I’m starting to layout my yard and I want to keep a 2 inch spacing between tracks. Common sense tells me to draw a line parallel to the mainline track at the right spacing, install the turnout, attach a 3 foot section of track and bend it to shape down the penciled line. But, I wonder… just how much ‘straight’ track like from point A to point B do you need and how would a person figure that degree of curve from point B to point C?
JaRRell
Hey,
Very, very cool subject line… Plus, it had 11 views and no answers! - Got to look as this one! 
I’m pretty sure the issue is defined beautifully in John Allens book, but I don’t have it with me right now, and I’m sure others will address the ‘math’ angle (no pun!) in other posts.
For me, with flextrack, you had it right - “Once it gets to the centerline, and the curves are nice and smooth, we’re good!” - NO stinkin’ kinks - Not even small ones that no one but you can see - never!..
My 2c. Even though the subject line should probably have been ‘and’ instead of ‘vs.’
Cheers,
Ian
Ian, thanks for the answer. I see it’s up to 16 views and one answer now. Either it’s too tough or it’s too simple for some to answer. My guess is that most modelers draw that line and bend the track to fit, but I’d like to know how far to go before you start bending. Maybe it just doesn’t matter?
I dunno.
JaRRell
If you can find one of the older Atlas books on Custom-Line track (assuming that’s what you are using - the Code 83 has the exact same geometry as the Code 100), in the back are some hand planners that show a lot of this. Or just use flex track and make it a smooth curve - it’s easy to bend the flex track into a position that result sin a very tight radious curve.
The other thing to do is lay the yard out the other way - so that the ladder turnouts are at an angle and the diverging route leads into each siding. Less S-curve to worry about then - only from the first turnout off the lead to the first yard track, all the others have enough straight track in them. This works for any line of track (except the snap-track type with curved turnouts that subsitute for a standard curve section).
–Randy
Cut a 22" curve the width of your track plus ties out of thin cereal box cardboard and use that to draw the outline that you hope to achieve. Next, solder your rails while straight, then curve it to suit the outline that you drew. If the curve stays true to form, you know you won’t be any sharper in curvature than 22", and will happily run everything but long steam, like a 2-10-4.
A To B should be 1 car length so the car isn’t dog tracking. This isn’t always easy to get so you need to learn some “tricks” like the rrinker suggested. For radius from B to C if it is a constant radius you can extend a line parallel to the first tie and a line parallel to the last tie. Where the line intersect is the center of your radius.
Truthfully, if it were me, I would 86 the sectional track and use flex. Your common sense is partially correct but you’re going about it the long way around, negating the common sense.
Just a thought…
Jeff
Take a college trig course. LOL Up is Y, sideways is X. You need lots of knowns before you can figure it with math, and nobody is gonna take the time when we have a box of track, a scale, and rail nippers. You need the diameters of the two circles (turnout and track) and the segment lenght of each so you can plot the centers of each circle and then use the 2 inch Y coordinate difference between the two circles centers to find the hypotinuse of the right triange to get the centers of the circle the right x disatance apart to make the Y=2 inches. The hypotimuse will be the AB distance. From memory. That’s basically it and is why you just cut and measure.
On your original photo, move ‘A’ to a point about 3/4 inch to the right of the frog point. Now measure the length over couplers of the longest car with body-mounted couplers that you expect to push into the siding. That length equals distance ‘A’ to ‘B.’ To the left of ‘B,’ you can eyeball the curve or use a template to assure that you don’t go below your desired minimum radius.
If you run only early transition-era freight cars, they should handle 2-inch centers nicely. On the other hand, if you body-mount the couplers on full-length passenger cars, 89 foot auto racks, humongous hi-cubes and the like, your spacing will go up dramatically!
To determine this you would first have to know the final angle of departure through the turnout.
The degree of curve needed from point B to point C, would be the same as the departure angle of the turnout. If it is a standard #4 the departure angle would be the arctangent of the opposite (1) over adjacent (4) or atan(1/4)=0.245 radians=14 degrees.
The amount of straight track needed would be depend upon the desired radius of the curve, and how much straight track is already included with the turnout. One would then take the cord for that degree and that radius and subtract the existing distance from the departure already in the turnout. The broader the radius the shorter AB would be. So it then becomes a trade off of a sharp curve with a longer straight to avoid the “S”, or a broad curve with zero straight making a true “S”.
Then If you want to calculate an easement type curve break out the calculus book.
[quote]
QUOTE: Originally posted by Texas Zepher
Agreed!
So, I stick with my original answer - “If it looks right, it probably is right” .
Assuming you know already what your rolling stock does on different radii etc and don’t tolerate no stinkin’ kinks you’ll be good - You can’t even ignore the kinks you didn’t see the first time you looked…
Good to see the math show up as well though.
Cheers,
Ian
Yep, I knew some of you guys knew the math though the explanations went right over my head about… oh… ten feet over I would guess. I’m going to do it the only way I can and that is to draw a centerline spacing of 2 inches… maaaaaybe 2 1/4… and gently work the flex track into the curve.
I appreciate the answers!
JaRRell
Geeee Whizzzz guys…thats awsome gray matter stuff…I gueess I kinda did it the hard way…drew two lines 2 in apart, a nice curve and hammered the spikes home. O well it works and I aint gona fix it…Just kidding…Sometime I jus cant help myself…John
Laying the ladder out like I mentioned avoids it altogether. For other places where it HAS to be that way, I do it by eye. I CAN do the math, but quite frankly that starts taking away from the ‘relaxing’ and ‘hobby’ aspect of things. After going through the trouble to use a CAD program to print my track plan full-size and trace that on the foam - I can say most definitely NEVER NEVER again. For the rest fo the layout - the track plan is done to scale in CAD but ONLY to verify that I can fit in what I want without making the curves too tight or having the track hang off the edge in mid-air. I have no idea why I did the full-size print thing, on my previous layout (just a small shelf switching layout), while I had a plan to work from (one of the ones in 100 Track Plans), I did not make an enlarged copy, or draw it out ont h benchwork, I just started building, and it came out fine. Same concept - the plan ensured that I could fit the turnouts in the space I had available, but I did nto and do not care that the track MUST go in EXACTLY this spot to some .001 inch tolerance.
–Randy
I am going through this process right now! Last night I did my subroadbed plywood rtibbon cutting with my jigsaw. My track plan is on 1 sheet of 8 1/2 x 11" sheet of paper and I am winging it. I use my eyes and feel to work the easements and a template for the set radii. Here’s a couple of photos for you …
I agree completely. I use CAD to keep me accurate on turnouts, radii, etc. But when it comes time to lay track, I print the layout on an 11x17 piece of paper and use that as a plan/guide, not a “to the n-th degree” template.
Thanks for the advice. I have a plan but I’m using as most of you do… just to let me know it will go there. I’m going to start laying the ladder out, get the track centers 2 inches apart and run with it.
I hope the heck it works…
Jarrell
I don’t worry about the S curve in a situation like this. I get another turnout the same as the first one and put it in place to form a crossover (frog to frog on the curved track). Then I trace one of the rails onto the roadbed, and match the flextrack to that.
Note that what you just wrote sounds about how I do it too. I just answered the question. Just because one can calcuate all that stuff doesn’t mean it needs to be calculated.
The method quoted above is the easiest way. What you wind up with is flextrack which curves at what is usually called the “equivalent radius” of the turnout in question. If you’re lucky, that value is already available from the manufacturer.
If not, and you feel that you’ve REALLY got to know that radius, you can find it as follows. First, measure the angle of the frog, in degrees. Or you can look up that angle in a table of frog numbers. You have to be careful though, a #6 turnout from a manufacturer may not actually be #6, but #5.5 or maybe #6.5 ( All of that manufacturers turnouts will be the same, of course, but they may have fudged a little on the numbering. In this context, that little difference will matter. ) Also measure the straight distance between the track centerline where the points touch the stock rail, and the centerline where the diverging route stops curving. Do a little math:
The length of the chord, that distance between centerlines, can be calculated by:
Length = 2r ( sin 1/2 A ) where A is angle in degrees you measured, and r is the equivalent radius of the turnout.
So therefore r = Length / { 2(sin 1/2 A) }
The method mentioned by BR60103 does the same thing, but avoids the calculations.
-Ed