Help! When laying out a curve on a plan how do you determine where to locate the apex of the curve? I’ve seen many drawings showing the theory but not the practical way of doing it.
Charles Sanchez
PRR-Perfect RailRoad
I don’t know that I understand your question. I have read that a railroad comprises curved tracks with tangents linking them. I have drawn up several track plans, and never felt the need to know where the apex of a curve is located. Instead, I figure out the purpose/destination of any length of tracks, and merely configure a series of curves and tangents to get a train there.
Far more important, in my view, are easements and coupler-friendly geometry. Radii are also important, of course, and I let the curve fall as it wants to once I determine the orientation of the tangent to follow.
As for your question, I use arc lengths. When a curve of a suitable radius for all of my engines and rolling stock is set in place, I merely adjust its arc to suit a reasonable plan so that my trains go where I want them to go. In that respect, the curve determines its own apex.
-Crandell
It all depends on whether you want an “early,” “mid” or “late” apex. Seeing as the train is stuck following its rails, the engineer really doesn’t have a choice.
It doesn’t really matter where your curve reaches it “sharpest” point, just as long as you get around the corner. I used large graph paper and a geometry set to plan, but if you lay your track with a geometry set it will not look real.
I drew up my track plan and started to throw down track. When it came to curves I made sure I eased into and out of the curve and did not go smaller than my smallest allowable radius. I checked the radius with these cardboard cutouts to make sure I didn’t go under it at any point.
I have some curves that needed to go 180 degrees but made the first or last part of the curve a larger or smaller. If you have the space let your track flow with your yet to be constructed country side. That’s what happens in real life. Good luck.
Brent
Darn, beat me to the racing reference.
If you really mean center, what I did to lay it out on my benchwork was extend the two straight lines past the curve, and since the center fell off the actual benchwork, I set up my camera tripod to use as the center pivot for my trammel. Tril and error lined things up with the straight part at each end of the curve, and then I drew the curve centerline using the trammel. Pretty simple in the end.
In the design process, I basically put the straight parts where they neded to go and used the CAD program’s connect tool to join them at my desired radius.
–Randy
Darn, beat me to the racing reference.
If you really mean center, what I did to lay it out on my benchwork was extend the two straight lines past the curve, and since the center fell off the actual benchwork, I set up my camera tripod to use as the center pivot for my trammel. Tril and error lined things up with the straight part at each end of the curve, and then I drew the curve centerline using the trammel. Pretty simple in the end.
In the design process, I basically put the straight parts where they neded to go and used the CAD program’s connect tool to join them at my desired radius.
–Randy
Hey Charles
My way is not rocket science but here goes. I took a piece of 1/8" Masonite just over 24" square, a thin strip, drilled with 1/8" holes one for a pivot at the end, with holes drilled at 18", 20", 22" and 24". put the pivot at one corner of the Masonite and draw quarter circles at 18" thru 24". Cut along these lines with a jig saw and you have gauges for your curves. You end up with 3 gauges with 2" difference, very handy.[tup] For shallow curves I pin a thin strip of wood or Masonite on edge at both ends where the track should enter and exit. bend the middle to where you want it and mark for track. If you don’t have a tool, make it. [:-^]
Just my way [:D]
Lee
If finding the center of the circle is what the gentleman means, yes, I agree that a trammel and a handy camera tripod are the tools to use. You can also tie some good fishing line, like Fire Line, around the screw on a tripod head, and measure along its length to where you should tie a pencil or a metal scribe for the radius you want. Then, keeping the fishing line taut, simply draw out the arc you need, plus about four inches on either end just in case.
-Crandell
Thanks for all the answers. Up to this point I’ve just been using a long piece of cork roadbed to lay out my curves but thought there must be a better way. Again, thnks to all.
Charles
PRR-perfect RailRoad