Rob,

Good to see you around here again, we've missed you.

Think about the old Slinky toy - the radius doesn't change when you stretch it out, does it? Neither will your railing, but there is one caution. If the railing is flat, oval or profiled in cross section it will tend to show a "twist" as you pull it up, and you have to counteract this by either pre-twisting the other direction before stretching or tweaking it afterward (my method).

Make a form to bend the rail around and go for it. With a couple of bending forks and a handful of clamps you'll get just fine, I'm quite sure.

Rich

One of the easiest methods is to bend to the finished stairs with a gas torch, twisting as you go ....we often tack to the treads to help us....that is, if you can put everything together in the studio ....or on site
good luck
Giusseppe

Where to bend next ... www.metalgarden.ca

Rich and Giusseppe-
Thanks so much for your responses- most helpful. I apologize for my belated reply. I ended up making a 1/4 scale model for the stairway, both for myself and for the building inspector. The miniature handrail worked out great. Now I guess the real thing should only be about 4 times as hard to make…?
Rob

Hi Rob, I tackled my first curved stair case last summer and it was quite a learning experience. We built it on site useing a handy, but not cheap, tool called a Portabender for the top and bottom rails. We tried bending each rail as one piece, but quickly switched to 6-8' sections because they were so much easier to manipulate that way. Every little adjustment had a dramatic effect at other points on the piece. We found out that there was not only a spiral but a twist as well so we would bend our piece to the appropriate curve and then put in a twist if we needed it. After all of the pieces were fit up we welded them together and cleaned up the joints. We were using rectangle profiles,flat bar and channel, so the twist might not matter with round tubing. The inside and outside rails are completely different. The outside being like what you have drawn above and the inside much much tighter. Lots of twist on the inside rail. I don't under stand the need for the twist and it took me 10 days of swearing and bloody knuckles to accept that i needed it for the rail to work, but after that it was pretty "easy", lol.

If you have the height and equipment in your shop, it might be easier to fabricate there if you can figure out the appropriate start and top points and can make it in pieces or figure out a way to install it as one piece. Except for the other contractors working around me and the fact that they installed a $15 sqr foot wood floor under us while we were working, it was nice to build the rail on site. I didn't have my shop's full complement of tools which was frustrating, but, we could custom work each piece to fit exactly they way we wanted it. Of course we had to hear every suggestion in the book from drywallers, painters, handymen, you name it while we were figuring things out. I've never like earplugs more, lol.

Post updates on the progress

Jake

Jake Balcom
Mettle Design
Lincoln, NE

If you are sure of your dimensions but cannot pre-build the stairs in the workshop then I recommend the use of a thin board cylinder stiffened from behind. You can mark the stairs on the flat then curve the board and stiffen .....I have even taken a board on site to check the radius if the stairs are already in place.(if on site, simply notch a stiffener when the board matches the curve then re bend back at the studio.) If you have an hydraulic press the shaping is easy, otherwise you can make a jig to fit part of the length and work along it hot.
sheet metal is even better because you can tack to it but not so easy on site.
If you get stuck with part of a curve on site then I recommend the use of a tree outside as you bending horns ....you can even twist against a v between strong branches.
Panels can also be adjusted outside with the back wheels of a car/truck and two pieces of 4x4 timber. Lie the panel on the timbers and back the car onto the panel ...a judicious use of stops under the panel will allow you to alter the curve in small increments.
Some of my stairs are very free form and I find a greater need for improvisation on site and often weld bending horns to one of the treads in order to sculpt shapes ...if I am near the end and have removed such an aid then I have to resort to spaces between elements in place as my bending jig. have a look at the staircase in Ireland from a couple of years ago and you will see what I mean.
I am not sure why you would have to make a scaled model for an inspector ...I would have thought a mock up of a section would be more convincing and all the parts can then be re used in the work ....you can even apply bending loads to such a section if the maths does not convince ....
Also .....mocked up sections make great exhibition fillers or gifts to mothers....or did I mean lovers
G

Where to bend next ... www.metalgarden.ca