Extending the Air Line to New Haven - Final Lines, Cutting/Installing Subroadbed

As I mentioned in the previous post, I wanted to save that plywood 24" radius curve I'd already cut out as a template for cutting out a duplicate. But the new piece would need a nice 24" radius centerline. Hmmm... how to do that.....

Turns out, it was easy - just a matter of having someplace to anchor your trammel, and somewhere to position your subroadbed for marking. Incidentally, my trammel is just a yardstick with a screw at one end and a pencil-in-a-hole at my desired radius. I've seen variations of this where the pencil is guided by a binder clip clamped onto the yardstick (so you can clamp it anywhere you want).

My subroadbed curve needed about 6" of tangent to get to the doorway, so I offset my tangent line from the curve centerline and freehanded a short easement as above.

Next, I marked the edges of the subroadbed so I'd know where to cut. Normally, this doesn't have to be that precise, but I may have this track be on top of a fill, so I didn't want excess subroadbed "overhanging" too much, needing to be trimmed later. Based on some quick research, I determined that 2 1/2" is the correct width for the top of an HO scale, single-track fill. Thus, I needed to cut at 1 1/4" from either side of my centerline.

One way to do that is to use a compass - put the point on the centerline and the pencil 1 1/4" out. But I didn't have a compass handy, so I used my ruler . . .

Pro Tip - Turns out, two of the holes are spaced exactly 1 1/4" apart. So it was only a matter of putting my Sharpie in one hole and guiding the ruler along the line, using the other hole as a window.  Alternatively, you could just follow the centerline with any marking on the ruler to get a different distance.

Here's the subroadbed, ready for cutting.

Pro Tip: Cover any models & track BEFORE you cut - especially if your staging yard is in your shop. Ask me how I know....

After my nice S curve was cut out and spliced to my 24" curve (using a plywood splice that is 4x longer than the width of my subroadbed), I glued down cork roadbed following my centerline and tacked it in place to dry overnight.

Now comes the fun part - installing the subroadbed/roadbed. It's just a matter of placing it in place, leveling it out, and screwing it all together.

But be sure you know where your risers are going beforehand! I guess I could have just used a block of wood as a riser on top of the plywood here, but I like how easy traditional risers are to adjust. So I cut out a section to allow use of a traditional riser. Just remember to cut out enough so you can still screw it into the subroadbed from below!

Now that the subroadbed is up to and through the wall, it's time to deal with the doorway and dropdown. . . .