With the mortises in the benchtop finished, I turned my attention to making the oak wedges that will be driven into the ends of the tenons. This joint will be strong and create a rock solid union between the workbench base and top. This will be irreversible, so I have to get it right the first time.
I went into my scrap bin and looked for some oak that would work as wedges. I learned my lesson about how important it is to use nice straight grained wood like oak or ash when I tried to use sapele as a wedge in an earlier part of this bench build. When it comes to wedges, don’t use sapele, it just splinters and shatters when you try to drive it in. I found a suitable piece of oak and figured that I could rip or plane it to width. I checked it against the thickness of the tenons and found that it was already perfectly sized. Lucky me!
I clamped the piece of oak to the benchtop and, using a rule, drew on some pencil lines to mark out the wedges. I used my LN dovetail saw to cut along the lines.
I dropped the tote end of the saw and cut as far as I could without over cutting the end line.
I then cut the five-inch section off and finished the wedge cuts.
Cutting them this way yielded three wedges for each section. However, you will notice that center wedge is thicker than the two outside wedges. I have a plan for thinning the center wedges down a little.
I have eight tenons that need to be wedged with two wedges a piece. I cut six five-inch sections of oak and made 18 wedges. This gives me two spare wedges if anything goes wrong during assembly.
To smooth the surface of the wedges, I took them to my combination sander. This should help to ensure that they go in smoothly when they are driven into the ends of the tenons. I also took the opportunity here to thin down the thicker center wedges.
I squared the end of the wedges on the disk portion of the sander. Back on the belt sander, “sharpened” the ends of the wedges to a fine point. I discovered the need for this when I made the wedges that I used on my frame and panel lid on the workbench base. If the end of the wedge is square and is the same size or slightly bigger that the saw kerf in the tenon, it is extremely difficult to start driving the wedge. Spending five seconds per wedge and the belt sander “sharpening” the wedge, completely eliminates this problem.
On some of the wedges below, you can see the sharpened point that I mentioned above.
With the wedges made, I turned my attention to cutting the kerfs in the tenons. The first question that I had to answer was, how far in from the edges of the tenon should I cut the kerfs? I widened the mortises by ¼” on each side, so I know that I need the wood that is on the outside of the kerf to deflect or bend by at least that much. The visible portion of the wedge will probably also be about ¼” wide when planed flush with the benchtop. My instinct was to cut the kerfs ¾” in from the edge of the tenons for best appearance (a 3:1 ratio). I thought about this a little, and decided that perhaps I was being a little overly ambitious trying to bend ¾” material. I decided to reduce this to 5/8″ and set my marking gauge accordingly.
I marked a line on the end grain and then on both faces of all eight tenons.
For some reason, I’m not a fan of starting cuts with a Japanese pull saw, I just feel that they wander of course too easily. I recognize that the fault is entirely mine and not the tool’s, but there it is. I started the cut with my trusty LN dovetail saw.
One the dovetail saw had bottomed out and could go no further, I switched over to the pull saw.
I cut all the way to the bottom of the tenon, being very careful not to cut into the shoulder of the leg.
Next post…. Assembly! Wow, and it’s only been a year!
– Jonathan White