14 August 2006
Day 4: It Ain’t Cabinetmaking
Now that the slats have been fitted, we put the bottom legs in a taper jig and bandsaw the taper on the bottom 10″ of the legs. Important note: bandsaw with curved part of leg up. Of course, you can also do this step with drawknife, plane, etc.
Brian goes over scraper tuning. Someone has a Veritas scraper (he said), but it had been punched out and was thin. Boggs asked someone for an LN scraper. He polished the back and front on a large fine diamond stone, then put the scraper in a block with a bandsaw kerf cut out to hold it vertical for sharpening the edge. Boggs uses a burr (this is, however, a controversial point).
He doesn’t use a file until the scraper becomes work-hardened and won’t sharpen any more, at which point he stops filing when the file stops chattering and starts cutting smoother.
Let’s talk about drillin’ holes.
Read Boggs’s article about drill bits (FWW 138 or online).
In his opinion, the only reliable brad point bits are from Veritas.
Brian grinds down the spurs. The spurs only need to score deep enough for one revolution. Longer spurs are needed for faster feed rates. For joinery, you really need to go only about 10 thou per revolution, about the thickness of a business card. Most spurs come about 1/8″ long, which is too long.
A high clearance angle is one thing that makes a drill bit cut aggressively. Boggs prefers a lower clearance angle, but most are high because it allows a dull bit to still cut.
Boggs hones his 5/8″ rung drill bit until it’s about 10 thou under dimension. I’ve got to say, the holes drilled were absolutely gorgeous — completely clean on the sides and bottom.
We transfered the front rung holes and drilled them, then gathered for “Lesson 42, Part A”: figuring out where to drill the holes for the rear seat.
Basically, you need to drill parallel to the chord formed by the slat. Put one slat in each leg, then rotate the legs appropriately. Make sure the slat is all the way home. Sight down the line to a framing square (clamped to a block clamped to the other end of the bench) and see if the angles of the slats are the same.
Someone called this the “slat-o-matic” procedure. 🙂
(I know I’m explaining it badly, but it really isn’t that complicated, it just seems it)
At this point, someone was stressed about trying to get the joints too close. Boggs replies, “It ain’t cabinetmaking.” Chairmaking is somewhat forgiving, far more so than some tight joinery. Despite this, his techniques are quite concise.
Then we got to the discussion of how to figure out where to drill the holes for the side rungs, someone asked what the angles would be. Boggs pulls out the jig. “We don’t need no angles, we just need blocks.”
Maybe it’s just that I was mathematically precocious as a kid, but I wasn’t entirely sure I believed him. However, it turned out to be right.
“The catch, of course, is figuring out the blocks.”
He showed a finished chair, pointing out that the front posts were 16-5/8″ center-to-center, and the rear posts were 13-5/8″ center-to-center. That’s 3″ different overall, so 1.5″ per side.
Draw a line, draw perpendicular at the front center distances, then draw a line 1.5″ in (conveniently, a framing square is 1.5″ wide). Draw from each corner to the inner line the calculated length of the side. Now draw a perpendicular line to that, and calculate how far that line is from the first line you drew. In our case, 1.75 inches.
So, basically, if the front rung is elevated 1.5″ on one side and 0″ on the other, you’ll drill at the correct angle. If the rear rung is elevated 1.5″ on one side and 1.5+1.75=3.25″ on the other, then you’ll drill at the correct angle.
We got our fronts and rears glued together (but not to each other today), all with hide glue. Boggs was very impressed with the Behlen stuff. We used 3-lb deadblow hammers to assemble, but in many cases, we needed to use clamps afterward to draw the joints together.