Legs – Part 3

2016.6.07

Call in the big guns

Well, since I wasn’t happy with the hand-chiseled tenon, I made a replacement leg and contacted a friend of mine with a lathe.  Frank has a big shop with lots of power tools and a youtube channel.  He’s helped me out a couple times before, but it’s been three or four years since I’ve visited his shop.

In the meantime, another challenge of the project is drilling the angled mortises in the battens, so the legs will have rake and splay.  For chairmakers, this is something that experience helps them do by eye with a brace and bit.  But the scale of this desk project means using a large forstner bit in a drill press.  To simplify things, Schwarz made the rake and splay identical on his worktable, and figured out the included angle was 16° at 45°.  He showed a simple jig he made to hold the battens at the correct angle on the drill press.

I think my jig is a little more involved than his, but there’s not much to it.  There are two pieces of plywood attached with a piano hinge, and then two blocks cut at 16° to set the angle.  I added two small fences set at 45° to the jig table, and borrowed the toggle clamps from the tapering jig.

Making jig for drilling angled mortises
Jig for drilling angled mortises

2016.6.10

When I got to Frank’s shop and explained what I wanted, he couldn’t resist using his CNC machine, which is about half the size of my entire shop.  He figured we’d end up with a more consistent cylinder that way anyway.  I had brought the botched leg, and we used that to test the setup until we felt like we had it right.

Leg set up on Frank's CNC machine to make tenon
Leg set up on Frank's CNC machine to make tenon

For each leg, we carefully centered the bit as close as we could.  Then the CNC would offset and start cutting around.  After a full pass, it dropped down a little further and went around again, and so on.

Frank's CNC machine milling tenon on leg
Frank's CNC machine milling tenon on leg

We tried the first leg in a scrap with a test hole I had brought along: perfect snug fit.  Frank had to hold onto the scrap while I pulled and twisted the leg back out.

The only problem was that the longest router bit Frank had was not quite long enough for the tenons I wanted.  So I asked him to turn them down a little longer on the lathe, just about another 5/8″.

Leg set up in Frank's lathe
Frank turning tenon longer after milling on the CNC