Laying FlexTrack Curves

[tgindy]

While this is a Flextrack question - Looking at Atlas sectional track specs can be instructive.

Atlas N Scale Code 55 track has much greater radius choices than N Scale Code 80...

http://www.atlasrr.com/Trackmisc/ncode55.htm 

Here are the track radius choices on center...

10.00, 11.25, 12.50, 13.75, 15.00, 16.25, 17.50, 18.75, 20.00, 21.25, 30.609, 71.00.

Note the minimum 1.25 inch track centers between parallel curves.  In "Atlas-world" you would either go with 1.25 inch center, or go to a 2.50 inch center, etc.  Now see what your overhang is on a curve from your longest passenger car as to function and/or appearance.

Atlas stock N Scale Code 55 track radius centers are what they are for good reason.  Sectional track is meant to be in a sense - plug 'n play.

Just some perspective that may help when measuring for flextrack.

[Trekkie]

so there are two answers depending on which is the true requirement.  

Two make life easier for the semantics.

I want two tracks, side by side in paralell that when go into a curve have a 19" radius.

If that means the inner track has a shorter diameter than the outer track, so be it. I pulled 2" seperation out of .. ahem so if the 1 and 1/8th inch is the right one for N scale that works for me.

If I understand it right I'm going to have a 19" radius outer curve, and then a 17 7/8ths inner curve with that. Any big engines or wide arc turn items should only be used on the outside edge if I want to do it right.

Or go to 22" outside and 20 7/8ths inside if I want to be a bit wider.

[Texas Zepher]

 So if he wants parallel curves, he will have to have a radius differential between the two of two inches. This is basic geometry.

True as long as one sticks to a single sub-set of the definition of curve (constant arcs), and Euclidean Geometry, and that would get back to the answer in my original post.  This often happens in projects when the specifications ask for two contradicting things.  One can't have "two parallell curves with a 19" radius.".   It is one or the other, so there are two answers depending on which is the true requirement.  

[selector]

Unfortunately if you do this the tracks are not parallel around the curve. If you want them parallel, the radii of the two curves must differ by the desired offset of the two tracks - in this case two inches. Reading the original post, we see that Trekkie is using flex track. So if he wants parallel curves, he will have to have a radius differential between the two of two inches. This is basic geometry.

Absolutely.  Parallel, by definition, means that the two arcs or lines deviate by 0% along their entire lengths, from start to finish.  That means they must have, if arcs, the very same centre, and deviate by no measurable distance between them at any one point.

Achieving it, however, could be a real challenge if easements are incorporated...at least, it would be for a semi-skilled track layer such as I.  I am sure it would be a piece of cake for many folks here.

[Trekkie]

Thanks for all the comments/setting me straight.  Think I'm going to do the single ruler with multiple holes idea the board I got is a bit to unwieldy.

Would really like to get some track down just so I can play with the soldering iron and do some things I've not done before by laying flex instead of buying bits and pieces.

[Pruitt]

So you have two parallel tracks.  We'll call the inside track A and the outside track B.  If you want them 2" apart, you have to make track B two inches longer than track A before the curve.  So if it is straight before the curves, track B will have two inches more straight than track A before the curve starts. 

Sorry, but this wrong. both track "A" and track "B" would be the same length. Only the radius of the out side track would be greater then the inside track by the amount of track separation.

No it is not wrong.  See the picture below.  Both curves are 19" radius.  But the outside curve is straight before the curve.  The length of the straight determines the separation between the double track coming into the curve.

 

Unfortunately if you do this the tracks are not parallel around the curve. If you want them parallel, the radii of the two curves must differ by the desired offset of the two tracks - in this case two inches. Reading the original post, we see that Trekkie is using flex track. So if he wants parallel curves, he will have to have a radius differential between the two of two inches. This is basic geometry.

[Eriediamond]

So you have two parallel tracks.  We'll call the inside track A and the outside track B.  If you want them 2" apart, you have to make track B two inches longer than track A before the curve.  So if it is straight before the curves, track B will have two inches more straight than track A before the curve starts. 

Sorry, but this wrong. both track "A" and track "B" would be the same length. Only the radius of the out side track would be greater then the inside track by the amount of track separation.

No it is not wrong.  See the picture below.  Both curves are 19" radius.  But the outside curve is straight before the curve.  The length of the straight determines the separation between the double track coming into the curve.

 

You are correct, of course, when using sectional track. My understanding was that  maintaining the same track spacing through the curve was the goal here, to which my answer was based because flex-track was being used. Ken

[Texas Zepher]

So you have two parallel tracks.  We'll call the inside track A and the outside track B.  If you want them 2" apart, you have to make track B two inches longer than track A before the curve.  So if it is straight before the curves, track B will have two inches more straight than track A before the curve starts. 

Sorry, but this wrong. both track "A" and track "B" would be the same length. Only the radius of the out side track would be greater then the inside track by the amount of track separation.

No it is not wrong.  See the picture below.  Both curves are 19" radius.  But the outside curve is straight before the curve.  The length of the straight determines the separation between the double track coming into the curve.

 

[Jacktal]

    Parallel track spacing in N scale should be 1 1/8 in. center to center (as per Atlas N scale book) so that a pair of turnouts creating a crossover will fit without any modifications.Peco is little different with their double crossover tracks set at 1 1/16.In yards,track spacing can be reduced to 7/8 to save space on straight track areas,but that complicates 0-5-0 switching considerably.

[bogp40]

Right.  If the one track is 19 inches and you want the other to be parallel and separated by 2 inches, it's gotta be either 17 or 21 inches from the same center.

I'm in HO so I can't help you with the N scale question, but it would seem that 2 inches is pretty large, BUT maybe not depending on where it was being used.  In a yard that would be huge, but might not be the case out on the mainline.

JaRRell

Don't forget to include any easments. You can have straight mainline tracks 1 1/2" OC and ease into the different radius and don't necessarily have to maintain the same 1 1/2. 2" does sound very wide spacing for N.

I do HO. What would be an appropriate track centers for N.

[TheK4Kid]

Heres what i did.  I took a 3 foot metal ruler and drilled holes in the 1 inch mark and then drilled a bunch of holes in the ruler at the number of radiuses i wanted.  With this method after finding the middle of circle i tacked the ruler their then used my sharpie and selected the hole of my radius plus 1.

For double curves choose the outside radius, draw the curve then move 2 inches in on the ruler and draw the next curve its that easy

 

 

NEAT IDEA!!!!!

 

 Ed 

[jacon12]

Right.  If the one track is 19 inches and you want the other to be parallel and separated by 2 inches, it's gotta be either 17 or 21 inches from the same center.

I'm in HO so I can't help you with the N scale question, but it would seem that 2 inches is pretty large, BUT maybe not depending on where it was being used.  In a yard that would be huge, but might not be the case out on the mainline.

JaRRell

[Eriediamond]

So you have two parallel tracks.  We'll call the inside track A and the outside track B.  If you want them 2" apart, you have to make track B two inches longer than track A before the curve.  So if it is straight before the curves, track B will have two inches more straight than track A before the curve starts.  HTH 

Sorry, but this wrong. both track "A" and track "B" would be the same length. Only the radius of the out side track would be greater then the inside track by the amount of track separation.

[gilligan]

Heres what i did.  I took a 3 foot metal ruler and drilled holes in the 1 inch mark and then drilled a bunch of holes in the ruler at the number of radiuses i wanted.  With this method after finding the middle of circle i tacked the ruler their then used my sharpie and selected the hole of my radius plus 1.

For double curves choose the outside radius, draw the curve then move 2 inches in on the ruler and draw the next curve its that easy

[Texas Zepher]

So you have two parallel tracks.  We'll call the inside track A and the outside track B.  If you want them 2" apart, you have to make track B two inches longer than track A before the curve.  So if it is straight before the curves, track B will have two inches more straight than track A before the curve starts.  HTH 

OR if the 19" curve is the inside then the outside would be 21" radius.  Or if the 19" curve is the outside then the inside would be 17".  The CENTER of both would be the exact same point.

On another note, isn't 2" separation for N-scale rather far apart?

[Conrail5]

Think about it, if you had two identical 19 " radius curves the outer one would intersect the inner one where the straight portion continues. If you want them 2" apart they both can't be the same radius one has to be 2" larger or smaller than the other. (i.e. 19", 17" or 19", 21" )

[KlickyMobster]

So you have two parallel tracks.  We'll call the inside track A and the outside track B.  If you want them 2" apart, you have to make track B two inches longer than track A before the curve.  So if it is straight before the curves, track B will have two inches more straight than track A before the curve starts.  HTH 

[Trekkie]

OK, I've gotten a few books, and I've bought some flex track, and I'm confused.

I want to have two parallell curves with a 19" radius. (N-Scale)

I've got a board with holes drilled in it 19" apart. One for the pencil and one to mark the center of my circle. I thought I remembered geometry/trig, I guess I don't.

I thought if I wanted them to be 2" apart, I draw one curve, move 2" in from the center of the last curve, and draw again.

Either my head is not on straight when I make the curve or I'm doing something wrong, as they keep overlapping at the ends.

Do I have the right idea? or am I doin it wrong.