Drawbore Pegs
2009.11.14
To help hold the mortise and tenon joints together, I am going to use a technique called drawboring, explained by Peter Follansbee here (note the cutaway photo at the end). For these large workbench joints, I will need 3/8″ diameter pegs about 5″ long.
The first problem with store-bought dowels is that they tend to have a lot of short endgrain along their length, which is not very strong. The dowel machinery doesn’t pay attention to how the grain runs through the wood. Because the pegs will need to bend in the middle as they pass through the tenon, they need long grain to allow them to do this without breaking apart. The way to make sure you have long grain throughout is to rive, aka split, the wood.
Riving Peg Blanks
I went to Home Depot and bought some 1/2″ oak. I carefully sorted through the boards to find one where the grain ran pretty straight down the face of the board. I made some pencil marks on the end, 1/2″ apart, as a guide on where to place my knife. I stood the first piece up, placed my knife across the end, and gave it a couple or three whacks with a hammer. Oak splits easily, and provided the grain is reasonably straight to begin with, the split will be as well.
Making a Dowel Plate
Next I needed a dowel plate to drive the blanks through. Lie-Nielsen sells a nice one, but it’s $50. I bought a piece of 1/8″ steel plate at Home Depot to make my own.
I started drilling with an 1/8″ bit. I put a few drops of machine oil on the plate for lubrication and to keep the metal shavings from flying around so much. Next I moved to a 1/4″ bit, then a 3/8″ bit. Each time I left one hole at the smaller size, for any smaller pegs I might need in the future.
Then I chucked up a 7/16″ bit. But as soon as I pulled the trigger, the drill wrenched out of my hand and went flying, taking the steel plate with it. Yikes. Too much torque to hand-hold I guess. I had planned to start the blanks through a 1/2″ hole. I would have to work them down closer to 3/8″.
2010.08.05
Later (many months later), I made a new dowel plate using some stepped drill bits. By starting each hole small and then incrementally making each one a little larger, I was able to have a range of sizes. One of the stepped bits goes up to 3/4″ but I stopped at 5/8″ for the time being.
2009.11.14
Rough Shaping the Pegs
Using a circle template, I drew a circle on the end of each peg, then used a chisel and mallet to make the blanks roughly octagonal, slightly larger than 3/8″. I tapered one end like a very blunt pencil to make it easier to start in the dowel plate hole.
Making Pegs with Dowel Plate
Then I pounded the peg through the 3/8″ hole with a hammer. The end result is not as smooth as a store-bought or turned dowel, but it doesn’t have to be.
My 3/8″ auger bit is a little oversized, and the 3/8″ twist bit I used to make the dowel plate is slightly undersized, so the pegs are a little small. I think it will be just enough space for glue, and the bend through the offset hole in the tenon should hold them in place anyway.
Test Mortise and Tenon
2009.11.17
I decided it would be a good idea to do a test run of assembling one of these mortise and tenon joints. I will be using epoxy, in the hopes that it will fill the gaps in my poorly-constructed joints. I have never used epoxy before, so that was one thing to experiment with. I have never used drawbore pegs either, so that was another experiment.
I cobbled together some 2x4 scraps, bored the holes for the peg, and then mixed up the epoxy. I spread the epoxy on the tenon.
I set the tenon in place, then drove in a peg with a hammer. (Ignore the crack in the mortise wall, that happened when I was driving screws.) Once I had the peg in place, I could not pull the joint apart, even though the epoxy was a far cry from setting up. I think I will let the mixed epoxy set up for a while in the container before I start applying it to the joints, so it will hold its shape better. I could see in the gap that it was oozing down with gravity.
Mortises V