Construction of curved gradients

Model Railroader Layouts and layout building
1

Hi all,

For my HOn3 ‘A. N. Bradford’ mine branch layout, I’m going to need to construct some curved gradients for the switchbacks I’m planning. The curves will be about 35-40" radius, but I’m not sure if I’ll be able to cut the subroadbed (plywood, 9mm) as one piece without it twisting the track in addition to elevating it. Could someone out there please advise?

Thanks in advance,

tbdanny

2

Sounds like a job for “SPLINEMAN”[(-D]

Brent

3

You needn’t worry. With vertical risers every 12 to 18 inches extended from framework girder pieces, there shouldn’t be any problem. There is no need for a solid table top underneath. That will just get in the way and waste you money.

I don’t want to spend money covering up the framework, preventing solid connection of the vertical risers to the framework’s girders. Besides, how would I have access to switch machines and such under the roadbed?

Mark

4

Mark gave you the answer.

With 9mm plywood you are going to want risers about every 12" (300mm) or thereabouts. I use 1x2 for the vertical portion of the riser with a 1x1 cleat as a horizontal at the top of the riser. This allows all screws from underneath, and leveling the 1x1 cleat keeps the plywood level across the grade. The technique is shown in detail in Westcott’s How to Build Model Railroad Benchwork.

My first try at cookie cutter plywood4% grades on 18" radius curves had the same twist you envision. But my risers were initially nearly 180 degrees apart with 1/2" plywood. I had to add risers to force the twist out.

Fred W

5

So if I’m understanding you correctly, you cut the one piece of wood with the curve in it, use the risers every 1’ or so, and screw it down to the risers to force the twist out of it?

6

You got it. And if you get one of those handy-dandy digital level (gives grade percentage plus other measures of gradient) like the 8-inch Sears model for around $20, you can measure the grade accurately/smoothly. Use C-clamps to temporarily hold the risers, then adjust/play with them to keep the grade “smooth” although you’ll want to have a lesser grade on curves as they increase train resistance. I’d recommend keeping the C-clamps before permanently attaching while one tests actual train operations so grades can be adjusted to achieve a greater operational consistency.

Mark

7

To all who replied,

Thanks for your advice. It’s 5 days until T-day, so once I’ve started building the layout I’ll let you know how it goes.

Cheers and thanks,

tbdanny

8

You can cut the curve from a single piece of plywood, or splice together several shorter pieces for a long curve. Rather than installing the risers to the benchwork first, I prefer to fasten them to the underside of the roadbed first, at appropriately-spaced intervals to match with the spacing of the benchwork crossmembers. I also prefer to leave the last riser before the curve and the first one after the curve unattached to the benchwork. Use splice plates to join the curved section to the roadbed at both the top and bottom of the grade, which will establish the extreme elevation of both the top and bottom of the curve. I next locate the riser closest to the mid-point of the curve, and elevate it accordingly to take any “sag” out of the roadbed. (I use 3/4" plywood for roadbed - with your thinner roadbed, you may need to perform this operation at both the 1/3 and 2/3 points of the grade). Clamp these risers to the benchwork crossmembers. There should now be no sag in the roadbed of the grade - if there is, correct it by elevating and clamping the appropriate risers. If you need only a simple grade, place a level across the tracks at the mid-point of the grade, then push the bottom end of the nearest riser in the direction needed to centre the bubble, then fasten the riser to the benchwork. Repeat for each riser.

It’s also a simple matter to add superelevation to curves using the above method, plus a couple of additional easy steps. After installing the curved roadbed and correcting any sagging, and with the necessary risers clamped in place but not yet permanently attached to the benchwork, mark a pencil line on each riser which corresponds to the top of the benchwork to which it will eventually be fastened. Remove all of the clamps, then choose the riser closest to the mid-point of the curve, raise it to the proper height, as indicated by the line. Next, push the bottom end of that riser towards the outside of the curve.