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 How to Create a Curve Radius
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Author Previous Topic: 30% off Walthers Catalog, do you get that too? Topic Next Topic: Grade discussions  

PRRGG1

Posted - 2005 December 30 :  11:11:40 PM  Show Profile
Folks,

My last layout was a massive Unitrack system which allowed me the pleasure of not having to calculate curve radii. So, now that I've moved on to flex track, how do i create and draw out on my sub roadbed say a 26" radius?

Also, any advice on easements?

Thanks!!

Country: USA | Posts: 84

da3151

Posted - 2005 December 30 :  11:30:46 PM  Show Profile
http://www.nscalesupply.com/EXC/EXC-70036.html

This will get you started. No hints on the easements here. Sorry.



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Rick F.

Posted - 2005 December 30 :  11:32:23 PM  Show Profile
To PRRGG1

You can take a long piece of wood and drill holes in it on 2" intervals for all the radii that you want to use. At the opposite end put a nail through it (take all dimensions from the nail). You can use this as a big compass. Micro-Mark has a tool you can buy that does the same thing, only, it's like a tape measure.

As for easments you can use a 1 inch offset, then connect the line with the curve about 1/3 of the way into the curve. This is not a good explanation. Best to look on the web under easements.

Rick



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dave1905

Posted - 2005 December 30 :  11:50:16 PM  Show Profile
I got a freebie wood yardstick back in the late 1970's. Drilled a hole at the 1' mark and then every inch mark from 18" to 35". Also drilled a hole at the 1/2 and 3/4 in marks later. Drive a brad at the center of the radius and then use the yardstick as a "trammel" by putting the hole at the 1' mark over the brad and a pencil in the appropriate radius hole (don't forget to add 1" because you started at 1" (for 24" radius use the 25" hole). If you don't know where the center is, put the pivot at the end of one tangent and strike an arc towards the inside of the curve, then put the pivot at the other straight section and strike an arc that intersects the first arc. That's your center for the curve. For easements, I make the curve 1/2" inside the tangents and then use the wooden yardstick to bend a smooth curve between them or just eyeball a smooth transition using flex track.

Dave H.



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sam

Posted - 2005 December 31 :  12:15:07 AM  Show Profile
prrgg1,
all good advice so far
you could even take a piece of string tied to two pencils at the correct distance,
and swing this for an arc
for calculating easements, i do as rick mentions...
draw the straight to the curve, an inch away, then swing in gradually into the curve.
i had a diagram of this, if i can find it, i'll try to post


sam

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TBat55

Posted - 2005 December 31 :  06:47:55 AM  Show Profile
Here's a helpful site to find a radius without using the center of the circle.
http://www.1728.com/circsect.htm
If you keep drawing lines between 2 points along a curve (the chord) and maintain the same distance to this line, the curve will be the same radius.


Terry

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sam

Posted - 2005 December 31 :  07:36:00 AM  Show Profile
quote:
Originally posted by TBat55

Here's a helpful site to find a radius without using the center of the circle.
http://www.1728.com/circsect.htm
If you keep drawing lines between 2 points along a curve (the chord) and maintain the same distance to this line, the curve will be the same radius.


nice!
havent seen this type of math in year
will have to try it next time.


sam

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charlief

Posted - 2005 December 31 :  4:06:34 PM  Show Profile
The compass made from a stick with a nail and holes in it for a pencil works great, BUT if the place where the nail is supposed to go is not over your layout [e.g. over an aisle or worse yet inside a wall] then you have to resort to an extra step. Trace the curve you want onto a piece of cardboard. Cut the cardboard curve and then use it to trace the curve onto your subbase.


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Silicon Revolution

Posted - 2006 January 01 :  04:37:39 AM  Show Profile  Visit Silicon Revolution's Homepage
quote:
Originally posted by charlief

Trace the curve you want onto a piece of cardboard. Cut the cardboard curve and then use it to trace the curve onto your subbase.
That's close to what I did for my module (where the centers of the curves lie outside the benchwork). I used Atlas's free track planning software to draw out the curves (including the adjacent tangent tracks and easements), then printed it out 1:1 scale. I taped the sheets together, taped the paper template over the benchwork, and used a pushpin to prick holes along the centerline of the track every half inch or so. I removed the paper template, used a marker to connect the dots, and laid cork and track from that centerline.

While printing an entire large layout wouldn't be practical, drawing up your proposed radii and easements and printing out some templates would accomplish the same thing.

Model Railroader Magazine's website has some generic printable templates that might come in handy. Have a look at this page.

SR



Edited by - Silicon Revolution on 2006 January 01 04:43:33 AM

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PRRGG1

Posted - 2006 January 01 :  08:59:21 AM  Show Profile
Great stuff, thanks guys!


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PRRGG1

Posted - 2006 January 01 :  09:02:17 AM  Show Profile
quote:
Originally posted by Silicon Revolution

quote:
Originally posted by charlief

Trace the curve you want onto a piece of cardboard. Cut the cardboard curve and then use it to trace the curve onto your subbase.
That's close to what I did for my module (where the centers of the curves lie outside the benchwork). I used Atlas's free track planning software to draw out the curves (including the adjacent tangent tracks and easements), then printed it out 1:1 scale. I taped the sheets together, taped the paper template over the benchwork, and used a pushpin to prick holes along the centerline of the track every half inch or so. I removed the paper template, used a marker to connect the dots, and laid cork and track from that centerline.

While printing an entire large layout wouldn't be practical, drawing up your proposed radii and easements and printing out some templates would accomplish the same thing.

Model Railroader Magazine's website has some generic printable templates that might come in handy. Have a look at this page.

SR



SR - Thanks! I can't seem to get the MR templates to print correctly. Any way, the Atlas software sounded interesting. How easy is it to do what you mentioned? Sounds like it may take care of not only getting the radius right, but the easements too.

Any help is greatly appreciated!



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Bob Elliott

Posted - 2006 January 01 :  10:17:32 AM  Show Profile
"BUT if the place where the nail is supposed to go is not over your layout [e.g. over an aisle or worse yet inside a wall] then you have to resort to an extra step."

If you have a camera tripod, you can use it to support the off-layout end of the yardstick or whatever you're using as a compass. Place your pivot hole on the threaded camera-support screw and move your tripod in and out to get the correct radius at any point you need.

Of course, this won't solve the problem of a curve that would require your pivot point to be inside a wall!

Bob Elliott



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Silicon Revolution

Posted - 2006 January 02 :  02:32:36 AM  Show Profile  Visit Silicon Revolution's Homepage
quote:
Originally posted by PRRGG1

Any way, the Atlas software sounded interesting. How easy is it to do what you mentioned?
I used RTS v5.0 to create my templates, and it was a bit of a struggle. But the current version (7.0) seems to have made things easier. If you select the "Special" menu, then select "Transition curve...", you'll see a dialog box that looks like this:



The "Radius" drop-down box has fixed values that you can pick, or you can enter your own (in this example, 28.00 inches). You probably want to specify the angle (how many degrees of the entire curve should be made by the easement), and have it calculate the curve. Next, select the direction you want the curve to go.

A nice feature that wasn't available in RTS v5.0 is the "Create complete curve" checkbox. If this is selected, RTS will generate a complete curve of the angle you specify with easements on both ends. Specify the total angle for the curve, click the "Calculate" button to have RTS do the math, then click OK to get back to your layout. Clicking on your layout will insert the easement(s) and curve you just created.

For making printable templates, I'd recommend going to the View->Properties menu, selecting the Desktop tab, and telling it to draw track as lines, instead of an outline or filled outline. This will give you the centerline of the curves, which is good if you're going to be laying cork. The end result is something that looks like this:



If you want to know how long the easement is, you can disconnect it from any adjacent tracks, select it, right-click, select "Properties," and look at the "Flex Track" tab, which will show you the current length of that piece of track.

Once you're happy with the easements and curves, change the zoom to 1:1, set up the page using "Page Setup" from the "File" menu (pay attention to the "Overlap" button; it lets you specify how much the printed pages should overlap one another), and print them out.

HTH,
SR



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