The grid section is 1' square. The drawing covers just the south room portion of the staging. The south and west walls are shown in light brown. The edges of the desk are shown in dark blue. The 1x2 and 2x2 sections of the grid benchwork that is to be built above the desk are shown in purple. The lower tier track is in red, the middle tier in blue, and the upper tier in brown.
Track is spaced at 1" within a single tier and 1.5" between tiers. In areas where parallel tracks are curved the spacing is increased to 1 1/8" -- no more is required because those curves are very, very broad (36" and more) and thus 1 1/8" is sufficient clearance even for the longest cars or super long steam locomotives.
1" is really too little for staging. Ideal is at least 2" to allow an extra 1" between tracks for fingers. Unfotunately, because the staging area width is limited to 24" (due to reach limitations) that would mean cutting the number of tracks in half, which would be just too few tracks. I dwelt on this issue for a while, finally settling on 1". I tried 1 1/8" and 1 1/4" as compromises, but the reality was that neither was any better in terms of finger room.
My experience with the last staging was that 1" can work if you use some Rix Rail-Its , Rix Pick Uncoupling Tools, and lay one Atlas Rerailer Track between every section of flex track. Those tools, plus minimizing derailments through good track laying, mean that the need for fingers is greatly lessened.
As part of the redesign the first thing I did was figure out the structure of the grid network that I'd put down under the loop. I decided to use mainly 2x2 lumber for stability (both stronger and the extra weight means less likely to be moved by bumping). I also wanted to have the loop section be removeable until construction on it was finished, so that I could take it out and access the far reaches.
The next change was to move the loops directly on top of each other, rather than askew. I'd originally made them a few inches apart with the intent of limiting the area where they would be on top of each other, but this ended up making the location of supporting piers more difficult without adding any real benefit.
The lower and middle tier were fairly easy to set up the track locations. I had to make some adjustments here and at the other end of staging to make sure that the length of each staging track was sufficient. I also had a few adjustments to avoid designing S-curves without having at least one long car length worth of straight track between the curves. For the middle tier there was also an adjustment to be made to allow space for an Atlas switch machine. I ran into that problem in the first staging attempt when I nested switches next to each other. You can mount them underneath, but a) this is staging, so looks don't matter, and b) although I fully test each machine before laying the track, I expect failures over time and having them next to the track makes for easier maintenance.
Of course, the return tracks are now placed next to their own tier's staging tracks. This means bridges have to be built near the loop for the top and mid tier return track. The mid tier return bridge will make it hard to access the trains immediately underneath, but it does not cross any switches, which is important as those are the tracks needing 99.9% of maintenance attention. The top tier bridge does cross some switches. I'm less worried about it crossing the lower tier switches, as the vertical gap will be 4", but for the mid tier I will try to route the bridge to minimize the access problem it creates (maybe even make the bridge removeable).
There was one design problem that you can't see in this 2D drawing, but which affected the final design. Each tier needs to make an elevation change to allow for sufficient (2 1/8" from rail to rail) vertical gaps at the loop end. The lower tier needs to drop about 3/8" -- which is easily taken care of with a 0.5% grade at the north end of staging. The middle tier is just about right, perhaps a 1/4" adjustment at the north end. But the upper tier needs to climb 1 7/8" from the point where it exits the layout to the loop -- a distance of about 19'.
This isn't a hard climb, it's less than the 1% maximum standard, but the problem is do we want an almost 1% grade in staging? I tested some cars on a 0.9% grade to see if they roll, and most would stay in place but did have a tendency to roll if pushed, and then they kept rolling for a while.
Fortunately, there is a little design trick I learned in one of my very early staging drawings. As luck has it, this staging design consists of one-way track. This means that you can plan for a long 1% grade in the upward direction and a short 3-4% grade in the downward direction without worrying about trains climbing up the 3-4% grade in the return direction.
So, my plan is to have the upper tier trains climb the entry track (this is the track next to the wall) at a 0.9% grade to the loop, then after looping around quickly descend at 3-4% to level over 3-4 feet, allowing a long area for flat staging. I won't have this designed exactly until I get to work with mockups on the actual staging.
So, design done, time to take apart the old staging.
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