Well, tomorrow (after much fiddling with plywood joint splices, etc) I'm ready to do the cookie cutter carving of the plywood tied together (flat) so I can start adding risers to get the elevations planned in various areas (a 5'9" x 10'8" HO layout). I've got one curving loop that goes about 14'10" up a grade and crosses itself. If I do the standard 4" plywood rise (about 3" lower rail to bridge girder above) that comes to about a 2-1/4% grade, ignoring any transitions at bottom and top. So I can be prepared to address the specifics when I get there I've got 2 questions:
a) when fine tuning the total rise, do I need to stick to the 3" NMRA clearance (rail to bridge above)? I will be doing transition era UP equipment mostly. I don't have any rolling stock yet so nothing to measure. I won't get into unusual modern equipment (it that is higher) like double decker Amtrak or auto carriers. I don't know if the tallest of my area of interest are UP observation (dome cars), a steam engine of the 1940's, a crane car, etc. I will leave some tolerance for sure, but if the standard 3" is overkill and I can shave some off the grade I will do so (leaving the needed tolerance, say 1/8" min to reduce the grade). If this is all too precise, saving nil, I will go with the 3".
b) How are vertical transitions best handled? I can easily add a tad of transitional height at the top (the ceiling is way above) but don't know the details of how to make it happen...with risers in series I'd guess that "hold" the track on a vertical curve until going flat at the top. Perhaps the natural flex of the 5/8" plywood will take care of any transition needed if the prior tie point is far enough away?? At the start of the long grade, I have a spot to "hold" (with a screw to the joist) the subroadbed at the 0" point, but that would create an instant 2-1/4% "kink" other than how the 5/8" plywood bends up the initial part of the grade. Should I cut the subroadbed past the nominal start of the grade (below a bridge) and ease up on the screw to allow the bend to extend past the nominal base of the grade, creating some more vertical easement and lessing of the initial grade? Any rules of thumb on how to do this, as I have no rolling stock to play with.
Your guidance will help me get the subroadbed right for additions of roadbed/track, bridges, abutments, etc. Thanks as always.
Paul
Modeling HO with a transition era UP bent
peahrens --
NMRA recommended practices are just that -- recommended practices. You don't HAVE to follow it. But you're asking for trouble if you don't. Especially since you don't have any rolling stock to test, I'd be very conservative. Don't forget that on top of your plywood, you're going to have almost half an inch of stuff (the roadbed and the track), and that's where your 3" gets measured from. If you allow less than 3", and end up without enough clearance, you'll have to rip out and redo. Ask yourself if this is worth the risk.
Since you're talking about running observation cars and 1940's era steam, you're probably going to have some pretty long rolling stock and motive power. i'd make the first 3' and last 3' of your slope at a 1% grade, stretching the location of the slope as necessary to achieve this. If the nominal start of your grade is below a bridge, this may necessitate changing the height of your bridge a little. 5/8" plywood is pretty stiff; I don't think you're going to create a real kink no matter what you do.
If possible, make sure you don't have a track joint at the beginning or end of your grade. This will also help avoid kinking.
Connecticut Valley Railroad A Branch of the New York, New Haven, and Hartford
"If you think you can do a thing or think you can't do a thing, you're right." -- Henry Ford
For transitions, just cut your plywood surface with two cuts on either side of your roadbed for several inches, say 8-10. Then cut transversely across the end of the two cuts on the end closest to the middle of the grade. Bend the cut end upward and prop it up just enough that it offers you the vertical curve you need, and follow that up with risers to get you to the top of your grade. The non-cut end of the twin cuts running parallel with your roadbed/centerline will anchor the roadbed and force a nice transition for you.
Crandell
simple math says 3 inches times 87 equals 261 scale inches in HO. 261 divided by 12 equals 21 and 3/4 feet. tallest thing we ran when i was on the railroad was tri-level auto racks at about 19' high. double stacks came along after i left.
charlie
hi,
most equipment is less then 2" high, it's up to you to buy or to not buy higher cars. Bridges differ lots too, so you can go your own way. I've seen some layouts with only 2,5 difference of rail head to rail head height. This might not be prototypical at all, it might keep you from owning cars you would "die for" later; planning a layout is finding the right balance for YOU.
Yes indeed the natural flex of plywood cares for vertical transitions, though you have to allow space for it. Both at the top and base of the grade the "length of your longest car" for every 2% of change of grade. I calculated the grade between the first and last riser of the graded part. So the length between the start of the grade and the first riser is dedicated to the vertical easement. When constructing i attached the subroadbed to all risers; but the first and the last one were not secured to the girders. After a few hours of leaving the plywood alone a natural curve is formed, and the last 2 risers were secured too.
BTW the curves add drag too. The added drag can be expressed in a grade percentage as well with the formula: added drag = 32 / radius. The added drag can effect the length of your trains; pulling power might not be sufficient or string-lining might creep in. John Armstrong found any grade above 4% an attraction by itself; resulting in shorter trains, doubling the hill or helper service. Train length is an important planning criteria anyway.
Finding your balance is the art of model railroad planning. Speaking of it, if an almost 6x11 island type layout with access along 3 or 4 sides is the best footprint for your empire is very questionable indeed.
Hi,
You have gotten excellent advice so far, and hopefully I can add to it............
In building my current HO layout three years ago, I did a cookie cutter to get a track from the main level down to a lower level staging area. I wanted a consistent 2 percent grade, and wanted the "tunnel opening" where the incline goes under the main level to be maybe 1/4 inch higher than absolutely necessary.
While I have NMRA gauges and respect them, I got a piece of track and placed my tallest cars and locos on them and measured. Being as I model - and adhere to - the '50s, there was no chance I would get taller rolling stock in the future. Anyway, I came to a measurement and added 1/4 inch.
Well, it didn't look right as I was fixin to finalize the construction and then it hit me, I forgot to include the roadbed in the calculation - which added another 1/4 inch. Whew, thankfully I caught that in time.
The point is obvious............
ENJOY !
Mobilman44
Living in southeast Texas, formerly modeling the "postwar" Santa Fe and Illinois Central
Regardless of NMRA recommendations, your overhead clearances need only suit your particular equipment, keeping in mind, of course, that you may then have to restrict future purchases because of this.On my layout, the bottom of this bridge is 2.5" above the top of the rails below. The lower track is the tail track for a wye, and is used by all locomotives, all passenger equipment (no dome cars on the roster), and most freight cars and most MoW equipment.
The exceptions are high loads on open cars, like this load of automobile frames...
...and this wreck crane...
Raising this bridge another 1/2" would have negatively altered almost all of the other grades on the layout, so these restrictions are ones with which I can live. I have purposely put other clearance restrictions on the layout to add operational interest - most of the overhead clearance ones restrict locomotives, while most side clearance restrictions affect MoW equipment. Since I'm the sole operator, I'm familiar with the rule book (and have no one else to blame if I make an error).
As for vertical easements, allow the plywood to make them for you. First, fix the bottom riser at the last point where the roadbed must be level with the lower level of track and then fix the riser at the point on the upper level where it must be at the desired height. Next, calculate the point on your grade which is exactly mid-way between those two fixed points. Insert a riser and lift the roadbed until its height is exactly half of that at the fixed top end of the grade. You can walk away for a couple of days to allow the plywood to form its own natural curve, as Paul suggested, but I doubt that it will change appreciably. Finally, install all of the intermediate risers, being especially careful to neither raise nor lower the roadbed from the position which it's assumed.
If your grade is especially long, you can further subdivide the grade into quarters or eighths and install risers as is done at the halfway point - my subroadbed is 3/4" plywood and did exhibit some sagging on my longest grade, which is just over 45' long.
Wayne
This may not fit for you instance, however, if clearance is tight and to keep the grade to a min, the lowered track can be dropped using the same cookie-cutter method. Other ways to gain added clearance @ the crossing/ bridge etc, is to build a ballasted deck with the track glued directly on 1/4 or 3/8" stock (if plywood is not suffificent, strip hardwood, maple for example, or flat metal such as aluminum will easily span the distance.. This allows for the greatest railhead to railhead clearance. Girders can then be glued to the sides of the spanning stock.
Modeling B&O- Chessie Bob K. www.ssmrc.org
I may have missed it if someone mentioned it already. However, when measuring clearances on the plywood, don't forget that once the roadbed and track are down, you'll lose however much clearance equals their thickness. Remember that you equipment had to fit through on the rails once everything's in place. This also applies to any reduction in clearance due to bridge protrusions down from overhead, so you'll want to think about how that will be handled, too, although Bob K's already suggested a solution for that.
Mike Lehman
Urbana, IL
Thanks everyone for the insight on this item (and others). I felt I might be overanalyzing this or bothering folks too much I but want to get it right the first time. For me, that means minimizing grade with a reasonablelower level clearance tolerance. Plus, the top and bottom vertical transitions are something I want to do right (not designing in a hard to correct operating problem). One of the top transitions will occur near a bridge so I need to understand how to handle that right. I will digest the comments above tomorrow (after a beer I'm not sure I've got it pinned down). One of my issues is a lack of equipment to measure or play around with, and it's tough to get specs online on things like rolling stock rail to top height.
I did the cookie cutter thing today! I made sure to do it when my supervisor was out of the house. My (relatively new) scroll saw has a dust attachment that seemed to minimize dust. I was afraid I'd follow the wrong line and make a cut I didn't want but I think I follwed the right yellow brick roads. I've got lots to do before starting roadbed install; i.e., adding risers, securing the various areas to the frame, etc. I'm pretty excited about the progress but also need to learn to enjoy the journey and take my time. And I've got a bridge to build (two when I get ahold of a girder bridge I will couple to the truss bridge). And an airbrush to figure out, and how to wire Tortoises and a control panel, and selecting the DCC system and getting a first loco and........(cutting the grass?).
As Paul notes, 5'9" x 10'8" makes for access challenges (I picked up on that in another thread). The rectangular layout works with my space available, gives reasonable radii and an interesting layout for something a bit bigger than a 4' x 8'. There sure are tradeoffs and compromises. If and when it's up and running routinely it will be in a corner...access to the front and one side. I have drawn out an access hatch in the area that would be inaccessible when in the corner, but will cut that if/when I decide it's really necessary to add. Since the layout has 2" leg casters, it moves very easily (on carpet) and I can have it out from the corner as much as I like during construction / maintenance. One could argue I'd have been better off with N scale but find HO small enough to struggle with the rolling stock (my grandson's 4' x 6') and can't imagine how (at my age) I'd get a N car's wheels on the track!
Your 5/8" plywood should fall into a natural vertical curve once you raise it on the first riser, provided it's not too close. If so, then move to the next riser and start there, then back towards the beginning of the grade.
What's key is that this isn't so sharp that the pilot of your loco hangs up when running through it. Since you don't have any rolling stock, testing by laying down some track and running things over it to confirmis not going to help. However, since you're not talking 4%+ grades, etc I'm pretty sure the natural droop of the plywood will put you about where you want to be.