The part ing tool is applicable either to catting grooves or for parting, or, in other words, cutting work apart. The cutting point, or end of the tool, is made thicker than the metal, both vertically and horizontally, behind it, so that the latter shall clear and not grind against the sides of the groove. This tool, especially if made thin to suit some especial purpose, is excessively liable to spring, in consequence of the pressure of the cut; and if it commences to spring, it is apt to dig into the cut, and then break from the excessive strain. It is to prevent this digging in that the top face of the cutting part of the tool is placed so much below the top face of the body of the tool, which may, however, be dispensed with when the cutting edge is held close in to the tool-post, and the grooving is not required to be very deep. When, however, these requirements do exist, the form illustrated is absolutely indispensable to rapid and reliable duty, whether the tool be used in a lathe or a planing-machine, the cutting edge of the tool being kept at about the horizontal centre of lathe-work, by packing-pieces placed beneath the body of the tool. If the width of the tool is not less than 3/16 inch, and does not require to cut a groove deeper than 5/8 inch, it should be hardened right out; if, however, these conditions are reversed, it should be tempered to a dark straw, and for very weak tools even to a purple color, as lowering the temper increases the strength of all tools. If the groove to be cut is sufficiently broad to cause the tool to spring, it is best to use a narrower one and cut it out in two separate cuts, moving the tool.

Parting Tool

Parting-Tool