Fig. 1955 (from The American Machinist) represents an arbor, having a cone at a, so that the cutter bore being coned to correspond, the cutter will run true, notwithstanding that it may not fit the stem b. It is obvious, however, that the nut and washer must be made quite true or the cutter will be thrown out of line with the arbor axis and therefore out of true, and also that such an arbor is not suitable for cutters of a less width of face than the length of the cone a.

Shank cutters that have parallel shanks as in Fig. 1928 should have their sockets eased away on the upper half of the bore as denoted by the dotted arc d in Fig. 1956, which will enable the cutter shanks to be made the full size of the socket bore proper, and thus run true while enabling their easy insertion and extraction from the socket. Or the same thing may be accomplished by leaving the socket bore a true circle fitting the cutter shanks in tight, and then easing away that half of the circumference that is above the centre line c in the figure. It is preferable, however, to ease away the bore of the socket, which entails less work than easing away the shanks of all the cutters that fit to the one socket. When the cutter is held in a socket of this kind it allows it to be set further in or out, to suit the convenience of the work in hand, which cannot be done when the cutter has a taper shank fitting into the coned bore of the machine spindles.

It is obvious that when the cutter requires to pass within the work, or cut its way, as in the case of milling out grooves, a nut cannot be used; hence, inch cutters are driven by a key as usual, but secured by a screw, as in Fig. 1957, which is from the pen of John J. Grant, in The American Machinist.

In many cases it becomes a question whether it is better to do a piece of work with plain mills, with an end mill, or with face mills, a common hexagon nut forming an example. Thus, in Fig. 1958, we have a nut being operated upon by a plain mill; in Fig. 1959 by an end mill, and in Fig. 1960 by a pair of twin face mills.

In the case of the face mills the pressure of the cut falls on both sides of the work, and the spring is mainly endways of the nut arbor; hence, it does not affect the depth of the cut nor the truth of the work. Furthermore, in both the end and the face mills, the work will be true notwithstanding that the cutter may not be quite true, because each point of the work surface is passed over by every tooth in the cutter, so that the work will be true whether the cutter runs true or not; whereas in the plain mill or cutter each tooth does its individual and independent proportion of finishing. This is shown in Figs. 1961 and 1962. In Fig. 1961 we have the plain mill, and it is obvious that the tooth does the finishing on the vertical line b, that being the lowest point in its revolution. After a tooth has passed that point the work in feeding moves forward a certain distance before the next tooth comes into action; hence to whatever amount a tooth is too high it leaves its mark on the work in the form of a depression, or vice versâ, a low tooth will leave a projection.

In Fig. 1962 we have a piece of work being operated on by a face mill, and it is obvious that while the teeth perform cutting duty throughout the distance a, yet after the work has fed past the line a it is met by the cutter teeth during the whole time that the work is feeding a distance equal to a on the other side; hence the prolonged action of the teeth insures truth in the work. On the other hand, however, it is clear that the work requires to feed this extra distance before it is finished.

Suppose, however, that the cutter being dead true the cutting action ceases on the centre line, and therefore exists through the distance a only, and if we take a plain cutter of the same diameter as in Fig. 1963 we see that its period of feed only extends through the length b, and it becomes apparent that to perform an equal amount of work the face cutter is longer under feed, and therefore does less work in a given time than the plain cutter, the difference equalling twice that between a and b in the two figures, because it occurs at the beginning and at the end of the cut.

There is, however, another question to be considered, inasmuch as that the face cutter must necessarily be of larger diameter than the plain one, because the work must necessarily pass beneath the washer (c, Fig. 1915), that is between the two cutters; hence the cutter is more expensive to make.

We may in very short work overcome this objection by feeding the work, as at k in Fig. 1964, the face l to be milled requiring to feed the length of the teeth instead of the distance h in the figure. In the end mill the amount of feed also is greater for a given length of finished surface than it is in the plain cutter, as will be readily understood from what has already been said with reference to face mills.

Face milling possesses the following points of advantage and disadvantage, in addition to those already enumerated: If the work is sprung by the pressure of the holding devices it is in a line with the plane of motion of the teeth, hence the truth of the work is not impaired. On the other hand, the teeth meet the scale or skin of the work at each cut, whereas in a cylindrical cutter this only occurs when the cutter first meets the work surface.

The strain of the cut has more tendency to lift the work table than in the case of a cylindrical cutter. The work must be held by end pressure; hence the chuck or holding jaws must be narrower than the work, rendering necessary more work-holding devices. Since, however, both sides of the work are simultaneously operated on, there is no liability of error in parallelism from errors in the second chucking, as is the case with plain cutters.

To cut V-shaped grooves in cylindrical work, when it is required that one face or side of the groove shall be a radial line from the centre of the work, two methods may be employed. First we may form the cutter, as in Fig. 1965, the side b of the cutter being straight and the point of the cutter being set over the centre of the work. The objection to this is that the finished groove will have a projection or burr on the radial side of the groove, as shown at d in the figure, entailing the extra labor of filing or grinding, to remove it; furthermore, that face will have fine scored marks upon it, as denoted by the arcs at c, these scores showing very plainly if the cutter has any high teeth upon it, and more especially in the case of cutting spirals, as will appear presently. The reason of this is that the side b of the cutter being straight or flat the whole of the teeth that are within the groove have contact with the side c of the groove, that is to say, all the teeth included in the angle e in the figure, because the teeth on the side a tend, from the pressure of the cut to force the cutter over towards the side c of the groove. The second method referred to, which is that commonly adopted for cutting the flutes of tapes, reamers, milling cutters, &c., is to form the cutter on the general principle illustrated in Fig. 1966, and set it to one side of the centre of the work so that one of its faces forms a radial line, as shown in the figure, the distance to which it is set to one side depending upon the angle of its cutting edge to the face of the cutter.

Fig. 1967 represents a common form of cutter of this class that is used for cutting spiral grooves on milling cutters up to 3 inches in diameter, which contain eight teeth per inch of diameter. The angle of the teeth on b is 12° to the side face a of the cutter, and the angle of the teeth at c is 40° to the face d.

The effect produced by making face b at an angle instead of leaving it straight, or in other words, instead of cutting the teeth on the face a, may be shown as follows:—

Suppose that in Fig. 1968 we have a sectional view taken through the middle of the thickness of a cutter for a rectangular groove, the circumferential surface being at a right angle to the side faces, and it is evident that the teeth, at every point in their length across the cutter, except at the extreme corner that meets the side faces as c, will have contact with the seat of the groove while passing through the angle f only (which is only one half of the angle e in Fig. 1965); or in other words, each tooth will have contact with the seat of the groove as soon as it passes the line g, which passes through the axis of the cutter; whereas, when the teeth are parallel with the side of the cutter, as was shown in Fig. 1965, the teeth continue to have contact with the side walls of the groove after passing the line g.

By forming the cutter as in Fig. 1967, therefore, we confine the action to the angle f, Fig. 1968, the teeth having contact with the walls of the groove as soon as they pass the line g.

In cutting spiral grooves this is of increased importance, for the following reasons: In Fig. 1969 we have a cutter shown in section, and lying in a spiral groove. Now suppose a tooth to be in action at the bottom of the groove, and therefore on the line g g, and during the time that it moves from that line until it has moved above the level of the top of the groove, the work will have performed some part of a revolution in the direction of the arrow, and has therefore moved over towards that side of the cutter; hence, if that side of the cutter had teeth lying parallel, as shown at b in Fig. 1965, the walls of the groove would be scored as at c in that figure, whereas by placing the teeth at an angle to the side face, they recede from the walls after passing line g, and therefore produce smoother work.

A cutter of this kind must, for cutting the teeth of cutters, be accurately set to the work, and the depth of cut must be accurate in order to cut the grooves so that one face shall stand on a radial line, and the top of the teeth shall not be cut to a feather edge. If the teeth were brought up to a sharp edge the width of the groove at the top would be obtained with sufficient accuracy by dividing the circumference of the work by the number of flutes or teeth the work is to contain, but it is usual to enter the cutter sufficiently deep into the work to bring the teeth tops up to not quite a sharp edge. The method of setting the cutter is to mark on the end of the work a central line r, Fig. 1970, and make the distance e in same figure equal to about one tenth the diameter of the work.

Obviously the cutter is set on opposite sides of the work centre, according to which side of the groove is to have the radial face. Thus for example, in Fig. 1970, the cutter is set to the left of line r, the radial face of the groove being on the left, while in Fig. 1971 the cutter is set on the right of line r, because the radial face is on the right hand side of it, the work consisting (in these examples) in cutting up a right and a left-hand mill or cutter.

The acting cutter j may in both cases be used to cut either a right or a left-hand flute, according to the direction in which the work w is revolved, as it is fed beneath the cutter j.

In Fig. 1972 we have an example of cutting straight grooves or teeth, with an angular cutter having one side straight, and it is seen that we may use the operating or producing cutter in two ways: first, so that the feed is horizontal, as at a, or vertical, as at b; the first produces a right-hand, and the second a left-hand cutter, as is clearly seen in the plan, or top view. The feeds must, however, be as denoted by the respective arrows being carried upwards for b, so that the cutter may run under the cut and avoid cutter breakage.

The number of grooves or flutes producible by an angular cutter depends upon the depth of the groove and the width of land or tooth between the grooves. Thus Fig. 1973 represents a cutter producing in one case four and in the other eight flutes with the same form of cutter, the left being for taps, and the right for reamers.

For cutting the teeth of cutters or mills above 3 inches in diameter, the angles of the acting or producing cutter are changed from the 12° and 40° shown in Fig. 1967, to 12° as before on one side, and a greater number on the other; thus in the practice of one company it is changed to 12° and 48°, the 12° giving the radial face as before, and the 48° giving a stronger and less deep tooth, the deep tooth in the small cutters being necessary to facilitate the grinding of the teeth to sharpen them.

In cutting angular grooves in which the angle is greater on one side than on the other of the groove, the direction of cutter revolution and the end of the work at which the groove is started; or in other words, the direction of the feed, is of importance, and it can be shown that the feed should preferably be so arranged that the side of the groove having the least angle to the side of the cutter should be the one to move away from the cutter after passing the lowest point of cutter revolution.

In Fig. 1974, for example, we have at r a cylinder with a right-hand groove in it, whose side c, representing the face of a tooth, is supposed to be a radial line from the cylinder axis, the side b representing the back of a cutter tooth, being at an angle of 40°.

Now if the work revolves in the direction of arrow a, and the cut be started at end g (as it must to cut a right-hand groove with the work revolving as at a), then the side c of the groove will move over towards and upon the side of the cutter for the reasons explained with reference to Fig. 1969, and the teeth on this side being at the least angle to the side of the cutter, do not clear the cut so well, the teeth doing some cutting after passing their lowest point of revolution—or in other words, after passing the line g in Fig. 1968. The effect of this is to cause the cutter to drag, as it is termed, producing a less smooth surface on that side (c) of the groove or tooth.

We may, however, for a right-hand groove revolve cylinder r, as denoted by arrow e, and start the cut at end d. The result of this is that the side c of the groove, as the roller revolves, moves away from the side of the cutter, whose teeth therefore do no cutting after passing their lowest point of revolution (g, Fig. 1968), and the dragging action is therefore avoided, and the cut smoother on this which is the most important side of the tooth, since it is the one possessing the cutting edge. When “dragging” takes place the burr that was shown in Fig. 1965 at d, is formed, and must, as stated with reference to that figure, be removed either by filing or grinding.

Obviously if the direction of cutter revolution and of feed is arranged to cause side c to move away from the side of the cutter, then side b will move over towards the other side of the cutter; but on account of the cutter teeth on this side being at a greater angle to the side of the cutter, they clear better, as was explained with reference to Fig. 1968, and the dragging effect caused by the revolving of the work is therefore reduced.

We have now to examine the case of a left-hand groove, and in Fig. 1975 we have such a groove in a cylinder l. Let it be supposed that the direction of its revolution is as denoted by arrow f, and if the cutter is started at h (as it must be to cut a left-hand groove if the work revolves as at f), then the side c moves over towards the cutter, and the dragging or crowding action occurs on that side; whereas if the direction of revolution is as at k, and the cutter starts at n and feeds to h, then side b of the groove moves towards the cutter; hence face c of the groove is cut the smoothest. Obviously then the direction of cutter and work revolution and of feed, in cutting angular grooves in which one angle of the cutter is at a greater degree of angle than the other to the side of the cutter, should be so arranged that the work revolves towards that side of the cutter on which its teeth have the greater angle, whether the spiral be a right-hand or a left-hand one. In cutting grooves not truly circular the same principle should be observed.

In Fig. 1976, for example, it is better if the side b is the one that moves towards the cutter, the direction of revolution being as denoted by the arrow, whether the groove be a right-hand or left-hand (supposing, of course, that the cutter starts from end e of the work).

Obviously, also, the greater the degree of spiral the more important this is, because the work revolves faster in proportion to the rate of feed, and therefore moves over towards the outer faster.

In cutting spirals it is necessary first to put on such change gears as are required to revolve the work at the required speed for the given spiral, and to then set the work at such an angle that the cutter will be parallel to the groove it cuts, for if this latter is not the case the groove will not be of the same shape as the cutter that produces it.

In Fig. 1977 we have a spiral so set, the centre of the cutter and of the groove being in the line o o, and the work axis (which is also the line in which the work feeds beneath the cutter) being on the line c c. The degrees of angle between the centre of the cutter, or line o o, and the axis of the work, or line c c, are the number of degrees it is necessary to set the work over to bring the cutter and the groove parallel, this number being shown to be 20 in the example.

To find this angle for any given case we have two elements: first, the pitch of the spiral, or in other words, the length or distance in which it makes one complete turn or revolution; and second, the circumference of the work; for in a spiral of a given pitch the angle is greater in proportion as the diameter is increased as may be seen in Fig. 1978, in which the pitch of the spirals is that in Fig. 1977, while the angle is obviously different.

To find the required angle for any given case we may adopt either of two plans, of which the first is to divide the circumference of the work in inches by the number of inches which the spiral takes to make one turn. This gives us the tangent of angle of the spiral.

The second method of setting the work to cut a given spiral is to chuck the work and put on the necessary change gears. The cutter is then set to just touch the work and the machine is started, letting the work traverse beneath the cutter just as though the work was set at the required angle to the cutter:

When the cutter has arrived at the end of the work it will have marked on it a line, as in Fig. 1979, this line representing the spiral it will cut with those change gears, and all that remains to do is to swing the work over so that this line is parallel with the face of the cutter, as shown in Fig. 1980. If the diameter of the cutter is small we may obviously secure greater accuracy by placing a straight-edge upon the side of the cutter so as to have a greater length to sight by the eye in bringing the line fair with the cutter. This being done it remains to merely set the cutter in its required position with reference to the work diameter.

If an error be made in setting the angle of the work to the cutter the form of groove cut will not correspond to that of the cutter. This is shown in Fig. 1981, in which the cutter being at an angle to the groove the latter is wider than the cutter thickness, and it is obvious that by this means different shapes of grooves may be produced by the same cutter. In proportion, however, as the cutter is placed out of true the cutting duty falls on the cutting edges on one side only of the cutter, which is the leading side c in the figure, while the duty on the other side, b, is correspondingly diminished.

The simplest method of holding work to be operated upon in the milling machine is either between the centres or in the vice that is provided with the machine. The principles involved in holding work in the vise so as to keep it true and avoid springing it for milling machine work, are the same as those already described with reference to shaping machine vises.

In milling tapers the work, if held in centres, should be so held that its axial line is in line with the axes of both centres, for the following reasons:—

In Figs. 1982 and 1983 we have a piece of work in which the axes of the centres and of the work are not in line, and it is clear that the horn d of the dog d will, in passing from the highest to the lowest point in its revolution, move nearer to the axis of the work. Suppose, then, that the driver e is moved a certain portion of a revolution with tail d at its highest point, and is then moved through the same portion of a revolution with d at its lowest point in its path of revolution, and being at a greater distance or leverage when at the top than when at the bottom it will revolve the work less. Or if the tail d of the dog is taper in thickness, then in moving endways in the driver e (as it does when the work is revolved) it will revolve the work upon the centres. Suppose, then, that the piece of work in the figures required to be milled square in cross-section, and the sides would not be milled to a right angle one to another. This is avoided by the construction of the Brainard back centre, shown in Fig. 1984, in which t represents the surface of the work table and h the back centre. The block b is fitted within head h, and has two slots a a, through which the bolts s s pass, these bolts securing b in its adjusted position in h. The centre slide c operates in b; hence b, and therefore c, may be set in line with the work axis.

For heads in which the back centre cannot thus be set in line, the form of dog shown in Fig. 1985 (which is from The American Machinist) may be employed to accommodate the movement of the tail or horns through the driver. Its horn or tail b is made parallel so as to lie flat against the face of the slot in the driver. The other end of tail b is pivoted into a stud whose other end is cylindrical, and passes into a hub provided in one jaw of the dog, the set-screw a being loosened to permit this sliding motion. This locks the horn in the clamp and permits the dog to adjust itself to accommodate the motion endwise that occurs when it is revolved. The amount of this motion obviously depends upon the degree of taper, it being obvious (referring to Fig. 1982) that horn d would pass through the chuck, as denoted by the dotted lines, when at the bottom of its path of revolution.

It is obvious that when the head or universal head of the machine is elevated so that it stands vertical, it may have a chuck screwed on and thus possess the capacity of the swiveled vise. It is preferable, however, to have a separate swiveled chuck, such as in Fig. 1986 (from The American Machinist), which will not stand so high up from the machine bed, and will therefore be more solid and suitable for heavy work.

Another very handy form of chuck for general work is the angle chuck shown in Fig. 1987, which is from an article by John J. Grant, in The American Machinist. The work-holding plate has T-grooves to chuck the work on and is pivoted at one end, while at the other is a segment and bolt to secure it in its adjusted angle. Two applications of the chuck are shown in the figure.

Fig. 1988 represents a top, and Fig. 1989 an end view of a chuck to hold rectangular bars that are to be cut into pieces by a gang of mills. a, a, a, are grooves through the chuck jaws through which the cutters pass, severing the bar through the dotted lines. Each piece of the bar is held by a single screw on one side and by two screws on the other, which is necessary in order to obtain equal pressure on all the screws and prevent the pieces from moving when cut through, and by moving, gripping the cutters and causing them to break.

In chucking the bar the two end screws d d must be the first to be set up to just meet the bar: next the screws b c on the other side must be set up, holding the bar firmly. The two screws between d d are then set up to just bind the bar, and then the middle four on the other side are screwed up firmly. By this method all the screws will hold firmly and the pieces cannot move.

Vertical Milling, Die Sinking, or Routing Machine.—Fig. 1990 represents Warner & Swazey’s die sinking machine. The cutter driving spindle is here driven by belt direct, imparting a smooth motion. The knee is adjustable for height on the vertical slideway on the face of the column, which is provided with a stop adjustable to determine how high the knee and work-holding devices can be raised, and, therefore, the depth to which the cutter can enter the work, and a former pin is placed 6 inches behind the cutter to act as a stop against which a pattern may be moved when work is to be copied from a former or pattern piece. The work-holding device consists of a compound rest and a vise capable of being swiveled to any angle or of being revolved to feed the work to the cutter, hence the work may be moved in any required direction, in either a straight line, in a circle, or in any irregular manner to suit the shape of the work.

Profiling Machine.—The profiling machine is employed mainly to cut the edges of work, and to sink recesses or grooves in the upper surface of the same to correspond to a pattern. A provisional template of the form of the work is fastened on the bed of the machine, and from this is cut in the machine a thicker one termed the “former,” which is then used to copy the work from.

Fig. 1991 represents Pratt & Whitney’s profiling machine. On the cross slide are two separate sliding heads, each of which carries a live spindle for the cutting tool, and beside it a spindle to receive a pin, which by being kept against the pattern or former causes the work to be cut to the same shape as the former.

The work is fastened to the table, which is operated upon the raised Vs shown by the handle on the left, which operates a pinion geared to a rack on the underneath side of the table. The handle on the right operates the heads along the cross slide also by a rack and pinion motion. The gearing and racks in both cases are double, so that by two independent adjusting screws the wear of the teeth may be taken up and lost motion prevented. By means of these two handles the work may be moved about the cutter with a motion governed by the form or shape of the former, of which the work is thus made a perfect pattern both in size and shape. The tool used is a shank or end mill, such as was shown in Fig. 1928. In some profiling machines the spindle carrying the guide or former pin is stationary, in which case the provisional template is put beneath it and the former is cut by the live spindle, and for use must be moved from the position in which it was cut and reset beneath the former spindle. This machine, however, is provided with Parkhurst’s improvement, in which the former spindle is provided with a gear-wheel, by which it may be revolved from the live spindle, hence the provisional template may be set beneath the live spindle in which the guide pin is then placed. The cutter is then placed in the former spindle, and the former cut to shape from the provisional template while in the actual position it will occupy when used.

Fig. 1992 represents Brainard’s machine for grinding milling cutters. It consists of a threaded column a to which is fitted the knee b, which as it fits the top of the threads on the column may be swung or revolved about the column without being altered in its height upon the same except by means of the threaded ring c. At d is a lever for clamping the knee b to the column after adjustment; w represents the emery wheel mounted on the end of the horizontal spindle having journal bearing at the top of the column. The face of the knee b has a slideway d for the fixtures, &c., which hold the cutters to be ground, and at e is a lug pierced to receive an arbor whereon to place cutters to be ground, the lug being split and having a binding screw to lock the arbor firmly in place. f is a slide for receiving the grinding attachments, one of which is shown at k carrying a milling cutter in position to be ground on the face.

Fig. 1993 shows the fixture employed to grind parallel cutters, s representing a stand upon slide f (which corresponds to slide f in the general view of the machine in Fig. 1992) in which is fixed the arbor h. The cutter c is slid by hand along arbor h and beneath the emery wheel, the method of guiding the cutter to the wheel being shown in Fig. 1994, which represents a front view of the machine. At e is the lug (shown also at e in the general view) which has a hole to receive a rod p, and is split through at s, so that operating binding screw l locks rod p in e. At r is a rod secured to the rod p, and g is a gauge capable of swivelling in the end of r and of being secured in its adjusted position. The end of this gauge is adjusted to touch the front face of the tooth to be ground on the cutter c, which must be held close against the end of the gauge in order to grind the cutting edge to a straight line parallel to its axis.