Читать книгу The Handyman's Book of Tools, Materials, and Processes Employed in Woodworking - Paul N. Hasluck - Страница 142

The proper formation of the burr edge is of the greatest importance. Having procured a suitable piece of steel plate, a usual but not recommended method is as follows: The plate is laid down on the bench as shown in Fig. 416, the edge of the scraper projecting slightly beyond the edge of the bench. A narrow bradawl, gouge, or special sharpener (Fig. 417) then is laid on the scraper horizontally, and, with considerable pressure, is stroked backwards and forwards from end to end of the plate, G to H (Fig. 416). After about ten or a dozen strokes, the scraper is turned upside down and the other side treated in a similar way. This completes the first part of the sharpening. Next, the gouge is placed vertically against the edge of the scraper, as shown in Fig. 418, and stroked to and fro with about the same degree of pressure and firmness as in the previous operation, and for about the same number of times. Or else, for this second part of the sharpening, the scraper is placed on its corner on the bench, as illustrated in Fig. 419, and held firmly in the left hand, while the right hand deftly strokes a gouge, with a quick action and considerable pressure, once or twice in an upward direction, as from I to J in Fig. 419. The scraper is then tried on the work to determine its sharpness or otherwise; often this trial is very disappointing. If, by good fortune, a satisfactory edge has been made, that fact is just as often due to the circumstances of chance as to the absolute skill of the workman. If the scraper fails to cut satisfactorily, it is laid down on the bench and the two processes are repeated. The following is a better method of sharpening a scraper. Grind the edge straight and square, and slope it up at the ends, as shown by A and B (Fig. 413). It should then be placed on its edge on a fine-cutting oilstone, as shown in Fig. 420, and rubbed backwards and forwards until all traces of the grinding have disappeared. Then it should be laid flat on its side, still on the oilstone, as in Fig. 421, and rubbed until the sides are bright and polished all along the edges. If any false burr or feather-edge has been created in this last process, the scraper must be set up on its edge again, as in Fig. 420, and rubbed a little more, until two perfectly square and sharp corners appear all along the scraper. Now, if due care has really been taken in making the corners perfect and square, the scraper in this condition would produce shavings tolerably well on any hard wood; but the shaving would be the result of abrasive and not of cutting action. It is purely a matter of choice if, at this stage, a smooth-backed gouge is passed to and fro over the side of the scraper, as in Fig. 416, with the object of imparting a still higher polish to the plate of steel at the places where the burr is to be formed. But the greatest care must be taken not to press too heavily, and also to maintain a perfectly level position with the gouge, while the polishing is being done. As stated, this polishing of the side is not really necessary, and the scraper would cut very well without its supposed assistance. Next, the scraper is placed on its corner on the bench, and a flat and smooth-backed gouge is passed once—or at most twice—along the edge. The scraper during this operation may be held either as already shown in Fig. 419, or as is here recommended and shown in Fig. 422; or it may be fastened in the bench-vice. The aim in this particular action is the production of an exceedingly fine burr, scarcely enough to be called a burr at all, but a perfectly regular bending over of the corner; the gouge must be very lightly pressed, or it will cause the burr to curl up too much, and also it must be kept nearly, though not quite, horizontal. With regard to resharpening the scraper, when this becomes necessary, the scraper must be placed upon the oilstone and rubbed up again to perfectly square corners as previously described in connection with Figs. 420 and 421.

Fig. 415.—Scraper in use.

Fig. 416.—Polishing Sides of Scraper.

Fig. 417.—Scraper Sharpener.

Fig. 418.—Forming Burr Edge on Scraper.

Fig. 419.—Forming Burr Edge on Scraper.

Fig. 420.—Squaring Scraper Edge on Oilstone.

Fig. 421.—Squaring Scraper Edge on Oilstone.

Fig. 422.—Forming Burr Edge on Scraper.