How to turn parts with nothing to grip?

[HandyNotHandsome]

I'm trying to turn the part shown in cross section below. This part is about 1.5" in diameter, steel. I know how to do the individual operations, but having trouble with the order of operations. At this point I have machined the entire part, except for the inset on the large diameter (shown by arrow). I don't have a good way to mount it in the chuck. If I mount it as shown, I can only grip maybe the leftmost millimeter of the part, which doesn't seem like enough. If chuck it the other way, I'm afraid the jaws will bend the 'bell', plus it will be a left-handed facing operation.

There's a trick in woodturning where you glue such a part to another piece for mounting, then separate at the glue line afterwards. I'm not sure that this is safe for a metal lathe operation.

Were I to start over (which I will, if I have to), I could leave enough extra material on the left hand side to mount, but then after separation, I'd still need to turn the 'cone' on the left hand side, which would mean gripping by the 'bell', so I'm not sure that helps. I guess I could mount by gripping the inset, with the 'lip' resting against the jaws - that seems best.

Any advice or suggestions?

 

[DavidR8]

I'm trying to turn the part shown in cross section below. This part is about 1.5" in diameter, steel. I know how to do the individual operations, but having trouble with the order of operations. At this point I have machined the entire part, except for the inset on the large diameter (shown by arrow). I don't have a good way to mount it in the chuck. If I mount it as shown, I can only grip maybe the leftmost millimeter of the part, which doesn't seem like enough. If chuck it the other way, I'm afraid the jaws will bend the 'bell', plus it will be a left-handed facing operation.

There's a trick in woodturning where you glue such a part to another piece for mounting, then separate at the glue line afterwards. I'm not sure that this is safe for a metal lathe operation.

Were I to start over (which I will, if I have to), I could leave enough extra material on the left hand side to mount, but then after separation, I'd still need to turn the 'cone' on the left hand side, which would mean gripping by the 'bell', so I'm not sure that helps. I guess I could mount by gripping the inset, with the 'lip' resting against the jaws - that seems best.

Any advice or suggestions?
View attachment 450685

I'm trying to imagine the finished part and am struggling a bit.

That said, you could make an arbor from aluminum, size it to fit the inset diameter and then use super glue to hold it on the arbor. Use heat to release the part.

 

[pontiac428]

Profle the left side first with the right side stock chucked, leaving a stub on the left with a center drill spot. Then machine the right with the left chucked to the stub. Part off when you're done. If it needs more support, mount it on centers using the inset feature and the spotted face with a drive dog on the stub. I think there are a half dozen ways to approach this one, which way is best depends on the whats and wherefores.

 

[HandyNotHandsome]

I'm trying to imagine the finished part and am struggling a bit.

The axis of rotation is a horizontal line through the center. Here is a 3D image:

 

[HandyNotHandsome]

Profle the left side first with the right side stock chucked, leaving a stub on the left with a center drill spot. Then machine the right with the left chucked to the stub. Part off when you're done. If it needs more support, mount it on centers using the inset feature and the spotted face with a drive dog on the stub. I think there are a half dozen ways to approach this one, which way is best depends on the whats and wherefores.

I'm not sure I understand. After I part off the left, I would still need to turn the interior cone seen above. The only way to do that would be to chuck the 'bell' shown on the right, which I'm not comfortable doing.

 

[twhite]

1. Turn up a bung to fit the cone section. ( Making sure to have it center drilled for your live center.)

2.Then chuck up your stock and turn up the cone section. Rough drill through at this point also.

3. Then put bung in using live center and turn the entire outside profile.

4. Flip part and secure to a faceplate if you have. Second option 4 jaw chuck. Then proceed to finish inside profile on second side.

That is how I would approach it.


Cutting oil is my blood.

 

[mmcmdl]

OOO . Order of operations . Turn your cone side to a straight shank above the finish diameter . Finish the left regular turning side . Mount in soft jaws and finish OD and ID of cone . No sweat .

 

[pontiac428]

I'm not sure I understand. After I part off the left, I would still need to turn the interior cone seen above. The only way to do that would be to chuck the 'bell' shown on the right, which I'm not comfortable doing.

No, you should not have understood what I said, because there was no axis of symmetry or centerline in your drawing, so I took it as something different than you were trying to express. When you put up the swept-revolved image of the part, it became clear, but before that I was seeing something different than what you were communicating. Good thing my consult is free, these would be billable hours anywhere else.

Should I ask why these parts look like K-baffles, or should we pretend you are doing something unrelated?

 

[twhite]

One other thing that would need consideration. What is the major diameter?


Cutting oil is my blood.

 

[HandyNotHandsome]

Should I ask why these parts look like K-baffles, or should we pretend you are doing something unrelated?

Ha! I had to look that term up. Does look similar!
At the risk of opening up a whole different can of worms, this is not a baffle, it is a nozzle for a rocket motor. (I am experienced in high-power rocketry, know what I am doing, follow all state/federal rules regarding this, have the proper certifications to fly these, etc. etc. I barely know what I'm doing in the machine shop, but absolutely know what I'm doing with rockets.)

Having said that, I'm pretty sure I could legally make baffles and the like in (parts of) the US, provided I had the proper stamps etc. Is discussion of these items prohibited/discourage on hobby-machinist.com? (But to reiterate, moot point, this is not what I am making.)