Modern Machine-Shop Practice Part 116

It is sometimes necessary, however, that a tool of the form in Fig. 1652 be used, as, for example, to shape out the surface of a slot, and when this is the case the tool should be shaped as in Fig. 1651, the bottom face having ample clearance (as, say, 15) from the heel A to about the point B, and about 3 from B to the front end. The front face should have little or no clearance, because it causes the tool to dig into the work. A tool so shaped will clear itself well on the back stroke, whereas if but little clearance and front rake be given as in Fig. 1652, the tool will not only dig in, but its cutting edge will rub on the back or return stroke.

[Ill.u.s.tration: Fig. 1653.]

For broad feed finis.h.i.+ng cuts the shape of tool shown in Fig. 1653 is employed, the cutting edge near the two corners being eased off very slightly with the oilstone. The amount of clearance should be very slight indeed, only just enough to enable the tool to cut as is shown in the figure, by the line A A. The amount of front rake may be varied to suit the nature and hardness of the metal, and the tool should be held as close in as possible to the tool clamp.

Smoother work may be obtained in shaping and in planing machine tools when the tool is carried in a holder, such as in Fig. 1654, which is taken from _The American Machinist_ because in this case any spring or deflection either in the tool or in the shaper head acts to cause the tool to relieve itself of the cut instead of digging in, as would be the case were the tool put in front of the tool post as in Fig. 1654. In finis.h.i.+ng large curves this is of great importance, because to obtain true and smooth curves it is necessary to shape the tool to cut upon the whole of the curve at once, and this gives so great a length of cutting edge, that the tool is sure to chatter if held in front of the tool post.

[Ill.u.s.tration: Fig. 1654.]

It is essential, therefore, to carry the tool at the back of the tool post as shown, and for curves that are arcs of circles tools such as in Fig. 1655 may be employed, or a circular disk will answer, possessing the advantage that its shape may be maintained by grinding its flat face to resharpen it.

Cutters of the kind shown in Fig. 1655 may be made to possess several important advantages aside from their smooth action: thus they may be made after the principle explained with reference to the Brown & Sharpe rotary cutters for gear-teeth, in which case the front face only need be ground to resharpen them, and their shapes will remain unaltered, and they may be given different degrees of front rake by placing packing between one side and the holder, and any number of different shaped cutters may be fitted to the same stock.

[Ill.u.s.tration: Fig. 1655.]

TOOL HOLDERS FOR PLANING MACHINES.--The advantages of tool holders for planing machines are equally as great as those already described for lathes, but as applied to planing machines there is the additional advantage that the clearance necessary on the tool is less variable for planer work than for lathe work, because in lathe work the diameter of the work as well as the rate of tool feed affects the tool clearance, whereas in planer work the tool feed is put on before the tool begins its cutting action; hence the degree of clearance is neither affected by the size of the work nor by the rate of feed, and as a result the tools may be given a definite and constant amount of clearance.

[Ill.u.s.tration: Fig. 1656.]

Fig. 1656 represents a planer tool holder (by Messrs. Smith & Coventry), in which what is, in effect, a swivel tool post is attached to the end of the holder, thus enabling the tool to be used on either the right or left-hand of the holder at will. The shape of the tool steel is shown in section on the right-hand of the engraving, being narrow at the bottom, which enables the tool to be very firmly held and reduces the area to be ground in sharpening the tool. A side and end view of the holder is shown in Fig. 1657, in which it is seen that the tool may be given top rake or angle to render it suitable for wrought iron or steel or may be set level for bra.s.s work.

[Ill.u.s.tration: Fig. 1657.]

In Fig. 1658 the tool and holder are shown in position on the planer head, the front rake on the tool being that suitable for wrought iron.

[Ill.u.s.tration: Fig. 1658.]

It is to be noted, however, that the amount of front rake should, to obtain the best results, be less for steel than for wrought iron, and less for cast iron than for wrought, while for bra.s.s there should be none; hence the tool post should be made to accomplish these different degrees of rake in order to capacitate such holders for the four above-named metals. It is an advantage, however, that by inclining the tool to give the top rake, this rake may be kept constant by grinding the end only of the tool to sharpen it, and as the end may be ground to a gauge it is very easy to maintain a constant shape of tool.

Furthermore as the tool is held by one binding screw only, it may be more readily adjusted in position for the work than is the case when the two ap.r.o.n clamp nuts require to be operated.

[Ill.u.s.tration: Fig. 1659.]

[Ill.u.s.tration: Fig. 1660.]

Figs. 1659 to 1661, show this tool-holder applied to various kinds of work, thus in Fig. 1659 the tool is planing under the underneath side of a lathe bed f.l.a.n.g.e, while in Fig. 1660 it is acting upon a [V]-slideway and escaping an overhanging arm, and in Fig. 1661 it is shown operating on a [V]-slideway and in a [T]-groove.

[Ill.u.s.tration: Fig. 1661.]

Fig. 1662 represents a tool holder by Messrs. Bental Brothers, the tool being held in a swivelled tool post, so that it may be used as a right or left-hand tool. In this case the front rake must be forged or ground on the tool, and there is the further objection common to many tool holders, that the tool if held close in to the tool post is partly hidden from view, thus increasing the difficulty of setting it to the depth of cut.

[Ill.u.s.tration: Fig. 1662.]

Another form of planer or shaper tool-holder is shown in Fig. 1663, in which a tool post is mounted on a tool bar, and may be used as a right or left-hand tool at will.

[Ill.u.s.tration: Fig. 1663.]

[Ill.u.s.tration: Fig. 1664.]

Fig. 1664 represents a tool holder in which two tools may be held as shown, or a single tool right-hand or left-hand as may be required, or the tool may be held at the end of the holder as in Fig. 1665. The advantage of such a holder is well ill.u.s.trated in the case of cutting out a [T]-shaped groove, because with such a holder a straight tool can be used for the first cuts, its position being shown in Fig. 1665, whereas in the absence of such a holder a tool bent as in Fig. 1666 would require to be used, this bend giving extra trouble in the forging, rendering the tool unfit for ordinary plain work, and being unable to carry so heavy a cut or to cut so smooth as the straight tool in Fig.

1665. In cutting out the widest part of such a groove the advantage of the holder is still greater, because by its use a tool with one bend, as in Fig. 1667, will serve, whereas without a holder the tool must have two bends, as shown in the figure, and would be able to carry a very light cut, while liable to dig into the work and break off.

[Ill.u.s.tration: Fig. 1665.]

[Ill.u.s.tration: Fig. 1666.]

The tool itself should be so forged that one side is flush with the side of the tool steel as shown at A in Fig. 1668, for if there is a shoulder, as at C, it sometimes prevents the tool from entering the work as shown in the figure.

[Ill.u.s.tration: Fig. 1667.]

Other examples in the use of this tool holder are given in Figs. 1669 and 1670.

[Ill.u.s.tration: Fig. 1668.]

In Fig. 1669, we have the case of cutting out the [V]-slideways of a planer bed, and it is seen that the tool point may be held close to the holder, the side of the tool box still clearing the side of the [V]-slideway, whereas in the absence of the holder the tool would require to have a considerable bend in it, or else would have to stand out from the bottom of the tool ap.r.o.n to a distance equal to the length of one side of the slideway.

[Ill.u.s.tration: Fig. 1669.]

[Ill.u.s.tration: Fig. 1670.]

In Fig. 1670 it is also seen that by the use of the holder the tool point may also be held as close as necessary to the holder, and still permit the side of the vertical slide S' and the tool box B to clear the vertical face of the work.

In all planer work it is an essential in the production of true and smooth surfaces that the tool be held as close in to the tool clamp or tool box as possible, and this forms one of the main advantages of tool holders.

CHAPTER XVIII.--DRILLING MACHINES.

POWER DRILLING MACHINES.--The drilling machine consists essentially of a rotating spindle to drive the drill, a work-holding table, and means of feeding the drill to its cut. The spindle speed and the force with which it is driven are varied to suit the work. The feeding is sometimes given to the spindle, and at others to the work table. In either case, however, the feeding mechanism should be capable of varying the rate of feed and of permitting a quick withdrawal of the drill. The spindle should be supported as near to its drill-holding end as possible. When the table feeds to the work the spindles may be held rigidly, because of their not requiring to pa.s.s so far out or down from the bearing supporting them; but when the spindle feeds, it must either pa.s.s through its bearings, or the bearing, or one of them, must either be capable of travel with the spindle or adjustable with relation to the machine framing.

In using small drills in a machine it is of the first importance that the amount of pressure necessary to feed the drill be plainly perceptible at the hand lever or other device for feeding the drill or the work, as the case may be, as any undue pressure causes the drills to break. To attain sensitiveness in this respect the parts must be light and easy both to move and to operate.

Fig. 1671 represents the American Tool Company's delicate drilling machine for holes of 1/4 inch and less in diameter. It consists of a head fixed upon a cylindrical column and affording journal bearing to the drill-driving spindle, which is driven by belt. The table on which the work is placed is carried by a knee that may be fixed at any required height upon the same round column. The knee and table may be swung out of the way, the column serving as a pivot. The table has journal bearing in the knee, and is fed upwards by the small lever shown.

Fig. 1672 represents Elliott's drilling machine for drills from 1/32 inch to 3/4 inch in diameter. The work table may be revolved in the arm that carries it, and this arm may be swung round the column or post. It is operated upwards for the feed by the hand lever shown. The conical chuck shown lying on the work table fits into the hole that is central in the table, and is used to receive the end of cylindrical work and hold it true while the upper end is operated upon.

The construction of the live spindle and its cone are shown in Fig.

1673. The drill chuck Q is attached to and driven by a one-inch steel spindle 19 inches long, which is accurately fitted through the sleeve bearings, within which it is free to move up and down, but is made to revolve with the cone by means of the connection O, one end of which slides upon the rods L. The drill is held up by means of the spiral spring M acting from the bottom of cone to the collar O. The weight of cone and spindle is carried upon a raw-hide washer, beneath which is the cupped bra.s.s P which retains the oil. The thrust of the feed lever G is also taken by a raw-hide washer R.

The machine is provided with a hand and a foot feed by means of the compound lever W Z, Fig. 1674, actuating the feed rod J, which pa.s.ses up within the column and connects to the lever K, the latter being suspended by a link H.

Fig. 1675 represents Slate's sensitive drilling machine, in which the lower bearing for the live spindle is carried in a head H that fits to a slide on the vertical face of the frame, so that it may be adjusted for height from the work table W to suit the height of the work. L is a lever operating a pinion engaging a rack on the sleeve S to feed the spindle. The table W swings out of the way and a conically recessed cup chuck C is carried in a bracket fitting into a guideway in the vertical bed G. The cone of the cup chuck is central to or axially in line with the live spindle, hence cylindrical work may have its end rested in the cone of the cup chuck, and thus be held axially true with the live spindle.

[Ill.u.s.tration: Fig. 1676.]

Fig. 1676 represents a drilling machine in which the spindle has four changes of feed, and is fed by a lever handle operating a pinion that engages a rack placed at the back of a sleeve forming the lower journal bearing for the spindle. This lever is provided with a ratchet so that it may be maintained in a handy position for operating. The work table is raised or lowered by a pinion operating in a rack fast upon the face of the column, a pawl and ratchet wheel holding it in position when its height has been set. A lever is used to operate the pinion, being inserted in a hub fast upon the same spindle that carries the pinion and the ratchet wheel.