I'd like to include helices in my new N layout. I have a run of 2 foot by 11 foot down one wall, linked by a shelf to a 36" long by 30" wide run on the opposite wall. The 2 foot wide run could be widened by maybe 6" or so at its far end to accommodate a helix. I'd like to have a helix at either end of the 'U' down to staging below (baseboards at 48" high currently). However, I'm unsure of the minimum radius I could get away with (i.e. to fit in the board widths). I'm using Atlas code 55, and they have curves down to 10". What can get round curves this tight? I've got a diesel only fleet (SP and Cotton Belt) of various sizes, but freight only rolling stock with nothing much longer than 65' gondolas. Also - does anyone know of a helix builder - I'm no woodworker!!