BY DAVE HELLER April 1, 2021 Updated: April 1, 2021
This article discusses a specific aspect of making a set of not-yet-completed Bing-style Art Nouveau dining room chairs of my own design. I will write an article for SAPFM on the overall design and construction of these chairs, hopefully for the 2021 publishing cycle. Fitting the splats is the most difficult portion of the construction, and writing this article forced me to think through the construction aspects in a more analytical way than I would otherwise, which led me to an improvement in approach. I hope that you find it useful.
When I designed this chair, <Photo 1> I briefly considered how I would install the splat, and thought that it could be interesting. That is not necessarily a good thing. W hen the customer accepted the proposal I had to think about it more seriously. I was concerned enough about this and other details of the chair to build a prototype, <Photo 2>. Overall I was pleased but the splat fitting had not gone as smoothly as I would have liked. Since I was making six of these there was considerable benefit in doing it efficiently in addition to well. This is the technique that developed:
1) Rather than having the one-piece chair rail shown, with the long curving top edge, I cut the chair rail horizontally (along the grain) to generate a flat top surface to inset the splat into. For this design, the upper surface of the chair rail is at a 14 deg angle to the back surface, which casts the splat at the correct angle to fit into the chair back. I used a sliding bevel in the chair back to mimic the splat, using the back of the chair rail as a reference surface (it is slightly concave). I set the perpendicular angle on the table saw and cut off the ears of the chair rail, which I will reattach later.
In photo 2 there is a horizontal line on the chair rail where the oval sits on top of the rectangular chair rail. That is where I made the cut. I then used a router to cut the mortise for the splat and a shallower surrounding mortise to house the edges of the splat, <photo 3>. I find this a more refined look to the joint, <photo 4>.
2) This is the key step, and wasn’t obvious to me. Even though the splat is a natural shape, it is necessary to define a center line for the splat, and an axis perpendicular to that center line which is the shoulder of the tenon. Defining the center line sets how the upper portion of the splat will register against the crest rail. I lay the splat down behind or on top of the assembled chair back, and rotated it until the splat was framed nicely by the back, <photo 5>. I transferred the top center and bottom center from the chair parts then connected the lines.
That was my center line. I determined where the tenon shoulder should be to get the upper portion of the splat where I wanted it, then marked the line perpendicular to that center line, <Photo 6>. I duplicated this across the six splats. In retrospect, I should have been more exact about locating the shoulder line vs the flowers. They vary between chairs by over 3 mm, which caused fitting issues.
3) Cut the base of the tenon parallel to the shoulder line. My tenons were 15 mm long, 12 mm thick, and 120 mm wide. Cut the shoulder line, front and back. The 3 mm mark on the photo is the portion that will would hidden in the housing.
4) Use the tenon dimensions to mark the dimensions of the mortise on the shoe. I generally make mortises first and cut the tenon to match but in this case the splat is difficult to work with and the chair rail simple, so I made the tenons on the splats first and made the mortises to fit. The front of the tenon is xx mm from the front edge, since I wanted the splat to sit front of center. Using a router with a micro-adjustable fence, the fit of the mortise can be dialed right in. The fit of the tenon isn’t critical – the splat will be held in place in five places besides the shoe, so having the some wiggle in the shoe makes fitting and final assembly much more forgiving.
5) Once I cut the tenon, I fit it and then confirmed the width of the housing, so that the entire base of the splat fit 3mm into the shoe. The housing needs to be snug. That makes the plants on the splat look like they are growing out of the chair rail, which is what we want.
6) Once satisfied with the fit, the first of the four sides of the chair back was done. The other three sides needed to be addressed, one at a time. Either the left or right leg needs to be fitted next. Do not try doing the crest rail second – there is no reference surface to get the alignment correct.
I chose the right leg. Fit the splat into the shoe and clamp it. Install the chair rail in the leg. It will need to sit a bit proud, since the splat will hit the leg and hold the rail away, <photo 7>. Notice the gap between the chair rail and the leg. That must be eliminated. Mark the contact location. This is where the mortise needs to be cut. My splat is ~22 mm thick since much of it will be carved away. The connection to the leg needs to be strong, but not 22 mm thick. I cut some thickness off of the front or back of the splat at each connection to get a 15 mm thick tenon. Also, consider how the splat will fit into the chair leg. Cut the splat shape so that it will slide squarely into the leg, and also respect the grain of the splat. The picture of the splat in photo 7 does not reflect those comments. The splat tenons into the crest rail in <photo 9> have been squared for better insertion and strength.
7) I drilled out the mortise then used chisels to cut the edges to shape. Cutting the mortise deep is OK. Test fit and adjust as necessary until the chair rail is flush against the leg, <photo 8>. Any increase in the gap between the chair rail and the chair leg than was there with no splat in indicates that the splat is holding the rail off the leg. This was fiddly, but fitting the first one on each chair was the hardest.
8) Once it is fit, two of the four sides are done. For this chair the (crest) top rail is captured inside the legs, so I slid the long mating surface of that rail along the leg and marked the contact point, <photo 9>. This technique only works with dominoes or floating tenons. Again, the splat thickness didn’t need to be 22 mm, so I cut 7 mm off of the front of the splat to more-or-less center the tenon in the top rail. In this case, the length of the splat was excessive, so I cut the splat parallel to the edge of the top rail so that it has ~15 mm of insertion into the top rail. Since the shape of the top rail is both steep and curved, cutting this mortise is more challenging than the others, but the same approach worked.
9) Fit the top rail onto the splat. In a perfect world, the two flowers would both contact the top rail at the same time, and both mortises could be cut together. In my case, the second flower was considerably shorter, so I fit the first flower while using the edge of the chair leg for alignment, <photo 10>. Be aware that it is easy to rotate the top rail to match up against the splat. I only did that once, and regretted it. The mortises were slightly in the wrong place and their depths were wrong.
The depth of the mortises needs to be sufficient for the crest rail joinery to line up. I used dominoes for this piece, and the alignment marks are on both the leg and rail. Keep fitting until the lines align.
Because the crest rail has two mortises to fit it takes a little longer but is straightforward. Fit both holes, and confirm that there is no gap between the chair leg and either the chair rail or the crest rail, as in <Photo 10>.
10) Once this is done, we’re almost home. The splat can now be inserted into the chair rail, the crest rail can be installed with its dominoes in place, then the whole assembly installed into the right leg squarely, <photo 11>. Then the left leg can be set onto the tenons in the chair and crest rails and lowered until it contacts the splat, <photo 12>. Mark the contact zone, remove the leg, and cut the mortises. This one always goes the best, since everything else is locked in place. Once it is fitted, you are done! It’s time to make fit the next one. <Photo 13>.
Editors Note: This article first appeared in the SAPFM Pins and Tails Magazine, Spring 2021