Box-tools.—Tools of this type are used for turning bar stock. There are many different designs, some of which are shown in [Figs. 8], [9] and [10]. Box-tools are held in the turret and they have back-rests opposite the turning tools, for supporting the part being turned. The box-tool shown at A, [Fig. 8], is for roughing. The cutter a is a piece of high-speed steel beveled on the cutting end to produce a keen edge. It takes a shearing tangent cut on top of the bar and the latter is kept from springing away by means of the adjustable, hardened tool-steel back-rest b. This tool is considered superior to a hollow mill whenever a fair amount of stock must be removed. If considerable smoothness and accuracy are necessary, the finishing box-tool shown at B should follow the roughing box tool, but in most cases, especially if the part is to be threaded by a die, a finishing cut is unnecessary.
The finishing box-tool B is also used to follow a hollow mill if special accuracy or smoothness is desired. This tool is only intended for light finishing cuts, the allowances varying from 0.005 inch to 0.015 inch in diameter. The cutters are made of square tool steel of commercial size, and are ground and set to take a scraping end cut. This particular tool has two tool-holders which permit finishing two diameters at once. If a larger number of sizes must be turned, extra tool-holders can be applied.
The single-cutter box-tool shown at C is bolted directly to the face of the turret instead of being held by a shank in the turret hole, and it is adapted for heavy cuts such as are necessary when turning comparatively large bar stock. The tool-holder a swivels on a stud, thus allowing the cutter to be withdrawn from the work while being returned, which prevents marring the turned surface. The high-speed steel cutter is ground to take a side cut on the end of the bar. The latter is supported by hardened and ground tool-steel rolls b which revolve on hardened and ground studs. These rolls are mounted on swinging arms which have a screw adjustment for different diameters. They can also be adjusted parallel to the bar, thus enabling them to be set either in advance of or back of the cutter. The opening in the base allows the stock to pass into the turret when it is not larger than the turret hole.
The box-tool shown at D is similar to the one just described, except that it has two or more cutters and roller back-rests, thus enabling different diameters to be turned simultaneously. The cutters are ground to take a side cut. Ordinarily this gives a satisfactory finish, but if special accuracy and smoothness are desired, two tools should be used, one for roughing and one for finishing, the latter being ground to take a light scraping end cut.
The taper-turning box-tool shown at E is designed for accurately turning tapers on brass or cast-iron parts, when there is a small amount of stock to be removed. The taper is obtained by cross motion imparted to the cutter slide as the turret advances. The taper-turning box-tool shown at F, instead of having a single-point cutter, is provided with a wide cutter a. This tool is designed to turn tapering parts of small or medium diameter, requiring the use of a support which cannot be provided with a straight forming tool and holder mounted on the cut-off slide. The cutter is backed up by the screws shown, which also provide adjustment for different tapers within a limited range. The bar is supported by the three back-rests shown, which also have screw adjustment.
Fig. 9. Box-tools and Work for which they are Intended