I’m laying out a trakc plan on the plywood in preparation for doing some cookie cutter elevation cuts, adding risers and then starting roadbed install. I will have 2 tracks on a lower level curve exiting at 1 or 2 tunnel portals and it occurs to me I need to plan carefully but I need help in how to address requirements and options.
I was planning 2-1/4" track center spacing, with concentric curves of 32" and 29-3/4" at the point of a portal exit. I’m concerned that a commercial double portal might not have an adequate opening width. I see, for instance, two Chooch double portals that have 4-1/4 or 4-3/8" opening widths. How do I determine what side clearances I need; e.g., for passenger cars (or a Challenger??). The side clearances will set the maximum track center spacing, I’d guess, and could rule out long equipment, for instance, by requiring just 2" track center spacing??
Alternately, I could use a pair of slightly separated single track portals. But this, I presume, would require spreading the 2 tracks center spacing in the area of the portals to provide side clearance from the portal leg of the adjacent track. A Chooch portal leg example i 15/16" width.
Any guidance here would be appreciated as I need to have a do-able plan before finalizing the track sketch on the plywood and then doing the cookie cutter thing (at which point certain changes would be at best impractical).
Before putting the portal in place I would put up a wooden mock up to see what will hit it, and what I have to move to make things work. You say a “Challenger” thus you will not be running double stacks or two level passenger cars. If you will run them, then be sure that you test your portal with these cars as well.
Once you have the minimum clearances figured out, and you do not want to build your own portal from scratch, then go out and buy two or more of the portals that you will want to use, and cut them so that you may enlarge the opening to match your requirements.
First, be sure that your track centers give you sufficient clearance for your long cars and locos. Set some track up and run those through to be doubly sure you have enough space. As LION suggests also set up some posts or other fixed objects to see how wide your portal will have to be.
As for the portal itself, if you don’t find a commercial one to alter as LION suggests it shouldn’t be too hard to make one. If you want a concrete one a simple form made from styrene or wood and plaster would get you started. You can make it fancier if you’d like. You could also use a similar form and scribe stonework into the plaster. Also, I have seen some nice stonework scribed onto extruded foam and painted and stained to look very nice.
Thanks, folks. I’m comfortable I can adapt by splicing 2 portals if needed to get more width. Actually at the other end the entry will need about 1-1/2 width as it’s at the divergence of a #8 turnout and does not need full double portal width.
On the overall issue of radii and track spacing, one problem is a lack of rolling stock to play with (e.g., Challenger or passenger cars, so I’m going by book guidelines plus what I read here. I’ve got 26" plus radii (except one 24" curve on a passing track) and I guess if I decide on buying those items they will physically make those (26") curves. Track spacing where there are parallel tracks are 2-1/4 or 2/3/8" center spacing. I’ll take a closer look before finalizing the track layout and see if I can incorporate some more leeway; e.g., minimum 2-3/8" spacing where curved tracks are parallel.