Woodworking Project: Bent Bookcases (Part 1)

A friend of ours did us a solid, and looked after our idiot cat while we were lying on a beach in Maui back in February, so as a small part of saying thanks, I offered to build her a bookcase for her living room and she eagerly (a little TOO eagerly) accepted and agreed to pay the material costs.

The only real guidelines I had were what the overall dimensions needed to be - she wanted a bookcase that would fit behind her couch, so 3 feet high and six feet long - and she would prefer, if at all possible, that the final design include some kind of curve.

Really, up until the curve part, this was sounding super easy, right?

I did what I usually do in these situations and turned to the Internet for inspiration. I found a few videos where people had successfully created curves in plywood (and other materials) using a technique called 'kerf cutting'. It's pretty simple, really: you just make a series of parallel cuts not quite all the way through the wood, and then you gently make it round. I ran a few tests and sure enough, it works just like you'd think:

The neatest part of this was figuring out that you can adjust the radius of the corner by increasing or decreasing the space between the cuts. (Turns out there's a calculator online that you can use to work it out, but it was way, way, WAY too mathy for me - I just made a bunch of test cuts. Okay, a LOT of test cuts.)

After playing around with a few ideas, I came up with a design consisting of two separate units, each more or less square, that could be placed next to each other, and with a curved top on the outside end of each one.

I know that sounds weird, so here's what they were supposed to look like when I was done:

Of course, the other advantage to this design would be if she decided to move them somewhere else, she could put the curved corners together instead of the squared ones, or separate them by a couple of feet and stick a plant in between, or even just have matching bookcases on the opposite sides of a room (or doorway, which I think would be seriously cool).

The design called for pretty standard construction - plywood carcasses, hardwood edge banding, dadoes for the bottom shelf, and adjustable middle shelves. The real challenge here was going to be that curve, and how to conceal the plywood edge on the other top corner joint. Usually, you'd be able to add a little extra edge banding here and there to cover it up (like the other bookcases I made way back when), but because I wanted to keep the edges clean and a uniform thickness, I wouldn't have that luxury. I eventually decided on a miter joint which, even though isn't the strongest in the world, would allow me to use splines, which are my favorite things.

Then it was off to Windsor Plywood to pick up materials, and where I made the first (and most costly) of several mistakes in this project. They had some beautiful sapele on sale, which was perfect for the edge banding, and some really cheap "Baltic birch" plywood  - only $40 for a 4x8 sheet! I bought what I thought I would need and brought it all home to start roughing out the cases.

Oh, but first, I made a jig! (I got to make SO MANY jigs for this project. It was awesome.) Possibly the largest jig I've ever made, and it worked (eventually) like a hot damn. Of course, moving it around the garage every day for six months sucked, but hey.

I cut all the plywood down to rough size for the various shelves and whatnot, and grabbed an offcut to test the saw set up before making the kerf cuts for the bent corners. Which is when the truth of that old adage was brought home in all its truthiness: you get what you pay for. That plywood was absolute garbage. Just trash. It didn't bend so much as just explode in my hands.

On closer inspection, yeah, I probably should have known. Look how thin that top layer of veneer is, compared to decent (actual) Baltic birch:

Needless to say, it was back up to Windsor plywood for a couple new 4x8 sheets of proper birch and a little more sapele as I'd underestimated the requirements just a little (as usual). Suffice to say that the new stuff was a bit (3 times) more expensive, but so, so, so much better quality.

After cutting down all of the new plywood into appropriate finished sizes, I began conducting some glue tests. The good news was that the actual Baltic birch worked like a dream, and I was able to refine my cuts and create the first real mockup:

The bad news was that the glue I was planning on using was not so good. See, I was going to use Gorilla glue which, being a polyurethane glue, expands much like insulating foam to fill any gaps in your joints. The problem is that once expanded, Gorilla glue has absolutely no holding power at all. The expansion really only works to fill minor flaws - not when trying to fill in a gap of a good 1/8th of an inch. The even worse news was that while Titebond III, my old standby, was certainly better, it wasn't a whole lot better.

I started to get a little bit worried about my design at this point, to be honest. I knew that, sooner or later, at some point someone was going to try and shift one of the bookcases slightly or try to move it outright and it was probably going to be full of books at the time. With a miter joint at one end and a curve that relied on removing a whole lot of material at the other, if that someone happened to pick it up by the top, the entire thing was likely to tear apart. If I was going to have any structural stability in the tops of these things at all, I was going to have to revise my design.

So I came up with a two-fold solution: first, I was going to glue in the top shelf using dado joints, just like the bottom shelf, leaving only the middle shelf adjustable. This would provide some rigidity and stability right near the top, where it was most important. Second, I would have to come up with some type of spline arrangement within the bent corner as well. I wasn't entirely sure how that was going to work, obviously:

But I felt pretty confident I could figure something out. In the meantime, it was on to the dado-ing!

I spent WAY too much time faffing about with a couple different designs of router-based dado jigs before throwing them all in the trash and going back to old reliable: chucking the dado stack in the table saw.

And even though the length of the boards was a little tricky, it worked!

Then I got to use one of my fiddliest jigs, the shelf pin drilling template:

After that, I couldn't really put it off any longer. It was time to stop making test cuts, and just bend the damn wood already:

Much to my delight and amazement, the jig worked perfectly. The bend happened in exactly the right spot, the kerfs closed tight without splintering, and the pieces even came out square. I managed to sort of impress myself, actually.

After they dried up, it was a relatively simple matter to (carefully!) cut them to length and miter the end at the same time. Considering how many things had to go exactly right for them to line up this way, I was absolutely ecstatic at how they turned out. They were virtually identical:

I did put in some biscuits in the miter joint for added strength, and cut a couple of really interesting gouges in my work top at the same time, just as an extra reminder of why I need to not get cocky.

Spoiler alert: this was not the last time I got this reminder during this project. But this blog post is getting too long already and starting to bog down the editor with all the pictures.

But fear not - Part 2 is right here.