Fig. 1650.
It will be noted that the radius from the point of support a is less for the tool in [Fig. 1649] than for that in [Fig. 1648], although both tools are at an equal height from the work, which enables that in [Fig. 1649] to operate more firmly. In these two figures the extremes of the two systems are shown, but a compromise between the two is shown in [Fig. 1650], the cutting edge coming even with the centre of the body of the steel, which makes the tool easier to forge and grind, and keeps the cutting edge in plainer view when at work, while avoiding the evils attending the shape shown in [Fig. 1648].
Fig. 1651.
Fig. 1652.
It is sometimes necessary, however, that a tool of the form in [Fig. 1652] be used, as, for example, to shape out the surface of a slot, and when this is the case the tool should be shaped as in [Fig. 1651], the bottom face having ample clearance (as, say, 15°) from the heel a to about the point b, and about 3° from b to the front end. The front face should have little or no clearance, because it causes the tool to dig into the work. A tool so shaped will clear itself well on the back stroke, whereas if but little clearance and front rake be given as in [Fig. 1652], the tool will not only dig in, but its cutting edge will rub on the back or return stroke.