I’ll be honest, this day was so busy that I only had the energy to write out some bullets the evening after we finished this day. Coming back to look at it now (2.5 weeks later) I’m sure I forgot a lot of what we did. Thankfully I did take some pictures on top of the bullet points.
Skim/match posts
Just like the front posts, we gave the back posts a few days to allow for surface drying before cleaning up. To the best of my recollection, we just took some time this morning to straighten out the lines as best we could with spokeshaves, then smoothed them out with card scrapers. To me, this is one of those tasks that you need to set a quitting time for, otherwise you could find yourself at it all day chasing perfection.
Layout and Cut Slat Mortises
Each rear post needed 3 mortises for the back slats. We marked them using the story stick as a guide. The story stick referenced from the bottom of the foot was easy to lay out the bottom two mortises. We used a marking gauge or square to layout the inside wall (3/8″ or 1/4″ from the flat face of the rear post); the width of our chisel defined the back wall (in this case 1/4″). The top mortise sits at or near the bend so it’s a little more challenging to lay it out with an inflexible stick. We accomplished the task by referencing off the top of the post for the top mortise. Using the story stick we marked the top and bottom of the mortise, used a marking gauge or square to mark the walls but only at the top and bottom of the mortise. Again, as this mortise sits near the bend, if we used a marking gauge or square to try to mark the walls, they would end up curved. To layout straight walls, we used a ruler, referencing the points where the walls met the top and bottom of the mortise.
Cutting the mortise was done with either a hollow chisel mortiser or a drill and chisel. The hollow chisel mortiser was quick and easy once the tool was set up; I cut 4 of the 6 mortises on it with ease.
The drill and chisel method took a little more time but left good results as well. We marked brad-point bits with tape to keep from boring too deep. I believe we bored somewhere between 3/4″ to 1″ deep but I can’t recall for sure (I hope it’s on the story stick or plans!). After boring with the bit, we came back with the chisel and cleaned it up.
Drill for Rung/Rail
In order to determine the length of the slats, we need to temporarily assemble the back part of the chair. If we used the actual rungs/rails, we might not be able to get the back posts apart again. So we build 2 extra rungs but shaved a little bit off each of the tenons to ease things back out.
Laying out and drilling the mortises was a lot easier thanks to a jig Andy developed. The jig, pictured below, allowed us to drill the mortise on the drill press without concern that the post might rotate or move. The jig is essentially a cradle with some pads that held the posts in place via carriage bolts and wing nuts.
Using a bevel gauge set to an angle from the plans (20-25 degrees?), we rotated the legs until the bevel gauge sat flush with the flat face of the back post. This identified the correct orientation of the posts to have the mortise pointing straight up. We used the story stick again to locate the center of the mortise vertically. The mortise was located horizontally on the post visually, just eye-balling the post and finding the center (side note: I might have cheated by using a square here…).
Insert “Dummy” Rung -> Measure for Slats
After boring the 2 rail/rung mortises on the drill press and paring down the dummy tenons, we fit the back together. We inserted the dummy rails into both back posts as far as they would go. Next we placed the back rail assembly into a vice so we could work with both hands. Using a tape measure, we measured the length of between each mortise (at the bottom of the mortise), writing down the length and calculated half of that length on our plans.
It gets a little complicated to describe here but the technique is actually really easy. For some background, when we bent the back-slats to their final curve, we also drew a center-line on the slats. Using the plans Andy gave us, we placed our slats on the plans, matching our center-line with a marked line on his plans. ***This is where I can’t remember the exact technique. We somehow used the divided calculation to mark the length of the back slat so that each side had an equivalent length from the center-line.*** After we marked the length of the on each slat, we added an additional 3/4″* (maybe more?) to each side for the tenon.
As the posts flare out, the tenons need to be flared to get the best fit we can in the mortises. To find the angle, we clamped a straight edge to just below the bottom of the lowest mortise and used that to help us capture the flare with a bevel gauge. The picture below explains it way better than I’ll ever be able to.
We transferred the bevel we got off the bottom mortise to all three of the back slats as shown below. The line you can barely see running nearly parallel to the bottom of the slat is actually a gradual 1/4″ curve. The slat is at it’s fullest at the center-line before tapering up by 1/4″ from the bottom. The top also tapers down, however it was left up to us to draw whatever design we liked best. I cheated and copied the designs from one of Andy’s chairs.
Cut and Fit Slats
After getting the top tapers, bottom tapers, and full length of the slat to include flare on the tenons we cut them out on the band saw. Most of us didn’t get any more work done on our slats Thursday but I’ll go ahead and describe what we did Friday morning.
After cutting them to shape, we did some rough cleaning with spokeshaves and scrapers. Before we could fit them we had to bring the tenon down to final thickness. With the back slats at 3/8″ and the mortise only 1/4″, we had to remove roughly 1/8″ of material. Andy showed us how to do this with the drawknife by eye. Not being one to trust my eye just yet, I marked the final thickness along the sides and endgrain using a pencil, square set to 1/4″, and referencing off the back of the slat. The bulk of the 1/8″ material removal was done with a drawknife using a scooping motion. This leaves a nice sharp transition from the slat to the tenon.
From here it was lots of back and forth between testing the fit then removing minimal material (with spokeshave, drawknife, or scraper) before testing again. This had to be done on all six joints until each tenon seated all the way.
Once they were seated, if we had time we could add additional features to the slats. I tried to bevel mine along the top and bottom the same way Andy did his. Mine didn’t come out nearly as nice as his but I was still pleased. I’d really like to add some carving to the slats on a future chair.
Make Side Rungs/Rails
During any downtime, we set to making more rungs and rails. We needed another 2 rails and 4 rungs for each side.
Bend Slats
Just like the additional rungs/rails, we took turns bending more slats during the breaks.
pass out…