Modern Machine-Shop Practice Part 140

EMERY GRINDING MACHINES. (For grinding-lathes and roll grinding, see article on Lathes.)--Fig. 2017 represents Brown & Sharpe's grinding machine. The bed, the table, and the cross-feed motion of this machine closely resemble those of the planing machine, but its work is far more smoothly and accurately done than can be performed in a planing machine.

The table traverses to and fro, accurately guided in ways, and the revolving emery wheel takes the place of the ordinary cutting tool, being carried in a sliding head upon a cross slide or cross bar. The drum for driving the emery wheel is at the back of the machine, as shown in the cut.

[Ill.u.s.tration: Fig. 2018.]

The vertical feed motion for adjusting the depth of cut of the emery wheel is capable of very minute adjustment, thus avoiding a difficulty commonly experienced in iron planing machines on account of the coa.r.s.eness of feed-screw pitch, which coa.r.s.eness is necessary to insure their durability. The means by which this capability of minute adjustment is effected is shown in Fig. 2018, in which D is the cross head of the machine and C the sliding head having the arm C', which provides at B a pivot for the wheel-carrying arm A. F is a stud fast in C and carrying E, which forms the nut for the feed screw. Outside this nut is the spiral spring S, whose force steadies the upper end of A.

Now suppose the feed wheel G be operated a full rotation, and the motion of that end of A will be that due to the pitch of the feed screw, but the motion at the centre H of the emery wheel will be the pitch of the screw divided by the difference between the length from the centre of H to the centre of the feed screw, and that from the centre of H to the centre of B. But even this diminished motion at H is still further reduced, so far as the depth of cut put on is concerned, because the motion of H is not directly vertical but an arc P, of which B is the centre.

The standards carrying the cross slide are segments of a circle struck from the centre of the driving drum, which is necessary to enable the raising and lowering of the cross slide, and maintain a uniform tension on the belt driving the emery wheel without employing an idler wheel or belt tightener.

[Ill.u.s.tration: Fig. 2019.]

Fig. 2019 represents Wm. Sellers & Co.'s drill-grinding machine, in which the drill is held in a chuck operated by the hand wheel A. The jaws of the chuck grip the drill at the outer corners of the cutting edge as shown in Fig. 2020, and so as to grind the point of the drill central to those corners. In order to give to the cutting edges a suitable degree of clearance in their lengths, and to allow for the difference in thickness at their points between large and small drills, the following construction is employed.

[Ill.u.s.tration: Fig. 2020.]

Fig. 2020 represents the jaws J J holding on the left a small, and on the right a large drill. The line of motion of the right-hand jaw in opening and closing to grip the drill is along the line _r_, while that of the left-hand is along the line _p_ _p_, the centre upon which the chuck is revolved to grind the drill being denoted by the small circle at S. _x'_ represents the centre line of the large drill when held in the chuck, and it is seen that the action of the jaws in closing upon small drills is to lift the drill point closer to the centre S upon which the chuck revolves (the cutting edge being ground to be on the line _y'_ _y'_). The reason for this peculiar and simple but exceedingly ingenious construction is, as before remarked, to maintain the cutting edge in its proper relation to the thickness of the drill point (which thickness varies in different diameters of drills), and to maintain a proper degree of clearance at every point along the length of the cutting edge. In other drill grinding machines the drill when rotated to grind the clearance is moved on the axis A A in Fig. 2022 as a centre of motion, and as this line is parallel to the face of the emery wheel it follows that if the drill were given a full revolution its circ.u.mference would be ground to a cylinder as shown in Fig. 2021 by the dotted lines.

In this machine the drill is rocked on the line B, Fig. 2023, as a centre of motion, this line corresponding to the axis of the shaft of lever F in Fig. 2019 upon which the chuck swings, and to the line B in Fig. 2024. As a result the surface is ground to the form of a cone as denoted by the dotted lines in Fig. 2024. The results of the two systems are shown in Figs. 2025 and 2026, which represent the conical holes made by a drill.

[Ill.u.s.tration: Fig. 2021.]

[Ill.u.s.tration: Fig. 2022.]

[Ill.u.s.tration: Fig. 2023.]

[Ill.u.s.tration: Fig. 2024.]

In Fig. 2025 a cylinder R is shown lying in a conical recess, and end views of the cylinder are shown at V and W. Now suppose the line of contact of the roll or cylinder upon the recess represents the cutting edge of the drill, and that we consider the clearance at the outer end, and at that part that in revolving would describe the circle Q, and on referring to circle V and the outer circle of the recess, and also to circles W and Q, it is seen that there is more clearance for V than there is for W, and that the clearance of the latter would be still less if Q were of smaller diameter, and it follows that the clearance is less in proportion as the point of the drill is approached. In determining the amount of clearance, therefore, we are compelled to make it sufficient for the point of the drill, and this under this system of grinding is excessive for the outer diameter of the drill, causing it to dull quickly, it being borne in mind that as the outer corner of the cutting edge of a drill describes the largest circle of any point of the cutting edge it obviously performs the most cutting duty in removing metal, and furthermore revolves at the highest rate of cutting speed, both of which cause it to dull the most rapidly. In Fig. 2026 we have a cone R lying in the coned recess, an end view of the cone being shown at V and W, and if we again consider the line of contact of the cone on the recess to represent the cutting edge and the circ.u.mferential surface of the cone as the end surface of the drill, we observe in the end views V and W that the clearance is equal for the two positions, or by varying the degree of taper of the cone we may regulate the amount of clearance at will. It is found preferable, however, to give more clearance as the point of the drill is approached so as to increase the cutting capacity; hence, in this case, the outer corner of the drill has the least clearance, which greatly increases its endurance for the reasons already mentioned, and which were further pointed out in the remarks upon drilling in the lathe. There remains, however, an additional advantage in this method of grinding which may be pointed out, inasmuch as that the clearance produced by the method shown in Fig. 2019, while capable of being governed from end to end of the cutting edge, yet increases as the heel of the _land_ is approached, making the central cutting edge (C, Fig. 2028) more curved in its length so that it approaches the form of cutting edge of the fiddle drill and this enhances its cutting capability.

[Ill.u.s.tration: Fig. 2025.]

Referring again to the general view of the machine in Fig. 2019, the chuck is supported or carried by the shaft having the ball lever F, which is clearly seen in the rear view, Fig. 2027, and the rod carrying the sleeve B (which holds the centre for supporting the shank end of the drill) is secured to the back of the chuck, as seen in the same figure.

When, therefore, lever F is moved over, the drill is moved through an arc of a circle of which the axis of the shaft of F is the centre, and this it is that gives clearance to the cutting edge of the drill.

The drill being chucked, the emery wheel is brought up to it by means of the hand wheel E, which moves the frame C laterally, the grinding being done by the side face of the emery wheel. On the same shaft as E is a lever which may be used in connection with the stop or pin (against which it is shown lying) to enable an adjustment of the depth of cut taken by the wheel separately when grinding each lip, and yet to permit both cutting edges of the drill to be gauged to the same length.

Suppose, for example, that the point of a drill has been broken so that it requires several cuts or traverses of the emery wheel to bring it up to a point again; then when this has been done on one cutting edge the lever may be set to the stop, so that when the grinding of the second cutting edge has proceeded until the lever meets the stop both edges will be known to be ground of the same length, and will, therefore, perform equal cutting duty when at work.

The depth of cut being adjusted, the lever D is operated to pa.s.s the side face of the emery wheel back and forth along the cutting edge of the drill, this lever rocking the frame C on which the emery wheel is mounted back and forth in a line parallel to the cutting edge of the drill. Different angles of one cutting edge of the drill to the other are obtained by swivelling the frame carrying the shaft of lever F. The emery wheel is cased in except at a small opening where it operates upon the drill, and may, therefore, be liberally supplied with water without the latter splashing over. Water is continuously supplied to the emery wheel by an endless belt pump, which also delivers water on the end of the drill, enabling heavy grinding cuts to be taken without danger of softening the drill at the cutting edge, which is otherwise apt to occur. The following is the method of operating the machine: Open the jaws of the chuck by means of the hand wheel A, insert the drill from the back of the chuck towards the face of the stone, letting the end of the drill rest on the lower jaw, with the cutting edge just touching the end stop; close the jaws temporarily, while the back centre B is run up and clamped; then release the jaws, hold the drill back against the back centre B with the left hand, at the same time rotating hard against the two side stops on the jaws; then tightly closing the jaws, clamp the drill by means of the hand wheel A, using the right hand for this purpose. Throw ball-handle F part way back, and by means of hand wheel E feed up the stone until it just touches the drill. Bring ball-handle F forward and give additional feed; pa.s.s the stone over the face of the drill, back and forth, by lever D, moving ball-handle F back a little between each two cuts. This slices off the stock to be removed; then when entirely over the face of the lip being ground, hold lever D stationary, and rotate the drill against the stone by means of ball-handle F. By this means a heavy slicing cut can be taken and a final smooth finish obtained without any risk of drawing the temper of the drill.

When one lip has been thus formed, slack up the jaws of the chuck, turn the drill half around, pressing its lips as before against the side stops on jaws, and at the same time be sure to hold the drill firmly back against the back centre B (pay no attention to the end stop, which is only used in locating the drill endways in the first setting), tighten chuck, and grind the second lip without any readjustment of the stone. The lips will then be of equal length. During all these manipulations the stop that is arranged in connection with hand wheel E can be slack, and may rest against the pin in the bed made to receive it.

[Ill.u.s.tration: Fig. 2026.]

Fig. 2027 represents a rear view of the machine, at which there is an attachment for thinning the point of the drill, which is advantageous for the following reasons. In Fig. 2028 we have a side and an end view of a twist drill, and it can be shown that the angular piece of cutting edge C that connects the two edges A and B cannot be given sufficient angle to make it efficient as a cutting edge without giving clearance and angle excessive to the edges A and B.

In Fig. 2029 we may consider the angle of the cutting edge at the corner H and at the points F and G. First, then, it is obvious that the front face for the point H is represented by the line H _h_, that for F by line F _f_, and that for G by G _g_, and it appears that on account of the spiral of the flute the front face has less angle to the drill axis as the point of the drill is approached.

[Ill.u.s.tration: Fig. 2027.]

Considering the end of the drill, therefore, as a cutting wedge, and considering the cutting edge at the two points C and E, in Fig. 2030, the end face being at the same angle, we see that the point C has the angle A and point E the angle B; at the drill point there will be still less cutting angle, and it has, therefore, the least cutting capacity.

To remedy this the attachment shown in the figure is employed, consisting of a frame or head carrying a thin emery wheel, and capable of adjustment to any angle to suit the degree of spiral of the drill flute.

[Ill.u.s.tration: Fig. 2028.]

By means of this emery wheel a groove is cut in the flute at the point of the drill, as shown in Fig. 2031, at A and B, thus reducing the length of C, and therefore increasing the cutting capacity and correspondingly facilitating the feed of the drill. It is found, indeed, that by this means the drill will perform 15 per cent. more duty.

[Ill.u.s.tration: Fig. 2029.]

[Ill.u.s.tration: Fig. 2030.]

[Ill.u.s.tration: Fig. 2031.]

It is obvious, however, that as the thickness of drills at the point increases in proportion to the diameter of the drill, this improvement is of greater advantage with large than with small drills. The reason for augmenting the thickness at the centre with the drill diameter is that the pressure of the cut acts to unwind the spiral of the drill, and if the drill were sufficiently weak at its axis this unwinding would occur, sensibly enlarging the diameter of hole drilled, more especially when the drill became partly dulled and the resistance of the cut increased. By means of the small grooves A and B, however, the point is thinned while the strength of the drill is left unimpaired.

[Ill.u.s.tration: _VOL. II._ =EMERY GRINDING MACHINERY.= _PLATE IV._

Fig. 2032.

Fig. 2033.]

Fig. 2032 represents Brown & Sharpe's surfacing grinder, designed to produce true and smooth surfaces by grinding instead of by filing. In truing surfaces with a file a great part of the operator's time is occupied in testing the work for parallelism, and applying it to the surface plate to test its flatness or truth, whereas in a machine of this kind both the parallelism and the truth of the work are effected by the accurate guiding of the machine table in its guideways. Furthermore, a high order of skill is essential to the production of work by filing that shall equal for parallelism and truth work that is much more easily operated upon in the machine. The machine is provided with two feed motions, the first of which is in a line parallel with the axis of the emery wheel driving spindle, and is communicated (by means of the small hand wheel on the right) to the lower table, which moves in [V]-guides provided upon the base plate of the machine. Upon this lower, and what may be termed cross-feed table slides, in suitable guideways, the work-holding or upper table, which is operated (by the large hand wheel) to traverse the work back and forth beneath the grinding wheel. Both these feed motions are operated by hand, automatic feed motions being unnecessary for work of the size intended to be operated upon in this machine. The grinding wheel spindle is carried in a bearing carried in a vertical slide, and is fed to its depth of cut by means of the vertical feed screw and hand wheel shown. The spindle pa.s.ses through the bearing and carries a pulley at the back of the machine, which pulley is driven by a belt pa.s.sing over idler pulleys at the back of the machine, by means of which the tension of the driving belt may be regulated.

Fig. 2033 represents The Tanite Co.'s machine for surface grinding such work as locomotive guide bars. The emery wheel N is mounted beneath a table T, whose upper surface is planed true, and which has two cylindrical stems C D fitting into the bored guides E. The stems are threaded at their lower ends to receive a screw, on the lower end of which is a bevel-gear F meshing into a similar gear G on the shaft actuated by the hand wheel W, hence by operating W the height of the table face may be adjusted to suit the diameter of the wheel.

The surface to be ground is laid upon the face of the table, and the operator moves it by hand, slowly pa.s.sing it over the emery wheel, which projects slightly through the opening shown through the centre of the table. The operator stands at the end of the machine so as to be within reach of the wheel, and the direction of rotation is towards him, so that the work requires to be pushed to the cut and is not liable to be pulled too quickly across the table by the emery wheel.

[Ill.u.s.tration: Fig. 2034.]

Fig. 2034 represents an emery grinding machine for grinding the bores of railroad car axle-boxes. The circ.u.mference of the emery wheel is dressed to the curvature of the box bore by a diamond tool A which swings on a centre in its frame, and can be adjusted to any arc. Once set, it can only turn the prescribed arc with accuracy. In order to avoid the necessity of the foreman having to set the tool, a gauge is also furnished. This consists of a spindle adjustable with a nut in such a way that its two points rest in the centres on which the diamond tool revolves. It is only necessary for a disk B turned accurately to the diameter of the bearing, to be prepared, and this the apprentice can place on the spindle, adjust the latter, and screw down the diamond tool until it touches the periphery of the disk. A nut is then fastened on the diamond tool, and the frame is lifted on the ways beneath the wheel, when the moving of the handle turns the face of the wheel to the exact circle desired.

To adjust the bra.s.s in the chuck C, it is first set on the axle D. The chuck is then placed on frame E, in such a way that the [V]s fit. Handle F then moves a cam that clamps the bra.s.s between the jaws G, one set of which swings on a pivot at H. The bra.s.s is thus adjusted in such a manner that, despite the imperfections in moulding, it is ground accurately with the least removal of metal. The chuck C fits into planed guides on the table I, and is thus brought in exact line with the motion of the wheel. The crank J serves to move the table to and fro on the rods K, and the table also rises and falls on planed ways, being pressed up by springs. The hand wheel gives vertical adjustment to the whole bed by means of a chain beneath it. There is a pulley by which a suction fan, to remove dust, &c., may be driven. The machine is capable of fitting from 150 to 500 car bra.s.ses per day.

[Ill.u.s.tration: Fig. 2035.]

Fig. 2035 represents an emery planing machine. The emery wheel, which takes the place of the cutting tool of an ordinary shaping machine, is upon a spindle driven by the pulley A upon the spindle B, which is traversed endways by means of the connecting rod which is actuated by a crank E driven by the cone pulley C. The work-holding table G is traversed by the handle K or automatically through wheel H, which through suitable gearing drives the spindle I. The blower or fan is to draw off the cuttings and emery. It is obvious that any of the usual forms of work-holding devices may be employed.

[Ill.u.s.tration: Fig. 2036.]

Fig. 2036 represents an ordinary form of emery grinding machine for general purposes. A represents the frame affording journal bearing for the driving spindle driven by the cone pulley P, having the fast f.l.a.n.g.es _f_ and collars C, which are screwed up to hold the emery wheel by the nut N, the direction of spindle rotation being denoted by the arrows.

The thread at the end K of the spindle must be a right-hand one, and that at the other end L must be a left-hand, so that the resistance against the nut shall in both cases be in a direction to screw the nuts up and cause them to bind or grip the wheels more firmly, and not unscrew and release the wheels. Upon the frame A are the lugs D to carry the hand rests R and S, which are adjustable, and are secured in their adjusted position by the handle nuts E. The rest S is of the same form and construction as a lathe hand rest, while that at R is angular, to support the tool while applying it to the side as well as to the circ.u.mference of the wheel.

Fig. 2037 represents a machine for grinding the knives for wood-planing machines, and having a hand feed only. It consists of an emery wheel mounted upon a spindle and with a slide rest in front of it. Mounted on the slide rest is a frame for holding the knife, and a set-screw for adjusting the angle of the knife to the wheel. The slide rest is traversed by means of the hand wheel operating a pinion in the rack shown.

Fig. 2038 represents a swing frame for carrying and driving an emery wheel to be used on the surfaces of castings, its construction permitting it to be moved about the casting to dress its surface. The overhead countershaft carries the grooved driving wheel A. At B is a vertical shaft pivoted at I by the forked bearing which swings upon the countershaft. The fork L at the lower end of shaft B carries a shaft on which is the fork C', C having journal bearing on it, and the driving pulley J. Fork D has journal bearing on the same shaft as pulley J, and is fast upon the rod or arm E, which affords journal bearing to the emery wheel K on a shaft having handles H H. Motion to the emery wheel is conveyed through the belts F and G. To counterbalance the frame the weight W is employed, permitting the frame to be readily swung. The upper fork carrying B, being pivoted to the shaft of A, permits B to swing to any required position. The pivot at I permits B to rotate in a vertical plane; the pivot of C' C at D affords vertical movement to E; the pivot at D allows E to rotate about its own axis, hence the wheel K can be moved about laterally, raised, lowered, or have its plane of revolution varied at will by simply swinging the handles H H to the required plane. The emery-wheel shaft is pivoted upon the fork carrying it, so that the emery wheel can be turned to stand in a horizontal plane if desired.

[Ill.u.s.tration: Fig. 2037.]