US3438156A - Method for form dressing a wheel and for grinding spherical surfaces therewith - Google Patents

Description

3,438,156 R GRINDING Aprll 15, 1969 H. A. LAKSO METHOD FOR FORM DRESSING A WHEEL AND FO SPHERICAL SURFACES THEREWITH Filed Nov. 28, 1966 m T N E V N (/6O A. AAKJO ATTORNEY April 15, 1969 H. A. LAKSO 3,438,156

METHOD FOR FORM DRESSING A WHEEL AND FOR GRINDING SPHERICAL SURFACES THEREWITH Sheet 2 of 3 Filed Nov. 28, 1966 I NVENTOR #060 ,4. ZAKSO ATTORNEY April 15, 1969 H; A. LAKSO 3,438,156

METHOD FOR FORM DRESSING A WHEEL AND FOR GRINDING SPHERICAL SURFACES THEREWITH Filed Nov. 28. 1966 Sheet 3 of 5 i INVENTOR //(/60 A. AAA so ATTO R N EY United States Patent Office 3,438,156 Patented Apr. 15, 1969 US. Cl. 51-289 7 Claims ABSTRACT OF THE DISCLOSURE A method of wheel dressing and of grinding the spherical surface of rollers for bearings. The rollers are plunge ground to a desired radius by the concave outer diameter of the wheel which has been transversely dressed by a diamond coated dressing cutter of the same radius as that desired on the rollers.

A method of dressing a grinding wheel for the specific purpose of grinding an accurate spherical or compound radius on workpieces such as the rollers used for self aligning roller bearings.

This invention relates to wheel dressers in general, but more particularly to a method for dressing the peripheral surface of a grinding wheel in order to produce a precise spherical or compound radius on the workpiece.

Many parts in precision machinery are produced by grinding methods, and many types of grinders are required, each adapted to a particular surface conformation.

One such conformation is the compound radial shape which has a variable radius depending on the plane through the shape being considered.

For the purposes of this invention we might define a compound radial shape as one which has a first center of curvature in the plane containing the parallel axes of workpiece and wheel, and a second in the plane normal to those axes which contains the first center of curvature. A special case of this, where these two centers are coincident, is a sphere.

In such grinding, the first center of curvature locates radius R, which is dressed on the wheel, while the second center of curvature locates r, and is controlled by the point to which the cross feed is advanced.

Thus we see that a disc having the first radius on its periphery is one extreme, and a barrel shaped roller with the same peripheral radius is the other. In the first case, the cross feed is stopped before the two center coincide making a sphere, and in the second, the cross feed passes through the sphere to a final position.

In order to explain this invention, we will take the latter type, a barrel roller, which are found in selfaligning roller bearings.

Since the quality of finish on the ground surface is very sensitive to the surface condition of the grinding wheel, the dressing operation becomes very important. In this invention we will concern ourselves with the dressing aspect only.

We will assume that the grinding wheel has already been selected, but the method of dressing the wheel is yet to be determined.

Many types of dressers are available-single point diamond following a template, radial single point diamond, spherical surfaced diamond truing cutter, etc. All have advantages, as well as drawbacks, some of which might be mentioned here.

(1) The single point diamond, of necessity, travels across the rotating wheel at a very slow rate making a fine groove or trace on the grinding wheel somewhat like a fine pitch thread. Being very nearly parallel to the direction of rotation, this trace tends to transfer its image to the surface of the workpiece as a series of minute rings normal to the axis, giving a surface finish not of the best quality for bearing rolls. Also, single point diamonds wear and therefore require periodic adjustment to keep the curvature within the specified tolerance.

(2) Wear can be greatly minimized by using a multiplicity of diamonds. However, the use of a multipoint diamond nib still has the disadvantage of creating the fine grooves parallel to direction of grinding face travel.

(3) A spherical surfaced diamond cutter can be used to add movement to the diamonds and further refine the dressed wheel surface. This is more difficult to make, and relatively expensive, since it not only has a more intricate shape, but carries many more diamonds. It will improve wear, make a substantial gain in the number of discrete grooves of the dressing trace, and tends to improve finish as compared with a wheel dressed with a single point diamond accomplished in the same time. But this method retains an inherent disadvantage of the cited grooves as a deterrent to achieving the best grinding finish.

With these considerations in mind, it is therefore an object of this invention to teach a method of dressing a grinding wheel which will inherently provide better finishes by dressing the face of the wheel transversely while reducing the dressing time.

Another object is to provide a dressing cutter of cylindrical shape made to the radius required on the wheel, which will generate an accurate curvature, averaging out errors of spindle or dresser contour, and avoiding the necessity for tracing templates, or pivoting a diamond.

A further object is to provide a dressing tool which is relatively low in cost, and simple to manufacture.

Still another object is to provide a dressing device with minimum maintenance or adjustment required during production runs, and longer truing-cutter life.

Other objects and advantages of such a device will become evident to those skilled in the art, as the present invention is described.

In the preferred embodiment illustrated:

FIG. 1 shows a typical external grinding wheel with a diamond truing cutter in dressing position.

FIG. 2 shows the plan view of FIG. 1 taken on line line 2-2.

FIG. 3 shows the plan view as in FIG. 2 with the dressing cutter removed and the workpiece in place.

FIG. 4 shows a section through the wheel and the workpiece at 4-4.

FIG. 5 shows an elevation of the wheel and cutter showing two methods of dress.

FIGS. 6 through 11 show applications of the grinding wheel dressed in the manner specified.

Referring specifically to the drawings, FIG. 1 shows an external grinding wheel 10, adapted to rotate counterclockwise on axis A. The wheel 10 is being dressed by a rotating dressing cutter 12 on axis B, at right angles to axis A but offset from it. The direction of rotation of the cutter 12 is not significant as it can rotate in either direction.

The outside diameter 81 of the cutter 12 is equipped with a cylindrical band of abrasive grains 14, such as diamonds, which dresses the peripheral surface of the wheel 10 in a direction substantially parallel to the axis A of wheel rotation, i.e. transversely of the diameter or wheel face 80.

FIG. 2 shows a plan view of the arrangement in FIG. 1, wherein the lateral symmetry is clearly shown. Consider that wheel 10 is split into two discs by a vertical dividing plane 16, also containing axis B of cutter 12.

The cutter 12, itself, has been manufactured to the desired radius R prior to installation. After the grinding wheel has been dressed by cutter 12, the diameter or wheel face 80 will have a concave radius R having its center outside the wheel 10. Consequently, the wheel 10 will grind the workpiece to a matching radius R, as shown in FIG. 3. The length 22 of the rotating workpiece 20 must, of course, be symmetrically placed in relation to the vertical plane 16, if the flat end faces 82 and 84 are to be equal in diameter, In other words, in order to grind the roller 20 to a symmetrical shape with both the end faces 82 and 84 of the same diameter, the center of the cutter radius R (shown in FIG. 2) must be in the same position relative to the wheel as the center of radius R on the work part (as shown in FIG. 3). The wheel width 24 will have to be greater than the length 22 of the workpiece and overlap the workpiece at both ends as is clearly shown in FIG. 3.

The major diameter d of workpiece 20, shown in FIG. 4, will be controlled by means not part of this invention, as the wheel 10 and workpiece 20 approach each other along centerline 28 in a horizontal plane. This is the cross feed direction, and d is equal to 21', or twice the workpiece radius.

The dressing operation itself is preformed in two possible ways, both shown in FIG. 5.

One method is to position the dressing cutter 12 as shown in solid lines at 38. The grinding wheel 10 is in line with it as shown in FIG. 2, but out of contact as shown in phantom at 30 in FIG. 5. The wheel 10 is fed into contact position 32 relative to dressing cutter 12 by movement as shown by arrow 34. When the contact is made, the wheel 10 and cutter 12 are fed at a controlled rate through a small compensation distance sufiicient to uncover new grains in the grinding wheel 10, and to fracture some old ones, thus providing a new grinding surface 80. The wheel 10 and cutter 12 are then separated along line 34 to a clearance position as shown in phantom at 30, which permits the dressing cutter 12 to be replaced by workpiece 20 in substantially the same relative grinding position, such as shown in FIG. 3 and FIG. 4. The mechanism for such replacement is not part of this invention and is not shown or claimed.

Another method is shown in FIG. 5, where the Wheel 10 is in position 32, and the dressing cutter 12 is in lower out of contact position 36. The rotating cutter 12 is then fed successively through the dressing contact position 38 to clearance once more at upper out of contact position 40. The cutter 12 is then replaced by workpiece 20 as discussed above. wheel 10, it is returned to position 36 once more. It will be understood that positions 36 and 40 could be interchanged without disturbing the intent of the invention, and the contacting and separating movements of wheel 10 and cutter 12 as shown by arrow 34 are relative to each other.

Referring now to FIGS. 6 through 10, we see several further applications of both internal and external grinding wheels dressed in the manner described earlier. These are all typical parts which are finished by grinding and which would benefit from the transversely dressed grinding wheel.

As before, the dressing cutter is represented by radius R, which also represents the radius of the contour on th e workpiece. Also, r represents the variable workpiece radius, not under control of the dresser.

FIGS. 6 and 6A show a disc 11, both in plan and side elevation respectively, in which the concave dressed wheel 10, dressed as before to radius R by cutter 12, is fed into the outside diameter 86 of the disc to grind radius R on its periphery. The feed is continued until the desired diameter a is reached. Since d=2r, if the feed Were n n e until R=r, we would have a sphere of diameter 2R.

When the cutter 12 is clear of the FIG. 7 shows a workpiece 13 such as an inner race of a roller hearing which is ground with the axis C of workpiece rotation transverse to the wheel axis A. The wheel 10 is fed into the workpiece 13 in a manner disclosed above.

FIG. 8 discloses an internal grinding application in which the two inside raceways 42 and 54 on one double bearing race 41 is ground. There are two ways in which the grinding could be accomplished using the transversely dressed wheel. The first method is shown in FIG. 8. Here the first raceway 42 is ground by an internal grinding wheel 44 which has been dressed to radius R by the cutter 12. It is necessary here to angle the axis D of wheel 44 with respect to the axis E of workpiece 41. While the first raceway 42 is ground, the bearing race 41 is located against end face 50. After completing this first grind operation, the wheel 44 is withdrawn, and the bearing race 41 is turned over so as to position the hearing race 41 against end face 52. The wheel 44 is then advanced and the second raceway 54 is ground exactly as was the first since it now occupies the same position.

The second method is illustrated in FIG. 9, where double bearing race 41 is ground at one chucking operation. This obviates the necessity of turning the workpiece over, as was done in the first method. The grinding wheel 56, is first dressed on its outside diameter 58 by means not part of this invention, after which the two concave surfaces 60 and 62 on the wheel 56 are dressed by cutter 12 in the manner previously described. It is noted that the axes F and G of the wheel 56 and workpiece 41, respectively, are parallel.

In FIG. 10 another bearing 63 having a raceway 64 is shown being ground internally by a grinding wheel 66, on which the outside diameter 68 is dressed by means of a conventional nature, not part of this invention. Then the cutter 12 is plunged into the wheel to the required depth X to dress concave surface 70 of wheel 66. Using the wheel 66 dressed as shown, the workpiece 63 can be ground by internal grinding methods well known to those skilled in the art. As in FIG. 9, the axes H and .T of the wheel 66 and workpiece 63 respectively, are parallel.

FIG. 11 shows a method for grinding the spherical back surface 74 of a bevel pinion gear 72. This is best accomplished by grinding with a grinding wheel 76 which has been dressed by truing cutter 78 to radius R, as disclosed hereinabove. The axes K and L of the wheel 76 and gear 72, respectively, are transverse.

It will be seen by those skilled in the art, that the rotary cutter as described fully meets the objects and aims of the invention, being simple, accurate, and economical. It will be further understood that the present disclosure is illustrative rather than restrictive and the various changes may be made in many details without departing from the scope and spirit of the invention as defined by the claims which follow.

What is claimed:

1. A method of grinding wheel truing by use of a rotating cylindrical cutter of precise diameter having a narrow band of abrasive grains around its outside circumference, comprising the steps of plunging said cutter radially into the circumference of a rotating grinding wheel, the axes of said cutter and grinding wheel being at right angles to each other, respectively, and said cutter being symmetrically located with respect to the width of said grinding wheel, and withdrawing said cutter when said wheel has been dressed concavely to the same precise radius as that of said cutter.

2. A method of dressing a grinding wheel for plunge grinding a spherical radius on a workpiece to a predetermined value comprising the steps of providing a cylindrical shaped dressing cutter with a narrow band of abrasrve grains attached around its circumference, and plunging said cutter radially into the outside diameter of said grinding Wheel to true a concave grinding sur face to the same radius as that desired for said workpiece.

3. A method of grinding the barrel shaped rollers for self aligning roller bearings as defined in claim 2, comprising the steps of plunging a grinding wheel which has been concavely dressed into said roller, and backing ofi said wheel when a desired roller diameter has been achieved.

4. A method of grinding spherically radiused workpieces comprising the steps of dressing the outside perimeter of a grinding wheel transversely of the wheel face to a smaller diameter near the center than at the corners, by means of a cylindrical dressing cutter coated with abrasive grains, and plunger grinding said workpiece to an exact radius section matching that of the dressed grinding Wheel.

5. A method of dressing a rotating grinding wheel by use of a rotating cylindrical truing cutter having a band of abrasive grains around its outside circumference, having a diameter twice the radius desired to be transferred into the concave periphery of said grinding wheel, comprising the steps of (a) locating the axis of said cutter in a vertical dividing plane passed through said grinding wheel normal to the axis of said wheel,

(b) locating the axis of said wheel in a horizontal plane which is normal to said cutter axis and passed through said band of grains, and

(c) moving said cutter and said wheel relatively toward each other along the line of intersection of said planes a sutficient distance to expose new grains on the wheel surface.

6. A method of dressing a concave radius on the outer periphery of a grinding wheel where the center of said radius lies outside the diameter of said grinding lwheel, comprising the steps of providing a cylindrical dressing cutter whose axis passes through the center of curvature of the radius to be ground on a workpiece, and whose radius is identical with the said workpiece radius, feeding said wheel and said cutter together, and withdrawing when said radius has been obtained.

7. A method of dressing a rotating grinding wheel diameter to a radius whose center lies outside said grinding wheel comprising the steps of positioning a rotating cylindrical cutter below the plane containing both the work and wheel axes, with the cutter axis of rotation normal to said plane, and passing through the center of desired workpiece radius in that plane moving said axes close enough together to dress off a compensation amount from said grinding wheel diameter as said cutter is displayed upward along its said axis of rotation, and elevating said cutter thru said plane from a lower out-ofcontact position, to an upper out-of-contact position.

References Cited UNITED STATES PATENTS 2,220,768 11/1940 Indge.

2,449,372 9/ 1948 Eglinton.

2,795,900 6/ 1957 Modler 51-289 XR 3,121,423 2/ 1964 Price 12S11 3,299,582 1/ 1967 Kohlstrunk --11 XR HAROLD D. WHITEHEAD, Primary Examiner.

US. Cl. X.R.

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