This might be common knowledge; but it just occurred to me, so I thought I’d post it:
When you use flexible track on a curve, the inner rail gets ahead of the outer rail and generally needs to be trimmed to realign the joints for subsequent track sections. The news is that the amount that needs to be cut off does not depend on the radius of the curve. It is also immune to multiple radii or even a continuously varying radius, as in a spiral curve. All that matters is the net change in direction from one end of the track section to the other.
The amount is the center-to-center distance between the rails multiplied by the net direction change in radians. For the outside rails of O-gauge track, this is about .024 inches per degree. For the center rail compared to one of the outside rails, it is half this, or .012 inches per degree. So, for a 90-degree turn, the outside rails differ by 2.16 inches. For S gauge, it’s about .0175 inches per degree.
Of course, you can put the track down first and then cut it to fit; but this rule might be handy when that order is inconvenient or when you can do a better cutting job at the workbench.
Another good point regarding cutting “Flextrack” (if you have known curves with multiples) is to make a jig on a sheet of plywood. makes it much easier to cut. I believe in one of the magazines in the last few years, they mention some of this, but I doubt they went as far as Bob on calculations…good to know.
Too much math for me lionelsoni. I just laid the track on the platform, held a straight piece up next to the curved piece, marked it with a sharpie and whacked it off with a fine bladed hacksaw. Much easier and my blood pressure stayed below 140/100.
To much math, but some like that sort of thing. I screw it down and cut with a Dremal disk. no headache from thinking. Plus you can install the entire curve before cutting.
“Plus you can install the entire curve before cutting.” If you don’t cut it first, this is surely what will happen. But are you suggesting that there is a problem with cutting first if you need more than one section in the curve? Not so! You can leave the first section uncut and take out all that you need from the second. Or, cut out a piece approximately appropriate from the first section and then subtract that (oops, more math!) from what you would have cut from the second. For example, if you’re going to need to cut 2.16 inches for a 90 degree turn and a track joint occurs somewhere near the middle, take an inch out of the first piece and only 1.16 inches from the second.
I’m not suggesting anything. do it any way that works for you. Me: I install the entire curve by sliding the rails to fit the next piece and when finished I square off the two ends, you can even run past the curve and cut at the next straight section.
