Are transitions only the flat areas preceding the rise of a grade and the flat area at the top, before descending a grade OR the curvature of cookie cut plywood (1/2") where those flat areas precede/follow?>P> I’m starting at the top of the grade with 3.5", keeping a flat area for about 24" to allow my longest loco (Big Boy) to keep it’s drivers on track.
Running a straight edge along the grade is easy BUT when I use my good friend’s digital level, I find that the grade readings aren’t constant along the grade. They vary.
At the bottom of the grade (after coming off of a long flat table top area, the natural curvature/transition starts out very steep, approx. 5-6% and doesn’t go up incrementally (1%, 2%, 3% etc. until about half way up) I’m very confused by this!
Logic tells me that a 9ft. run with the top of the grade (at an entry lift gate area) at 3.5" that the entire grade should read 3.5%. What’s going on?
Obviously where the natural bend of the ply starts the grade there will be a slight “hollow” and I’m wondering if non-sprung steam loco drivers will all touch.
I will do some dry runs/tweaking when the track gets laid (soon) but aside from the usual math formula (height of grade top divided by the run’s length X 100) why do my digital level readings vary along it’s length?
I may not be understanding at all what you are describing, but it sounds like your transition ended up being too sharp. You need both a level area between grades and a transition to the grade. This transition increases in grade from 0% (flat) to the desired grade – or vice-versa.
This is why so many published plans are full of grades that are not practical in real life – because they don’t allow for flat spots between grades and the necessary transition from flat into the grade.
You may need extra risers to “muscle” the plywood into the proper transitions and grade – as sharply as you are changing grade, the natural curve of the plywood may not form the perfect transition by itself.
If you only have allowed for a 9 foot run at a 3.5% grade, you also need a couple of feet (in addition to or removed from) the run at each end of that run. This will allow for a transition into or out of the grade to keep your large locos’ drivers on the track. That may end up creating a steeper grade than you hoped between the transitions, but hopefully you’ll be able to work it all out.
The transition to the grade is of necessity less steep than the desired grade, so in effect it increases the overall length needed.
I have to assume, since your friends dig. level is reading different grades, that your grade is not constant. Only the flat part of the grade will be included in the calculations when calcing grades. I usually add (10" X grade percent) for the length of vertical curve. 2.68% X 10"=26.8", 26.8 / 2 or 13.4" are the lead in and out lengths.
My 4 ft. metal straight edge lies flush on the ply most of the way down the grade. Only at the bottom few inches where the slight 'hollow" occurs (near zero level) is the grade 5-6%. Is this correct IF the digital level’s readings ARE progressive from about half way up to the top of the grade?
Byron, I have level track for “miles” leading in the start of my grade at “zero el.”
I have 24" of level area at the top of my grade (where the lift gate will be).
I"ve subtracted the 24" of flat area from the 9 ft. and come up with 4.1%.
If I reduce that top level area by half it will lower the grade a bit What % would the result be? I appear to have 8’ of grade length with the top level area’s 24" subtracted. If my top of the grade is 3.5" I’m not clear yet on why the flat area might make my grade steeper than 3.5% Sorry I’m conceptually thick-headed… R.F.& PRR, (and Byron), if my longest loco is 20" with tender and I’m running 60’ passenger cars, does that mean that I’ll only need one half of that (10") for my level area at the top of the grade?
Byron, thanks SO much for your diagram. That was extemely helpful and I do have that gentle S shape.
I SEEM to have done what you both have described but I’ll keep playing with it and I’ll ask my digital level’s owner to check my work out when he can get the chance. I’ll try adding a few more risers.
I figured this layout would by necessity be a helper district so I knew that going in. The layout design had so many other features that were perfect for me that I figured running eight to ten freight and hopefully at least 4 shorty passenger cars would be realistic.
Byron warned me about the limitations and i’ve accepted them but want to be sure i’m maximizing steam driver contact along the entire grade, understanding the concept properly.
No idea. But if you have a “hollow”, the grade is more than you intended, I think.
Not sure, it depends on couplers, the stiffness of the loco, the flexibility of the loco-tender coupling, etc, etc. You don’t want to “high-center” the loco over the hump. In an ideal world, I’d look for more than 10" on the flat between steep grades.
If you have an obvious “hollow” or “hump”, the transitions may be too abrupt to work smoothly – that could explain the 5% grade reading, if it’s accurate.
Thanks again Byron. That makes sense to me instinctively.
If the grade is constant/correct then there should be NO hollow or will just a “titch” of a hollow? (I guess there’d have to be, but approx. what length would be appropriate? (1/8"-1/4")? (Edited).
I’ll keep moving risers. I’ve almost entirely placed them on 16" centers (joists). I’ll try adding more. Thank you sincerely for taking the time to help with advice everyone.
Judging by the immense number of archived threads regarding vertical transitions it’s a harder than usual concept for most beginners. Without someone showing you in the room or without graphics.
I think I’m getting closer and will keep at it 'til it’s right.
There should be no hollow if you are using properly fastened, and the right resistance in, materials to generate the vertical curve to match the mean grade until the transition out of the grade.
If you were to securely fasten a narrow strip of 1/2" plywood along a 10" length, flush and level with the surface around it, and then take the rest of its length, hopefully near 6’, and force it up to a 3% grade, with supports every 10" below it, you should get the best type of vertical curve possible.
My formula for vertical curves is to curve into the grade at the rate of 4"/half-percentage intended of the final curve. IOW, if you want a 3% grade, you would need 6 X 4", or about 24" of vertical transition. However, it isn’t quite that simple. Your any one engine may trump the formula by having a plow or pilot that is so low as to actually jam itself into the tracks rising up in front of it. Obviously, the longer the transition, the less likely that any one engine will have this problem.
Plywood joints (and their splices) at the ends of the vertical curves and along the vertical curves themselves are problematic and should be avoided. Plywood sections should be joined where the grade is constant or where the change in grade is very small.
Thank you Selector. Daveinga, yes the level is calibrated in %s. That was why I was so excited to borrow it!
I’ve had some success since I first posted. I found a way to lengthen the grade a bit, getting it into the 2.2-2.5 range which not only makes me happier but now the straight edge shows no hollow at the bend/start of the grade and now shows a consistent grade all the way up and down the slope!
I loosened up all risers and started from scratch yet again. The natural bend of the 1/2" ply seems to be behaving itself now with the additional length so I’ll proceed from there.
I think if I can let go of some preconceived scenery ideas from my original plan, I can get a 10.5 foot run on the 2nd grade. This grade also has 3.5 inches (edited/changed from %) at the top.
I’ll be sure to keep you all posted either with success by the end of the week or else another question or two.
Thought of an additional idea. Is it ok to use the level portion of a lift gate as my approach to a grade? I was concerned about gaps, the ever so slightly “jiggly” nature of a lift gate, causing problems with steam locos.>P
I’m afraid you may have an additional problem. if you are planning to have the upper end of your vertical curve come out to just level at the lift gate, you will not have the usual straight portion of the plywood (if the lift gate were not there) to help you “spring” the wood into the desired curve, but will have to do it all with risers from beneath. It’s not impossible, but will be a lot harder to convince the wood into the proper shape.
As an option, I would think of using a much thinner, more flexible plywood piece (1/4"?) for the subroadbed on each side of the liftgate and screwing it to a continuous “spine” of a thick board that has been shaped to the vertical curve shape, so the whole thing has a T cross section - can you visualize this? Then you have much more control over what’s going on and are not fighting the stiffness of your regular subroadbed to get a smooth transition onto the liftgate.
Or, what you could do is to extend the vertical negative curve onto the lift gate. You use a suitable length of 1/2" ply suported by beefy blocking such that it is cinched down to form your curve returning to level track…but it all extends as one monolithic block to the midpoint of the lift gate where it is also securely fastened.
The part that will make this work is to have close-set blocking at the edges of the gap between main frame and lift gate frame, and to use a saw to cut the cinched down curved roadbed over the gap, thus freeing the lift gate to rise…but retaining your transition. This will add weight and some complicaton in carpentry, but not much else. For this portion, something like 3/8" ply might be better, or masonite.
The hinged end of the lift gate will be a problem, though. This method won’t work where parts must rotate toward each other, thus compromising the gap on that end. In that respect, I would recommend a lift-out gate.
I took my HO Scale BLI 4-4-4-4 Duplex engine with the long rigid wheelbase and put on the woodland scenics 2% Grade. I found that the engine needs about 16 inches prior to the actual start of the grade to ease into it going uphill. That way the wheels will not ride too high above the rails and hang flanges in open air.
At the top I needed about 16 inches to settle the engine down without hanging the front wheels in open air with flanges above the Rails.
My Walthers heavyweight cars would bottom out until I moved out to 18 inches prior and after the point of grade change.
With that in mind call it 12 feet for the grade itself and about 3 total feet for transitioning at both ends.
Another way to cheat the linear grade is to introduce a “By eye” S curves (With at least engine length straight between bends) to extend your grade and ease it in the same 12 feet of run or in my case, a total of 16 feet run including transitions.
I was disappointed at such a large amount of room for the big engine to change grades. I resorted to using a ABBA Set of F units (4 axle) and brute force to haul up and over the 12 feet grade with much shorter transitions.
Crandell and Gerhard, thanks for the lift bridge suggestions. I think I can keep two out of three tracks that will cross it, level so a simple standard lift out will work there. (The other track, I’ll have to start the grade on the solid top). So I’m assuming that a flat/level lift out will “count” as my level track approach to a grade?
Thanks for the info on your locomotive Last Chance. I think then, I’ll likely try to keep things to 24" to be on the safe side with a long loco hauling 60’ passenger cars if I can.
I’d rather have to deal with helpers/pushers, double heading than uncoupling.
My only rigid framed loco so far is a Russian Decapod (Spectrum). It’ll be used in the initial test runs for sure along with the longer-articulated locos.
You’re the first one here who actually has quoted a direct experiment - congratulations and thanks!
But I’m uncertain about your terminology (note the added ** in the quote above) - was the length of the transition 18 inches on each side of the (theoretical) point where the level and the 2% grade intersect, i.e., 36 inches total, or was the total length of the vertical curve just the 18 inches, at each end of the grade?
