CRAFTSMANSHIP
Traditional Tool Saw sharpening The skill of sharpening a saw has all but disappeared from boatbuilding, since power saws and disposable hardpoint blades have rendered it almost redundant. Back when high-carbon Sheffield steel was the norm, the boatbuilder took particular care in maintaining the set and sharpness of his saw. A meticulous craftsman might even recut the tooth profile of a brand-new saw to his liking – or be forced to do so if a careless colleague borrowed it and ploughed into a forest of unseen fastenings. The first step is topping, also known as jointing, in which a flat file is worked along the cutting edge from heel to toe bringing teeth to a uniform height. The file is maintained level and perpendicular by a topping clamp, steadied against the blade by a vertical fence. Depending on the degree of bluntness and the unevenness of previous sharpenings, the topping can vary from a couple of light passes with the file to removing the teeth entirely. The topping clamp shown here was made in the 19th century and still does its job.
Circumstances dictate what happens next. If much metal has been removed in topping, the teeth must be recut to their characteristic triangular shape with intervening triangular spaces or gullets. Rip teeth are filed with steep faces while cross-cut teeth are given more negative rake, leaning back by around 15°. Otherwise it is usual to adjust the set. This is the extent to which teeth are bent left and right, typically by half a tooth’s thickness, so that the saw cuts a kerf slightly wider than the blade and does
Clockwise from above: topping clamp, wrest and file; the saw wrest with its adjustable guard; tapered triangular saw file
not bind. Setting is achieved using the saw wrest, which has slots for different blade thicknesses. The wrest is fitted over a tooth, to about half its depth, then levered downwards. A sliding brass guard prevents the tooth from bending too far. Next, each tooth is sharpened using a tapered triangular file. For a rip tooth the file is pushed square to the saw blade to produce a chisel-like cutting edge, while for a cross-cut tooth the file is angled to produce a knife-like bevel known as fleam.
ADVICE
Bolt alignment jig While replacing the mizzenmast step recently on the ketch Lady Isabella, I needed some unusually long bolts. As none were available locally I asked one of my workmates if he could make them for me by welding short lengths of threaded bar onto some machine screws. To make the jig he simply chose a piece of angle bar approximately 6in (152mm) long and cut a small hole in it about 2½in (64mm) from one end. The hole was cut into the apex of the angle and was roughly ¾in (18mm) square. The jig was then put in a vice with the apex down so that it formed a V-shaped channel. The screw and the threaded bar were placed in it with their ends meeting in the centre of the hole. Resting in the angle bar like this they were perfectly aligned, while the hole ensured that they only got welded to each other and not to the jig. RG
magali bellenger
Story and photographS ROBIN GATES
CLASSIC BOAT NOVEMBER 2013
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