The rockers and back braces for the chair are made with bent laminations. In the last post I showed the jig and process that I used to cut the thin strips to be laminated. So, now it was on to the actual glue-filled lamination process!
There are a bunch of potential ways to do laminations of this type – everything from a using a vacuum bag to building a form and using veneer screws to create a press. I don’t have any vacuum press equipment or veneer screws so I elected to make a couple of forms to be used with clamps for this process.
The forms were built out of construction lumber that I laminated together to double thickness and squared up with the jointer and planer. I then band sawed the curves into each form and carefully smoothed the curves to eliminate any flat spots This is especially important for the rocker form because a flat spot on a rocker will be easily felt when rocking in the chair. Next, I drilled a series of holes in each form to accept the heads of C-clamps. Along one edge of each form are metal stops (I used some scrap aluminum angle and steel straps that I had lying around). These stops allow the parts to be aligned evenly along one edge while they are being laminated.
As a first step, I laminated a backer strip on each form with the extra strips that I had previously cut. This allowed be to get acquainted with the clamping process and to determine how much glue to use and open time I would have. After the backers were dried I cleaned up the glue squeeze-out and trimmed them to be slightly narrower than the finished parts will be.
The moment of truth arrived and it was time to laminate the first rocker. I went about the process of spreading the glue as quickly as I could. I am using Titebond III for the gluing and it does not allow a lot of extra open time – the rockers have 9 strips so I had to move fast. With the wet stack on the form I went to work clamping – progressing from front to back on the rocker with the stack lightly clamped to the metal alignment strips. In the end it worked out OK, but let’s just say I had no time to spare when tightening that last clamp and let me tell you, there was a lot of glue squeeze-out! I left the rocker to dry in the form for 24 hours. Laminating the second rocker went a bit smoother as I was more prepared and familiar with the sequence of operations.
In the picture you can see the stacks of strips for the back braces. I am using Ash for the two inner strips for flexibility (I am also using original Titebond for this to avoid the dark glue lines that Titebond III would give). The Walnut strips on the front and back of the stacks were cut in sequence from the same piece of stock to give a visual repetition to the braces when viewed from the front and back of the chair.
The process for laminating the back braces is similar to the rockers except that they are done two at a time – one on top of the other. This process does alter the curves of the top brace somewhat when compared to the bottom brace. However, they are laminated in an order such that the bottom braces (with the greatest curves) are placed toward the outside of the chair and the top braces are placed toward the inside. This results in a change in the curves that is consistent across the back of the chair. With seven back braces, this arrangement requires four gluing operations with a 24 hour drying period in between each. While that’s going on, I can move on to some joinery for the chair.
Next up: Joinery for the seat and legs