Need some framing help.

[MHSTech]

I'm working on a wooden curved staircase for a show. I'm having problems figuring out how to frame this. Any ideas would be appreciated. The inside of the stairs is a 14 inch radius. Also, despite how my drawing looks, I want the inside radius to be a curve , not a series of straight segments like it is drawn.

[Van]

Well... You could use "wiggle Board" which, if you're unfamiliar with it, is a plywood product that can be easily formed into curves. Ask for "wiggle board at a lumber yard they'll know what you ar looking for. Alternatively you could build up the curve by using several layers of thinner material, such as 1/8" Luan, Upsom board, or heavy card-board < Not the corragated kind>. Notice all these are "cover" or Finish treatments. With a 14" diameter there is no reason you can't have all the sides of the steps be " Flat" or perpendicular to the front edge of the tread, then let the cover treatment create the smooth curve look you are trying for. If you don't have access to either of the afforementioned materials you can also use 1/8" masonite but you're probably going to want to wet down the back side of it for a while to help mold to the curve. That help ?

[MHSTech]

Yeah, that helps.

[bobgaggle]

assuming a 8" rise, and a 10" run, and 1" plywood for steps:
All you have to do is build a 1x4 frame for each step. example. Step number 2 is 16" from the ground. So build a frame that is 15" tall. Then all you have to do is nail another piece of 1x4 to the front of it, at the height of the previous step (minus the plywood). this board would be at 7".
See the pic...

staris.jpg

This setup is great because it can collapse and be stored for future use, and because each frame is independent of the others, they can be aligned in any curve and a step can be cut to fit. Naturally braces will have to be added for additional support and rigidity

[Van]

Kinda like the old Parallel platform idea. Cool !

[Lemonjello]

Draw a full scale on sheets of ply on the ground(birds eye view), cut out treads, build in sections, straight, curved and platform, easier to move later. Use 1/2" ply use PL glue and screws 2x4 on edge as braces under steps and at section connections, join with bolts/washers/wing nuts. dont forget the tread thickness in calcs. Here is a link to a calculator for sizing,http://www.blocklayer.com/Stairs/StairsEng.aspx

use centerline of stairs as tread length ie: stairs 4' wide, measure at 2' this will give you a Total "run", figure out how high you need to go to get "Rise" and plug in you #'s to get the dimensions you need.

Use your full size template to get inner/outer tread lengths, skin with "bending ply" for smooth curves.

Not exactly an easy job but doable. If you have more questions, i can likely answer them, I was a framer/ Carpenter for 10+ years.

Edit:
Use ideal run on the calculator, it will in general stay close to 7/11. may change number of steps but you can add/subtract risers for good fit. As far as the stringer, in your case it would be just a big plywood triangle with a saw tooth cut out. Does the outside radius need to be curved also? If not it would be easier to square it off on that far side for framing, the the only curve you have to deal with is the inside radius. I'll post a pic.

[Lemonjello]

here are some quick (not at all to scale!)drawings of what I mean.

[bobgaggle]

Haha, is everyone on here using SketchUp?