Calculating curves?

[Anonymous]

Hi all,

I live in the UK and I keep reading things like "17 degree curve". Can anyone please tell me what it means and how it is calculated?

Over here we use radii and chains!

many thanks

Roger Murray

[Marty Cozad]

Roger I've heard the answer to this one, but never can remember it. I use radis also.

[Anonymous]

Hi Roger,

[#welcome]

Majority of us use ready made track, I use 8' diameter. A handy site for conversions is
http:/www.onlineconversion.com

Cheers,
Kim
[tup]
Another BRIT!!!!!

[Anonymous]

OOps I should have said that the referance was to the real railway but I guess it could be used for models also.... I just wondered what the theory was?

[Anonymous]

If a 100 foot chord, laid out on the perimeter of the circle, subtends a 3 degree arc, then that curve is called a 3 degree curve.
An example: a circle of track with a 100 foot radius is pretty tight in real railroad terms. A chord of 100 feet laid out on the track would subtend 60 degrees (you'd have a equilateral triangle, too, as the legs from the chord extending to the center would measure 100 feet, also).
And that's the way it is.
Art

[Anonymous]

The way I understood it was it told you how many you need to make a circle.
A complete circle is 360 degrees.
If you get a 90 degree curve (you won't find one in G scale), you have a curve that goes quater of a circle. So you need 4 to make a complete circle.

So for your 17degree curve you will need (360 / 17 = 21.1 ) 21 and a bit pieces to make a full circle.
What it doesn't tell you is what radius the curve is, so you still don't know if you're getting a 4ft diameter or a 20ft diameter curve.

Glen Anthony.

[Anonymous]

Roger, if you know trigonometry, you can compute the radius of a curve knowing what the curvature is in degrees. In the tight curve in the previous example, the chord and both legs of the triangle were 100 feet.
But if we didn't know the radius, but we knew the curvature was 60 degrees, we could bisect the isosceles triangle (acutally an equilateral one in the example) making two right triangles with short sides of 50 feet, look up the sine of 30 degrees (0.500), and divide the 50 feet (half the chord) by the 0.500 to get an answer of 100 feet.
For curvatures less than 5 degrees, you don't need to divide everything by two: just divide the 100 feet by the sine of the angle. You'll only be off inches and unless you need accuracy better than plus or minus .01 percent, you're home free.

[Anonymous]

Hello Roger,
Here in the South East I'm running 9' Aristocraft curves.I must admit that I don't go into the geometry side of things however it is useful to know that some people out there can actually do it.I looked at artschlosser's post and it went straight over my head.However,my Wife looked at it and it made perfect sense to her!.Mind you,She can't scratchbuild rolling stock.But then again ,as pointed out by her,she doesn't want to.[:D]

[Anonymous]

Glen is correct. Another way, without trig, is this.
With a 1 degree curve, the loco travels 1/360th of a complete circle. If he did this 360 times, he'd have a complete circle and the circumference is 360 times 100 feet, or 36,000 feet. From that you can compute the radius: radius equals circumference divided by 2 pi (6.28).
If it was a 2 degree curve, you'd multiply 100 feet times 180 (360/2).
But again, this is not exact as we are using the chord, not the length of the arc; but for degrees less than 5, this is fairly accurate but always a little less than the actual radius.

[Anonymous]

I really don't care about all this; I bend and assemble my own track and all i care about is the radius to the outside track. I make my own home made compass out of string and and a couple of old screwdrives; and draw a line in the dirt and bend my curves to suit that.

I'm getting hungry now so i'm off for lunch all the best!

Regards Ian

[Anonymous]

Hi Roger,
Well, I think you've just sampled this forum at its best. Bet you're really glad you asked this question!!, but you got your answer.
When you get to laying track use Aristocraft, takes the hassle out.
Cheers,
Kim
[tup]

[Anonymous]

Only just got on line.... had no emails to say I had replies....What can I say, a BIG thank you to all.....I am going to go away and study them now.....I may be back....thanks again

Roger Murray UK [:D]