US2777260A

US2777260A - Machine tool

Info

Publication number: US2777260A
Application number: US407070A
Authority: US
Inventors: Raymond A Mahlmeister
Original assignee: Sheffield Corp
Current assignee: Sheffield Corp
Priority date: 1954-01-29
Filing date: 1954-01-29
Publication date: 1957-01-15
Anticipated expiration: 1974-01-15

Description

Jan. 15, 1957 R- A. MAHLMEISTER MACHINE TOOL Filed Jan. 29, 1954 IN VEN TOR. K 4 W1,

of the method of this invention.

United States Patent MACHINE TOOL Raymond A. Mahlmeister, Dayton, Ohio, assignor to The Sheflield Corporation, Dayton, Ohio, a corporafion of Ohio Application January 29, 1954, Serial No. 407,010

11 Claims. c1. 51-206) This invention relates to an improved grinding wheel and a method for forming such a wheel. It is an object of this invention to provide a ribbed grinding wheel having a unique combination of surface characteristics whereby a grinding operation is possible without the generation of excessive heat and by a grinding wheel which will accurately hold its shape for the grinding of a large number of workpieces without breaking down.

It is a further object to provide such a grinding wheel wherein outer rib portions have surface characteristics such as result from a cutting operation and inner rib portions have surface characteristics such as produced by a crushing operation, thus providing a grinding wheel having nonuniform surface characteristics wherein the type of surface resulting from each forming operation is utilized where its advantages are important and its disadvantages unimportant.

It is a further object to provide a method for forming ribbed grinding wheels wherein a portion of each rib is formed by a cutting operation and the remainder by a crush-ing operation.

It is a further object to provide such a method wherein the grinding wheel is initially formed by a cutting operation, as by diamond dressing, and portions of each rib are further formed by engagement of the grinding wheel and a crusher roll carried for relative axial movement and positioned axially during crushing by contact of the "crusher roll with the previously cut grinding wheel rib surfaces whereby an accurately annularly formed grinding wheel is produced having unique and advantageous surface characteristics.

Other objects and advantages of the invention will be apparent from the following description, the appended claims and the accompanying drawing, in which;

Figures 1.3 illustrate steps in an exemplary applicatio Figure 4 illustrates a crushing unit comprising a crusher roll carried for rotation and for free axial movement and discloses one exemplary way in which the crushing phase of this invention can be carried out, and

, Figure 5 discloses a phase in a second exemplary application of the present invention.

The present invention relates to formed grinding Wheels, 'as examples, to annularly or helically ribbed Wheels having single or multiple ribs. The exemplary grinding wheel illustrated for the purpose of disclosing the features of this invention is one having annular ribs and is provided for grinding fine pitch taps.

The grinding wheel of the present invention has unique surface characteristics resulting from the fact that the complete rib surfaces are not uniformly dressed or formed in the same manner, as has been the previous practice,

The dressing or forming of grinding wheels by means 2,777,260 Patented Jan. 15, 1957 of a cutting element such as a diamond or other hard material which traces a predetermined path while in cutting contact with a rotating grinding wheel is commonly referred to as a diamond dressing operation. It is a characteristic of grinding wheel surfaces dressed by this method that grinding wheel particles are sheared, resulting in fiat particle surfaces in the plane of the grinding wheel.

As a result the grinding wheel surface particles are closely adjacent and there is a comparative lack of voids between the particles in the surface. Because of the lack of voids, and the flat particle surfaces resulting from this dressing method, grinding wheel surfaces dressed by this method are not free and rapid cutting. Heat is generated rapidly due to rubbing of the fiat surfaces along the Work surface during grinding and cannot be freely dissipated because of the lack of voids between the particles, thus requiring comparatively slow grinding with a fully diam-0nd dressed wheel to avoid burn-ing the workpiece. However, a diamond dressed rib can be more accurately formed and is not subject to breaking down in grinding.

In crush dressing an annularly formed crusher roll having a profile identical to that to be formed into the work by grinding is brought into pressure con-tact with the surface of a rotating grinding wheel and is urged toward the grinding wheel axis to crush the crusher roll form into the grinding wheel. In dressing by this method grinding wheel surface particles ar broken away or cracked out of the wheel bond instead of being sheared or cut, thus leaving sharp edges on the surface particles and voids between the particles. In grinding by a grinding wheel surface dressed through this method free and rapid grinding results and less heat is generated because of the sharp grinding surface particles. Such heat as is generated is dissipated because of the voids between the particles. Such a surface will give cooler and more rapid grinding.

The outer rib portions of the grinding wheel of this invention are formed by a cutting operation and the inner rib portions by a crushing operation audit will have surface characteristics resulting from each of these forming methods.

The sides of the rad-iallyouter rib portions which are most subject to breaking down have the characteristics resulting from a diamond dressing or cutting operation and will hold their accurate form for precision grinding of a large number of workpieces between dressing operations. The cut rib surfaceswill grind the radially inner portions of the work where the most rapid heat dissipation from the workpiece surface into the mass of the workpiece is possible. Thus the limiting disadvantage of a diamond dressed wheel is avoided because diamond dressed surfaces are not disposed to engage the radially outer portions of the Work where burning is most likely to occur.

The inner grinding wheel rib portions which engage and grind the radially outward portions of the workpiece where the least heat dissipation is possible from the surface of the workpiece into the workpiece mass are characterized by voids between sharp edged cutting particles giving a cooler grind-ing operation on these portions of the workpiece, Should excess heat be generated, it is possible to distort the surface of the workpiece and to change its physical characteristics from those desired. Also the crushed surfaces are inward on the grinding wheel ribs where breaking down of the grinding Wheel is least likely to occur.

Figures 1 to 3 illustrate progressive steps in an exemplary application of the method provided by this invention for forming such grinding Wheels. V

In Figure 1 the profile of a rotating grinding wheel 10 is shown in association with a diamond cutting element '12. It will be noted that the grinding wheel is dressed by means of the diamond cutter 12 to form the grinding wheel tip portion 14 to the finally desired configuration. Below the tip portion the surface of the grinding wheel steps out at 15 to an enlarged root portion 16 which has a form similar to that finally desired but of a transverse dimension greater than the final grinding wheel profile form.

The grinding wheel 10 in Figure 2 has been contacted by a crusher roll 20 beginning the second phase of the forming operation. It will be noted that the crusher roll 20 is so conformed as to contact the root portion 16 of the grinding wheel rib and to clear the outer end of the rib tip portion 14. The crusher roll 20 is relieved at 21 to avoid contacting the outer rib tip of the grinding wheel throughout the crushing phase of the operation.

The grinding wheel 10 has been finally formed in Figure 3 as the crusher roll 20 has reached its maximum displacement inward toward the axis of the grinding wheel. The excess material previously found at the rib root portion 16 has now been removed by crushing and the grinding wheel rib has been formed to its 60 degree thread profile section. Because of the crusher roll relief 21 the outer end of the rib tip 14 has not been touched.

Figure 4 illustrates a crusher roll 20 in initial contact with the surface of the grinding wheel 10 as in Figure 2. In this exemplary structure the grinding wheel 10 is driven by a structure not shown and the crusher roll 20 is forced in toward the axis of the grinding wheel 10 by means of a hand wheel 22. The crusher roll 20 is mounted on a shaft 24 carried for rotation in a carrier 25 which is positioned by the hand wheel 22.

It will be appreciated that if the crusher roll 20 were fixed to a shaft 24 which is in turn carried for rotation and held against axial movement by hearing members mounted in the carrier 25, irregularities in the bearing members which support shaft 24 would cause axial movements of the shaft 24 and the crusher roll 20 as the crusher roll rotates. This will result in a grinding wheel which is not truly annular but which has high spots along its surface. Because these high spots are the only surfaces which will be in grinding contact with the work, an efiieient or accurate grinding operation is impossible with such an imperfectly formed grinding wheel.

In application of the present invention the crusher roll and grinding wheel can be mounted for limited relative axial sliding. For purpose of disclosing this phase of the present invention, it will be considered that in Figure 4 it is the crusher roll which is free for limited axial movement along the shaft 24 or, as an equivalent, the shaft 24 itself is carried for limited axial movement in the carrier 25. The profile of the grinding wheel 10 at this stage of this exemplary application is as shown in Figure l and is formed by diamond dressing. It will be seen that when the crusher roll 20 is brought into engagement with the periphery of the grinding wheel 10 it will be located axially by the previously dressed rib surfaces. The position of the crusher roll 20 will be established as it continues its operation by the balanced forces between it and the opposite sides of each grinding wheel rib. The guided inward movement of the crusher roll 20 continues until the roll has removed the excess material remaining at the rib roots following the diamond dressing operation, as seen in Figure 3. A truly annular grinding wheel is thus provided.

One means for determining when the inward crusher roll movement has been completed is by the gauge structure illustrated in Figure 4. As therein shown a dial indicator 27 is mounted on a fixed crusher unit housing 28 and has its movable contactor 30 in engagement with a fixed projection 31 on the carrier 25 to gauge the movements of the carrier 25. Thus by the gauging of the inward movement of the crusher roll 20 the excess material existing at the rib root portions can be crushed away, the outer portions of the rib tips cleared or touched up slightly by crushing and the ribbed outer tips left in their cut configuration by the relief 21 of the grinding wheel on the crusher roll 20.

In Figure 5 is illustrated a further application of the present method. The ribs of the grinding wheel 35 are initially formed by cutting the sides to an angle greater than the final desired form. Then, by use of a crusher roll as indicated at 36, the grinding wheel is crushed to the desired angle either touching up the rib by crushing or clearing the rib tip by a crusher roll relief 37 as shown in this specific application.

It will be understood that while this method in the applications as illustrated and previously described involves an initial cutting operation followed by a crushing operation the operations could be reversed in sequence; as for example, forming the wheel first by crushing, leaving excess material along the outer rib portions, and then cutting these portions away by a diamond dressing operation or the like.

Because the inner and outer grinding wheel rib surfaces in this invention are formed by different dressing processes and will have the characteristics resulting therefrom, the most advantageous features of each process have been utilized where most expedient on the grinding wheel surface with unusual advantages achieved in grinding. By the relative positioning of the crusher roll and grinding wheel by engagement of the crusher roll with previously cut grinding wheel rib surface, a grinding wheel is provided which will have a true annular eonfiguration wherein all surfaces will be in contact with the work during grinding.

While the grinding wheel and the applications of the method herein described constitute a grinding wheel having preferred surface characteristics and preferred applications of the method, it is to be understood that the invention is not limited to such but that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

l. A method for forming a ribbed grinding wheel having the characteristic that it can be crush formed comprising forming the radially outer portions of the sides of the ribs to the final desired form to be used in grinding a workpiece by a cutting or shearing operation and forming the radially inner portions of the sides of the ribs to the final desired form to be used in grinding the workpiece by a crushing operation.

' 2. A method for forming a ribbed grinding wheel comprising first forming the radially outer rib sides to the final desired form to be used in grinding a workpiece and the radially inward rib portions to approximately the final desired form by a cutting operation and then further forming the inward rib portions to their final form to be used in grinding the workpiece by crushing.

3. A method for forming a ribbed grinding wheel comprising first forming the grinding wheel by cutting the radially outer portions of the rib sides to the final desired form to be used in grinding a workpiece and the radially inward rib portions to a form similar to but of a greater transverse dimension than that finally desired, and then crushing away the excess inward rib material to complete the rib form to the configuration to be used in grinding the workpiece.

4. A method for forming a ribbed grinding wheel to a substantially V-shaped rib profile comprising the steps of first diamond dressing to cut the grinding wheel to form sides of the rib tips to the final desired configuration to be used in grinding a workpiece and the sides of the inward rib portions to a form similar to but of a greater transverse dimension than that finally desired; and then removing the excess inward rib material by means of a crushing operation to form the inward rib portions to the final desired form to be used in grinding the workpiece.

5. A method for forming a ribbed grinding wheel having the characteristic that it can be crush formed, to provide the peripheral portions of the wheel with a substantially V-shaped rib profile, comprising the steps of first diamond dressing to cut the grinding wheel to form the radially outer portions of the rib sides to the final desired configuration to be used in grinding a workpiece and the radially inner rib sides parallel to the outer rib sides but with a step therebetween, the inner rib poitions having a form similar to but of a greater transverse dimension than that finally desired, and then crushing away the excess inner rib material Without changing the form of the diamond dressed tip to complete the rib profile to that to be used in grinding the workpiece.

6. A method for forming a ribbed grinding wheel to a substantially V-shaped rib profile comprising the steps of first diamond dressing to cut the ribs to a V-shaped profile having an included angle between the sides of each rib greater than that finally desired, and then finally forming the ribs to the configuration to be used in grinding a workpiece by means of a crushing operation.

7. A method for forming a ribbed grinding wheel comprising the steps of first forming the grinding wheel by means of a cutting or shearing operation and then further forming the radially inward rib surfaces by means of a crushing operation while the crusher roll and grinding Wheel are free for relative axial floating movement, relatively positioning the crusher roll and grinding wheel by engagement between the crusher roll and the previously cut or sheared rib surfaces.

8. A ribbed grinding wheel, the rib root portions of the grinding area to be used in grinding a workpiece having minute voids between the root surface particles such as are produced by a crush dressing operation, and the rib tip portions of the grinding area to be used in grinding the workpiece having cut surfaces characterized by comparatively few voids between the tip particles, such as are produced by a diamond dressing operation.

9. A ribbed grinding wheel, the rib root portions of the grinding area to be used in grinding a workpiece having sharp edged surface particles and minute voids therebetween, such as produced bya crush dressing operation; and the rib tips of the area to be used in grinding the workpiece having numerous surface particles having cut surfaces in the plane of the grinding wheel surface and being characterized by comparatively few voids between the surface particles, such as produced by dressing by a cutting operation.

10. A method for forming a ribbed grinding wheel having the characteristic that it can be crush formed, to provide the peripheral portions of the wheel with a substantially V-shaped rib profile, comprising forming the radially outer sides of a rib to the final desired form to be used in grinding a workpiece by a cutting or shearing operation, and forming the radially inner rib sides to the final desired form to be used in grinding the workpiece by a crushing operation.

11. A method for forming a ribbed grinding wheel having the characteristic that it can be crush. formed, to provide the peripheral portions of the wheel with a substantially V-shaped rib profile, comprising forming the sides of the rib tip to the final desired size and configuration and the sides of the inward rib portion to a form similar to but of a greater transverse dimension than that finally desired, the sides of the rib tip being cut to the final form to be used in grinding a workpiece by diamond dressing; and crushing away the excess material along the inward rib portion to form the inward rib sides to the final desired size and configuration to be used in grinding the workpiece.

References Cited in the file of this patent UNITED STATES PATENTS 2,112,679 Rickenmann Mar. 29, 1938 2,482,784 LOhtltkO Sept. 27, 1949 2,482,785 Lohutko Sept. 27, 1949 2,555,852 Hawley June 5, 1951