I’m getting ready to design and build my own portable version of a D-147 display layout.
I need some help with designing.
When I hear a track size, for example O-27 or O-31, is the diameter measured to the center rails, to the outside rails, or to the outside edges of the ties?
I believe that diameter is measured to the center rails.
No, no, no, no, no! The correct answer is “It depends.”
Somewhere, there must be a chart that gives the critical dimensions for various track types. I don’t know where one is, but the question is critical for the planning of layouts and the operation of various sized trains. There was a brief thread on this subject very recently. Perhaps there is something on the “sticky” general info thread at the top of this forum. A search of the archives will turn up much information, but some of it is wrong.
I’m too old and tired to try to create such a chart, but one is sorely needed… Can someone point the way?
That depends on the type of track you want to use.
Yes, it depends is the most correct answer.
O31 and O27 are measurements to the outside edges of the ties.
Most all modern track systems are center to center. In addition to this, tubular O72 track is also measured center to center.
I believe that tubular O42 and O54 are measured outside rail to outside rail, although I’m not positive. They could also be center to center.
Butch,
If you obtain a copy of RR-Track they do a very good job of rendering the track. I used this to design (transfer from paper to computer) my layout and have all the available track libraries for O-Gauge.
Thanks,
I use AutoCad at work, and based on information I rec’d, have drawn a circle of track. It will be easiest for me to use this since I am familiar with it.
How long is straight O-27?
How long is straight O?
Butch,
If you can tell us what track system you plan to use we can provide all that info, the track systems come in various lengths and curve radii.
For example Atlas O comes in:
Straight:
1.25"
1.75"
4.5"
5.5"
10"
40"
Curves:
O-27
O-36
O-45
O-54
O-63
O-72
O-81
O-90
O-99
Turnouts:
O-36
O-45
O-54 (Short)
O-54 (Long)
O-72 (Short)
O-72 (Long)
O-72/O-54 curved
#5 (Short)
#5 (Long)
#7.5
O-72 WYE
#5 Double Slip
So it really depends on the track system you are using what sections are available and if there is ‘cut-to-length’ section available.
Traditional Lionel Track:
O and O-27
O-27
Straight:
Half = 4.8"
Full = 8.75"
Long = 35"
Curves:
O-27
O-42
O-54
Turnouts:
O-27
O-42
Crossings:
45 degree
90 degree
— Make sure you are buying Lionel and not K-Line
O Gauge:
Straight:
Half = 5.5"
Full = 10"
Long = 40"
Curves:
O-31
O-42
O-54
O-72
Turnouts:
O-31
O-72
O22 (requires use of makeup sections)
Crossings:
45 degree
90 degree
I’ll add some more for Lionel tubular track
True centerline diameter of:
031 curves is 28 1/2", (the dimension to outside of ties is nominal)
027 curves is 12 1/2"
031 straights are 10" long
1/2 031 sraights are 5 1/2" long
Note: You cannot measure the chord of tinplate curves and calculate the true diameter. By themselves, there is some springback and the arc is not true. They spring to the true diameter when you connect them together.
Thanks for the wealth of information. I’m ready to design the trackplan. I’ll report my progress as I build with more questions.
I also want to photograph the construction.
The goal is to make a D-147-type Display layout that fits on a 36" door cut to 6’ long.
The diameter of “O31” or “O30” to the center rails is 28.284 inches; so the radius is 14.142 inches. The length of a straight section is 10 inches.
The diameter of O27 to the center rails is 25 inches; so the radius is 12.5 inches. The length of a straight section is 8.839 inches.
In each case the ratio between radius and straight section length is the square-root of two, so that a passing siding ideally can be constructed from uncut sections. Actual track sections do vary somewhat in their dimensions.
If you can figure out how many of the curved sections make up a complete circle, you can in fact calculate the radius from measurements of just one of them.
Measure the chord length between the ends of the center rail of the curved section. Then divide half of this by the sine of half the angle that that piece would occupy in a circle, to get the radius to the center rail. For example, with 8 pieces to a circle, divide half the chord by the sine of half of 45 degrees, which is 22.5 degrees, or .382683. With 12 pieces to a circle, divide by the sine of half of 30 degrees, which is 15 degrees, or .258819. With 16 pieces to a circle, divide by the sine of half of 22.5 degrees, which is 11.25 degrees, or .19509. Be sure to measure the chord exactly between the centers of the ends of the railheads (excluding any track pins, of course). This method is not very sensitive to whether the track has been bent a little to another curvature, especially for the gentler curves–it will tell you the original or intended radius. But, if you have any worry about that, pretend that you have divided the piece into two equal parts and measure each part separately, using the sine of half the halved angle, then average those two results. Here’s an example: Suppose we have a piece of ordinary O27 curve. We measure the chord and find that it is 9 9/16 inches, or 9.57625. We divide that by 2 to get 4.78125, then by .382683 to get 12.494, which we round