# How to get the correct radius with flex track



## Jimganley (May 28, 2016)

I am having a hard time getting the correct radius, I cut a strip of wood 24" long and drilled four holes one at 24" one at 22" one at 18" and one for an anchor pin/pivot. When I marked 22" I then laid 22"r section track to follow the mark and they do not line up, is there another way and please easy on the math.
Thanks


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## fcwilt (Sep 27, 2013)

I use these:

http://www.handlaidtrack.com/sweepsticks

You can order them in just about any desired radius.

Frederick


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## mesenteria (Oct 29, 2015)

What I use is a drawn centerline on the roadbed. I use a camera tripod and either string with a pencil held at the right radius or I use a trammel.

A trammel is a length of lath/furring strip with 1/4" holes drilled every inch. I use a countersink drill bit to flare the holes so that a sharpened pencil nests into the holes well enough to let the point protrude below the nether lip of the holes. My laths are at least 40" long because I have the room for wider curves, and boy do they work and look great!! You drive a machine screw or something about half-inch from one end so that its point can serve as a pivot. Then, every inch, you drill those holes. For HO, I don't start until 18". You take a sharpened pencil, insert the tip into the hole at the radius you need, and with the pivot properly anchored, maybe on a small piece of wood screwed into the bolt atop that photography tripod set at a reasonable height, you draw your centerline. Then, take flex and lay it along the curve using track nails to keep it in place. If you want eased curves, just let the flex track ends flare a bit outward, not much, but they should eventually closely parallel your centerline about half an inch outboard of that line.


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## wvgca (Jan 21, 2013)

if it makes a difference, as far as I understood, the radius is measured on the center line of the track, so your 22" radius sectional track should be evenly spaced on both sides of your 22 radius pencil mark?


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## redman88 (Nov 25, 2015)

I made my own radius tool from a yard stick. Drilled the pivot hole at 1inch and the 22incb radius at 23inches. And the 18inch radius at 19. Didn't check against sectional track but it looks good on my table and so far things run smoothly.


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## Chip (Feb 11, 2016)

Being a no plan plan kind of weirdo, I just "suss" it out with a sting to make sure it is not TOO tight for the longer stuff and run my straightaways as far as I can and let the flex do it's thing and flex. 

22"-24""ish" has worked so far, even my Bachman 4-8-4 took em ok "at speed" and that thing is REALLY "stiff" and prefers straight track.


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## Fire21 (Mar 9, 2014)

Jimganley said:


> I am having a hard time getting the correct radius, I cut a strip of wood 24" long and drilled four holes one at 24" one at 22" one at 18" and one for an anchor pin/pivot. When I marked 22" I then laid 22"r section track to follow the mark and they do not line up, is there another way and please easy on the math.
> Thanks


I'm just curious...if you used 22" sectional track, how does this relate to flex track? :dunno:


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## Bwells (Mar 30, 2014)

With all the joints on the sectional track tight and it still does not follow your circumference, I would say the sectional is really not 22 inch radius.


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## CTValleyRR (Jul 26, 2014)

Well, first of all, Chip's point is well taken. "Close enough" is good enough, as long as there are no kinks.

Assuming that you were measuring at the centerline of your track pieces, your sectional track didn't have kinked joints, and / or you didn't inadvertently include a sectional piece of a different radius, then the problem is slop in your trammel. You have to be very precise in where the holes are drilled, where the center of your curve's radius really is, and make sure the pencil can't wiggle or lean as you draw it, not to mention making sure your fixed end doesn't move.

The trammel method is a tried and true way to draw curves. That said, I also like the sweep sticks that Frederick mentioned in his post.

I also use MicroEngineering flex track, which stays curved. I find it easier to get a nice smooth radius that way.


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## CTValleyRR (Jul 26, 2014)

Fire21 said:


> I'm just curious...if you used 22" sectional track, how does this relate to flex track? :dunno:


He's using it as a guage or template to check his measurements. Rather like using sweepsticks or any of the other radius tools out there.


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## Chip (Feb 11, 2016)

The flex is great stuff but if you can, use sectional track on curves as much as possible.

I use a combination and have avoided many headaches just going with sectional on curves that need to be precise. I have used flex on curves down to 15" with no problem but it can be hard to work with at first. It was only as a last resort because I ran out of sectional.


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## Jimganley (May 28, 2016)

Here is a picture of my marker,


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## CTValleyRR (Jul 26, 2014)

You don't say how much your radius is off by, but I see a couple of potential problems.

A tape measure can have some slop in the end where the hook is. It looks like that distance may be slightly short of an inch.

It also looks like both the pencil and nail are canted slightly inwards, which is going to give you some more slop in your measurements.

Assuming that you're using the track centerline in all cases, there are three possibilities here: either you drew an arc which isn't really 22" in radius; the pieces of sectional track that you are using to test aren't exactly a 22" radius; or your center point from which you drew the arc wasn't perpendicular to the tangent track at the beginning of the curve, so your chord is part of an ellipse rather than a circle.

Figure out which it is, fix it, and you're all set. Trust me, the trammel method works.


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## Chip (Feb 11, 2016)

A tape measure MUST have "play" in the end that matches the thickness of the "hook" to precisely measure both "inside" and "outside" lengths! I yousta harangue my guys for "crimping" the ends and RUINING them! (OY!) It's not what you want to be using for this task. A yard stick or some piece of wood or metal is best.


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## CTValleyRR (Jul 26, 2014)

Chip said:


> A tape measure MUST have "play" in the end that matches the thickness of the "hook" to precisely measure both "inside" and "outside" lengths! I yousta harangue my guys for "crimping" the ends and RUINING them! (OY!) It's not what you want to be using for this task. A yard stick or some piece of wood or metal is best.


No argument. But I've seen tape measures with too much play (the holes get enlarged) and too little.

The point is that the distance between the fixed point and the pencil may not be EXACTLY 22", despite what the tape measure says. The pictures may not be the best tool for estimating, but it looks like that first "inch" is too short, even accounting for the fact that he's measuring from the far side of the nail, not the center.

And yes, I would use a steel ruler for this measurement.


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## Chip (Feb 11, 2016)

My solution will be to lay sectional and trace a line, then put down flex along that line. No way do I have enough sectional for the entire layout!
Here we see my 24" "outside" line will interact with the 22" if I don't "fudge it". Using the flex I lay along the 24" and a block of wood for a guide, I'll lay the "22"" in there and hope the big steamers can take it.


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## fcwilt (Sep 27, 2013)

Chip said:


> hope the big steamers can take it.


Hope is not a good design tool.

Frederick


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## mesenteria (Oct 29, 2015)

....and why I recommended that you mock it all up with track nails first. Power the rails with clips and run trains back and forth along the curves. When you find the radius where you get wheels lifting out and over the outside rail, add one more inch and that should be your minimum radius anywhere on the layout where you intend to run those rolling stock at anything approaching 'track speed'. I said earlier that I add 10% for insurance.

Believe us when we say that hope and some unpleasant outcomes will have you learning a painful lesson about not knowing what you're doing with scale trains. Conducting realistic trials gives you hard evidence. Your trains can't lie to you.


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## Chip (Feb 11, 2016)

mesenteria said:


> ....and why I recommended that you mock it all up with track nails first. Power the rails with clips and run trains back and forth along the curves. When you find the radius where you get wheels lifting out and over the outside rail, add one more inch and that should be your minimum radius anywhere on the layout where you intend to run those rolling stock at anything approaching 'track speed'. I said earlier that I add 10% for insurance.
> 
> Believe us when we say that hope and some unpleasant outcomes will have you learning a painful lesson about not knowing what you're doing with scale trains. Conducting realistic trials gives you hard evidence. Your trains can't lie to you.


Bad choice of words on my part. This is set up #2, I've done the same thing in the me spot before so I'm SURE the "big steamers"(it is only one, my STIFF Bachman 4-8-4) will take the second line. I only have the one loco that just refuses anything less than 22" everything else can do it on its own or has been modified by me to take tight curves.


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## regme (Oct 23, 2014)

It's probably a bit late, but what I did was draw the layout in SCARM or drawing package. Scaled it to true size, printed it on A1 (for my layout that was 12 sheets).

Make sure you have matchlines or some overlap to join all the sheets together. Put the whole thing on the board and lay the track over the top, then rip out the paper.

I did it using a drawing package than way any radii I had the corrent tangent point


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