Modern Machine-Shop Practice Part 133

The rear slot is wider and is a segment of a circle. The screw bolts being slackened the back centre is raised, lowered, or tilted to any required position to bring the centre in line with the work axis, and is then clamped in place. One bolt holds this part of the machine to the work table. The centre is adjusted to place in the end of the work in the ordinary way, with a hand nut, &c.

For gear cutting, the universal head is enlarged and somewhat modified in design, as is shown in Fig. 1896, the worm and worm-wheel being much larger in diameter and exceedingly accurate by the following method having been adopted to test them: Two cast-iron disks were placed side by side on an arbor or mandrel held between the centres, and lines of division were marked across the edges of both of them (the index plate, of course, being used for the division). The disks were then separated and one of them moved and the lines of division again compared with a microscope, and no sensible errors were apparent.

The provisions for taking up the wear of the worm and its bearings, and of the worm and its wheel, are as follows: The worm-shaft runs in compensating bearings of phosphor bronze, and the bracket carrying the worm-shaft is adjustable towards the worm-wheel by the means already described for the ordinary universal head, and this head is said to be capable of making divisions as fine as one minute of an arc, or dividing the circle into 21,600 parts.

The employment of a worm and a worm-wheel necessitates that the index pointer arm be given a certain number of revolutions, in order to move the spindle the requisite amount for all divisions except those equal in number to the number of teeth contained in the worm-wheel, and to avoid any mistake in counting the number of revolutions of this index pointer arm the following device is employed: On the worm shaft is a pin, and to the right of the index plate is a dial plate which is clearly shown in the engraving. The circ.u.mference of the latter is cut with ratchet teeth, and the length of the pin on the worm-shaft is such that at each revolution it moves one tooth of the dial plate. In front of the dial plate is a fixed pointer, and as the face of the ratchet wheel is graduated and marked 1, 2, 3, &c., it is obvious that the pointer shows how many revolutions the dial plate, and therefore the worm shaft, has made. After the requisite number has been made and the index pin has been set in the index wheel, the small lever, shown on the right of the dial plate, is moved and a spring brings the dial plate back so that its zero number comes back to the pointer ready to count the number of revolutions when the worm-shaft is revolved for the next division or movement of the worm and wheel. For this head there are three index plates drilled with 23 circles of holes, making, in combination with the worm and wheel, all divisions up to 90, all even divisions up to 180, with most of the other divisions between 90 and 180, or 135 divisions and multiples of these divisions up to 16,200. The index plates are interchangeable, and additional ones for other divisions may obviously be added.

[Ill.u.s.tration: Fig. 1897.]

The device for cutting spirals as arranged for hand feeding is shown in Fig. 1897, while in Fig. 1898 it is shown arranged for automatic feeding, and is shown in position on the machine.

Referring to Fig. 1897 the hand wheel operates a worm engaging with a worm-wheel on the shaft of the largest gear shown in the engraving. From this gear motion is conveyed through intermediate wheels to the pinion on the same shaft as the first bevel-gear, which obviously drives the bevel-gear shown on the end of the head. The back face of this latter gear is provided with index holes, and the usual index arm and pin are provided.

The change gears provided for this device are sufficient to cut twelve different pitches, ranging from one turn in 2 inches to one turn in 6 feet. Obviously right or left-hand spirals are produced according to the direction of revolution of the hand wheel.

In the general view, Fig. 1898, the device is placed upon a box bolted to the work table, and obtains its automatic feed through the medium of the worm for the table feed.

[Ill.u.s.tration: Fig. 1899.]

The cam-cutting attachment, Fig. 1899, consists of a base bolted to the machine table and adjustable to any required position thereon. This base has a slide way in which a gibbed slide carrying a head is free to travel longitudinally. The pattern or former cam and the work are carried on the live spindle of the head, and the former cam is supported by circ.u.mferential contact with a roll carried on the vertical bracket shown on the right of the engraving. As shown, the device is arranged for cutting face cams, the cam-holding spindle being placed in line with the machine spindle. All that is necessary for cutting _cylinder_ cams is to set the device with its spindle at a right angle to the machine spindle and move the supporting bracket so that its roller will meet the perimeter of the former cam. In either case the slide carrying the head is pulled forward by weights suspended over the wheel shown on the end of the base, and the feed is put on by revolving the spindle by means of the worm and worm-wheel shown in the engraving, the ordinary crank handle of the machine fitting the worm shaft.

A hand feed for cam cutters is preferable to the automatic feed, because in turning corners or curves the rate of the feed requires to be reduced in order to obtain smooth work.

Fig. 1900 represents a universal milling machine. The live spindle head is fitted to a horizontal slide on the top of the main frame, and may therefore be moved on that slideway to adjust the cutters to the work, the motion being effected by a pinion operating a rack on the underside of the head, as shown in Fig. 1901, which is a sectional view of the machine.

[Ill.u.s.tration: _VOL. II._ =EXAMPLES OF MILLING MACHINES.= _PLATE II._

Fig. 1898.

Fig. 1900.]

At the handle end of the pinion shaft there is provided a dial (which is seen in the general view of the machine) having an outer circle graduated to sixty-fourths of an inch, and an inner one graduated to fortieths of an inch. The driving shaft is at a right angle to the live spindle, and drives it by means of a hardened steel worm operating a bronze worm-wheel fast on the live spindle, and which runs in a trough of oil to provide ample lubrication.

[Ill.u.s.tration: Fig. 1901.]

The spindle is hollow and has tapered journals. The arm for supporting the outer end of the cutter arbor is cylindrical, and fits to a bore provided in the top of the frame of the head, which is split and has two binding screws. When these screws are loosened the arm may be readily adjusted for position, while when they are screwed up they lock the arm in its adjusted position. By this means the arm only projects out as far as the particular work in hand requires.

The knee for carrying the work table and chucking devices terminates at its top in a circular box cast open on top. This box is covered with a circular cap, in the upper face of which are the slideways or guides for the work table. The cap is recessed into the box so as to be kept central, and is fastened therein by an expanding ring operated by a single stud which projects through the walls of the box. This ring has a [V]-shaped groove on its periphery, which in expanding closes over corresponding bevelled ledges on the inside of both the cap and the box.

The edge of the cap is graduated for cutting spirals.

By this arrangement the table can be set to move at any required angle with the live spindle and quickly clamped in position, while the ring being of larger diameter and bearing evenly around the entire circle, the cap is rigidly held. In this box, securely protected from the cuttings or dirt, is a large worm-gear secured to a short vertical shaft, on the upper end of which is a pinion projecting through the cap and engaging with a rack upon the underneath side or face of the work table. This shaft also carries a bevel-pinion which meshes with a pinion on the end of the short shaft seen projecting through the front of the box and provided with a hand crank, the hand lever shown behind this crank being for securing or releasing the cap to or from the box. The gearing is so arranged that one revolution of the hand crank traverses the work table a distance of 2 inches, thus providing for the rapid motion of the table to expedite putting in and taking out the work.

The knee is operated vertically by a pair of bevel-gears, the shaft for operating which is shown on the left-hand side of the knee. On this shaft is a pointer for an indexed dial, which has two graduated circles, the outer of which is divided so that each division corresponds to a knee motion of 1/32 of an inch, while the inner one denotes a knee motion of 1/1000 inch.

Automatic feed motion for the work table is provided as follows: The cone shaft projects through the live head and carries a leather-covered friction disk which drives a vertical shaft carried by a bracket hinged to the head. A small pulley splined on this shaft, and held at any point by a spring-pressed catch, bears against the leather-covered face of the disk, and it is obvious that the nearer to the centre of the disk the pulley is set the slower the latter will be revolved, and therefore the finer the feed will be, while the direction of revolution of the small pulley will be reversed if it be set on the upper half or above the centre of the disk, thus providing for reversing the direction of feed.

By this arrangement both the rate and direction of the feed can be set without stopping the machine.

This vertical feed shaft carries a splined worm driving a worm-gear splined on a horizontal shaft which is carried by the knee, which has a projecting arm or bracket for carrying the back end of the shaft, so that the latter rises or falls with the knee. A worm on this horizontal shaft engages a large worm-wheel within the box and fast upon the short upright shaft, whose pinion engages the table rack and thus completes the feed motion.

It will be seen in the sectional view that the worm-wheel for the automatic feed is in one piece, with a smaller bevel-wheel engaging with a bevel-pinion for the hand feed.

A clutch joint near the centre of the horizontal shaft affords the means for putting the automatic feed either into or out of action.

The table can be fed its full length in either direction, and when placed so that one end will pa.s.s the main frame or column may be swung around parallel to the spindle, thus enabling the machine to be used as a boring mill for short holes, or by turning the table a half revolution work may be done on both sides of a piece at one chucking, thus insuring perfect parallelism.

[Ill.u.s.tration: Fig. 1902.]

[Ill.u.s.tration: Fig. 1903.]

The construction of the index head of this machine is as follows: Fig.

1902 represents it on a plate with a back centre and a centre rest, and Fig. 1903 represents the head elevated. The head is a hollow box, the outline of which is about two-thirds of a circle. The opening, in front or chord side, is surrounded by a f.l.a.n.g.e, and bored out as large as permissible. This forms the front bearing of the spindle and face plate, which is cast in one piece. A rear and smaller bearing is provided on the circular part of the case. The end of the spindle projects through the case, and is held from coming out by a recessed nut and washer. The spindle also carries an accurately-divided steel gear of sixty teeth.

This gear is made as large as will go through the opening in front, or about 6 inches in diameter. Directly under this gear the box is pierced from the side. In this opening is inserted a long bush, through which a steel worm engages with the gear. An index plate secured to the outer end of the bush, and an adjustable arm and index pin attached to the projecting end of the worm, complete the dividing mechanism. Substantial but delicate adjustments are provided for eliminating lost motion.

On the periphery of the case is turned a dovetail shoulder, which slides around in a corresponding groove in the quadrant-shaped base. The case is graduated on its edge, and may be clamped at any angle of elevation from 15 degrees below a horizontal line to a vertical position, being equally stable in all positions. The face plate is no farther from the bed in one position than another, and being seated to the case, and adapted to hold work directly on its face, forms a stiff and substantial device for cutting bevel-gears and other work requiring angular motion.

The tail centre is also of a strong and substantial design.

An adjustable centre rest of novel design also accompanies the outfit, and an extra bed or table, with straps for securing it to the table of the machine. With the centres arranged on this bed the line of centres may be set at any angle with the sliding table, A sufficient number of index plates are provided to divide all numbers up to 100 and all even numbers to 200.

Fig. 1904 represents a machine in which the base column and the head are constructed upon the same design as that in Fig. 1900, but the circular top and cap are replaced with a larger and heavier knee of rectangular form, and the table is longer. A cross sectional view of the head is shown in Fig. 1905. The bearings for the live spindle are solid bushes slightly tapered, and are driven into the head from each end up to and against the f.l.a.n.g.es.

The spindle is of tool steel 3-1/2 inches in diameter at the front bearing, tapering uniformly 3/4 inch per foot to the back end. This simple construction allows the spindle to be perfectly ground, and accurately fitted to the boxes by sc.r.a.ping. After this is done the spindle is withdrawn about the 1/100 part of an inch, and a flat babbitt metal washer fitted to exactly the s.p.a.ce between the shoulder on the spindle and the front box. A check nut and sliding collar on the back end holds the spindle in place. A perfectly uniform s.p.a.ce for oil is thus formed between the spindle and bearings. The worm-gear is forced tightly on the taper spindle with a nut, and keyed to prevent turning.

The spindle has a hole 1-9/16 inches through its centre, tapering in front to receive the arbor to 1-7/8 inches. The taper is made 1/2 inch per foot, and for ordinary work is sufficient to prevent the arbor turning, but for driving gangs or large mills an arbor is used having a hexagon enlargement just outside the spindle. A cap to screw over the end of the spindle, having a hexagon opening in it to fit the arbor, completes a positive driver that has none of the objections to cutting a mortise or keyway in the spindle or otherwise disfiguring it. This cap protects the thread on the spindle, and may be readily removed for a face plate or large facing mills.

[Ill.u.s.tration: Fig. 1904.]

[Ill.u.s.tration: Fig. 1905.]

The cone shaft and its bearings are made independent of the head. A long sleeve, which is provided with a large f.l.a.n.g.e, projects through cored openings in the side of the head. The bosses around these openings are faced off square and parallel, and a large flat ring threaded on the end of the sleeve draws the f.l.a.n.g.e against the opposite face. The large end of the sleeve is counterbored to receive the worm, and is cut away on the under side to allow the worm to drop into mesh with the gear. The worm is feathered on the shaft, the thrust of the worm being taken in one direction against the shoulder in the sleeve, and in the opposite direction (the machine can be driven either right or left-handed) against the end of a bush, which is screwed in the sleeve and forms one bearing for the cone shaft. Friction washers are placed to form the step, and all wear or lost motion can be removed by s.c.r.e.w.i.n.g in the bearing, which, when adjusted, is prevented from turning by a small set-screw. The cone-shaft bearings are babbitt lined, but the spindle bearings are made of cast iron, in which steel sc.r.a.p has been melted.

The worm-gear has 40 teeth, and the worm is triple threaded, thus making a back gear equivalent to 40-3, or 13-1/3 to 1. As the sleeve does not fit the openings in the head, the worm and gear may be readily adjusted to each other at all times, and held firmly and squarely in place by drawing the f.l.a.n.g.e tight against the side of the head. Set-screws through the head prevent accidental displacement of the sleeve after being adjusted.

[Ill.u.s.tration: Fig. 1906.]

Fig. 1906 represents a double spindle milling machine. The second spindle is for driving the finishing cutters, so that as the two spindles are capable of independent adjustment, the work may be finished at one feed traverse, thus avoiding the necessity of removing the work or making special adjustments.

Fig. 1907 represents a milling machine for globe valves and other similar work. Here there are two cutter-driving spindles, one on each end of the bed, and the work is held vertically. It is provided with an index wheel for milling squares, hexagons, or octagons, and the pen for the index wheel is operated by treadle. The work is fed across the bed, the chucking devices being carried on a slide rest. In the figure a globe valve is shown chucked between two plugs or arbors fitting its bore, but it is obvious that centres or other work-holding appliances may be used to suit the kind of work.

Fig. 1908 represents an eighty-inch milling machine, the table of which has longitudinal motion; and provision for vertical and crosswise movements are made in the head which carries the driving mechanism.

The machine table sets low on a bed supported by four box legs, and is actuated by a steel screw driven by a worm and worm-gear connected with a pair of spur-gears. The gearing is outside the bed, and therefore accessible, and is protected by a shield, as shown in cut. The arrangement for belting to feed works is also shown too plainly to need description. The head upon which the spindle carrier is mounted travels in ways upon the bed, and is adjusted crosswise on it by means of a screw connected with a hand wheel, partially shown at the left of engraving. For convenience and ease in fine adjustment this wheel, and also the wheel at top of machine, connected with the elevating screw, are worked by a hand lever, the wheels having sockets in their periphery for this purpose.

The carrier, upon which is mounted the driving spindle, is gibbed to the head, and has a vertical range sufficient to allow work 18 inches high to pa.s.s under centres. From this carrier projects a large arm for outside centre support of mill spindle, intended for use on work where a back stand is not admissible. There is, however, as may be seen, a back stand or tailstock of a very solid character. The arm is readily removable, when desired, or the tailstock can be slid off its seat if required. In most cases, however, the arm need not be removed, the yoke on it being swung up out of the way, leaving the centre of mill arbor free to engage with that on the back stand. This combination provides for operating on a wide range of work.

As shown in the engraving, the s.p.a.ce between head and tailstock is about 24 inches, but if required the tailstock can be made to travel in line with the head, and its support be extended to any distance desired.

The method of driving the spindle is simple and strong, and allows of free adjustment of the spindle without disarrangement of the driving and feed belts.

The cone, which is made for 3-1/2 inch belt, is mounted in a stirrup which is pivoted to the bed, and the pinion which engages with the driving gear on the spindle is held at correct distance by a connecting yoke, and is driven by a feather.