US2706872A - Grinding machine - Google Patents

Description

April 26, 1955 E. v. FLANDERfs rs1-AL 2,706,872

GRINDING MACHINE Filed June 1, 195s :s sheets-sheet 1 w "Sk APIX 26, 1955 E. v. FLANDERS Erm.

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United States Patent O GRINDING MACHINE Ernest V. Flanders and Carroll H. Drury, Springfield, Vt., assignors to `Tones & Lamson Machine Company, a corporation of Vermont Application June 1, 1953, Serial No. 358,862

Claims. (Cl. 51--95) This invention relates primarily to machines for grinding relief in the threads of taps, but embodies principles which can be used in machines for grinding relief on reamers, milling cutters and other tools. For simplicity the description will be restricted to a thread grinder for taps. It is known that the threads on the lands of a tap should be relieved in a radial direction so that there will be no rubbing on the work back of the cutting edges. To accomplish this it has been the practice to move the grinding wheel toward and from the work piece as many times during a revolution of the latter as there are flutes on the tap, or to mount the work supporting spindle in a carriage which was given a similar movement toward the grinding wheel. This is a practical construction where the taps are large in diameter and the speed of rotation of the work piece is therefore not very high. It has proved quite impractical, however, in the grinding of taps of small size, say one-half inch in diameter or less, as these must be rotated at high speeds to get the volume of production necessary to maintain a competitive cost. It has become the custom, therefore, to grind these small taps with no relief whatever.

It is a major object of our invention to provide novel means whereby the work is oscillated toward and away from the grinding wheel, but the amount of weight which has to be oscillated in the combination of the work itself and the work supports has been reduced to practically zero, so that the speed of rotation in the grinding from the solid of threads with relief on a guarter inch tap, for example, can be increased from 100 R. P. M. on former machines to at least 600 R. P. M. in machines constructed in accordance with the present invention. This makes it perfectly practical to grind and relieve the threads of small taps on a normal production basis, thus making superior free cutting taps at low cost. Briefly, this is accomplished by mounting within the work-driving spindle a coaxial shaft which has a tapered hole supporting the headstock center on which the work is mounted. Opposite the headstock is a tailstock having a similar center supporting shaft, with, of course, no surrounding spindle. The two shafts are driven at a higher speed than the spindle, being two, three or four times as fast depending on the number of lutes on the tap. The worksupporting centers are made with their points eccentric to the axis of rotation, and preferably with a counterweight ground into the part between the point and the taper shank, so that the combined counter-weighting of the two centers will compensate not only for the offbalance of the eccentric points but for the off-center weight of the tap itself.

The invention will now be more completely described, as well as the manner in which the above objects are achieved, with reference to the accompanying drawings, in which:

Fig. 1 is a front view of a portion of a thread grinding machine in which our invention is embodied;

Fig. 2 is a section on line 2 2 of Fig. l;

Fig. 3 is a view, on an enlarged scale and with eccentricities exaggerated, of one of the work supporting centers;

Fig. 4 is a development, or stretch-out, view of the headstock and tailstock with the associated gearing;

Fig. 5 is a diagrammatic view showing the relation between the work piece, its axes of rotation, and the grinding wheel at the beginning of the grinding of a thread on one of the lands of a tap; and

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Fig. 6 is a similar View showing the land about to pass out of contact with the grinding wheel;

Figs. 7 through 10 are views of a modification of the gearing arrangement of Fig. 4 for purposes to be described.

The headstock 10 and the tailstock 11 are mounted on a suitable base containing driving mechanism, coolant and lubricant reservoirs, and various other parts which are not important here and which will therefore not be described. Such a machine may be as described in U. S. ,l Patent 2,184,011 issued December 19, 1939, to R. E. t

Flanders. A grinding wheel 13, mounted in a housing 14, is driven, dressed, and fed radially by mechanism which may be standard as far as the present improvements are concerned. If there is a helical thread to be cut there must, of course, be a steady longitudinal feed between the wheel and the work. If, on the other hand, the grooves to be cut are annular' as in a hob with no lead, an intermittent longitudinal feed is required. The present invention is usable with either type of feed, and since they are well known in the art, they need not be referred to in detail here.

Within the headstock is a spindle 15 mounted in ball bearings 16. Within the spindle is a center supporting shaft 17 mounted on bearings 13 between it and the spindle. In the tailstock 11 is a center supporting shaft 19 mounted on bearings 20. The two shafts 17 and 19 are driven from a shaft 21, mounted in the frame in bearings 22, by pairs of gears 23, 24 and 25, 26, each having a two to one ratio. Thus the shafts 17 and 19 rotate at all times in synchronism and in a definite angular relation; and, as will be seen, with the center supporting shafts rotating at a speed which is an integral multiple of that of the spindle.

The shaft 21, which drives both the spindle and the center supporting shafts, is itself driven from a shaft 27 having a worm gear 28 engaging the main drive worm 29. Between shafts 21 and 27 is a change speed mechanism consisting of two cluster gears 30 and 31, the latter of which is keyed so as to slide on shaft 21, while the cluster gear 30 is xed on shaft 27. The cluster gear 30 has a gear 33 meshing with a gear of the same size 34 fixed on the spindle. Since Fig. 2 is made as a developed or stretched-out view for clarity, as otherwise some gears would be hidden behind others, it happens that gears 33 and 34 are not shown as being in mesh except by the conventional device of joining them by dotted lines. This is much clearer than showing the gears in their geometrically true positions with some partially tucked away behind others. It will be understood, however, that gears 33 and 34 are actually in mesh at all times, and that through them the spindle 15 is driven at the same speed as shaft 27.

The function of the other gears in the clusters can now be considered. Gear 3S in the cluster 30 can be made to mesh with a gear 36 in the cluster 31 having half as many teeth. Since the spindle is driven at the same speed as shaft 27 and the center supporting shaft 17 is driven by gears 23, 24 at twice the speed of shaft 21, this combination drives the center supporting shafts at a speed equal to 2X2 or four times the speed of the spindle. This is the condition desired for a tap with four llutes. For a tap with three flutes a gear 38 on cluster 31 is shifted to engage a gear 37 on cluster 30 having 2/3 as many teeth. This drives the center supporting shaft 17 at 2X3/2 or three times the speed of the spindle. When a gear 39 on the cluster 30 is in mesh with an equal gear 40 on the cluster 31 the center supporting shaft rotates twice as fast as the spindle,'which is suitable for a tap with two flutes.

The center supporting shaft 17 (which is always synchronous and in angular alignment with the center carrying shaft 19 as pointed out above) and the spindle 15 are coaxial; the oscillation of the work necessary to cause the cutting teeth to be relieved is done solely by the work supporting centers. One of these is shown in Fig. 3 on an enlarged scale and with the eccentricities greatly exaggerated, as can be seen from the fact that the actual eccentricity of the conical point with respect to the axis of the center carrying shaft is radially about 0.004". Since this would be invisible on the drawing it has been can be entirely eliminated.

magnified many times. The center 41 has the usual taper shank 42 fitting into the tapered socket 43, but in the present case has a keyway 44 engaging a key 4S in the socket to preserve the correct angular orientation and to ensure that the two centers will have their eccentricities lying in the same direction.

The tapered shank 42 has a center line at 42a and is joined by a reduced portion 46 with an eccentric cylindrical portion 47 having its center line at 47a. The center 41 terminates in a cone 43, having its center line at 48a and, which aside from this center line offset, is like the usual lathe or grinder center. it will be plain that as the center rotates about its axis 42a, the cylindrical portion 47 will also rotate about it, but with its own axis displaced as shown in Fig. 3. Likewise the conical point 4S will rotate about the axis 42a but with its own axis 48a displaced, in a direction exactly opposite to the axis 47a. The two centers shown in Fig. l have their respective axes in line7 and since the work piece 52 to be ground is supported on the conical points 48 (though rotated with the spindle by a dog to be described) it executes an orbital motion around the spindle axis.

This orbital rotation is more rapid than the rotation of the spindle, being a multiple of it corresponding to the number of flutes 53 on the tap being ground. For a two ute tap the orbital speed will be twice that of the spindle, for a three flute tap three times, and for a four iiute tap four times. The way in which the difference in relative speeds is made possible by the cluster gears has been described above. The orbital motion, as will be seen from Figs. and 6, acts to displace the work piece gradually toward the grinding wheel during the period when one of the lands is being ground, or rather when threads are being ground on it since the threads will in general be ground completely, with relief included, from a cylindrical but fluted tap blank.

The operation of the orbitally moving centers in securing the desired relief has been shown diagrammatically in Figs. 5 and 6, which for simplicity and for the purpose of showing the versatility of the invention omit any idea of threads. In the first of these figures the grinding wheel is just making contact with one land of the tap or other workpiece and the axis 48a which is the axis of the conical point 48 and therefore also the axis of the tap itself, is on the side of the axis 42a of the spindle remote from the grinding Wheel. ln Fig. 6 the spindle, and therefore the tap which is dog-coupled to it, has moved through an angle X suicient to bring the heel 55 of the land against the grinding wheel. During this time the axis 48a of the tap has moved through an angle 4X around the axis 42a of the spindle, thus crowding the land 54 gradually, but at an accelerating rate, into the grinding wheel. The rst part of the grinding of the land is substantially concentric, while the remainder becomes more and more eccentric. The relation between the concentric and eccentric portions can be changed as desired by varying the placement of angle X either by the setting of the workholding dog 58 or by the location of the keyway 44, the relative positions of the axes 42a and 48a at the time the land first makes contact with the wheel. lt should be realized that in the position of the axes in Fig. 5 their relative circular motion produces much less change in the eccentricity of the grind than the same relative motion does in the position of Fig. 6. The axis 48a which has completed only a portion of its rotation about axis 42a in Fig. 6, will complete its rotation to the position of Fig. 5 while the flute is passing the grinding wheel.

The function of the cylindrical but eccentric portion 47 of the center 4l can now be considered. If this were coaxial with the axis 49 of the spindle there would be an unbalanced force developed by the orbital motion of the tap around the axis 42a as well as by the orbital motion of the conical point 48 around the same axis. This unbalance would tend to create vibration which, though slight, would adversely affect the finish produced on the work. To avoid this the rotative speed of the work would have to be kept down. Even so the permissible speed would be much higher than in prior constructions in which either the entire spindle or the grinding wheel were bodily oscillated, but by proper correlation of the eccentricity of the cylindrical portion 47 with the unbalance of the conical tips and the work piece, unbalance While this may require ih center to be made especially for a particular size and weight of work piece, this is entirely feasible in production work, for the centers are relatively inexpensive. Due to the identity and alignment of the two centers 41, the whole rotating mechanism, including the work piece, will be in complete dynamic balance.

Fig. 2 shows one arrangement for driving the work piece S2 from the spindle. The spindle has the usual face plate 56 which is here provided with two pins 57 between which lits the tail of the usual dog 58. it will be apparent that the slight angular and radial motion which the oribital motion will give to the dog can readily be accommodated by the pins without disturbing the driving action of the dog.

The arrangement described above will grind a relief on taps or reamers having straight flutes, but both taps and reamcrs are also made with helical utes and it is desirable that the grinder should be able to handle either style. We provide novel arrangements for making the machine adaptable to helical as well as straight flutes. The fundamental principle underlying this form of our invention is that the center supporting shafts 17 and 19 are given, in addition to the rotation corresponding to the number of utes as described above, an angular displacement relative to the spindle corresponding to the position 0f the grinding wheel longitudinally of the work piece. This rotative displacement causes the position of a land relative to the grinding wheel to be the same all the way along the work piece being ground.

Figs. 7 through l0 show one form of device which is adapted for grinding helical as well as straight tinted tools. The basic mechanism is the same as that previously described, and has been designated by the same reference characters. The distinctive feature of the present form is in the connection between the shaft 27 and the shaft 2i which drives both center supporting shafts through pairs of gears 23, 24 and 25, 26. Shaft 21a is keyed to a bevel gear 59, while gear 23 is driven by a gear 60 of the same diameter keyed to the hub 6l of a second bevel gear 62. The gears 59 and 61 are coupled by bevel pinions 63 rotatable on studs 64 carried by the hub 66 of a ring gear 67. This ring gear meshes with a rack 68 guided in the headstock casting wall as shown in Figure 8 actuated as will be described. if the rack is not moved the operation will be the same as that described in the original form. However, if the rack is moved at a rate related to the rate of traverse of the grinding wheel along the longitudinal axis of the work, the center carrying shafts will be displaced pro gressively by an amount in addition to the integers of clusters 30 and 3l so that they will make the same shift with respect to the lands in all positions of the wheel, even though the flutes and lands in the work blank are helical.

To accomplish this we provide an adjustable cam 69 in which rides a roller 70 secured to the end of rack 68. The cam 69 is fastened to the stationary portion of the machine bed, while the rack and associated mechanism move with the longitudinal traverse of the work past the grinding wheel. It should be understood that this provides for movement of the rack a certain distance for a given longitudinal movement of wheel relative to work. This can be done by mechanical means whether the work moves, as in the Flanders type of machine referred to, or in other types of machines in which the wheel head is moved along the work.

The ratio of rack movement to work-wheel movement is, of course, determined by the setting of the cam 69 along the graduated scale 7l. The cam is pivoted on the stud 72, and may be locked in the desired position by the locking nut 7 3. By proper selection of gear ratios in the differential and between the rack and gear 67, the scale 7i may be calibrated directly in degrees of flute angle on the work blank.

By setting the cam to zero on scale 71, no correction will be fed into the differential and the machine will relieve lands formed parallel to the work axis.

From the foregoing description it will be apparent that we have disclosed a grinding machine mechanism adapted to solve long standing problems in the tool grinding field. Our invention has been found to be particularly advantageous in the grinding of taps, reamers, hobs, milling cutters and the like where heretofore full relief grinding has been inconsistent with high production and consequent 10W cost. Variations and modifications within the spirit of this invention may occur to persons skilled in the art to which it pertains. Therefore, the foregoing specification is presented by way of description and example rather than by way of limitation.

We claim:

1. In combination, a machine bed, a headstock on said bed, a hollow spindle rotatably mounted thereon, a shaft journaled in said spindle and adapted to carry a work engaging center, means for rotating said spindle at a denite speed, a tailstock on said bed, a shaft journaled on said tailstock and adapted to carry a work engaging center, centers carried by both said shafts, said centers having work engaging portions, the axes of which are offset from the axes of said shafts and means for rotating said shafts together at a speed other than the speed of said spindle.

2. In combination, a machine bed, a headstock on said bed, a hollow spindle rotatably mounted thereon, a shaft journaled in said spindle and adapted to carry a work engaging center, means for rotating said spindle at a definite speed, a tailstock on said bed, a shaft journaled on said tailstock and adapted to carry a work engaging center, centers carried by both said shafts, said centers having work engaging cones, the axes of which are parallel to but no collinear with the axes of said shafts and means for rotating said shafts together at a speed which is a selected multiple of the speed of said spindle.

3. In combination, a machine bed, a headstock on said bed, a hollow spindle rotatably mounted thereon, a shaft journaled in said spindle and adapted to carry a work vengaging center, means for rotating said spindle at a definite speed, a tailstock on said bed, a shaft journaled on said tailstock and adapted to carry a work engaging center, centers carried by both said shafts, said centers having work engaging cones the axes of which are parallel to but not collinear with the axes of said shafts and means for rotating said shafts together at a speed which is a selected integer multiple of the speed of said spindle.

4. In combination, a machine bed, a headstock on said bed, a hollow spindle rotatably mounted thereon, a shaft journaled in said spindle and adapted to carry work engaging center, means for rotating said spindle at a definite speed, a tailstock on said bed, a shaft journaled on said tailstock and adapted to carry a work engaging center, centers carried by both said shafts, said centers having work engaging cones the axes of which are parallel to but not collinear with the axes of said shaft means for rotating said shafts together at a speed which is a selected but not collinear with the axes of said shafts, means for moving said headstock and tailstock together axially along said bed, and means for adding to the integer multiple speed a preselected factor as the headstock and tailstock move axially.

5. In combination, a machine bed, a headstock on said bed, a hollow spindle rotatably mounted thereon, a shaft journaled in said spindle and adapted to carry a work engaging center, means for rotating said spindle at a denite speed, a tailstock on said bed, a shaft journaled on said tailstock and adapted to carry a work engaging center, centers carried by both said shafts, said centers having work engaging cones the axes of which are parallel to but not collinear with the axes of said shafts, means for rotating said shafts together at a speed which is a selected integer multiple of the speed of said spindle, a cutting tool adapted to engage Work mounted between said centers, means for producing relative motion between said tool and the work axially along said bed, and means' for adding to the rotation of said shafts a factor produced by said relative motion.

References Cited in the tile of this patent UNITED STATES PATENTS 1,100,265 Smith June 16, 1914 1,239,268 Hammon Sept. 4, 1917 1,297,396 Olson Mar. 18, 1919 1,365,337 Muller Jan. 11, 1921 1,478,433 Harris Dec. 25, 1923 1,739,753 Flanders Dec. 17, 1929 2,209,228 Judge July 23, 1940 2,401,561 Gruenberg June 4, 1946

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