Determining Angle of Crossover for Figure 8 and a stable trestle for indoor use

[Anonymous]

My first question is how can determine before purchasing/trying out a track section for a crossing (forming an "X"), what angle of track section crossing is needed. Suppose, for example, you have an 11.5ft. diameter, 16 curved pieces of track and want to configure it into a figure 8, what crossing section and possibly additional other track would you need to do that; and is there a general rule of thumb that will apply to different diameters of track?

The second, related question is, give you have a figure 8 and want to elevate part of it so the track will pass over other tracks and the train would go under its on track at some point, aside from fastening the trestle pieces to the floor or a board that serves as a floor, how could you stablize the trestle so it can take the load of say and SD45 plus several cars?

Thanks for your insights and thoughful comments.

[kstrong]

If you're using sectional track, each section makes a set curve, depending on how many sections of track make a full circle. For instance, if your loop takes 12 sections of track, that's 360° ÷ 12, which gives you each section making a 30° curve. If the loop takes 16 secitions, then the individual sections are 22.5° each.

To determine the angle of the crossing, simply take the number of curve sections you're using, and multiply that by the curve of each seciton. Then subtract that number from 360. So, if you're using 9 sections of 30° curve, then you've got a 270° curve, which will require a 90° crossing.

For the over/under aspect, your biggest concern will be the grade needed to get you up and over. You'll want probably at least 9 or 10 inches of vertical clearance so the train can pass under itself. Your maximum grade should be no more than 4% (4" of rise for every 100" of track), so to get 10" of rise, you'll need 250" of track between the lowest and highest point. That's just under 11' of track, which with a 11' radius will not be a problem. If you can make the grade shallower, that's even better.

As for supporting the track, I'd try to do it every 6" to 9" or so at the furthest. You don't need anything fancy--blocks of 2x4 cut to length will work well. But you do need support under the rails, lest they sag under the load of the locomotive.

Later,

K

[Big_Boy_4005]

This is a matter of track geometry. To form a figure 8, you will need at least a circle and a half of track. The angle of the crossing will depend on how many curved sections of track you place in each half of the figure 8.

For example, the most common figure 8 uses a 90 degree crossing with 3/4 of a circle on each side. You will need to have some straight sections coming off all 4 legs of the crossing as filler. The number and size will be determined by the size of the circle.

For circles made up of 8, 16, or even 32 sections, a 45 degree crossing can be used, by adding more curves to each side. Straight fillers might still be needed.

12 to the circle is the unusual one when it comes to sectional track. This needs 30, 60, or 90 degree crossings for figure 8's, though if you have a half curves available, you could use a 45.

When it comes to over under, simply leave out the crossing, and fill with straights. The key is clearance where the tracks cross. It is important to have enough length of track so as to keep the grade from being too steep. You can always add straights by maintaining symetry.

[Anonymous]

Thanks very much for the informative, insightful responses!! I think now I have enough intellectual momentum to move out on this. This Forum is great.

[Anonymous]

There is one more fly in the ointment - LGB crossings are not all symmetrical, only the 22.5 degree one is, that is both legs are the same length, 375mm, with the crossing right in the middle..

The 90 degree crossing is 150 mm across one way with the crossing in the middle. The track at right angles is about 184 mm across, with one leg 82 mm long and the other side 102 mm long. By butting the two 82 mm legs of two crossings, the parallel tracks will mate with a crossover made with two R1 switches. I have no idea what the 102 mm length is for except that it's about twice the length of the 10050.

The 30 degree crossing has two lengths, 300 mm (same as a straight section) crossed by a 346 mm section, each leg 173 mm in length.

I have only LGB sectional track so I don't have any data for other manufacturers.