Seat frame reinforcement, sliding stopped dovetails
As previously mentioned, I wanted to reinforce the seat slats so that they won’t sag. I don’t want the slats to be very thick, and during this build I went back and forth on wide vs narrow slats. The reinforcements needs to have the seat curvature as well as being tapered on the underside in order to accommodate the different height of the seat rails. I chose to use the router to create stopped sliding dovetails. This type of joint will keep the rails from bowing out while maintaining strength in the rails. Plus – I’ve never done it before, so I wanted to try it out. 🙂
After routing the dovetail in the reinforcements, I squared them to the rails and marked the joint lines. By running the router along a fence – I registered the flat spot on the router base to the fence – I cut the dovetail dadoes. I deliberately made the dadoes a hair too narrow, and snuck up to a tight fit by trimming the tails (the dovetailed tenons).
The next time I’m doing this, I’ll cut the tenons by hand. Probably the dadoes too, as the router didn’t give a satisfactory finish. I could also tell that it would be VERY easy to do irreversible damage to a piece if the router decides to take off on me. It is a very versatile and a fantastic tool, but it certainly can make a minor whoopsie into a situation where tools and parts starts flying around! To each his or her own, but in my opinion: hand tools give you control and finesse, which a power tool just won’t do. They sure are nice to have at my disposal, though.
To do this with hand toos, I would make a regular tenon, but saw the shoulders almost down to the dovetail line. I would cut the dado as usual (knife wall on both sides, chop the waste like you would do a mortise, pare and router plane to level the bottom). I would then cut the correct angle by clamping a guide block along the edges, using a wide chisel to pare the waste. A bit more cumbersome, but with total control.
In order to make the curvature for the seat, I cut the waste with the band saw then refined with a spoke shave. What a wonderful, versatile tool! Look at the shine in the surface!
I put the side frame seat rail part (or SFSRP for short?) together with the seat support in the vise, and checked the parts with my combination gauge to make sure the curvature was identical.
And by NOT marking the parts as I should have, I managed to make the first screw-up of the project. The seat reinforcements are longer than the corresponding side frame parts, and have a flat spot at the back (it will be underneath the back of the bench). At the BACK of the part! I cut the curvature so that the flat spot were at the front on one part…
I laminated a thin veneer piece to fill in the saw kerf, then glued the cutoff back in place. I could not flip the piece around since the dovetails were fitted to their respective dadoes. This is of course the drawback of this method: a tenon can be altered a lot more than a sliding dovetail. If you cut the tenons so that the part becomes too wide, just lop off the amount of wood needed. Not so with dovetails, at least it’s really not an easy operation. Oh, well. I cut the arch correctly after the glue had cured and moved on with my life. Problem went bye-bye.
Slat design choices
I wondered whether I should opt for thin slats or wide boards for the seat, so I assembled the bench and tested both options. It became obvious to me what I should choose – the thin slats made the bench look way more elegant. Sitting on it (very, very carefully) proved the point – the thin slats felt much nicer to sit on. Less “facets” so to speak.
With that decided, it was time to slather some gravy. In other words:
I got some 80cm F clamps for this job, and the side frames were quick work to glue up. The undercut tenon shoulders closed the joint perfectly, with very little glue squeeze-out. And I was rather generous with the glue. I left the parts in the clamps over night. Usually, you don’t really need to since the glue will hold just fine after about an hour or so. But it won’t hurt playing it safe sometimes.
My long sash clamps came in very handy – I would love to get hold of those clamps in a shorter version, but I haven’t been able to find them locally. I might actually end up just chopping off some of the bar on some of the clamps. There is a limit to how many clamps of that length one really need on a regular basis. These have a capacity of 160cm, or 5’3”. That’s ample!
On the next page I’ll start work on the back rest.