The bases of each tray are going to be covered in thin sheets of ferrous metal so that terrain pieces with magnets on the bottom will stick to them.
I could have had pieces of sheet metal custom cut for each base, but that would have cost me $20-$30+ per tray. Instead, I used some 8"x8" square pieces of flashing for sale cheap at Home Depot. I experimented with these a bit when messing around with my magnetic Battletech hex board project. Back then, I used 3M Super 77 spray adhesive to hold my test samples in place. While that gave great adhesion and instant bonding, I had great difficulty getting my test pieces to line up. The glue stuck instantly, and I was not able to shift the pieces at all once they two surfaces had touched.
Knowing that I would need to be placing lots of pieces into precise places for this project, I decided to experiment with using PVA glue (Elmers). Normally I would have been concerned about the glue underneath away from the edges not drying since there wouldn't be any exposure to air (which is why I don't use PVA glue between the layers in my foam projects). But this time around I would be gluing sheets of metal to bone-dry luan plywood. Given enough time, the wood should absorb all the water in the glue and let it evaporate into the air.
Because my vertical walls are only 3/4 of an inch thick, and the final walls will need to be 1 inch thick to match my grid, I needed to leave a 1/4 inch gap all the way around the walls. I made a 1/4 inch thick guide for my pencil and traced around the edge of all the trays.
The topmost tray has a an exposed metal floor that is exactly 8 inches square, so I was able to just drop in a single piece of flashing and be done.
For the first two trays, I tried pouring glue directly onto the bottom of the tray and spreading it around with a brush before adding the metal. I ended up using WAY
too much glue. The metal pieces floated around and slid all over the place. I slopped up some of the excess, and the glue did eventually dry making a great bond, but the pieces of the second tray were a serious pain to line up.
For the rest of the layers, I dipped my brush in the glue and painted the back of each piece of metal with a modest amount of glue. This worked much better. The glue was still "slidey" enough for me to maneuver the pieces as needed, but it took some effort, and after just a minute or so, the wood had absorbed enough moisture to make the glue tacky enough to hold the metal pieces in place for the next piece to slide up against them without shifting.
It was at this point that I came across two problems.
Firstly, when I cut the flashing down to smaller pieces, my sheers left a slight upraised edge that either stuck up and was sharp, or lifted up the metal slightly when it was faced down. After a few moments' thought wondering how I could "iron" down these edges, I came up with a quick solution.
The head of a hammer is made up a much harder metal than the flashing. I Just laid the flashing down on the concrete floor and rubbed the hammer over the upraised edge a few times while pressing down firmly. It took almost no effort and the edges were nicely flattened.
The second problem was more troublesome. It turns out that when the factory cut the flashing, they did not make the sides exactly square. I could have shaved down every piece to make the corners exactly 90 degrees, but I wanted the joints to line up with my 1-inch grid in case they showed through. That would mean I would need to carefully trim each piece down to 7x7 squares, which would mean that I would need to cut a lot more times. And all of that was assuming that I could cut lines straighter than the factory.
In the end, I decided that the slight gaps that would be left behind by the unsquare flashing would be something I could live with. I do plan to cover the metal with a grid of tile pattern later, so I should be able to disguise any problems.
After that bit of angst, it was just a matter of taking the time to cut and glue down pieces.
The last layer needed no cutting at all. A nice coincidence that made the end of the gluing more pleasant.
Once I was done, I had five metal floors. (The topmost floor will be special as it will have a cut-away trapdoor center.)
I had worried that the added metal might make the trays too heavy, but the amount of flashing used was so small that the added weight of the steel was hardly noticeable compared to the the wood.
The edges of some of the pieces did stick up a bit as some of the flashing was not perfectly flat. Once everything completely dries, I'll try securing these spots with drops of super-glue.
The bottom layer is huge. Scout trooper looks lost in the middle of it all. (While he feels at home surrounded by all the flat steel, it still needs a coating of proper imperial gray to be complete in his mind.)
Even though the flashing is thinner than the recycled magnetic dry erase boards I used for my Battletech terrain, it is plenty thick enough for magnets to hold on to.
Here you can see one of my rough-and-ready D&D ships sticking to the flashing.
It uses only cheap ceramic magnets glued into recesses in the underside to hold it in place.
To show what this will look like in use, I grabbed some of my other foam wall pieces, each with one or more similar ceramic magnets in the base. The idea is that the game master will be able to create the dungeon ahead of time and transport it without having to worry that all her work will slide around.
While these walls were made super fast for a different set of terrain, the ones that will accompany this set will be much nicer and in an Egyptian theme.
The magnetic terrain will all be short enough that the layers above will easily fit, with enough of a gap that the game master will have the option to use pieces of foam core to cover the dungeon in a fog-of-war effect that is gradually revealed as the players explore.
Next step is either to line the walls in preparation for putting down the floor tile pattern, or to work on the exterior steps. Unfortunately, I won't be able to get much more work done this weekend due to other commitments.
Here's hoping for more work time during the week.