Cfrtjryk

The Easy Way

Fortunately, you're holding up a model train, not an actual train, so you can take some liberties.

The easy way to do this is not follow the rounded corners, just install four shelves as long as the straight parts of each wall, then measure and cut four trapezoid shaped connectors for the corners. Just about any method would work to join the trapezoids to the main shelves - pocket screws, maybe half lap joints if you have the router etc. available.

The Hard Way

You could do some geometry, measure diagonals, get out a protractor, etc. etc., and find the angles. You may even be able to use an app that works with your phone to determine the layout. But in my experience these things don't end well :)

Here's how I picture doing it ... be warned, these things don't always work the way I pictured it.

Install your shelf brackets first

You'll want to rest the shelves on the brackets as you figure things out. I'd place them all on the straight (not rounded) part of the wall, but try to get one as close as possible to the point where the wall starts to round.

Make each shelf as if it was going to be the only shelf

This will be the most time consuming step.

Use a contour gauge, make a pattern out of cardboard, and cut each shelf to hug the rounded part with a jigsaw or coping saw. A rasp may be handy for fine adjustments. Be prepared to spend some time and possibly waste some material.

Err towards removing less material and you'll be less likely to have to scrap it and start over. Remember that a 5-6mm gap will be fine, you're not machining an engine block, you don't need thousandths of an inch precision.

Look forward to the steps where these shelves are cut to fit - don't waste time fussing with a good fit in the portion that's going to wind up cut off.

Lay the shelves in place and mark intersection points

This step is easy but it's the key to the layout. Lay the North and South shelves in place on the brackets, then lay the East and West shelves on top of them. Mark the inside intersection points in each corner, on both shelves.

Cut the East and West shelves

The exact angle isn't important, you don't have to bisect the angle perfectly as long as you start the cut from the intersection point. That will be the key to making these fit nicely.

Mark and cut the North and South Shelves

Now you're coasting... put the East and West shelves back on top of the North and South shelves and mark the cut lines.

Check the fit, and fasten the shelves to the brackets, and you're ready to put tracks on it.

You don't. You transfer cut marks.

You don't need to make a paper plan of your cuts. Just lay the shelves on each wall.

Don't attempt to span a whole wall with 1 shelf board, it should always be 2 boards for ease of handling. If the wall angle is less than 90 degrees, initially cut each shelf at 80 degrees so its back can go all the way into the corner. The shelves will overlap at the corner.

Now see where the shelf fronts (lips) meet. From that point to the actual wall corner on the upper board, snap a line. Pull that board, cut on that line, and reinstall it. Trace (transfer) that cut line onto the lower shelf. Take the lower shelf off, cut on that line, and reinstall it. They should fit within a pencil's width of snug. You really don't want it snug snug. 5mm of gap is better than 0.

You don't want to fit it too perfectly, or ordinary expansion/contraction could jack against your walls and do damage.

When you get to the corners, figure out the radius that your train will need. It's the same trick, clamp up the piece and then transfer the cut marks from the pieces it needs to attach to.

Just four simple cuts.

I would use slightly oversized brackets and leave a gap against the wall. It might actually make for a nice floating effect.

Set a shelf along one wall, leaving a uniform inch or so behind and keeping all shelf boards in alignment with each other. Leave gaps at the ends, also. Now lay the shelving on an adjacent wall, overlapping slightly with the first. Trace the first shelf onto the second and cut to that angle. Rinse and repeat twice more.

You'll end up with well-fitted corner joints and avoid the whole wavy wall, rounded corners debacle altogether. The best part? Just four simple cuts*.

12 or 16" pre-finished or melamine particle board shelving would probably work just fine for this technique, assuming supports every 32". All cut edges would be hidden. Make your cuts from the visible side (top or bottom, depending on shelf height) because the tearout side won't have as clean an edge.

_{*I realize that additional rough cuts may be necessary to fit the shelving for tracing. The four cuts statement refers to finish cuts--those required to make everything work together and look nice.}

I'd suggest going with the plywood over the particle board. Will probably be a lot lighter, and probably more dimensionally stable as well. Depending on your scenery goals, I might suggest using 1/2" ply with a foam top to allow ground contours for visual interest. Use blue or pink foam, and not the white beaded foam, as that is much more messy. To cut the foam, use a florist's hot knife, though make sure to have suitable ventilation.

If you have at least a power miter saw, I might suggest doing the corners in pie-type trapezoidal segments like I have done on my layout, and then gluing the corners together with the top layer offset from the bottom layer by 50% for gluing surface. Such as this:

It looks like your current diagram is to have it all the way around the room. How about windows, closets, or doors? Those need to be accounted for in your plans, along with anything else. If you're planning on a high-level run (i.e. close to the ceiling, above any doors or windows), HO is not the gauge to do it in, as it will be too far away for easy viewing by children.

Is the target audience (i.e. child) already a train fan? If not, you may be going for a whole lot of extra work that will never be appreciated nor used enough to justify the cost and time you'll be spending. If this is the case, then I would suggest setting up a 4x8 foot sheet of plywood on some crates or legs and doing some loops of track at child level so they can interact with the train.

From personal experience, a child needs to be able to interact with the train to be able to keep their interest, and don't skimp on quality of the train, as a poorly performing train layout is not going to keep the child's interest for long at all.

The comment about using cardboard or foam board is exactly why I was thinking.

I would cut 4 identical straight pieces, make their edges square and mount them centered on each wall.

For the corners, tape a wire to the outside edges, between two of the boards to define the inside arc. Hold up the cardboard and cut out the walll edge, then trace out the cut using the straight boards and the wire as guides.

Repeat for the other three corners.

PS: I'm not a big fan of particle board, it's okay when covering with a laminate, but it chips easily and doesn't paint well. For this kind of project, I'd use ply with an iron on edge band.

This is doable. To get a better idea of the actual shape of the room, measure its diagonals - that should help you find the correct angles for corners. The curvature will make this tricky, but if the curvature is relatively equal in each corner measuring the diagonals should still give you a more accurate model to work from.

After that there will be be some trial and error involved in cutting the shelves, so it's a good job particle board is cheap. Your design is good because the four main shelves can be cut with confidence - only the corner pieces will need to be cut to match their environs.

If you want to stick close to the walls, there's a simple four-step process.

1: Cutting Corners

First, start with the comment by Kinnectus - get four pieces of paper or foam, and cut them to fit nicely in each corner. Leave enough space to make sure the wall has flattened out. Use a square to make sure the ends are at right angles with the wall

Importantly, number each piece of cardboard, so you don't mix them up! If you have to, put up pieces of tape on the walls, marked with the corner number.

Also importantly, measure at the installation point! I have some wacky walls in my own home, and nothing is more frustrating than realizing the walls tilt in or out, as well as in and out, and you've cut your board 2cm short.

2: Corner Installation

Once you have the corners templated, transfer the corners to your boards and cut them out, taking care to number the cut-out pieces to match. Then install them - temporarily, at least.

Install the first corner, and make sure it's level. Then, install the second corner, and using a long, straight board and a level, make sure the two corners are level to each other. Next install the corner diagonal to the second, next to the first corner, and make sure it's level. Finally, install the fourth corner, and level it with the two adjacent corners.

3: Cutting Straights

Place a board against the wall to make sure it's flat. If it is, you're in luck; measure between each corner, mark your boards, and cut them.

If it's not flat, you'll need to repeat the previous process: use cardboard to measure the curve of each wall, then transfer that curve to your board. The room-facing edge can be flat.

If the walls are really out of whack, you may need to cut once to match the curve of the wall, then set the board on top of the corners and mark the edge, and cut that next.

4: Final Installation

Make sure the corners are well-affixed, then attach the boards. Place brackets no more than 60cm apart, more if you're expecting to use the shelves for something heavier later. If the wall has any small irregularities (trust me, it will), you can file or sand the boards to get them to fit.

All that's left is to install the tracks!

Other Notes

I don't know what the speed controller looks like, but don't forget to plan where it goes. You may want it next to the track, on a shorter shelf, or mounted on the wall; make sure the wires have a place to go.

If you want the shelves to have a finished look, I'd suggest using painter's caulk to fill in any gaps in the wall, and give it a nice coat of paint.

Am I perhaps going at it wrong and there might be a better, easier, (saner), way of going about it?

As a slightly out-of-the-box idea, you could have the gap and build model bridges for the model trains - it would mean that you weren't highlighting the odd shape for the next person to walk in, and might add some interest to your setup? (depending on your modelling ambition, it might also make it easier to make each side a different 'zone', focusing on different ages or landscapes...)

You need to know in advance what are the curvatures available for the curved tracks of your model train system and how much they can be bent to adjust for the non-straight angles of your room. With this info you can proceed as follows

1. put in place the brackets, on level,


2. cut the straight boards, taking into account a minimum radius of curvature that https://www.thesprucecrafts.com/minimum-curve-radius-model-trains-2382285 reports in the range of 30 to 40 cm for HO models, you have to take into account the curved tracks available for your project — to determine the length of the board you are going to use against a wall of length L take into account the gap d between the board and the wall, the width w of the board and the radius you have chosen for the curvature r, the length ℓ of the board must be ℓ = L - 2 r - w - 2 d (of course you do not need extra precision),


3. place and fix the boards on the brackets, trying to put them at the centre of each wall,


4. for each corner, measure using a pen and a (large) sheet of paper the quadrilateral (almost a trapezoid) that is defined by the four corners of the converging boards,


5. using a compass and a ruler, find the centres of the two circles (outer and inner) that connect the boards (no extra precision needed) and draw the circles on paper,


6. transfer each drawing to a plank of wood and cut accordingly,


7. using supports mounted under the boards put in place the four corners,


8. lay down the tracks.

My general cowboy approach: put in two shelves on walls opposite each other, exact elevation is not critical, but should be within 1-2". Then overlap the other two shelves over the first two. Add some wood wedges to navigate the track elevation changes between the two sets. This might add some small interest to the track by creating elevation changes in the track for the train to go up/down. Hide the overlapping areas with scenery. If the overlaps do bother you, just mark the overlapping areas on the top shelves and cut that off. The shelf bodies will be supported by your shelf mounting system. Vibration at the joins can be controlled by using screw in flat metal straps.