When we say that a curve track (Unitrack in particular) has a certain radius, does that refer to the distance to the inside of the inner rail, outside of the outer rail, or the center of the track? I assume it does not include the roadbed. I'm trying to make a scale drawing for a layout.
Thanks
We lay out track elements using a drawn arc, often with a trammel or something that helps to lay a smooth curved line. That is meant to be the centerline. You should lay your track elements the same way, with the mid-point between the rails along the centerline.
This is a convention in the hobby. The radius is drawn at the intended centerline, and that's how you measure your curved pieces' radii.
Later, you will learn about eased curves, or easements. This is where the entrance and exit of a curve take the shape of a cubic spiral, or an approximation of that curve. When you think of your car, how it turns from tangent into an ever-tightening curve as you enter an intersection intending to turn left or right, your turning steering wheel does this for you as you begin to make the car turn; the rails need to have this feature as well to prevent 'lurch'. This is something you can do with flex track, and to a lesser extent with fixed radius track elements such as the Kato Unitrack.
Do yourself a favor and get Track Planning for Realistic Operation by John Armstrong (Kalmbach books). It will save you posting a lot of questions here and give you all the fundementals.
Rio Grande. The Action Road - Focus 1977-1983
Thanks. I actually just assembled a circle of Unitrack and yes, the radius measurement is to the center of the track.
N scale Unitrack is 1" wide including the roadbed, so you will always have to add and subtract a half inch to/from the radius to account for the roadbed when planning a layout. A 15" radius N scale Unitrack actually has a total radius of 15.5", or an outer diameter of 31", and inner diameter of 29".
I'm going to have to learn about easements. I have "Track Planning for Realistic Operation" on my Amazon wish list. If I don't get it as a gift I will buy it.
I'm using Photo Shop because I'm good at it and it's easy to draw a circle with a fixed diameter, and to draw a line and rotate it a fixed number of degrees using the center of the circle as a pivot point. This will allow me to accurately make a scale drawing of a piece of curved track using the radius and number of degrees.
I think you might have much better availability with our hosts, Kalmbach Publishing, Inc, since they have the copyright on Armstrong's book. They sell it via their outlet store on line. I don't know, not having searched, if it's available except second-hand at eBay or through amazon.
I haven't found it via this website yet but if they own the copyright then I'd imagine they are getting a piece of the sales on Amazon.
The beauty of the Amazon wish list is that my family can check it and buy me things that I actually want. I can't expect them to scour the internet for it.
If I end up buying it for myself I will try to buy it directly from Kalmbach.
Thanks for giving me impetus to poke around this site more though. Lots of valuable resources outside of the forums.
Excellent, and I do commend you to the book. I go back to it each time I decide to build a layout. Here is a link if you get the hankering:
https://kalmbachhobbystore.com/product/book/12148
Another factor is that Kato doesn't use the typical 15", 18" and 22" radius of other makers (like Atlas for example).
Traditionally in HO, 18" radius curves are "sharp", 24"R "conventional", and 30"R "broad". Kato starts with 24"R "conventional" curves, then has three curves with sharper radius and three with broader radius, each 2-3/8" different from the next size up or down. So Unitrack has 16-7/8", 19-1/4" and 21-5/8" radius track instead of 15", 18" and 22" radii, and goes all the way up to 31-1/8" radius.
Not a big difference, but just something to keep in mind if looking at a track plan with 18" or 22" or whatever curves.
I should clarify that my measurements were for N scale Unitrack.