better way to do this?
 
If you need it perpendicular to your shaft +/- .002" I think you will have to finish it on your lathe no matter what method you use. Making the disk in one piece will reduce the possibility of stacking errors.

For holding the disk onto the shaft I would probably use an interference fit with heating the disk and cooling the shaft to secure it in place. Also I would make the inner 2" of your disk as thick as practical to give some holding power. This is assuming it won't need to be disassembled for any reason.

Would do all operations on your lathe so have a central reference to work from but I'm a novice at this kind of stuff so take that for what it's worth....

John
 
For true squareness, make the dist oversized first by maybe 0.060 to 0.100 larger than required.
Then press disk onto the shaft.
Then put the shaft in the lathe, indicate it centered and true, and face the disk off to 3/8".

This gets rid of stackup errors.
 
Dan, you should be able to do this easily. If you think about it, the accuracy of the disc depends on:
  • The accuracy of the backing surface or "collar" as you noted. If your shaft is accurate and you lock the collar in place and face the surface that contacts the disc then it will be square.
  • The accuracy of the disc. If you face the disc square and clean then it should run true.
  • The accuracy of the bore in the disc. Keep this tight, on the order of half a thou or less if you can.
  • The accuracy of the collar that holds the disc in place on the shaft. This is less critical but make it as accurate as you can.
 
Is the disc aluminum too? I suppose that you want the disc to stay accurate when in service :)
All of the above but I would use as big a collar as possible cut as accurately as possible. One on each side of the disc. Both threaded to the shaft.
One collar with a nose of say 1.375" to act as an arbor and the other with a recess so they can sandwich the disc tightly. Avoid heat build up during all cutting operations.
Bore the disc for a tight slip fit on the 1.375'' arbor.
Assemble and turn between centres to final dimensions and trueness.
 
Thank you for the follow up questions.
The 1 inch shaft is 1 1/4 inches long. I was planning making the disc and the collar out of aluminum.
 
Would it be feasible to buy an aluminum block and make it one piece?
 
Em..
I would maybe aim to make the bored hole about 0.02mm undersize, heat the disc to about 200C, and slip the shaft in.
This would be a permanent fit.

The collar is only needed if you want to make the disc removable.
 
I'm wondering what the application is?

Is the 1-1/4" length of the shaft the total length of the piece or the available length?

If you can achieve the necessary tolerances, the three piece assembly will be the most work and the least wasted aluminum.
Fewer parts will probably be less work (quicker) with more aluminum turned into swarf.

Does the disk/collar have to be removable from the shaft?
 
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