Modelling what might have been in southeast BC and northwest Wasington

Curlew and the quest for flat plywood

The town of Curlew WA was the most recent to be built and while loosely following the arrangement of the real Curlew, several liberties were taken to increase the number of industries serviced by the railway. As such, the model version ended up mostly flat with a lot of tracks. This suggested that maybe a different style of construction was warranted.

All of the previous benchwork construction is traditional L-girder with joists and two layers of narrow, laminated 3/8” plywood for the track sub-roadbed. This worked very well for Grand Forks and the mountainous areas, but it required a lot of fill-in between the tracks for buildings in town. So, I thought I’d try to laminate large sheets of 3/8” plywood to cover the entire area, with the thickness matching the main roadbed at the edges. I didn’t want to use the readily available modern pine plywood because it has a very thin veneer on both surfaces that makes it hard to plane down to get precise joints. I have always used good old fir plywood, so that’s what I went in search of. It seems to only be available at specialty lumber yards these day, so ok, a trip into Burnaby for a few sheets. Well, soon after getting them home I noticed a distinct curl to them, but I figured that with glue and clamps they would flatten out nicely. Big mistake! I soon realized that decent flat fir plywood is a thing of the past.

Cutting a very long story short about trying to flatten it, suffice it to say that even with a LOT of glue, clamps, and a laser level to check everything the stuff was so resistant to flattening out, that it was lifting up the entire benchwork at one point because of the strength of the clamps trying to bend it down. Everything just came up instead. That was solved with a lot of weights and patience. I did find out how great laser levels are in a darkened room where you can split the thickness of the beam on the edge of a bunch of 1×4″ pine blocks. Good enough for our work!

The joint between the sheets required quite a lot of planing to flatten it out where the tracks would cross, but thanks to the thick plys of the fir plywood, that worked just fine.

In the end it all worked out and is almost level throughout to prevent cars from rolling away.

Trying to get the #$@&%*! plywood flat

After all of the work that went in to installing the joists and risers so that the section would be level, the stars conspired against us in the form of warped plywood. This is the tale of that pursuit.

But first, a bit of background on my usual construction methods. All of the sub-roadbed so far on the layout is composed on two layers of 3/8” fir plywood, laminated together from narrow arcs and straight bits that fit under the tracks. With this approach there are no splice plates per se, as the plywood pieces form a continuous two layer sandwich all around the layout. This has proven to be a very good approach as can be attested to by the lack of running issues on the rest of the layout. One problem with it, however, is that the areas between the tracks are wide open, and more bits have to be pieced together to fill in for buildings, etc. This was quite a job under Grand Forks, as it seemed that I was always adding another bit to support something or another.

And then the bright idea hit me! For Curlew, as it was all going to be completely flat so as to facilitate switching and not having cars roll away from the operators, I decided to try laminating two layers of large sheets of the same 3/8” plywood, in the hope that I could get a nice flat area for both the tracks and the town, all at once. All of the plywood these days seems to be warped in one way or another, and the best that I could find locally was no different. I have always glued the layers back to back, so that any warps should cancel out. This has worked very well on the thin strips used before, so I assumed that it would be similar for the larger sheets. Well, it seems that I was wrong. Once everything was glued and dried, I noticed that there were in fact a few places where it went up and down, and not just a tiny bit. My guess is that the dynamics of the wood are different along the edges than in the middle of the sheet as the worst spots are where there is a joint on one side or the other. The three big main pieces were all offset from one another to avoid having adjacent joints on both layers. While this works well with the thin strips, it seems that it doesn’t for large sheets. At one spot the two top sheets curl up a bit making a cusp, even though they were screwed and clamped together as flat as I could make it. Earlier posts show the lengths I went to to clamp them flat.

Ok, I thought, no real problem, as we can sort it all out when the plywood gets screwed down to the risers. They can be adjusted upwards and downwards to fix bumps or dips. John’s pictures show the effort that went into getting the many risers attached at just the right elevation, by using the laser level (thank you very much!). Again, it seemed like a good idea to all of us at the time…

I quickly realized that I needed some specialized tools to see just how warped the plywood was. I devised some targets for the laser level that show if any point on the plywood is at the correct height or not. I realized that using the laser on the edge of the plywood is not good enough when it is wide and may be cupped. I came up with a two step block idea where the goal is to split the beam on the edge, with the upper half of the beam hitting the second block. That one is set back a bit, so it is easy to see if the beam is only on the lower block, (too high), only on the upper block (too low), or split between the two (just right). I will make up some from high grade birch plywood so that they are all the exact same thickness. I had to hunt through many pieces of my 1×4 supply to find a bunch that were the same thickness, so it’s time for a special tool.

Movable laser leveling blocks
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