3 (or 4?) piece plywood desk over bike trainer

Question

I am trying to build a platform for my laptop that can be positioned over my bike trainer. I hope to make it out of plywood and have 3 pieces that slot together. I'm trying to sketch up some designs, but I'm wondering if anyone has advice on making a tall structure like this. It would end up looking like this:

but, of course, be a lot taller and skinnier.

Edit: Something basically like this design:

but with the legs much taller. I am wondering if this would be stable? Also, what tools would I need to cut the holes an shape the interlocking parts that sticks up from the legs.

Edit- Results and possible upgrades:

I am thinking about adding support cross bars at the points indicated by the red arrows:

There really isn't a lot spaces where cross bars/supports would fit. The bike frame and my pedaling legs cover a wide range of areas. Both supports would take the form below with the bottom support resting on the floor with the opening (cut-outs) facing upwards.

Answer 1

but with the legs much taller. I am wondering if this would be stable?

No guarantee but I think it could be stable enough if you use thick ply (3/4" / 19mm or better) and if the joints are made very neatly for a good fit. Ideally I'd want to see a brace lower down on the legs but I assume that won't be possible with the bike trainer in the way.

Also, what tools would I need to cut the holes an shape the interlocking parts that sticks up from the legs.

This is the bad news, that you're asking the question probably indicates you don't already own suitable tools for the job and are practised enough in using them. For furniture like this to be firm and stable the slots need to be cut quite accurately, if too tight the pieces simply won't go together. But too loose and it'll wobble.

There are numerous ways of cutting the ply for something like this, and many guides out there will assume a table saw is available! You could do this entirely using hand tools (panel saw, drill and files or sandpaper) but it would be much easier with a jigsaw and a power drill.

Note: if you're unfamiliar with modern plywood most common stuff (and some supposedly better than this) is not very well made, and there can be numerous voids inside and possibly irregular interior plies. These don't necessarily affect strength in any noticeable way, but it can make the exposed edges uglier than you'd prefer.

If you look closely at the first image you posted there's a black line near the bottom of the front-right corner, that's a void. Some boards can have many of these unfortunately and you may want to fill them to improve looks. This is not at all hard to do but it's an additional step that many step-by-step guides don't mention.

Answer 2

In simplest terms, what you are trying to do is create a stable platform at a specific height. To remain stationary the top must resist shifting in all three dimensions. Both tops in your photos are held in place vertically by the legs (no problem here), and resist movement forwards and backwards because of the long connection between the legs and the top. The first table also has a vertical board at the center that supports the top, stiffens the legs and helps prevent movement of the top from side to side. The lower bed table appears to be lacking this feature, but because of its small size the legs can be secured to the top and provide enough stiffness through the glue or screws to prevent side to side movement and keep the legs aligned vertically. The forces acting in each direction will have greater impact on the pieces sturdiness as the length of the legs or width of the table increase. Eventually, the forces will be great enough that the plywood panels will not be able to resist them adequately and will begin to bow out.

So what to do? A 3/4" plywood top should be adequate to span the 20"-24" width needed. The same is true in the front/back direction where the vertical stiffener (or two) will support the top. The legs will work best if they are vertical or are stiffened with additional wood at the vertical edges, especially if on an angle as in the first example. Consider that each intersection is a potential hinge and must be held in place firmly. Do this with glued mortise and tenons or other appropriate wood joints The bed table looks like the legs just fit in a slot in the top. This will not work at the scale of your desk, but not as the table gets larger. Make the vertical cross board(s) as deep as you can to increase their stiffening effectiveness. Of course the simplest solution may be to get a stool and build a table platform on top at the correct height or get a taller standing desk/table. But if the idea is to make something more stylish, then be prepared to make it a bit more hefty that the examples.

What you have shown looks simple, but furniture design is just as complex as constructing a building, only at a a smaller scale. The same engineering principles apply to both. It is unclear what level of woodworking experience and tools you have. You may want to consult a friend to help design and build your piece if needed. If you draw up a design and post it in a question with dimensions you may get further feedback on how well it will work.