Dentistry on the Turntable Pit

Those who saw this turntable at the Vancouver Train Expo this weekend already know about the disaster that befell the pit wall when I was completing the scenery. That part of the MDF that was not sealed before was still not sealed, and the swelling was nothing short of hideous.

Swollen MDF on turntable pit wall

At the show, I talked bravely about pulling out the whole wall and replacing it with a wall built up with ties. However, the more I thought about that, the more I wondered how I would make a flat foundation for this wall of ties. What’s more, by removing the wall, I would expose more MDF, and if this behaved as the rest, then I risked swelling under the ring rail, at which point, I may as well start over. So, I decided to remove as much of the affected MDF as I could and fill it with something impervious to moisture.

I started by drilling in through the pit wall all the way to the plywood behind. I felt a lot like a dentist drilling out a cavity, feeling for the soft decaying matter and the interface with sound material. I then swapped my drill for a knife and a screwdriver. With the knife, I was able to carve almost all the punky softened MDF out, and the screwdriver helped to retrieve it from the slot.

Cavity cut out

I then removed anything that would get in the way of the rails re-seating themselves from the surface. Notably, the spikes had to come out for about a half-dozen ties or so where the rails were floating in the air.

Spikes removed from rails

I clamped the rails down so they matched the height of my turntable. This was a delicate operation, and because of the clamping boards, I was really only able to check the two outermost rails. Hopefully all the others average out between them.

Then, I filled the hole with construction adhesive, which I applied using a small syringe and a large diameter needle – the type you’d rather never get an injection with. I pumped adhesive into the back of the cavity until it started coming out the front, and then I move the needle along a little ways.

Cavity filled

I’m hoping this means I have completely filled the cavity, but I’m going to avoid more wet scenery methods in this area anyway. I’m further hoping I won’t find a big gob of adhesive gluing my clamping boards to the rails when I go to remove them tomorrow.

That’s a whole lot of hoping! Cross your fingers!


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