With the remaining kneebraces cut to size, it’s on to the mortises in the posts.
Each post and beam corner holds two kneebraces and so I showed the dovetail to each respective post and beam and traced the edge to help with a snug fit. To temporarily hold the kneebrace in place, I used the time honored bungee cord technique.
Once the lines were marked, I removed the kneebrace and using a large and small forstner bit, I removed as much wood in the mortise as possible.
Following that, I then used a 1″ mortising chisel and a 1/4″ paring chisel to finish the job. This gave me ample opportunity to practice my sharpening skills.
While this type of joint can be implemented after the post and beams are up, it’s somewhat difficult to mortise wood at or above eye level, not to mention the inherent danger of holding a chisel at that height. Full disclosure-I managed to drop the mortising chisel once-and while I didn’t make the mistake of trying to catch it, it took a random bounce of the ladder and struck me in the rib. At about this point my first thought was that I’d have to spend a good hour sharpening the chisel, when in fact, I was about to spend three hours at urgent care. The cut was textbook, a 1 1/2″ incision, perfect really thanks to an ultra sharp, 6000 grit Japanese waterstone edge.
The physician at the clinic was rather complimentary-she said it was a beautiful laceration and proceeded to glue it back together rather than use stitches.
After the top and bottom mortises were cleaned out, I tapped in the kneebrace-for some of the fits, I had to file things down to get them to slide in, and in a couple case the fit was less than ideal.
The braces didn’t always line up perfectly with each other which didn’t really bother me.
Once the kneebrace was fitted, I drilled two holes in each tenon and inserted 3/8″ oak pegs.
I chose to leave the pegs proud of the joint for aesthetic appeal.
The entire process of cutting the tenons and cleaning out the mortises has been the most time consuming part of the project. It is also possibly the most interesting aspect of the pergola. The biggest gaps in the joints are around 1/8″…with some possibly a bit more:-) This has been a good learning process and since it’s a pergola and not a house, I’m OK with the imperfections. It’s a balancing act no doubt when it comes to accuracy, aesthetics, structural integrity and expediency. What is sound vs what is adequate vs what looks good. Of all the joints there was one kneebrace that truly annoyed me in terms of not fitting right. Rather than fidget with it, I let it be. It’s still sturdy as hell and I was able to shim it so that the gap was minimized.
Next up are the joists and then the 1 1/2″ x 2″ strips to complete the lattice.