Floating Serpentine Shelf #4: Cutting the Torsion Box Skins

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Blog entry by Ron Stewart posted 07-14-2017 06:08 PM 3559 reads 0 times favorited 0 comments Add to Favorites Watch
« Part 3: Building the Torsion Box Skeletons Part 4 of Floating Serpentine Shelf series Part 5: Completing the Torsion Boxes »

My original design for the individual shelves would have been significantly easier to build than the ones I actually built. I had planned to build the outer torsion box frames from hardwood, mitered at the front corners, with a rabbet in which top and bottom skins would sit. My miter saw would have made quick work of the mitered corners.

Those plans fell apart after I shopped for lumber and plywood. I found some 1/4” birch plywood that looked pretty good (apart from being rotary cut), even though it was pricey at $30 a sheet. (I needed four sheets.) Also, there was no matching birch hardwood for the frames.

At Lowe’s, I found an interesting product called RevolutionPly. It was 5mm (about 3/16”) thick, mostly flat with clean edges, one bare wood face, and one primed face. (One of its applications is flooring underlayment.) The nice thing about the wood face is that it has a tight, straight grain pattern (as if had been quarter sawn). It was also just $14 a sheet. Later, I did some research, and the wood face is apparently reconstituted (fake, but made from actual wood) veneer, which explains the low cost. Consider it quarter sawn mystery wood.

At that price, I bought a sheet for testing, along with a short poplar board I hoped to use for the frames. The RevolutionPly looked very nice when finished with Watco—just the shade we wanted to complement the wall color and desk in our study. But I had no luck finishing the poplar board to match. I may have been able to succeed with a dye or toner or something on the poplar, but I didn’t relish the idea of all the experimentation that implied.

So I decided to go with Plan B—using the plywood for all faces: top, bottom, front, and sides. The difficulty with that approach is that it meant many dozens of feet of beveled edges, in 5mm thick material, if I didn’t want any exposed plies (and I didn’t). As Charlie Brown would say, “AAUGH!”

I decided to give it a try. But how was I going to bevel all of those edges? For the long edges, my options were my table saw with the blade tilted 45 degrees or my router table with a chamfer bit. I decided against the saw, because I didn’t think I’d be able to keep the plywood flat on the table, and any lift would result in a wobbly edge. With the router table, I could use featherboards and hand pressure to keep the plywood flat as it crossed the bit.

The routing worked pretty well. I first cut all of the skins to final width (using 90-degree cuts) on my table saw, then carefully adjusted my router bit height to shave off the corner without taking off any actual width. Then I rigged up some crude infeed and outfeed tables and went to work.

That took care of the bevels on the ripped edges. Now I had to deal with the bevels on the crosscuts. After much deliberation, I performed minor surgery on my table saw crosscut sled (see my Combination 90/45-degree Crosscut Sled Conversion project for details) to convert it into a bevel-cutting sled.

That worked very well. The biggest challenge was keeping the long shelf skins tight to the sled’s fence. I addressed that by using a clamp and my workbench and a piece of hardwood as supports.

The result of all of that work was a stack of nicely beveled skins.

As I mentioned in my previous post, I actually cut the skins first, and then used them to size the skeleton parts. After I assembled the skeletons, the last remaining hurdle was gluing the skins to the skeletons. I’ll cover that next.

-- Ron Stewart

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