At this point, we’re ready to start building the cross beams that will connect the posts. We know that each post is about 3.5″ thick. I need 76″ wide to fit the king size bed, and the side rails will be about 1.25″ wide, centered. That means each post will have 1 & 1/8th inches of width on the inside. The cross pieces will then need to be 74″ from the inside of each post. Since the tenons and dovetails will go totally through the post, that means we’ll need an extra 7″ of length (3.5″ on each post) for a total of 81″ in length for the cross pieces. Using your miter saw and table saw, take one of your 6/4 boards and make it 3.5″ wide and 81″ long.
The way the bed will go together, the 3.5″ width will be the “face” of the board that we see. Meaning the 6/4 dimension is where we will trim down the tenon. We know the dimensions of our dovetails, so we want to transfer those to the edge of the 6/4 lumber like pictured below:
Now, using the widest chisel you have, start shaving the wood down to that line. Try to go a little thicker than the line, test the fit, and then trim as necessary.
Finally, we need to use our hand saw to cut 3/4″ off the bottom of the dovetail so that we can cut our groove into the board (steps for that below).
Do the same for the tenons on the bottom, but instead of tapering the cut, make it 3/4″ the whole way through.
Now we need to cut in the grooves that will accept the the plywood paneling. Our design incorporates three vertical pieces that go between the cross posts: one on each side, and one in the middle. Measure the distance between the cross pieces (in my case it was 25″). Then, add 3/4″ on each end (which will become a tenon) for a total measurement of 26.5″ in my case. The two pieces on the sides will get a groove cut on only one side, while the middle piece will have a groove on both sides.
Place a 1/2″ straight cut bit in your router and mount it on your table. Using a piece of 6/4 scrap, measure 1/4″ in from both sides and 3/4″ tall on the scrap. Adjust your router bit so that it cuts perfectly down the center of the board at about 3/8″ depth (just eyeball at this point). If we try to take the full 3/4″ in one pass, we risk splitting the board. Now, take your long cross pieces, place the side of the board that has the notch taken out of the tenon and lay it down on the table, then cut out the groove. Do this with the vertical pieces as well, making sure your center piece gets grooves on both sides. Then, adjust the router bit to a 3/4″ depth, and run the pieces through again.
To make the tenon, you need to take a quarter inch off each face of the board, measured 3/4 inch off the end grain. This will leave a 3/4 inch deep tenon that will go into the cross beams. Use your router again to do this. Here’s an example of what that looks like (this one is dovetailed, from later in the process, but use your imagination to think of it as a straight tenon that will fit in the slot on the cross beam pictured below).
Place both beams next to each other, and measure to the center of what will be the visible part of the beam (meaning, don’t include the tenons in the length when you calculate. One tenon might be slightly longer). Then, measure the width of the tenon you made on your center vertical piece. It SHOULD be 2″ wide (3.5″ minus 3/4″ on each side). In reality, it’s better to measure just in case. Take that measurement, transfer to to the center of the board, and cut a mortise on the top and bottom piece to accept the tenon. I went 3/4″ deep.
Do the same on the ends of each board where the tenons/dovetails are. You can do this by hand, but I just set up my router to take a 3/4″ channel from the center of the wood, used painters tape to mark where the edge of my bit was, and marked 2.75″ into the piece with a pencil. When the line on the board and the painters tape meet, stop routing.
Now for the relatively easy part: the plywood paneling. All you need to do is measure the size of each rectangular void in the picture above, and add 1.25″. Though we will have a total of 1.5″ of space created by the grooves in each direction, I want to leave some room for wood movement so that’s why we’re going a little shorter.
Cut the plywood out. We’re using 1/2 inch plywood here. I was worried 1/4 inch would be too thin, and 3/4 would be too bulky. If you’re using alder plywood, make sure to cut it to orient the boards vertically. Any other plywood won’t have this characteristic, likely, so direction doesn’t matter as much. Just plant everything out to make sure 1) the grain direction looks good and 2) you maximize your material use.
Dry fit everything to make sure it all fits! Use a rubber mallet and a piece of scrap wood to avoid damaging the wood when you tap everything together. Next stop, staining and finishing before final glue up!
***You may be thinking, “Wait, it doesn’t look done. Where’s the cap piece on top?” Very observant! I will be putting that on at the end. I am still toying with exactly how I’m going to attach it (likely dowels) but it’s an easy and non-structural step, so it can wait!
Important note: Do not glue the joints together before staining and finishing the wood. We want to make sure we get the stain in all the nooks and crannies, and if we glue first, the glue might make the stain look blotchy.