Building a curved module; framing

[pedro]

If this ends up being a duplicate or triplicate posting I apologize, I tried it once by attaching a copy of my drawing and got an error saying the upload folder was full. Tried it again without the attachment and it said I had already posted the message (I don't see it) Third try here...

Anyway, I'm working on a sectional layout design and was wondering if anyone here had ever built a curved corner module. That is, with both the inside and outside module faces curved, as opposed to the nTrak method of a trapezoid shape, or having the inside straight, both of which are easier to frame. I have an idea of how to do it, but if anyone has a suggestion on framing it out, I would like to avoid reinventing the wheel.

Frame material would be 1/2" ply, with the curved pieces being 1/4" ply and the whole thing decked with 1/4" ply. The curve radii are very large: approx. 46" inside and 82" outside. I don't imagine bending 1/4" ply to that radius would be too hard. The three "x" joints near the outside curve in the drawing would be lapped.

Does anyone see any problems with this or have a better suggestion?

Pete

[ednadolski]

I find 1/4" ply hard to bend.  I use two layers of 1/8" ply glued/laminated together.   (takes a fair number of clamps tho).
 
The other thing I do is add diagonal braces to help stiffen it up & prevent flexing.  These I make from 1/4" ply strips to form an "X" shape and would go inside the two largest rectangles that you show in the drawing.   I'd hot-glue them their whole length to the 1/4" ply top, and where they connect to the frame corners.   You want to keep the top from flexing, these braces help transfer any flex/torsion forces to the adjoining members of the frame.   Kind of a hollow-core door principle, you'll be surprised at how rigid it can be for the weight. 

[pedro]

Good suggestions, thanks. That's what I'm hoping for - rigid and light.

[tom mann]

Can you share a bigger photo?  What is the minimum radius?

[pedro]

The thumbnail should take you to a slightly bigger version on trainboard. (I know, I need to do something about hosting).

The minimum mainline track radius is 55" if used as an inside corner, and 72" if used as an outside corner. (48" minimum in staging) The benchwork radius would be about 46" and 82". The module width would be 3', with 12" of that being staging behind a backdrop.

Pete

[ñiao]

If you use 1/4", try to build at least the module heads with 3/4" plywood. Takes away some stress.
Give the areas where you screw on the 1/4 a slight bevel. Gives a bigger surface.