and if then rinsed in boiling water they will dry before becoming rusty.

Adjustment of Cutters.-Collars are used to adjust the cutters in position on the cutter mandrel, and should be made of steel. Lead hammers are frequently used in fixing and releasing milling cutters. In practice this is established, that finished work must be struck only when absolutely necessary, and then either hard wood blocks or lead, or copper hammers are used, but in forcing hardened bushes or cutters the blows must be light because of the danger to fracture.

Cutting off stock can be conveniently done in a milling machine with a slitting saw, but better still by a broad-gauged toothed circular saw, 12 in. diameter. In the use of the latter there is no danger of the saw teeth becoming choked and galled by cuttings. It is necessary to secure the saw to the spindle flange in addition to keying it, owing to the strain set up in cutting. A further strength is given by screwing a flange to the saw, thereby increasing the length of the driving key.

Hand-feed Milling Machines. For some classes of work milling machines constructed with "hand feed" are found more suitable than those having power feed to the table. Types of these machines are given in A, B, and C, Fig. 311, by the Anglo-American Machine Tool Co. The machines are made with the feed of the table arranged in two methods; one with a screw-and-crank handle at the end of the table, while the other has the table fed by a pinion and rack, moved by a hand lever.

Designed for Light Work. The ordinary milling machine, with the table overhanging from the front of the frame and held to it by sliding surfaces, is not adapted to suit all the work a horizontal milling machine is capable of performing. In this type all the light milling can be satisfactorily done without much vibration.

Use of Arm Braces.-The "arm braces" are very useful to connect the table with the overhanging arm, and certainly give an increased support to the cutter mandrel, but when heavy work is fixed on the machine table, and several cutters are operating at the same time, it is often difficult to maintain a proper feed and speed without causing a visible vibration or chatter marks."

Table supported on Rigid Box Casting.-There can be no doubt as to the increased rigidity of a machine in which the table is fixed on a box casting which has a large base extending to the floor.

Vertical Milling Machine. The vertical milling machine shown in Fig. 312 is capable of a variety of operations. (A. Herbert, Coventry.) Surfacing, i.e. plain milling on flat surfaces or on the sides or edges of an object by means of the longitudinal or transverse feeds.

Circular work, by means of the rotating table.

Profiling, i.e. irregularly shaped forgings or castings may be machined true on their exterior by means of a controlling object used as a pattern. For example, cams may be conveniently machined to proper shape or dimension and correct in appearance to the templet cam which is fixed on the machine table as a guide.

Recessing, undercutting, or milling out tee slots, also for dealing with work having a number of facings on different levels.

When high speeds are required for light milling, and where a smooth drive is important for small cutters the drive is directly by belt. The gearing, which is mounted directly upon the spindle, is used for heavy work.

Two Tables, each of which is provided with automatic feeds and stops, are used interchangeably. The circular table, used for rotary work, is made with a tray on its rim to catch the cuttings and lubricant. When long objects are to be milled the rectangular table is used, or it is useful for setting a gang of objects in line when doing repetition work.

A further advantage is that one piece can be set while another piece is being milled,

thus saving the greater part of the time required for setting. The spindle head is balanced, can be raised and lowered by a hand wheel which gives motion to a worm and wheel and a rack and pinion. Vertical measurements are obtained by means of a graduated disc and at dead stop.

This machine has twelve speeds, varying in geometrical progression from 13'5 to 333 turns per minute. The feeds are sixteen in number, varying from 0:334 up to 8.5 in. per minute. All the gear wheels are enclosed, and the adjustments are made with handles, without the use of spanners.

Accurate Milling.-In milling work which has to be accurate to dimensions, dead stops are used. By this arrangement the automatic feed is used as in ordinary practice, then the final cutting is effected by hand for a short distance after the automatic stop is released.

Slab Milling Machine.-Slab milling, or plain-surface milling, is now extended to the longest surface in both engine and machine construction.

Fig. 313 represents a slab milling machine designed for any heavy work having long surfaces, such as the coupling and connecting rods

for locomotives, slide bars, etc., while in the machine-building trades these machines do much of the work which was formerly planed. The machine, bed, table, standards, and cross slide are very similar in appearance to a planing machine.

Referring to Fig. 313, it will be seen that the cutter spindle is carried by two adjustable bearings, which will open out to receive a cutter up to 24 in. wide, or a gang of cutters to the same width. The cross slide is made with an inclination so that the periphery of the cutters will just allow the surface of the work to comfortably clear the cross rail. This being so, a cutter of much smaller dimension is available than would be the case were the faces of the cross slide vertical.

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To obtain a uniformly smooth surface on the work, spiral-cut gearing is employed to drive the table, while all other gears are machine cut. The feed, which is variable, ranges from in. to 10 in. per minute. Provision is also made for pumping a copious supply of oil or soapy water upon the mills, which keeps the cutting edges cool, and also prevents the cuttings from clogging the teeth. The lubricant is drained into a tank, and used again.

A somewhat recent development is the screw milling machine. This applies the principle of the milling cutter to the formation of screw threads, and will cut screws of any section from 3 in. to 13 in. diameter, and a pitch of from 2 to 10 threads per inch. The headstock carrying the cutter is situated at the right-hand end of the bed. The spindle and bearings are of hardened steel, and the machine is driven through a train of gears. The headstock may be moved vertically and transversely, and the spindle may be swung to any desired angle up to 25 degrees with the screw which is being milled, either right or left hand to suit the different dies and pitches being cut.

An index is provided by which the spindle may be set to the angle required, and a table is sent out with each machine, from which the correct angles may be ascertained.