Before putting the frame together you must cut diagonal slots in the inside faces of the stiles which will hold the louvres in place. I used a dado set to cut these slots a quarter of an inch wide, at 45º. Not having a mortising machine, I chopped the mortises by hand, which proved a tedious task, especially when dressing them to try to get the tenons to fit. Since the stiles are only 2¼ inches wide, next time I will set up a jig and rout them, going halfway in from each side. Now I glued up the frame, wedging the tenons for greater strength and integrity. I used a one-part, powdered resin marine grade glue, which is mixed with water, is very strong and becomes fully waterproof in 48 hours. When the glue had cured, I ran a rabbett down the inside of what was to be the central edge of the shutter, so as to provide a neat overlap with its opposite number when closed. On the outside of this same vertical edge I ran a simple bead as per the original, to dress it off. You can see the rabbett in the photo which shows the trial installation of louvres below.
Next I had to make some trim, which goes around the two apertures, front and back, mitred so as to line up exactly with the inside edges of each louvre aperture. I wasn't able to exactly match the original, so I made a ½" wide by ¼" high cloverleaf profile using my old Sears molding head on my equally ancient radial-arm saw.
At this stage the trim is applied to only one side of the shutter frame, using finish nails and the marine glue. Now the shutter is turned over so as to fit the louvres, which will be prevented from slipping right through the slots by the side pieces of trim, which retains them underneath.
Having first cut the slots, it was now easy to plane the stock for the louvres to the exact thickness for a perfect fit. Using an extra-thin ripping blade, I resawed one-inch pine stock (19mm thick) exactly in half. This gave me two thin planks about 8.5mm thick. My slots actually turned out at 6.7mm wide, so it was a quick and easy job to finish plane the louvre material to this thickness.
In the nature of things, there were subtle differences in the actual precise length of the 39 louvre slots, so I now cut the louvres to length and laid them up in a trial fit, numbering them lightly in pencil. In cases where a louvre was slightly too tight or too loose for the slot I had cut it for, I would find another slot where it would fit just perfectly!
Until this point I had left the louvres slightly oversize in width. They are designed to sit slightly proud of the frame on each side, just about to the level of the upper surface of the trim. In practice, the frame stock being 1¼ inches thick, this meant that the louvres were to be two and one eighth inches (54mm) wide. I quickly accomplished this by clamping the louvres together in batches of thirteen, and running them through my 13" Delta planer on their edges as a block.
Almost finished now: all that remained was to apply the trim on the second side so as to hide the shoulders of the louvres, and lastly, to pin all the joints with wooden dowel.
I was reluctant to use commercial dowel for this purpose, feeling that an unknown species of wood might not survive so well as if I used the same cedar out of which I had built the frames.
It shouldn't be that hard to make enough dowel to pin six joints; and it wasn't. I split a cedar offcut to first get a stick about half an inch square. Then I whittled it with my pocket knife until it was more or less round and roughly 12mm in diameter. I puzzled over how to achieve a precise three-eighth round dowel from this. There is a tool, but I don't have it. It is a metal plate with serrated tapered holes in it. You drive a stick such as I had made through the appropriately sized hole. I looked around the workshop, and my eye fell upon the old handsaw that was one of the first tools I acquired, back in the late sixties. These old handsaws have holes in the tip end of the blade, so that you can hang them up on a nail. Sure enough, here was a three-eighth hole in a piece of hardened steel! I laid the saw flat on my bench with the hole over a benchdog hole and drove my stick through it with a wooden mallet. A mite rough to be sure, since the hole hadn't been made for purpose and sharpened, but a true round dowel. The job was done.