US2347280A - Diamond dressing tool and method of determining diamond sizes therefor - Google Patents

Description

April 25, 1944.

ABBASIVE GRAIN SIZE (NUMBER or HESHES PER INCH F SCREEN THROUGH WHICH GRAINS PASS) A omnouo SIZE m cAraATs E 27- 0 102.03 114.05.06. 71899 J JZJ .1415 J6 J1 J8 19,215,? 11.25 .25

A B E F I ZT'LVE'TZZEF Jo /v Z. PETE/E.

IA d Patented Apr. 25, 1944 DIAMOND DRESSING TOOL AND METHOD OF DETERMINING DIAMOND SIZES THERE- FOR . I John L. Petrle, Detroit, Mich, assig'nor to Wheel Trueing Tool Company of Delaware, Detroit, Micln, a corporation of Delaware Application .jluly 12, 1941, Serial No. 402,054

1 Claim.

This invention relates to diamond tools for dressing abrasive wheels wherein the. size of the diamonds in the tools is. selected in accordance with the-characteristics of the abrasive wheel to be dressed. l

More specifically this invention relatesto diamond wheel dressing tools having the diamonds thereof especially selected for carrying out'most.

effectively the dressing of specific types orgroups of abrasive wheels for which the tools are intended.

In my copending application Serial No. 349,513,

entitled: "Diamond dressing tool and method of dressing grinding wheels,. filed August 2, 1940, now U. S. Patent No. 2,254,392, issued September 2, 1941, there is described and claimed diamond dressing tools having small diamondsranging from one-quarter carat down to 0.0L carat, or down to a small size so as to be just largeenough not to pass through a 200-mesh screem These dressing tools have the diamonds thereof arranged in a single plane. The single" plane of diamonds is preferably composed of a plurality of tiers havingthe diamonds thereof in over lapping relation. For example, one tier of dia-v monds can contain three or four'diamonds, while the next tier. can contain two or three diamonds. In this manner the diamonds are staggered and, as the same become worn, a newdiamond will come into operation before theworn diamonds are completely spent.

I have. found that these small diamondto'ols are especially.,adapted for use in truei'ng that class of precision grinding abrasive wheels whose grain sizes are 30 mesh or finer 'but'not appreciably finer than 120 mesh. That is, the grains of such wheels are sized so that they will pass through screens nct 'coars'er' than 30 frnesh' per "linear inch, nor finer than 120 mesh per linear {inch} Coarsegrain wheels below size 30 grain I not'need to betrued with accuracy, since they K enerally u ed for snagging or roughing op .eratiQ lS there precisio n,,.grin ding finish is not .requiged xQn'the other hand, fine grain wheels .ofraboye 120 'sizegrain require dressing tools with diamonds. large fenough to resist abrasionbut, 1f

the; diamonds are too large in relation to the #fin e. grain, they will tend to crush the grains and I .ifclose up 'or fglaze. the wheel. Tohave good grinding characteristics the wheel must be open fsharpi. 1 t o According to l the present lIiVBIllFlOIl, diamond slfor-suchjsmall ,diamon'd tools are posit vely l with the characteristics of abrasive wheels controlled in accordance l of the abrasive wheel or group having grain sizes not appreciably coarser than size 30 nor finer than size 120. The efliciency ofthe diamondtools is greatly enhanced since each tool is specifically designed or engineered for a particular job and, if the characteristics of the abrasive wheel are known, this invention now furnishes the correct dressing tool for the Wheel.

Therefore, the diamond tools of this invention not only utilize small diamonds in place of the heretofore-required large diamonds but, in addition, the small diamonds in the tools are so selected as to most effectively perform on particular types of abrasive wheels. I

The characteristics of the abrasive wheels controlling the sizes of the diamonds includes the following:

(1) Grain size of abrasive grit.

(2) Hardness of wheel (holding power of bond).

v (3) Nature and hardness of grit.

wheel dressing tools should increase in direct proportion to the grain size of the abrasive wheel grit. I have found that the size or diameter of the Wheel itself is not controlling.

I have further found that the hardness of the abrasive wheel is also an important factorin determining optimum diamond sizes since the bond grade or grit holding. power, to a great extent, determines the wear on the diamond itself. The hardness of the wheel is determined by the grade-of the bonding material and the amount of bond as compared with the amount of grains. In any given type of bonding material such as'a vitrified bond; for example, the wheel is "harder as the amount of bond relative to the amount of grain increases. Thus the more bond, the greater the holding power for the grits. In the harder grinding wheels, while the abrasive grits are not necessarily harder, there is more bonding agent holding the grits together and it is therefore necessary in the successively greater bonded abrasive wheels to use successively larger diamands,

much as it is necessary to increase the size of the the grain or grit in each wheel.

bide grit wheel requires a dressing, tool with larger diamonds than those necessary in a tool for dressing an aluminum oxide grit wheel even therefore cause increased heating of the diamonds. The aluminum oxide grits throw off the heat generated on cutting. Therefore the diamonds must be larger as the heat retention properties and hardness of the grits increases so as to be able to resist the increased heat.

It is, then, an object of this invention to selectively size diamonds in wheel dressing tools in accordance with characteristics of abrasive wheels to be dressed thereby.

A further object of the invention is to provide diamond dressing tools with small sized diamonds selected to perform best on certain types of abrasive wheels.

A further object of this invention is to provide diamond dressing tools which are engineered for the particular jobs which they are to perform.

A specific object of this invention is to provide diamond dressing tools having a plurality of small diamonds arranged in tiers in a single plane, so that they will line up one behind the other in substantially the same cutting track when acting on an abrasive wheel and wherein the size of the small diamonds is carefully selected in accordance with the characteristics of the abrasive wheels to be dressed thereby.

Another specific object of the invention is to selectively control the sizes of diamonds in diamond dressing tools in accordance with the grain size, grain hardness and bond characteristics of the abrasive wheel to be dressed by the tools.

A further specific object of this invention is to provide wheel dressing diamond tools with diamonds less than one-quarter carat and selectively sized in direct relation to the grain size of A the abrasive wheels to be dressed thereby.

tional view of a. diamond dressing tool embodying my invention with parts brok n away and in section to show the positioning of the diamonds.

Figure 3 is a top plan elevational view of the diamond dressing tool.

Figure 4 is a fragmentary sectional view taken substantially along the line IVIV of Figure 3.

Figure 5 is a chart showingthe relationship between the diamond sizes and grain sizes of abrasive wheels to be dressed by the tools of this invention.

As shown on the drawing:

In Figure 1 the reference numeral Ill designates generally a mounting for a grinding wheel II. A tool holder l2 serves to-hold a dressing tool l3 of this invention in dressing relationship to the surface of the grinding wheel. A set screw ll fixedly secures the tool l3 in the holder.

the particular form and shape of the tool is not critical.

The metal of the tool end l5. comprises a ma trix in which are embedded a plurality of diamonds i9 which, according to the invention, are arranged in one or more tiers with the diamonds in each tier in substantial alignment. Three such tiers A, B and C are illustrated with the diamonds of the tiers in overlapping relation so that. as

. the diamonds in one tier become worn, the diamonds in the next successive tier come into cutting or dressing position. The diamonds preferably have' their long axes parallel to the axis X-X of the tool end l5, as shown in Figure 2.

While it is not essential that the number of diamonds in the successive tiers be as shown, via, 3, 2 and 3, this arrangement gives very desirable results, but the advantages of this arrangement can be realized also by employing a 43-4 combination as well as other combinations, such as 2-2-2; 3-3-3; and 4-4-4. All of the diamonds lie in substantially a single plane and the tool is set in the holder 12 so that rather than a crushing action on the grains of the abrasive wheel. As a result the surface of the abrasive wheel is freer and more open with less fine grit packed in between the grains.

The middle diamond indicated by the reference numeral IOM in Figures 2 and 3 is, as shown in Figure l, positioned so that it lies on a radius line The tool i3 is preferably provided with an 03- 76 RL passing through the axis of the grinding wheel mounting Iii.

According to previous standards it had been thought necessary in the dressing of grinding wheels that the size of the diamond should bear some fixed relation to the diameter and width of face of the wheels to be trued. For example with a wheel of six inches and under in diameter a half-carat diamond was generally considered necessary while with wheels as large as thirtysix and forty-two inches in diameter, it was considered necessary to use a diamond of six or eight carats respectively. Likewise, larger diamonds were considered necessary for dressing wheels with wide grinding faces than for wheels with narrower grinding faces.

I have now found that the diamond dressing tools of this invention can utilize small diamonds varying from a size just large enough to be retained on a 200-meshscreen up to one-quarter carat; The diamonds should preferably weigh between 0.01 and .25 carat, but the optimum weight of the diamond is controlled bythe type of abrasive wheel on which the tool is to be used.

I- have found that there is a definite relationship between optimum diamond size and the abrasive grain size of the abrasive wheel. Abrasive grains or grits are designated by numbers corresponding to the number of meshes per lineal inch of the screens through which they are graded. Thus a 36-grain wheel constitutes an abrasive wheel having abrasive grains or grits embedded therein which pass through a screen having 36 meshes per linear inch. The grains are graded, however, so that they will not pass through the next size smaller screen.

I have also found that the hardness of the abrasive wheels as determined by the bond grade must be considered'when determining the optimum diamond size for the dressing tool. For example vitrified bonded wheels are usually classified as soft, medium and hard, depending upon the amount of bond in the wheel as compared with the amount of grain or grit in the wheel. The same size abrasive grain in a hard vitrified Wheel will require larger diamonds in the dressing tool than when the medium or soft vitrified wheel is used. The vitrified bond usually consists of a clay mixture subjected to sufficiently high temperature to fuse to a molten glass condition.

The hardness of the particular abrasive grain or grit likewise has some efiect upon proper selection of diamond sizes. For example, aluminum oxide-grains r grits are quite tough but are not as hard as silicon carbide grits. The silicon carbide grits, being harder and retaining more heat than the aluminum oxide grits, require larger The aluminum oxide hard abrasive wheels best acted on by the dressing tools of this invention .have grain sizes varying from 30 to 60 and, as shown in curve C, the diamond size should be 5 within the range of .155 to .10 carat and decrease in direct proportion to the decrease in grain size.

The curves D, E and F relate to silicon carbide abrasive grains in soft, medium, and hard vitri fied bonded wheels respectively. The silicon car 1 bide soft wheels best trued by the tools of this invention have grain sizes varying from 60 to 120 and should be dressed with tools having the diamond sizes varying from .04 to .03 carat. The silicon carbide medium hard abrasive wheels best trued by the tools of this invention have grain varying from 36 to 60 should have the diamond size of the dressing tool vary from .1975 to .16.

The curves A, B, C, D, E and F were plotted from actual data obtained as a result of comprehensive tests summarized in the following sized diamonds than the aluminum oxide grits. chart:

Abrasive grain size Diamond carat sizes:

Aluminum oxide soft wheels (curve A) 05 .045 .04 .0375 .035 .03 .0225 Aluminum oxide medium wheels (curve B) 075 07 .065 .06 055 .05 .04 03 Aluminum oxide hard wheels (curve C). 145 135 1175 ll .10 Silicon carbide soft wheels (curve D). Silicon carbide medium wheels (curve E) Silicon carbide hard wheels (curve F) It should be noted, however, that the hardness of the abrasive grain does not determine the hardness of the grinding wheel itself. The grinding whee1 may be made of very hard abrasive grits and still be considered a soft wheel if.

bond grade (amount of bond), type of grit, wheel 50 structure (relative grain spacing), and the like, all data necessary for selecting the proper dressing tool in accordance with this invention is available.

In Figure 5 the graph illustrates the relationship which I have discovered between correct diamond sizes for dressing tools and abrasive grain size, abrasive grain hardness and hardness of wheels to be dressed by the tools.

The curves marked A, B and C in the graph are plotted for aluminum oxide abrasive grit wheels in soft, medium, and hard vitrified bonded wheels respectively. The aluminum oxide soft wheels best acted on by the dressing tools of this invention have grain sizes varying from 36 to 70. As shown by curve A, the proper diamond sizes for the dressing operation should be within the range of .05 to .0225 carat and should decrease proportionally to. the decrease in grain size.

The aluminum oxide medium hard wheels best acted on by the dressing tools of this invention have grain sizes varying from 36 to 80 and, as shown by curve B, the diamond sizes should be within the range of .075 to .03 carat, and decrease directly with the decrease in grain size.

From the above descriptions it will be apparent that this invention now provides diamond tools with a plurality of diamonds setin a single plane 40 so as to line up one behind the other in substantially the same cutting track. The diamonds vary in size from .01 to .25 carat but are of uniform size in each tool. The sizes of the diamonds are selectively controlled in accordance with the nature of the abrasive wheel to be dressed by the tool. The size of the abrasive whee1 grains or grits, the hardness of the wheel as determined by the amount of bond in the wheel, and the hardness of the grits themselves control the size of the diamond. The diamond sizes increase in substantially direct proportion to the increase in the grain size; increase in grain hardness; and

increase in wheel hardness.

I claim as my invention:

The method of dressing abrasive grit grinding wheels of the class having abrasive grits of a size not appreciably coarser than size 30 nor finer than size 120 with a plurality of small diamonds which comprises determining the grit size of each wheel to be dressed, selecting substantially unifomily sized diamonds within a size range of .0225 to 0.1975 carat in accordance with the grit size" of the wheel to be dressed to provide the smaller diamonds for the finer grit size wheels 65 .and the larger diamonds for the coarser grit size wheels and with the diamond sizes increasing in substantially direct proportion to the increase-in grit size, holding a plurality of the thus selected substantially uniformly sized diamonds against 7 the wheel of determined grit size for which the

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