# How to bend flex track into a speific diameter?



## jimtyp (Jan 2, 2008)

Is there a way to bend flex track into a specific diameter? I have some 8' and 9' pre-curved track, so if I need to bend some flex track that diameter I can eyeball the pre-curved track to try and match it. But if I want to make, say a 12' curve is there a way to determine how much bend to make? I'm using 5' long pieces of flex, so maybe if I measure the length of a straight line from one end to the other until it is X long? Any ideas?


----------



## aceinspp (Jan 2, 2008)

I think I'd just bend it to meet the eye ball. If it looks good go with it.







You could lay out on a flat area and use a string and mark a 12' diameter then bend to it. Later RJD


----------



## altterrain (Jan 2, 2008)

I lay the track on the ground and then mark the track center with spikes. That will give you the spots to dig the holes for supports. 

-Brian


----------



## Semper Vaporo (Jan 2, 2008)

Google to the rescue... kind'a.

I googled "circle arc radius chord" and found: http://www.1728.com/circsect.htm

This has a built-in calculator for various circle calculations... You select which of the "Knowns" you have and it calculates the "Unknowns".

Unfortunately, it did not have a selection for the Knowns of Arc and Radius... but it did have Arc and Chord

So, I selected that and entered 5-ft for the Arc (the length of the rail and then tried 4-ft for the Chord (the distance between the ends when it is bent into an arc) and the displayed Radius was way below 12-ft. So I tried 4.9-ft and it was still low, so I tried 4.95 and that was still too low, so I tried 4.95-ft and that was too low, so I tried 4.975 and that was over 12-ft Radius, so I backed off a bit and kept at this "try one and see what happened" narrowing down the answer until I got to 4.96391-ft and the answer came out to "12" for the radius.

So, converting 4.96391 to Feet and Inches, I get 4-ft, 11.56692 inches... or about 4' 11.57".



EDIT: note, I was doing 12-ft RADIUS, not DIAMETER, so you can try 6-ft RADIUS if that is what you meant.


----------



## GG (Jan 1, 2009)

Posted By Semper Vaporo on 03/20/2009 5:26 PM
Google to the rescue... kind'a.

I googled "circle arc radius chord" and found: http://www.1728.com/circsect.htm

This has a built-in calculator for various circle calculations... You select which of the "Knowns" you have and it calculates the "Unknowns".

Unfortunately, it did not have a selection for the Knowns of Arc and Radius... but it did have Arc and Chord

So, I selected that and entered 5-ft for the Arc (the length of the rail and then tried 4-ft for the Chord (the distance between the ends when it is bent into an arc) and the displayed Radius was way below 12-ft. So I tried 4.9-ft and it was still low, so I tried 4.95 and that was still too low, so I tried 4.95-ft and that was too low, so I tried 4.975 and that was over 12-ft Radius, so I backed off a bit and kept at this "try one and see what happened" narrowing down the answer until I got to 4.96391-ft and the answer came out to "12" for the radius.

So, converting 4.96391 to Feet and Inches, I get 4-ft, 11.56692 inches... or about 4' 11.57".



EDIT: note, I was doing 12-ft RADIUS, not DIAMETER, so you can try 6-ft RADIUS if that is what you meant.



Semper...Semper...

Once again you kill me with this quick google stuff... and this based on other threads. I love it. 

NOTE: you are using the two research venues in concert with each other yes? AND then using the appropriate thread to communicate and point people in the right direction.. 



My response to this thread: tape measure and common logic. 

KISS theory

gg


----------



## rpc7271 (Jan 2, 2008)

In HO scale they make these track alignment gauges that sit inside of the rails that when you bend the track to a specifis radius they fit inside of the rails and hold it to that radius while you nail or spike the track down. Perhaps you could come up with something similar. see: http://www.walthers.com/exec/productinfo/170-1020 http://www.walthers.com/exec/productinfo/170-5


----------



## Pete Thornton (Jan 2, 2008)

is there a way to determine how much bend to make?


When I was building my garden layout, I took a pencil and a long piece of string and drew some curves of 7', 8', 9' and 10' radius on my work table top. I also drew them on some cardboard and cut them out as 'templates', or 'track alignment gauges, as mentioned above. Works for 12' curves too (radius OR diameter.)


----------



## GG (Jan 1, 2009)

Pete, I have used your technique on other venues. 

For the GR&G railway, I will measure and stake the center of the circle be whatever diameter, attach 2 point string to obtain a straight vertical on the circumference peg and then drag it along, making the curve and marking it out with a string of flour. 

With the flour line in place I am now ready to set up my ladder. 




gg


----------



## StanleyAmes (Jan 3, 2008)

On my shop floor I have drawn my mimimum radius curve. When I bend rail I check it to the drawn arc. 

Stan


----------

