I’ve been continuing with my operations to rough out and glue up chair components. With the rear legs already roughed out, I next turned my attention to the headrest.
The headrest (as well as the back braces of the chair) curves substantially to provide a more comfortable position while sitting. To obtain the necessary curve for the headrest you either need a very thick piece of stock (with a lot of resulting waste) or the pieces must be put together using a process known as coopering. For this headrest I am coopering individual pieces of stock with the grain oriented vertically.
The coopering process is much like the process that would be used to build a wooden barrel. The individual pieces are beveled on along their edges so that when glued together they form a segmented curve. The bevel angle on each edge can vary depending on how much of an overall angle or curve is desired and also how many pieces are being assembled. In my case, I needed an overall width of about 26″ for the headstock with an overall included angle of 40 degrees. I started with six pieces at 8″ high by about 4 to 5 inches wide. The six pieces provided 5 interior glue joints (the ends of the headstock are not beveled). Each of these joints has two edges to bevel. Put that all together and you have 10 bevels to provide a total of 40 degrees which equates to 4 degrees per bevel.
To create the bevels I elected to make multiple passes over my jointer with the fence set at 4 degrees from vertical. With a setup for a very light cut (less than 1/32″ per pass) this operation was much safer than using the table saw with the relatively small size of these pieces. After the beveling was done on the jointer I elected to take a few swipes with a hand plane over each edge to eliminate the mill marks and to assure a pristine glue surface. In the picture you can see the pieces dry fit after beveling the edges.
Because of the bevels on these pieces, the glue up operation was very tricky. The glue up of the six pieces was initially done in three pairs. Next, two pairs were glued to each another with the use of angled blocks faced with sandpaper adhered to the clamps. Because the headrest now exceeded the depth of the heads on my clamps, the final glue up required the addition of some temporary blocks glued to the headrest to act as clamping points. At a later stage, these glue blocks will be cut off and the curve will cut into the headstock at the band saw. In the pictures you can see the sequence of this series of gluing operations.
Setting the glued up headstock aside, I moved on to cutting the thin strips for the laminated rockers and back slats. This was a repetitive operation that required precision and safety. So, I created a simple jig to allow me to rip thin strips at the table saw to a very tight dimensional tolerance. The jig also allows the strips to be ripped on the waste side of the blade so that strips can be ripped from a larger piece of stock and avoiding the dangers of trying to do this between the blade and the fence.
Each rocker requires 9 strips at 1/8″ thickness and each back slat requires four strips at 90 thousandths of an inch thickness. For the rockers, I made additional strips because some will be needed to create stacks under each leg where they join the rockers. I also made some extra strips to create a curved backer for use when these strips are later laminated with a clamping form. There are seven back slats required but I made an extra for safety as well as some additional strips to create a backer. for their glue up as well. In the picture you can see the resulting strips for the rockers.
Next up: Bent lamination and creating the leg joints in the seat