Hi, new here to the forum.
I am using 3/4" plywood and the "cookie cutter" approach on an n-scale layout. I am trying to build a vertical curve from a flat yard to a 4% grade on the mainline. The grade begins at the same point a 14" radius curve begins. The 1 and 1/2" wide sub-roadbed starts at the same point. It is cut from and attached to a wider section of plywood that supports the yard.
As I lift the sub-roadbed to screw it in place on the first riser at the proper height, I'm finding that the sub-roadbed twists because the plywood is cut in the shape of a 90-degree curve in the same place the grade starts. No matter how well I use reinforced blocks and braces, I can't keep the sub-roadbed level across the track on the grade, especially in the area of where the vertical curve begins where it attaches to the wider sub-roadbed. I hope this makes sense.
Is the problem that I'm using 3/4" plywood that's too stiff for me to twist backwards against its natural tendency to twist? Would switching to 1/2" plywood allow me to hold it level as I bend the curve upwards to the grade profile? Or is there another solution? Thanks in advance!!
Steve
I wouldn't worry about it. Unless your grades are too steep, the amount of flex should be minimal. If it's visibly noticeable, you can glue cardstock shims under one side of your roadbed to keep it level -- or even superelevate it in the right direction.
--Steven Otte, Model Railroader senior associate editorsotte@kalmbach.com
The way that I deal with this issue is to clamp the riser to the joist, screw the subroadbed to the riser, then un-clamp the riser and use it as a lever to level the subroadbed. Start the screws that will hold the riser to the joist first so when you get the subroadbed level you can easily drive the screws home. In some extreme cases I have temporarily attached an extension to the riser to gain extra leverage. Doing it like this I have never been unable to get the subroadbed level side-to-side.
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Yeah, I saw the same phenomenon the (one) time I tried the cookie cutter method at a curve. I concluded that the likely cause was that the starts of the two cuts for the raised curved portion were exactly across from each other and evidently should have been staggered a bit. (Sorry to say I no longer recall which cut, the inside of curve or outside of curve, I decided I should have started first.)
But it is true that the wood can be "bulled" to go where you want, and also as Steve Otte points out that you can have the subroadbed do what it pleases and address the issue above it with shims. I tend to use plastic rather than cardstock.
Dave Nelson
SteveSullivan Hi, new here to the forum. I am using 3/4" plywood and the "cookie cutter" approach on an n-scale layout. I am trying to build a vertical curve from a flat yard to a 4% grade on the mainline. The grade begins at the same point a 14" radius curve begins. The 1 and 1/2" wide sub-roadbed starts at the same point. It is cut from and attached to a wider section of plywood that supports the yard. As I lift the sub-roadbed to screw it in place on the first riser at the proper height, I'm finding that the sub-roadbed twists because the plywood is cut in the shape of a 90-degree curve in the same place the grade starts. No matter how well I use reinforced blocks and braces, I can't keep the sub-roadbed level across the track on the grade, especially in the area of where the vertical curve begins where it attaches to the wider sub-roadbed. I hope this makes sense. Is the problem that I'm using 3/4" plywood that's too stiff for me to twist backwards against its natural tendency to twist? Would switching to 1/2" plywood allow me to hold it level as I bend the curve upwards to the grade profile? Or is there another solution? Thanks in advance!! Steve
When you get to the end of the 90-degree cookie curve, you are no longer modelling vertical slope, but rather cross slope. The subroadbed is in effect exhibiting 4% super elevation. You will have to twist that end back to flat horizontal.
The best solution would be to separate horizontal and vertical curves if at all possible, but your overall layout design might already be fixed. Good luck .
LINK to SNSR Blog
ROBERT PETRICKThe best solution would be to separate horizontal and vertical curves if at all possible, but your overall layout design might already be fixed.
Yeah, Robert's point is a good one, but may not help here depending on what options you have. Certainly, do everything you can to ease a transition/vertical curve located at such a joint, because a sudden shift to a 4% grade will otherwise be problematiic once track is down.
Steve point on shimming is a good tip. The subroadbed is a good foundation, but need not be perfect in itself, just mostly so while providing a solid base to shim on where needed.
If you have the space, doing some shimming where the track crosses the joint from the table top to the grade will help with the transition I mentioned earlier. In this case it won't be side-to-side, but end-to-end to help adjust to the grade from level.
Mike Lehman
Urbana, IL
I think I understand what you are describing. Lifting the one end into a vertical curve makes the curved end want to point downward. I fasten both ends to their risers, because that's important to maintain the grade. Next, if I must, I place a joist or horizontal beam below the twisted area and attach another riser to meet grade between the two on the extremes. Then, forcing the middle portion to meet the intermediate riser, I use screws to force it to a level tranvserse lie.
Thank you everybody for your help. Even knowing I'm not crazy is a help!! I will try your suggestions to get it as level as possible and then shim where I need to. I have been so obsessed with getting it perfect I didn't even think of that option.
THANK YOU ALL SO MUCH!!!!
This turned into a big roadblock on my first layout. Now I can get moving again.