When the tip becomes unduly thinned, as a result of resharpening, the tool should be reground to restore the cutting edge to its original form.
The scrapers illustrated in Figs. 43 and 44 are both made for tooling hollow surfaces such as bearing brasses.
The triangular form depicted in Fig. 43 can be made from a triangular file by hollow-grinding its three surfaces against the periphery of the grinding wheel as illustrated in Fig. 43b.
Although the writers have, without difficulty, ground triangular scrapers in this way to form three sharp edges, care must be taken to prevent the file from tilting and its upper edge digging into the surface of the wheel, thus possibly causing serious damage. As an ordinary measure of safety, the file, before being ground, should be fitted with a wooden handle to afford a secure hand-hold. During the grinding operation the file must be kept firmly pressed against the grinding rest but in light contact only with the wheel, and grinding should be stopped a little before the ground area reaches the edges of the file ; in addition, the rest should be set close to the wheel in order to give the maximum of support to the tool.
Those who have misgivings as to their ability to use this method with safety should remove the grinding rest and grind the file free-hand, or, as an alternative, the wheel may be made to revolve in the reverse direction by crossing the belt, but in this case, a lock-nut should be fitted to secure the spindle clamp nut, and thus prevent the grinding wheel from working loose on its seating.
The final sharpening is carried out as shown in Fig. 43c with the blade laid flat on the oilstone, and during the backward and forward strokes along the stone, the handle is alternately raised and lowered to form the curvature towards the end of the blade.
The curved scraper, shown in Fig. 44, is essentially similar to the preceding form, except that it has but one working face and two cutting edges. A scraper of this pattern can be made from a flat file, but to obtain the necessary curvature at the end of the blade the file must be heated to a cherry red and hammered over a lead block, after which, it can be filed to shape and then hardened, and afterwards tempered to a light straw colour. The working face should be ground hollow as in the previous type, and the edges are ground against the periphery of the wheel, as illustrated in Fig. 44B.
The working face is sharpened on the oilstone in the
ABOVE: A box-mounting for the oilstone of the type advocated by the author. Some workers have suggested that a piece of felt set on the top of the box helps to protect the surface of the stone when not in use; additionally, if well soaked with oil the felt provides sufficient lubricant to fit the Arkansas stone for immediate use. See page 2.
BELOW: The jig detailed in Figs 11 and 12.
SODY Of ARANCE DIAMETER
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