Cut a spiral on a mill? My idea is a failure

[drrags]

I need to cut 180 degree spiral at a 20 degree angle. In my head, I thought I have what I need, but when I practiced with a sharpie, I see the flaw in my thinking. My convoluted method will just cut normally across the circumference and not at an angle. Is there a way to cut a spiral groove in round stock or tubing that doesn't require a lathe attachment?
(I didn't even notice until I posted the pic, but that little cylinder on the lower-right of the table is what I'm trying to mimic)

 

[drrags]

Staring at this pic for awhile, I think the answer, since it will be a tube, will be to just clamp everything down and run the table in the Y direction. Who cares how deep the mill goes since it's a tube. Hmmm...

 

[Reddinr]

Or, your basic rethought idea and a slitting saw?

 

[Jim F]

or

 

[RJSakowski]

Staring at this pic for awhile, I think the answer, since it will be a tube, will be to just clamp everything down and run the table in the Y direction. Who cares how deep the mill goes since it's a tube. Hmmm...

What you are proposing will be the circumference of an ellipse rather than a helix.

There are ways to cut a spiral on a mill but they involved having a rotary index linked to the table feed.

This is a piece of cake for a CNC mill with a 4th axis.

 

[epanzella]

It looks like 3 straight cuts to me. If that's true put the rotary base of the indexer at the angle you need, plunge in at one end of the angled cut and feed with the Y axis. Then Adjust your angle to match the 2 short slots on either end of the long cut and feed that with the X axis. Leave the spindle of the dividing head locked for all 3 cuts.

 

[benmychree]

Yes, to generate a true helix, a dividing head needs to be geared to the table screw with suitable change gears, usually done with a universal dividing head that has an input shaft that rotates the dividing plate, although, if the worm can be disengaged and a shaft extended through the spindle taper, the change gears can be connected to the table screw that way. The setup is illustrated in Brown & Sharpe's book, "Practical Treatise on Milling and Milling Machines.