Sorry guys:
I ask so many questions, and can add no value to the board or give anything back in return. I am at the point of waiting for my TO’s, and purchasing a good-quality 1/2" plywood. What width is appropriate for subroadbed (1/2" plywood on risers)? 2", 3"? Something else? I have been following L. Sassi’s “A Realistic Layout, etc”. He calls for 3". Is this the standard of sorts. Any info and help is appreciated. Thks.
Mike S.
The width of the subroadbed is a variable, directly tied to the track arrangement, the profile of the scenery and the financial status of the prototype.
For single track on a high fill, or even in a deep cut with drainage ditches, a well-built railroad will have a ‘step’ between the ballast and the top edge of the fill. 3 inches in HO would give that look. On the other hand, less financially endowed roads might not have that ‘step,’ in which case the subroadbed should be the same width as the bottom of the ballast.
The prototype, and most modelers, build multiple parallel tracks on the same piece of subroadbed, so it could range from 4 inches to three inches more than the width of your X track division point yard.
One thing you should strive to do, if at all possible, is to build all of a yard throat or passenger station specialwork on a single piece of subroadbed. That makes it a lot easier to salvage intact if you ever have to move your layout.
I use anywhere from about 2 1/2 inches wide to four inches wide.
Most curves are four inches wide, just because I have notches cut for the pencil every two inches on my radius bar.
I cut my plywood 3" wide, and I agree that 1/2" is a good thickness. It is an easy thickness to handle and should not sag in between the risers. I made the mistake of using 3/8" and although it is useable, I have to use more risers to support it than had I gone with at least 1/2".
I typically use 4"
Thanks guys for your responses. I really appreciate you taking the time to respond, and more so for your help and info. I’ve never done an open grid before, so I’m just curious as to what the “norm” might be, if there is one. Just want it to end up being realistic-looking when it comes time for scenery.
Thanks for the help. GL with your layouts, and go Brother Derek.
Mike S.
Mastiff:
Yea, I think 1/2 " is the way to go (IMO). I’ve tried thinner plywood before, and had it “move” over time. Anything thicker for me, is harder to work with, especially when it comes to grading. I am planning on my 4 X 8, to grade it upwards by 1/4" up to the midway point, then another 1/4" up to the backend (4’ level). The 1/2" will work with this, whereas, a thicker sheet of plywood would be too stiff to provide a natural contour, and too hard to fasten underneath to the risers. Thanks MD for the post.
Mike S.
PS. Mastiffs are cool dogs, if you have one. Had one growing up (Matty), and she was the best dog EVER. She looked like an overgrown boxer, but I still think about her to this day.
A caution on using plywood for subroadbed. If you have sharp curves and steep grades combined, do NOT use 3/4" plywood. Even 1/2" plywood will take some effort to bend in the twist necessary to prevent unwanted superelevation and negative superelevation. I found this out the hard way using 18" radius curves and 4% grades in HO. Using a single sheet of plywood for my subroadbed - layout size was 4ft x 6ft - I had substantial portions of the curves at either end of the oval that were visibly not level going across the track.
Ways I learned to fix the problem:
keep your subroadbed as narrow as possible where you have combined sharp curves and grades. Narrow strips of plywood will twist easier than wide strips. Since I was using plaster over fiberglass window screen for scenery, I could fasten the screen to the underside of the subroadbed or to the riser cleats where it was really narrow.
use 1x1 cleats at the top of risers to fasten the plywood to. With the cleats, I could use the force of tightened screws to twist the plywood into the level I wanted. Screwing into the end grain of a riser doesn’t provide enough leverage to twist 1/2" ply - the screw will strip its threads first.
I had joists on 16" spacing. I found I had to add extra risers and joists on the 180 degree curves to force the subroadbed to be level across the track. 16" spacing is fine for straight track but not for curved where the direction of the curve actually increases the spacing.
use multiple pieces of plywood for the curves. This is not a preferred solution because getting perfect alignment vertically across the whole width of the subroadbed is impossible. Be prepared to sand the joints to get the alignment correct.
Again, from discussions on forums this really only becomes a visible problem at smaller radii on steeper grades.
Why do I always have to learn from my own mistakes?
Fred W
Fred:
You’re right, I think I might want to add a few joists and risers where the curves are. I’ll have to see where after I lay down the cutouts. My grade will not be so steep though. Unless my calcs are incorrect, 1/2" rise over 4’ is only 1/2 % grade increase. This shouldn’t be so severe as to cause major track problems, yet add a little visual interest, more than just a flat 4 X 8.
Mike S.
Re the plywood thickness subhead; I’m using 9/32, but I laminate two thicknesses glued with Liquid Nails and held together with lots of screws (which get removed after 72 hours). So far I’ve had no problems with 3% grades on 24 inch radius curves. I will admit that I cheated and made my worst grade (8%) straight. Roadbed on hidden track is about 3 1/2 inches wide for single track on curves.