The Master grade Western Red Cedar top is extremely stiff with very tight annular rings so I plan to bring the center thickness to 130 thousandths of an inch (130/1000″). I am using accurate calipers to measure the starting thickness. I will create a gradient from the center to the perimeter of the top, bringing the perimeter to 100/1000″.
Using my Performax drum sander, I carefully remove thin layers from the top. It takes over 100 trips through the sander to arrive at 140/1000″. I will use a random orbital sander, a scraper, and sanding blocks to achieve the final thickness but this will happen after joining.
The bookmatched top pieces need to be joined using a butt joint. This is an extremely important join as the top radiates as a whole and the join should never fail with the continual stress exerted by the movements of the top. In order to ensure the stability of the join, I prepare each Cedar half using a trim router and 1/4″ straight bit. I run the router several times along the edge of each piece. To test the evenness, I hold the two pieces together in front of a bright light source to see if there is any “candeling” (any light showing through). Fortunately, the first candeling test is successful.
To join the top pieces, I use a method developed by Spanish luthiers over 200 years ago. I built a jig that uses rope to pull together two thin pieces of wood while keeping them flat. I apply a thin line of glue on each side, place it in the jig, and wrap several runs of rope in four positions along the width of the top. I then insert Mahogany wedges under the rope to pull the tops together by tightening the rope.