A few years ago I ran across an article and downloaded the file that helped you calculate the angle to cut the straight plywood so you could join these pieces together and they would form a curve for both the sub-roadbed and the roadbed. This worked great, now my problem, I must have deleted this file a while back and did not notice, have since overwritten my backups and don’t have a recovery method.Does anyone out there remember coming across this or even better developed the file and included it in your web page etc? I will soon need to build some more on curves on my layout, so… HELP!
I don’t have the calculator program. There was an article in RMC that I remember, but I don’t remember if there was a calculator there, either. But I did find a graphical representation of what you are looking for. Maybe you can use the picture in the link to lay out and determine the sizes you need. I think it should be pretty easy to figure out how to get what you’re looking for as I think it is just a geometry problem. Even if you’ve forgotten all your geometry, like me, I think you can manually lay out most of the information such as radius and desired lengths to the inside and outside of the trapezoid, make a paper template, and then use that to set the end angles.
I might be missing something in your situation here, but if you used a computer app to develop your track plan you can do as I did and simply print that out full size and create templates from the printout to trace the subroadbed shape(s) on your plywood. This has the added advantage of enabling you to lay the templates out on your girders and joists (L-girder in my case) beforehand to confirm everything fits.
Unless I miss my guess, the OP wants to cut segments from a rectangular sheet to minimize waste. I did something very similar to develop a cut-and-bend pattern when I turned a couple of steel studs into a base for a (tight, steep) spiral a while back. A 350mm radius required 12 segments to maintain inside-the-stud clearance. Haven’t worked out what a 610mm radius will require yet.
I, too, use full size track templates - but they’re developed with straightedge, trammel, flex track (forms natural easements) and a couple of sharp pencils, right on the site where the trackwork will end up. That sometimes requires me to set up a temporary worktop - a 4 by 5 sheet of 1.5 inch foam insulation that will eventually be chopped up to provide stock for landforms when I start building scenery. My templates are card stock, and (after being sealed with paint) end up as part of the permanent track construction.
Take a look at the link I posted above. You’ll see that the circle ends up surrounded by trapezoidal sections. Once you determine what this trapezoid looks like, you can use it as a template to cut like pieces from the plywood. These are then joined to make a circle, curve, or what have you. Particularly helpful if a helix is being constructed.
If one wanted to just cut out circular pieces from the plywood, there is a lot of curved waste that might not be useful anywhere else.
My hat’s off to all who can work with what’s been posted above. I tell myself I could do it, but it would be a struggle. And, maxman, your point about waste is well taken, although I took care to arrange my templates to minimize it (an interesting challenge in itself). It’s all part of the fun!
“What we have here…is a failure to communicate”.[:)] Maybe I confused you with the words?
The dark circle on the picture represents the circle he wants to cut. The distance from the center of the picture to the dark line is the circle radius. The dotted lines from the center of the picture are all at a 45 degree angle. So you have what looks like 8 pieces of pie. What you need to know ahead of time is how much width you want on each side of the track centerline.
So, just to pick a couple numbers, let’s assume that you wanted a 30 inch radius with about 3 inches of width on each side of the circle. Measuring from the center of the picture along the horizontal axis to the right, the distance from center to the dark line would be 30 inches. The distance from the center of the circle to the right where the horizontal dotted line is joined by those two other dotted lines (the ones with the dotted boxes) would be 27 inches, and the distance along this same line all the way to the right would be 33 inches.
You make these same measurements along the next line up from the horizontal at a 45 degree angle. Now connect the two points that are at the 33 inch distance, and connect the two points that are at the 27 inch distance. Now if you eat the other 7 pieces of pie, and trim away the pieces that are outside of the two connecting lines you just drew, you will be left with what looks like a trapezoid with a piece of your circle drawn on it. This becomes your cutting template. You can see that if you had a straight piece of plywood of the appropriate width, all you’d need to do would be to cut the end angles. This is where a chop saw would come in handy. Plywood waste is minimized.</
Amazing, maxman; thanks for the patient and thorough explanation. It’ll take a few readings and trials for me to get comfortable, but this looks really intriguing. I’ve never seen anything like it before.
I have to confess that I’ve never made one of these before. Like explaining time travel without ever personally achieving warp speed. But it should work as I described. I think the key things to do are to lay the pattern out initially on some expendable material, and then maybe put down a section of flex track to your intended curve and see if you get the proper clearances you need to the edges of the piece and whatever you’d use for the vertical risers (assuming you’re making a helix). If you’re just making curved sub-roadbed, then the clearances to the edges are not so critical.
My understanding (having never built one) is to cut 2x the number of pieces needed out of half thickness plywood. They are then overlapped and glued with clamps or weights to hold till the glue sets.
To double up and glue, the trick is to cut trapezoids with the shorter side to the outside (full overlap at every angle) and then fill in the topside with four smaller trapezoids. Outside supports go at the angles, while inside supports would be better on the four double-thick straights.
When I cut my steel stud helix I wasn’t trying to save material, so I got a floor overlap at each corner by only cutting one side of the ‘waste’ triangle, then bending the outer wall and screwing the overlap together. I had to be careful that the threaded ends of the sheet metal screws didn’t intrude on the clearance diagram - railhead to bottom of next level is NMRA minimum.