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Sunday, 11 July 2010

A Visit to David Charlesworth

I dropped in to visit to David Charlesworth's superbly appointed workshop on the beautiful Hartland Peninsula in Devon last week. David and his students were examining the task of sawing to a line. David has a painstakingly methodical approach to woodworking that drives some people nuts, however the result of his academically thorough analysis is often a simple 'now-why-didn't-I-think-of-that-before' alteration of technique that saves a bunch of time and effort. Here's an example:

When sawing to a line you normally rest the saw on the compressed side of the cut. If you are holding the saw with a light touch, have the timber perfectly horizontal in the vice and keep the blade perpendicular to the workpiece, the saw drops in diagonally during the first couple of strokes and the left hand side of the kerf proceeds along the line. Rob Cosman advocates starting the saw on the solid timber adjacent to the knife line to take advantage of the way it naturally moves along the path of least resistance until it reaches the mark like this:

Now consider a situation where you are forced to cut on the uncompressed side of the knife line - for example cutting dovetail pins that have been marked out using the tail board as a template:

If you try to balance the saw on the waste it will naturally want to fall towards the unsupported side and you will end up cutting the component rather than the waste. One solution that David picked up from Robert Ingham is to offset the template component to compensate at the layout stage. The amount of offset required varies depending on the kerf of your saw and the angle of your dovetails but Robert's rule of thumb is to have the tail board overhanging towards you by about 1.5mm.

The alternative method that David and I arrived at was to mark out on the line that you want to cut and then lay a chisel into the layout line to guide the saw for the first couple of strokes until the cut is established. Metal on metal is not ideal, so making a simple wooden chisel from something harder than the workpiece for the purpose would be the best solution. Because the fibres on the bevel side of the cut have merely been compressed rather than cut, they can be made to expand back to their original position with the application of a dab of water after the joint is assembled, indeed the fact that they are compressed makes for easier assembly and a reduced chance of damaging the edge during the process:

David runs short 5 day courses throughout the spring and summer and a long 12 week course starting in September.

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