Thanks to all for your responses.
One thing that I forgot to mention is that an 11.25 degree spacing would be easier to actually layout on your layout. 12.5 degrees is not evenly divisable into a 360 circle but an 11.25 degree spacing is. The result would essentially be half way between the 10 degree and 12.5 degree measurements shown on the drawing. It is amazing what a difference one silly little degree will make.
It is easy to make an 11.25 degree template for spacing tracks. Remember how to make paper airplanes? Just take a large piece of paper (with a 90 degree angle) and carefully fold it 3 times.
Folding 1 time = 45 degrees, 2 times = 22.5 degrees, 3 times = 11.25 degrees. Unfold it and the creases show the spacing.
Or one of a dozen other methods for bisecting angles.....
Thanks again,-John
loathar wrote:VERY useful info! Thanks a bunch!!
and . Thanks, RustyRails!
Jim in Cape Girardeau
This is not an installation tutorial for the Walthers HO scale turntable but it does provide information on track spacing that might come in handy. I had to go through this exercise for myself so I thought it might be useful for others. I wanted to know the optimum spacing angle for service tracks radiating from the turntable.
This turntable has a 12 3/4" pit diameter and a 13 3/4" diameter outer edge. What would be the best spacing angle for tracks coming off of this turntable? The drawing below shows the turntable and various spacing angles. Further discussion follows the drawing.
Green = Turntable and locomotivesBlue = TrackBlack = Roundhouse structures
Tracks A & B show a 15 degree separation between tracksTracks C & D show a 10 degree separationTracks E & F show a 12.5 degree separation
Note that my following comments have nothing to do with prototype practices. This analysis simply trys to determine how much space is required to "cram" a turntable and service tracks into a model layout. The real world had other needs and typically had much more real estate to work with.
A 15 degree separation is a waste of space since even at the edge of the pit there would be plenty of clearance between locomotives. With this separation a lower number of service tracks can actually installed in a given space.
A 10 degree separation requires a minimum of 1 3/4" past the turntable rim for clearances between locomotives. This requires longer service tracks and more space on the layout.
A 12.5 degree separation allows the service tracks to be as close together as possible but still have clearance between locomotives almost at the turntable rim. This appears to me as being the optimum angle for modeling with this turntable.
Roundhouses
The roundhouse made by Walthers has a 10 degree angle between bays. Walthers specifies that the front roundhouse wall should be 5 3/16 inches from the turntable edge as shown on tracks C-D.
The Atlas roundhouse has a 15 degree angle between bays. Assuming the same front wall measurements as the Walthers roundhouse, this would put the front wall of the roundhouse about one inch from the edge of the turntable.
As far as I know, no one makes a roundhouse with a 12.5 degree angle between bays but if there was one, the front wall of the building would be about 2 5/8" from the edge of the turntable.
SO...If you are tight on space and want a roundhouse, the Atlas roundhouse would take up less space. However, it would look a little "funny" being placed that close to the edge of the turntable.
You have to make your own decisions as to what spacing and structures fit your needs and restrictions the best. I just thought I would pass along this information for your edification.
-John
p.s. The MRR book on Locomotive Servicing Terminals has a good introductory chapter on turntables and roundhouses.
p.p.s. The locomotives shown in the drawing are drawn to be 1 1/2 inches wide. This is 10.875 HO scale feet wide and is actually wider than the more typical 10 foot width of most rolling stock.
p.p.p.s. Though this information is give for HO scale the relationships would be the same for any scale.