How to turn parts with nothing to grip?

[HandyNotHandsome]

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

Major diameter is roughly 1-1/2 inches.

 

[pontiac428]

No, it's not prohibited here. Just a popular pursuit among newcomers. To be honest, I really like the project idea of a rocket nozzle, it's an excellent application of home shop skills.

Turning thin shells like that will make a better machinist out of you; it looks like a tough part to make. Order of operations is probably the most important thing to sort out. Like I and others said, figure out if you can leave behind a piece to hold so that you can flip the part and work the other side. If you can make parting off your last step, you won't have to worry about fixturing after that.

Sometimes, it becomes necessary to make a custom arbor or fixture to clamp the machined features of the part so you can finish it. It's the preferred way to do it in production, but for one-off parts, you just want to be able to hold the part so you can machine it. It may use some sacrificial stock, but sometimes there is no other way.

 

[HandyNotHandsome]

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.

Thanks - I hadn't considered a faceplate; I think some combo of bung/faceplate/center/glue will do the trick for me!

 

[DavidR8]

If it’s a part that you foresee making multiples an arbor to hold the shallow taper might make sense.

 

[HandyNotHandsome]

To be honest, I really like the project idea of a rocket nozzle, it's an excellent application of home shop skills.

It's a fun hobby. Some of us are making our own motor casings (6061 aluminum tube), nozzles/closures, and propellants. And then of course the rocket itself, which is a different set of skills - the rockets are typically some combination of paper/plywood/fiberglass/carbon fiber etc. and typically doesn't require much in the way of machining. Hobbyist high-power rockets can easily exceed Mach speeds, go thousands of feet high (sometimes hundreds of thousands of feet - so, technically into 'space'), and weigh hundreds of pounds. Not the same model rockets we flew as 12-year olds!

 

[ChazzC]

I’m with @DavidR8 : make an arbor to accept the “inset,” which will keep all pressure off the bell. As an alternative to super glue you could make the arbor with slits not unlike a custom collet and hold it in a chuck. This part would be a good application for an Eccentric Engineering Flexi-Chuck

Other suggestions are valid if you didn’t already have the part almost complete.

 

[homebrewed]

The outer taper of the nozzle isn't functional, is it? The form as shown looks pretty cool but if it's not functional you can simplify the machining steps, in terms of the workholding issues. The nozzle would be more robust as well.

I can see the purpose of reducing the weight of the nozzle but perhaps it's not a significant percentage of the overall package?

 

[markba633csi]

Removable glue is a good method- lens makers use a type of rosin also to hold glass pieces for polishing

 

[OTmachine]

Do the right side first. Part off to length. Second / finish operation, hold by inset diameter in bored out soft jaws to machine the cone.

 

[HandyNotHandsome]

The outer taper of the nozzle isn't functional, is it? The form as shown looks pretty cool but if it's not functional you can simplify the machining steps, in terms of the workholding issues. The nozzle would be more robust as well.

I can see the purpose of reducing the weight of the nozzle but perhaps it's not a significant percentage of the overall package?

Correct; the outer taper is just to reduce weight. As it turns out, the back end of a rocket is the worst possible place to have extra weight (it affects stability), so every gram saved back here helps. And steel is heavy (compared to the other materials used in a rocket) so IMO it's worth the extra effort to take it off.