In response to a question regarding scarfing plywood on another thread, I thought I'd start a new thread.
Here is what has worked for me in scarfing (1:8) together 4mm plywood sheets for the planking on my first build, a Wee Rob canoe.
A pair of sturdy (250x30x1200mm) lower and upper clamping battens, edges chamfered at 1:8, are used to:
- assist in clamping the plywood to the bench top
- support the lower (future feather edge) and upper ends of the sheets
- provide a reference surface for planing the scarf at the correct angle
Here the Rali block plane was used to remove the bulk of the material, still quite a way to go:
A block plane set to take a fine cut, skewed relative to the direction of cut (here, parallel to the long edge), was used to do the final planing, until the edges start to feather:
The final planing was done using a combination of free handing (shown above) and using the guide shown below (the guide is also used to bevel the plank laps). I'm not yet entirely convinced that the guide helps in the scarfing process:
The planed scarf is then fine tuned with P80 sandpaper on a sanding block to produce this (note the tear out bottom right, the result of the block plane set to take too coarse a cut!):
Don't forget to:
- make sure that the plywood sheets are securely clamped along the scarf edge (both above and below) - any loose edges can potentially result in a wavy, inaccurate scarf or tear out
- use a sharp block plane set to take a fine cut when planing down to the final line
- skewing the plane, when planing parallel to the lamination lines, helps to prevent tear out
- mark each plywood sheet, on the sides of both ends of the scarf, with a 'middle of scarf' point - these are used to align the two sheets during glueing; the feathered edges of the plywood sheet are not good enough for accurate alignment