3. ATTACH THE BOTTOM, BACK, AND TOP
After the glue on the face frame boards dried, I glued the bottom piece onto the carcass. In fact, you could just as easily glue the bottom piece on before the face frame boards. In the photo above you can see that I used liquid hide glue (this Titebond hide glue). Mostly because it was closer to my workbench. Just be careful to check the expiration date on your liquid hide glue, because it really does expire, and won’t hold like it should. You could alternatively heat up your own fresh hide glue crystals if you can find a hide glue pot.
I clamped the bottom piece on, but didn’t reinforce it with nails, because there will be no stress on the bottom. It just needs to hang in there!
After the bottom piece was glued on, I applied several coats of Danish Oil, a nice penetrating wiping varnish. I didn’t need a super protective finish, because this cupboard will be hanging on the wall, and won’t be exposed to all the spills and abuse that a table or chair is. I also applied finish to the slide-in-back piece, and let all the pieces dry. A wipe-on varnish is an easy and fast finish, but if you’re in a real hurry, try a dewaxed (and properly thinned) Shellac finish. You could do all the finishing in a couple of hours.
After all the parts dried (over several days of applying the coats), I slid the back into the grooves.
I made sure that the width of the slide-in-back was about 1/4-inch narrower than the distance between the walls of the grooves. That gives me 1/8-inch of a gap on each of the sides, because my grooves were plowed to about 1/4-inch deep. When humidity levels change, wood expands & contracts in width, so you don’t want the back to expand to be too wide, or it could break the back or the carcass.
I drilled pilot holes in the top piece, then spread glue on the top of the carcass, and slid the top board in place. Notice how the top board has a notch cut out in it to make room for the protruding back piece:
I made sure the top was aligned properly, and then used traditional cut nails to fasten the top piece. I aimed to have them enter the carcass in the middle of the vertical sides and face frame boards. Make sure you align the long edge of the rectangular nail with the grain. If you do it backward, there’s more of a chance that the nail will split your wood (think splitting firewood). The nails go in a lot easier with some soft wax:
Sometimes I dip my nails in my beeswax finish (see the recipe here), and sometimes in a wax introduced to me by my friend David Ray Pine, who teaches several classes here (see his classes here and his workshop tour here). He mixes 3-in-1 multi-purpose oil with melted wax (beeswax or paraffin wax). This makes the nail go in easier. It also works great for screws.
Why did I use nails on the top piece, but not on the bottom piece? You’ll notice that when you hang the knob hole on a shaker knob, all the weight will be pushing up against the top piece. So nails work with the glue to keep the top piece from flying off. You can also hammer some small finish nails into the back piece, to add greater strength.
An alternate (and more common) type of cupboard back, is setting ship lapped boards into rabbets in the carcass, and nailing them into the back:
The rabbet joints would be used in place of the grooves that I plowed in the Shaker cupboard. And the ship lap joint is just two rabbet joints facing each other, so they can expand & contract with changes in humidity.