Part too large for a 5" chuck?

[Mini Cooper S]

If you have a piece of 5" stock that you can grab in the chuck, I would recommend this.

1) Face
2) Turn the step
3) Turn O.D. back about 3/8"
4) Bore and C'Bore
5) Flip part seating the shoulder against the chuck jaws, indicate the bore
6) Face
7) Turn the taper

This way everything accept the 2nd face and taper are all done in one setup, assuring it concentricity and runout of most of the part.

Richard

 

[epanzella]

I don’t see how the suggestions to drill a hole and put it on an arbor or threaded rod is going to work, you need to machine the tapered counterbore before flipping it and doing the large taper, so there can’t be anything through the bore to do that.

You're not thinking it thru. Once on a mandrel the step to 3.7" can be machined on one end. Then flip it around and put a step in the other end that will later be removed when machining the taper. Now you can grab it in the 5 inch chuck and machine the counterbore. Flip it once more in the 5 inch chuck and machine the taper. Miller time.

 

[Ischgl99]

You're not thinking it thru. Once on a mandrel the step to 3.7" can be machined on one end. Then flip it around and put a step in the other end that will later be removed when machining the taper. Now you can grab it in the 5 inch chuck and machine the counterbore. Flip it once more in the 5 inch chuck and machine the taper. Miller time.

thanks, yeah I was missing that step

 

[Jimsehr]

Are you all saying it's not safe to machine the 5" part with outside jaws extending ~1/2 way out? Even with light cuts?

thanks, yeah I was missing that step

the post started out ( could this be safely machined ) .
So I posted a cheap safe way to keep part from flying out of machine.
I don’t know what the chuck is like but after running a lathe for more then 60 years I know I would not like a slug of metal that size coming out of the chuck.
Jimsehr

 

[itsme_Bernie]

Are you all saying it's not safe to machine the 5" part with outside jaws extending ~1/2 way out? Even with light cuts?

If the outside jaws are sticking out a bit it often doesn't matter. "1/2 way" I would need to see to give a real opinion. Like Jim F said above, you would want a few jaw/scroll "threads" engaged to be sure it didn't work it's way out, but if you are doing light cuts and keeping a good eye on everything, you are probably fine

Bernie

 

[Chewy]

I go with Jim F on the three threads holding the jaws. I have machined with the jaws further then 1/2 way out. I took a point from Jo Pie and marked the chuck at the point of three point engagement and that is max safe diameter. If the jaws don't hit the bed or carriage, you are good to go.

 

[Parlo]

Assuming the billet is 5" diameter I see no reason why a billet the same O/D as the chuck can't be held safely with external jaws.
Turn step - drill hole & counterbore then turn round and cut the taper.