Question on indicating a billet in a 4 jaw. Bonus content - order of ops question

[tominboise]

I am going to make a new dual v belt sheave for my new to me Logan lathe. I have an 5" diameter aluminum biscuit, 3" long. I chucked it up in my 4 jaw but am wondering where I should be indicating - at the end nearest the chuck, the middle or the end farthest from the chuck?



Also, order of operations? I thought I would chuck it as close as I could in the 4 jaw for run out,
face the end,
Center drill and drill the (undersize) mounting hole.
Rough the sheave form pretty close to final dimensions, maybe .030 over size.
Ream the center hole to final diameter.
Cut the key way in the bore.
Mount the sheave to an arbor/mandrel.
Do the final machining on the belt grooves.

Oh, and Merry Christmas to everyone!!

 

[pontiac428]

My comment would be to skip the mandrel entirely and machine the whole thing in one fixture. Flip it and face off the back side as the final step. I'd broach the keyway in a press if possible to save wear and tear on your lathe. It won't matter where you put the indicator on this case, just get it close to centered and start peeling off chips.

 

[rwm]

I agree with the above. That is a good plan. BUT, I would make sure the work piece is bottomed out in the jaws and I would consider using tailstock support for safety. You don't have much grip length there.

 

[tominboise]

I agree with the above. That is a good plan. BUT, I would make sure the work piece is bottomed out in the jaws and I would consider using tailstock support for safety. You don't have much grip length there.

Actually, I think I can reverse the jaws and still clear the bed. That will give me close to an inch of grip length on the billet.

 

[tominboise]

My comment would be to skip the mandrel entirely and machine the whole thing in one fixture. Flip it and face off the back side as the final step. I'd broach the keyway in a press if possible to save wear and tear on your lathe. It won't matter where you put the indicator on this case, just get it close to centered and start peeling off chips.

Thanks, I need to figure out how to broach the key in a press.

 

[pontiac428]

I think the jaws are good as they are, but you are the final judge on what is safe and prudent.

Broaching in a press is done with a guide plug and a keyway broach, not all of us have a set. I just don't like broaching in the lathe because it's hard on your carriage pinion bushings. Opinions might vary about that, which is why we ask and discuss those things here. There are always alternatives and good answers out there.

 

[rwm]

I would not reverse the jaws. Just carefully face it, drill a center and bring in the tailstock. Then you can hog with impunity.

 

[mmcmdl]

Face it and clean up the diameter just to have a square face and true diameter . Reverse in chuck as you have it . Finish complete in one set up . Don't try to run a full form tool while machining the belt grooves . Make your straight grooves ( parting/groove tool ) to the needed diameter and then compound your angled sides . Drill and bore or ream . Should be a piece of cake . Found some pics of some that I shipped out to Cali for a breakdown . Done on my first lathe . 1760 Voest .

 

[Pevehouse]

Keep us posted with some pictures. Really trying to work on my order of operations in general when it comes to jobs like this. Very interesting