"steamer" wrote in message
...
--A friend of mine wants to build some big-ass Hero's turbines. He
wants to have the steam exiting from tapered tubes on either side of the
devices. What we need is a method to roll, or otherwise form oh, say, 18
or 20 ga. steel into tapered tubes; maybe 12" long with 1" dia on the
small end and 2 to 3" on the other end. So how is this normally done; i.e.
do we need to make a mandrel or some conic sections to drop into a custom
roll former, or what?
--TIA,


It's done with a slip roll (roll former). I haven't done this since high
school shop, so you may want to get some advice that's more up-to-date. g

There are two ways to do it. You can set the back roll at an angle, if your
slip roller is made for it; or you can "drag" one end of the work through
the rollers, so that the wide end is moving faster through the rolls.

In my high school shop class we had to do it both ways. I never really got
the hang of dragging the work, but I think it's a matter of practice.

Any good HVAC or sheet-metal shop should be able to do it for you, pretty
cheaply.

Ed Huntress