Modern Machine-Shop Practice Part 71

If, for example, a piece of work requires the use of two or more such tools, and the holder is once set, the tools may be removed and interchanged with a certainty that each one put into place will stand at the exact angle and position required, not only with relation to the work, but also in relation to the other tools that have preceded it.

Each hollow or round will not only be correct in its sweep, but will also stand correct in relation to the other sweeps and curves, no matter how often the tools may be changed. Inasmuch as the tool is ground at the top only for the purpose of resharpening, it maintains a correct shape until worn out.

[Ill.u.s.tration: Fig. 1026.]

The pin shown at _f_ in Fig. 1024 is fast in the holder, and fits loosely in clamp C to prevent it from swinging around on B when B is loosened.

When the tool requires to preserve its exact shape it may also be made circular with the required form for the cutting edge formed round the perimeter. Thus Figs. 1028 and 1029, which are extracted from _The American Machinist_, represent tool holders with circular cutting tools.

[Ill.u.s.tration: Fig. 1027.]

The holder A fits the lathe tool post, carrying the cutting tool B, which is bolted to the holder and has at F a piece cut out to form the cutting edge.

To facilitate the grinding, holes are drilled at intervals through B. A plan view of this tool and holder is shown at C, the shape of the cutting edge being shown at D. The cutting edge is shown in the side view to be level with the centre of the tool holder height, but it may be raised to the level of the top of the tool steel by raising the hole to receive the bolt that fastens the cutter, as is shown at E; or the cutter may be mounted on top of the holder as shown at H, having a stem pa.s.sing down through the holder, and capable of being secured by the taper pin I. A plan view of this arrangement is shown at J.

[Ill.u.s.tration: Fig. 1028.]

[Ill.u.s.tration: Fig. 1029.]

[Ill.u.s.tration: Fig. 1030.]

[Ill.u.s.tration: Fig. 1031.]

Another form of circular cutter is shown in Fig. 1030. It consists of a disk or cutter secured to a holder fitted to the tool post, the cutter edge being formed by a gap in the disk, as shown in the figure, which represents a cutter for a simple bead or round corner. The front end of the holder has a face A, whose height is level with the line of lathe centre when the holder is set level in the tool post. Hence the top face of the cutting edge may be known to be set level with the line of centres when it is fair with the face A of the holder. The bottom clearance is given by the circular shape of the cutter, while side clearance may be given by inclining the face B of the holder (against which the face of the cutter is bolted) to the necessary angle from a vertical line. The face C is ground up to resharpen the cutting edge, and may be reground until the circ.u.mference of the wheel is used up.

Figs. 1031, 1032, 1033, and 1034 represent lathe tool holders by Messrs.

Bental Brothers, of Fullbridge Works, Maldon, England. The holder consists of a bar A, having at the front end a hub H, containing a bush in two halves, through which the tool T pa.s.ses; this tool consisting of a piece of [V]-shaped steel. A set screw on top of the hub clamps the two half-bushes together, and these, as their faces do not meet, grip the tool.

[Ill.u.s.tration: Fig. 1032.]

[Ill.u.s.tration: Fig. 1033.]

[Ill.u.s.tration: Fig. 1034.]

The advantage possessed by this form of holder is that the top face of the tool may be given any desired degree of side rake or angle required by the nature of the work by simply revolving the bushes in the hub of the holder. Thus, in Fig. 1034 the top face of the tool stands level, as would be required for bra.s.s work; in Fig. 1032 the tool is canted over, giving its top face angle a rake in the direction necessary when cutting wrought iron and feeding toward the dead centre; and in Fig. 1033 the tool is in position for carrying a cut on wrought iron, the feed being toward the live centre of the lathe. This capacity to govern the angle of the top face of the tool is a great advantage, and one not possessed by ordinary tool holders, especially since it does not sensibly alter the height of the tool point with relation to the work. Again, the [V]-shape of the tool steel causes the bushes to grip and support the tool sideways, and, by reducing the area of tool surface requiring to be ground, facilitates the tool grinding to that extent. Altogether, this is an exceedingly handy device. It is obvious, however, that it cannot be moved from side to side of the tool rest unless a right and left-hand tool holder be used; that is to say, there must be two holders having the hub on the opposite side of the body A.

[Ill.u.s.tration: Fig. 1035.]

[Ill.u.s.tration: Fig. 1036.]

Figs. 1035, 1036, 1037, and 1038 represent tool holders in which the tools consist of short pieces of steel held end-wise and at a given angle, so that the amount of clearance is constant. The holders Figs.

1035 and 1036 are split, and the tool is secured by the screw shown.

Fig. 1037 represents a tool holder in which the tool is held by a clamp, whose stem pa.s.ses through the body of the holder so as to bring the fastening nut out at the end, where it is more convenient to get at than are the screw heads in Figs. 1035 and 1036. It is obvious, however, that such a holder is weak and unsuitable for any tools save those used for very light duty indeed, while all this cla.s.s of holders is open to the objection that the side of the holder prevents the tool from pa.s.sing up into a corner, hence the cut cannot be carried up to a shoulder on the work. This may, however, be accomplished by bending the end of the holder round; but in this case two holders, a right and a left, will be necessary.

Fig. 1038 represents a form of tool holder of this kind in which the tool may be set for height by a set screw beneath it.

[Ill.u.s.tration: Fig. 1037.]

Fig. 1039 represents a tool holder and work-steadying device combined.

The holder is held in the lathe tool rest in the usual manner, and affords slideway to a slide operated by the handle shown at the right-hand end.

[Ill.u.s.tration: Fig. 1038.]

The tool is carried at the other end of this slide, there being shown in the figure a cutting-off tool in position. At the end of the holder is a hub and three adjusting screws whose ends steady the work, and which are locked in their adjusted position by the chuck nuts shown.

[Ill.u.s.tration: Fig. 1039.]

THE POWER REQUIRED TO DRIVE CUTTING TOOLS.--From experiments made by Dr.

Hartig, he concluded that by multiplying the weight of the metal cuttings removed per hour by certain decimal figures (or constants) the horse-power required to cut off that quant.i.ty of metal might be obtained. These decimal constants are as follows:

Lbs. of metal cut off per hour, cast iron .0314 = horse-power required to drive the lathe.

" " " wrought iron .0327 = "

" " " steel .4470 = "

FOR PLANING TOOLS.

Lbs. of steel cut off per hour .1120 = horse-power required to drive planer.

" wrought iron " .0520 = " "

" gun metal " .0127 = " "

CHAPTER XI.--DRILLING AND BORING IN THE LATHE.

For drilling in the lathe, the twist drill is employed not only on account of its capacity to drill true, straight, and smooth holes, but also because its flutes afford free egress to the cuttings and obviate the necessity of frequently withdrawing the drill to clear the hole of the cuttings.

In the smaller sizes of twist drill, the stem or shank is made parallel, as in Fig. 1040, while in the larger sizes it is made taper, as in Fig.

1041, for reasons which will appear hereafter.

[Ill.u.s.tration: Fig. 1040.]

The taper shanks of twist drills are given a standard degree of taper of 5/8 inch per foot of length, which is termed the Morse taper. A former standard, termed the American standard, is still used to a limited extent, its degree of taper being 9/16 inch per foot.

[Ill.u.s.tration: Fig. 1041.]

Parallel shanked twist drills are driven by chucks, while taper, shanked ones, are driven by sockets, such as in Fig. 1042, from C to D, fitting into the lathe centre hole, while the bore at the other end is the Morse standard taper, to receive the drills E E, which have a projection such as shown at A, which by fitting into a slot that meets the end of the taper holes in the socket, lock the drill and prevent its revolving in the socket, while affording a means of forcing the drill out by inserting a key K, as shown in the figure.[14]

[14] See also Shanks and Sockets for Drills used in the Drilling Machine.

[Ill.u.s.tration: Fig. 1042.]

Each socket takes a certain number of different sized drills, the shanks of the smaller drills being in some cases longer than the drill body.

Number 1 socket receives drills from 1/8 to 19/32 inch inclusive.

" 2 " " 5/8 " 29/32 " "

" 3 " " 15/16 " 1-1/4 " "

" 4 " " 1-9/32 " 2 " "