Calculating the Width of a Curve

[Eggbert]

Hi All

Is there a picture, document that shows the distance between the ends of each curve if you just use the curve pieces of each radius? Trying to plan yhr layout and board size.

Cheers

 

[Tim Allen]

3 hours ago, Eggbert said:

Hi All

Is there a picture, document that shows the distance between the ends of each curve if you just use the curve pieces of each radius? Trying to plan yhr layout and board size.

Cheers

 

https://d63oxfkn1m8sf.cloudfront.net/6617/1447/1661/2024_Hornby_TT120_Catalogue_40pp_Ediiton_24.3_WEB.pdf

Page 30 shows track. You can also download software, I use RailModler for Mac, which allows you to drag and drop tracks into place .

[ntpntpntp]

Just use the radius stated for the curved piece and double it - that will give you the diameter.  The measurements are always the centreline of the track.

So for example, TT:120 first radius is 267mm.  This means the diameter is 534mm.    Remember you need to make the actual baseboard a bit wider to allow for the full width of the track and the overhang of the locos and stock on tight curves. You don't want to be running right on the edges of the board.

 

Hornby TT:120 track spacing is 43mm:
R1 = 267mm
R2 = 310mm
R3 = 353mm
etc.
This info is all in the Hornby TT:120 catalogue as Tim has linked above 🙂 

Edited August 7 by ntpntpntp

[Hobby11]

The diameter (distance across a circle of track) is double the radius.

BUT: the radius they quote is down the centre line of the track as it shows in Hornby's catalogue above. So you have to add roughly an inch (2.5cms) to that figure so the track doesn't overhang. However it's not a good idea to have the track on the edge of the board, it needs to be at least half an inch, preferably more. So with the radius of 310mm/12ins (R2) you need a minimum board width of 26"/66.5cms, and that's a bare minimum and gives you half an inch each side. 

You do see people with track right on the edge but it's asking for stock to fall/get knocked off, mine's to the minimum half inch but I'd rather it were wider but I had the boards before i got the track.

This is my layout, you will see there's a half inch gap between the track and the edge of the board, using R2 and R3 and a 750mm wide board.

Edited August 7 by Hobby11

[Paul M]

Radius 3 needs a min of 750mm, 760 is better, board width. All sidings etc wil then need to be inside the oval, as per @Hobby11 above.

Mine is in the track plan thread, both Scarm and photos.

 

 

[ntpntpntp]

25 minutes ago, Paul M said:

Radius 3 needs a min of 750mm, 760 is better, board width.

At least that, I'd go for an even wider board, say 800mm.   At 760mm that's still only 27mm from R3 centreline to board edge, which doesn't leave much clearance nor safety margin. Models WILL derail and if close to the board edge they WILL fall off to the floor no matter how good your tracklaying  is and how carefully and slowly you run 🙂 

[Eggbert]

Thanks all that makes sense now, I appreciate the help.

[Fishmanoz]

And more closely you need to add 20mm to the nominal diameter, rather than the 25.4mm above, leaving inches aside.

[Rog RJ]

And when the loco falls off the edge it will often drag all the wagons/coaches with it!

[LTSR_NSE]

Since gravity has no consideration for aesthetics…

Attaching borders/frames (that are approx 1 inch taller than the baseboard) prevents unwanted falls.  If made of clear acrylic/perspex they needn’t hinder visibility.  However if used, all rolling stock overhang must be within baseboard confines otherwise damage will occur.