Jefferson Bookcases – A Back for the Oversized Case

Originally written Aug 9, 2020

For the normal cases, the backs are rabbeted into the sides of the case. It makes for a very strong case, the back is attached solidly on two sides, and can move with the seasons thanks to the lapped joint in the middle, and it can still bear some weight thanks to the nails holding each of the two pieces in.

For this oversized case, I needed to put the back onto the sides of the case. This changed a few things in the construction. Rather than mitering the back corners, I can just do a normal dovetail. The back will still be glued on two sides, and nailed all around, so it can expand and contract with humidity changes and not tear itself or the case apart.

The first order of business is cutting the shiplap joint between the two back pieces. Since I'm working with ¾ inch finished stock, I did the laps ⅜ inch deep, but overlapped by ¾ inch, which looked about right from laying the two boards on top of the case and measuring with my eye.

Detail of the ship-lap joint as used on the first extra-large case

I also noticed that the narrower of the back boards was the right length for insetting it into the back of the case. That is, it's ¾ inch too short. Oh well. The wall will see it, and I'll know it's there, but it shouldn't hurt anything.

Once that was done, laying the two boards on the case and eyeballing it with them overlapped showed me I had about ⅛ inch too much lumber. So I put the shorter board in the vise, and quickly planed a little less than a quarter inch off it.

Both back boards on the extra-large case

I also noticed that the case wasn't quite square (one diagonal was about a quarter inch longer than the other), so I applied a clamp across the longer diagonal and cranked it until the case was square. Didn't take much, and the difference was too small to mess with while gluing up the carcass yesterday.

Using a diagonal clamp to square up the case

After gluing the two long edges to the case, I nailed on the backs. This should hold the case square, in addition to holding the back on.

Back boards nailed onto the case

And then I added clamps between the nails. Probably didn't need to, but a tiny bit of glue squeezed out, so I figure it was worth the effort. If the joint had moved before the glue dried, it would be significantly weaker, and a few clamps is a pretty easy solution.

Clamping the back boards in addition to the nails. This will keep the glue-joint from moving at all, which would weaken it

And that's where I left it for the day. I'll plane the outsides of the case smooth and fix up any minor imperfections tomorrow and apply the first couple coats of shellac.

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