Builders' Forum Archives
Re: Joining panels
Posted by John Beck on Feb 14, 2007
Butt joints with a butt block behind the seam are used on relatively flat surfaces. This is done while joining the forward and aft sections of many CLC plywood decks.
If the simple butt joint with one layer of glass on each side was a suitable joint then we would all be doing it rather than going through the trouble of a scarf or puzzle joint. No free lunch, I'm afraid.
However, I've seen skiffs with butt joined plywood where multiple layers of glass cover the joint on each side. Each layer of glass is 2 to 3 inches longer than the previous layer to make it smoother and stronger. The resulting seam is not flat, cannot be perfectly faired, heavier, may require filler to hide the transition to the bump and is not suitable for a varnish finish. In the end I'm sure the scarf joint is faster and cheaper, and least as strong as the plywood itself.
A sharp low angle block plane makes creating a scarf joint in 4mm ply rather simple. Stack up the pieces and step each layer back 32mm from the end of the layer beneath. Two layers is the minimum and up to 6 or 8 is doable. Draw a line 32mm back from the end of the top layer. The ramp created by the steps provides the proper planing angle. As you remove material the glue lines provide additional tell tales of how you are doing. It's not as hard as it sounds. Give it a try.
Good luck, John
In Response to: Joining panels by Randy Powell on Feb 14, 2007