Bill,
I doubt a T-1 that's available today, like BLI's, would negotiate 18" radii curves; don't know about the old Bowser versions, however. If you can make your table 48-54" wide, you could use 24" radius curves, which today's more prototypically sized locomotives and cars need to operate successfully. A lot of people claim today that anything less than 30" radius curves result in poor operations. If you have the room, I'd seriously consider going larger than 39" assuming you're talking HO. Not sure you can find hollow core doors wider than 39", if that's your idea, however building a 'table' isn't too difficult, with some plywood, and 1x4s. Some people even skip the plywood, and use foam insulation that you can find at most lumber yards, etc. Its usually the pink or blue stuff, not the white styrafoam that makes a mess everywhere. I'll leave it to others to provide insights on the advantages and disadvantages of foam vs plywood.
while the Atlas snap switches are cheaper, as they include the switch, + machine, etc, they are also amongst the tightest in terms of the curved part of the turnout. If you want to plan to operate something like a T-1, I'd seriously consider going with #6 or #8s, particularly if you want to operate thru the crossover at speed. I mainly used #4s (which is actually a #4.5, if you go with Atlas) for industries and such, not on the main line for passing sidings, or cross overs.
While I'm still analog DC at the moment, I believe there are at least one or two companies that make some sort of DCC reversing unit that you can wire to the reversing section, that takes some of the wiring headaches out of that section of track. Reverse loops in analog DC aren't really that complicated to wire, if you pick up say an old Atlas wiring book, which has a lot of diagrams.
Will the lower and upper levels of the mainline(s) be connected? Or separate loops? While some will say that anything over a 2% grade is not prototypical except for anything other than lumber company trackage with say Shay locomotives and alike, if you go much over 4% in HO, you will need to be operating very short trains. Woodland Scenics make styrafoam grade sets in 2, 3, and 4% gradients, which I believe create 4" of separation. You can combine them to get steeper grades if you want, but even with the 4% grade, you need a run of like 120" or about 10 feet, if I remember right. I've used these in the past, successfully, but have no affiliation with Woodland Scenics. Just throwing out different ideas that might come in handy now or down the road. Kalmbach had a book or two years ago on layout construction techniques that you may want to get a hold of, if you can't find anything on google.
FWIW, people always love to see photos of layouts, etc.
Good luck, and keep us posted,
Thanks for the repy. I should of updated a few points. The T1 is just not going to work for me no matter how much I love that engine. Around the room layout also won't work because of the wide entrance at one end and because I don't want to attach anything to the walls. Wife keep talking about moving Yeeeecch !
I'm thinking 4 axle desiels and maybe a 060 or 080 Steamer. I realize the #4 switches look more prototypical but I'm not that fussy at this point. First layout in many years. I originally wanted to do the Valley Forge Central which has a 4% grade to a second level and actually built a 4 X 8 table for it. After finishing it I just thought the width would eat up too much of the room which is also my music studio. I decided to go with the 18" curves. I'm not too happy with that but compromises arise.
Carl
