US3778936A

US3778936A - Mounted abrasive point

Info

Publication number: US3778936A
Application number: US00252618A
Authority: US
Inventors: W Steadman
Original assignee: Norton Co
Current assignee: Saint Gobain Abrasives Inc
Priority date: 1972-05-12
Filing date: 1972-05-12
Publication date: 1973-12-18
Anticipated expiration: 1990-12-18
Also published as: CA987112A

Abstract

A relatively small diameter mounted abrasive point or grinding wheel with a supporting drive spindle of increased strength provided without increasing the hole size or reducing the amount of usable abrasive in the abrasive wheel. The spindle has a wheel mounting end portion, including a knurled portion and a shorter adjoining plain cylindrical portion of equal diameter and greater strength embedded in the abrasive point rigidly supported by and fixedly secured thereto. An inner side of the abasive point is positioned in a plane which passes through the adjoining plain cylindrical portion of greater strength. Initially the knurled portion is preformed to cylindrical shape with a diameter equal to its pitch diameter and thereafter the metal is displaced by knurling to the diameter of the adjoining cylindrical portion.

Description

United States Patent [1 1 Steadman [451 Dec. 18, 1973 MOUNTED ABRASIVE POINT Wilfred A. Steadman, Holden, Mass.

[73] Assignee: Norton Company, Worcester, Mass.

[22] Filed: May 12, 1972 [21] Appl. No.: 252,618

[75] Inventor:

2,771,719 11/1956 Fuglie ..51/168 Primary Examiner-Donald G. Kelly Attorney-Walter Fred et a1.

[ 5 7 ABSTRACT A relatively small diameter mounted abrasive point or grinding wheel with a supporting drive spindle of increased strength provided without increasing the hole size or reducing the amount of usable abrasive in the abrasive wheel. The spindle has a wheel mounting end portion, including a knurled portion and a shorter adjoining plain cylindrical portion of equal diameter and greater strength embedded in the abrasive point rigidly supported by and fixedly secured thereto. An inner side of the abasive point is positioned in a plane which passes through the adjoining plain cylindrical portion of greater strength. lnitially the knurled portion is preformed to cylindrical shape with a diameter equal to its pitch diameter and thereafter the metal is displaced by knurling to the diameter of the adjoining cylindrical portion.-

5 Claims, 4 Drawing Figures PATENTEDDEE 18 I975 3.778.936

PRIOR ART PDN MOUNTED ABRASIVE POINT BACKGROUND OF THE INVENTION l. Field of the invention The invention relates to mounted abrasive points or wheels and particularly to an improved relatively small supporting drive spindle therefor.

2. Description of the Prior Art it is conventional practice to knurl or roughen the end portion of a relatively small supporting spindle and then fixedly bond an abrasive point or wheel of the desired size, shape and grade thereon. However, in the past the knurled portion of the spindle was of greater diameter than the adjoining cylindrical portion which may extend from either a small end ofa tapered portion or shoulder of the spindle. Hence, the adjoining cylindrical portion, sometimes called the neck portion, was no stronger than the knurled portion which was the same diameter prior to being knurled. Knurling or roughing of the spindle by pressing rollers against the spindle is not strictly a cutting action but a means of displacing the metal below the surface to a point above the original surface. As a result, the surface is formed into a plurality of valleys and peaks and has a pitch diameter substantially equal to the adjoining neck portion. it has been determined that relatively small spindles fail most frequently in a plane of weakness located diametrically of the spindle at the inner side or end of the wheel from which the spindle projects or tapers to a shank of larger diameter adapted to fit the driving means. During use the relatively small spindles are subjected to rapidly reversing bending stress which increases with the applied grinding pressure. The problem of increasing strength is further complicated by the fact that the drive shank ofthe spindle must be of a diameter to fit a drive collet or chuck or a specific size or capacity and the initial diameter of the spindle is further reduced to accommodate a small abrasive point of a specific shape and size that can enter into relatively small holes and crevices.

. I rapr sat t s wn i F G. antt of th drawings labeled "Prior Art an example of the construction of a conventional prior art spindle, discussed above, before and after knurling.

In FIG. 1 there is disclosed an unfinished or unknurled relatively small drive spindle or arbor having at one end a cylindricaldijve portion or shank 12 of a diameter A adapted to fit into and be held by a drive coupling, chuck or adapter on, for example, a conventional high speed ,air or electric motor driven portable grinder or machine spindle.

Adias m the shank i a tape ed p n 41 of length T extending to a small end thereof at the junction of a partly finished preformed cylindrical portion 16 extending therefrom to the opposite end of the fiirfiT'ThJhd56mm; [6 has a length E substantially equal to the axial depth of the hole in the mounted abrasive point to be mounted thereon and a diameter PD substantially equal to the pitch diameter of the knurl that is to be formed thereon.

The same preformed drive spindle 10 is shown in FIG. 2 after a knurling operation has been preformed on and transformed the cylindrical end portion 16 to an abrasive point mounting or supporting end portion 18 comprising a serrated or knurled end portion or surface 20 and an adjoining shorter plane cylindrical portion 22'. Character E designates the total axial 2 length of the mounting portion 18' of which'the greater p is the a t sstmt iqa 20 ?fas ia s stfisa d. length C and the shorter adjoining cylindrical portion of length D and diameter N equal to PD of FIG. 1.

A preformed abrasive wheel or point 30' with a central mounting hole 32 of cylindrical shape therein is mounted on and bonded in a conventional manner to the mounting portion 18 inserted therein to a maximum depth substantially equal to the length E of the mounting portion 18' and with the inner end or side 34 of the abrasive point 20 positioned in a plane PW passing through the plain cylindricaljportion 22 substantially at the small end or diameter of the tapered portion 14 of the spindle 10.

- It has been discovered that knurling tends to set up and produce stresses in the knurled portion 20' which then becomes slightly weaker than the adjoining plain portion 22' of substantially the same cross sectional area but of smaller diameter. However, after the rigid abrasive point 30 is firmly bonded to the mounting portion 18 it reinforces both the knurled portion and the adjoining cylindrical portion 22 and the weakestlt is also known to increase strength 6r these spindles a slight amount by swaging or rolling them to form instead of turning them with a cutting tool which tends to leave more pronounced lines of weakness. Swaging or rolling simultaneously displaces the work hardens the metal thereby increasing the strength of the spindle made thereby.

In US. Pat. No. 1,625,463, issued Apr. 19, 1927 Gouthier discloses a spindle wherein the mounting end portion is fluted or corrugated in the manner shown wherein the diameter of the fluted portion is of the same diameter as the adjoining portion. However, unlike the applicants knurl the flutes are produced by cutting shots which extend axially beyond the inner side of the mounted wheel and do not provide any resistance against axial displacement of the wheel relative to the spindle. Further the hole is fluted and the wheel does not extend axially beyond the flutes and therefore, the inner side thereof is not located in a plane passing through portion of greater cross sectional area and strength as does the applicants abrasive wheel.

Other spindles with tapered knurled attaching por- SUMMARY OF THE INVENTION A mounted abrasive point or wheel with greater resistance to failure comprises a relatively small spindle.

having a supporting end portion onto which an abrasive point is fixed. On the supporting end portion is a knurled portion of substantially uniform diameter and of shorter axial length than the supporting end portion embedded in the abrasive wheel and a relatively short plain cylindrical portion or neck adjoining the knurled portion of substantially the same diameter as but of greater strength and cross sectional area than the relati'vely longer knurled portion. The abrasive point is preferably a conventional preformed bonded abrasive structure made of the desired abrasive and bonding materials, to the desired size, shape and grade with a cen- BRIEF DESCRlPTlON OF THE DRAWINGS FIG. 1 is an enlarged view showing the configuration of the preformed mounting end portion of a prior art spindle, before knurling or roughing thereof;

FIG. 2 is an enlarged view of the prior art spindle of FIG. I after the preformed mounting end portion has been knurled or roughened and an abrasive point or wheel mounted thereon;

FIG. 3 is an enlarged view showing the configuration of the drive spindle of the instant invention prior to knurling or roughing the preformed mounting end portion thereof; and

FIG. 4 is an enlarged view of the drive spindle of the instant invention after the mounting end portion has been knurled and an abrasive point or grinding wheel bonded'thereto.

DESCRIPTION OF THE PREFERRED EMBODlMENT(S) Referring to the drawings, there is shown in FIG. 3 and FIG. 4 a spindle 10, similar in size and shape to the prior art spindle 10' shown in FIG. 1 and FIG. 2, but made according to the instant invention before and after knurling and with a conventional preformed abrasive point ofidentical size and shape as that mounted on the prior art spindle 10 shown in H68. 1 and 2. The prior art FIG. 1 and H6. 2, provided for comparison purposes, are deemed to be necessary for a clearer understanding of the invention and the features thereof which distinguish it from the prior art. In the interest of clarity basic characters followed by primes, for example l, identify portions of the prior art spindle which are similar to portions of the spindle 10 of the invention identified by the same basic character unprimed. Also, both the prior art spindle l0 and the applicant spindle 10 is shown to be a size to fit the same drive means and to receive identical abrasive points thereon.

The invention concerns itself primarily with mounted abrasive points with relatively small drive spindles havingdrive shank portions it of an inch or less in diame- 'ter.

By example only the instant invention comprises a mounted abrasive point assembly with a spindle l0 therefor of increased strength. Referring to FIG. 3 there is shown a relatively small preformed unfinished and unknurled or unroughened abrasive point drive spindle, mandrel, or arbor 10. The drive spindle has preferably a finished preformed shank 12 of predetermined length, size and shape adapted to fit and be held by the drive coupling, chuck or adapter on a conventional high speed drive means such as an air or electric motor driven grinder. However, the end of the shank 12 could be squared off, flatened off or of any other configuration necessary to adapt it to the drive means. Adjacent the shank 12 is a finished tapered portion 14 of length T, extending to a small end thereof at the junction of a finished short plain cylindrical portion 22 adjoining a relatively longer unfinished cylindrical preformed end portion 16 of smaller diameter extending to the opposite end of the spindle 10. The preformed portion 16 has a length C and a diameter PD equal substantially to the pitch diameter of the knurl to be formed thereon and the plain finished portion 22 has a length D and a cross sectional dimension or diameter N substantially equal to the maximum cross sectional dimension or outside diameter of the knurled surface to be formed on the portion 16.

The finished spindle 10 is shown in FIG. 4 after portion 16 has been knurled thereby providing the drive spindle 10 with an abrasive wheel mounting or supporting end portion 18 which includes a knurled surface'or a knurled end portion 20 of diameter B and the adjoining plain cylindrical portion 22 of a diameter N and relatively shorter axial length. Length E is the sum of C and D and the maximum axial length of the mounting portion 18, and both dimension B of the knurled portion 20 and dimension N of the adjoining plain cylindrical portion 22 are of substantially the same diameter. Mounted on and bonded to the mounting portion 18 in the conventional manner, such as disclosed in U.S. Pat. No. 3,184,797 issued to Eves on May 25, 1965 and hereby incorporated by reference for details not disclosed herein, isa mounted abrasive point or grinding wheel 30 with a central cylindrical hole 32. The hole 32 has a diameter slightly larger than diameter B and axial length substantially equal to E of the mounting portion 18 inserted therein. However, the axial depth of the hole 32 can vary but is of sufficient axial depth, greater than axial length C of the knurled portion 20, so that the inner end surface or side 24 of the mounted abrasive point 30 will lie in a plane passing throughthe adjoining plain portion 22 of greater strength than the knurled portion 20. Preferably the inner side 34 is situated in a plane PW which lies either substantially at or close to the small end of the tapered portion and at least 1/32 beyond the end of the knurled portion 20.

By close inspection, it can be seen that the roughened or knurled portion 20 comprises a knurled surface with a plurality of alternating valleysand peaks of substantially uniform depth or height situated in rows that extend circumferentially around and axially along the mounting portion 18, thereby preventing relative movement between the spindle and the abrasive point bonded thereto with a cured binder or cement 36, such as, a thermosetting resin or an epoxy resin. The cementing material contains preferably a powdered phenolic resin with a pulverized flint'filler and a large proportion of an accelerator placed in the hole of the abrasive point prior to insertion of the spindle therein.

Hence a mounted abrasive point and spindle made according to the invention is obviously stronger than a similar one made according to the prior art and therefore will not fail as readily at the point of greatest stress. The increased cross sectional area and diameter of the plain adjoining portion 22 also causes a corresponding increase in the diameter and cross sectional area of the small end of the tapered portion 14, thereby increasing the amount of material in and strength of the tapered portion as'well.

Instead of having a tapered portion 14 the spindle may have as shown by phantom lines in FIG. 4, a cylindrical drive shank 12a of same diameter B as the portion 22, or a cylindrical drive shank 12c of a diameter either greater than the diameter B of shank 12c or of the same diameter A of the spindle turned spindle extending to a shoulder abutting the inner side 34 of the abrasive point 30.

The drive spindle, arbor or mandrel may be pre formed out of any suitable material, but preferably by either turning or swaging it out of a bar or rod of a metal selected from a group including stainless steel, carbon steel, and cold rolled steel with a tensile strength of at least 100,000 pounds per square inch.

The greatest strength is obtained by swaging the spindle to form because swaging displaces and work hardens the metal instead of cutting it away as is done either by turning or grinding it to form. However, the cost of a swaged spindle is considerably more than either a turned or ground spindle and it has been discovered by a series of tests that a turnedspindle made according to this invention is at least as strong as a similar swaged spindle of the same metal made in the manner taught by the prior art.

In most instances the strength was increased as shown by the following strength test data which was compiled after torque testing similar mounted points having swaged spindles of the prior art design and turned spindles made according to the instant invention. The torque tests were made by using a 10 lb. Chatillon spring scale with each division or graduation thereon representing two ounces of force applied, through a lever arm of identical length fixed to each abrasivepoint of identical grade, size and bond while the shank of each spindle was rigidly clamped in a vice.

pered spindles made of either 410 or 4 l 6 stainless steel of the same tensile strength of 102,000 p.s.i. with each of the various portions shown in the drawing corresponding to the dimension indicated in the table. Five spindles of each type were tested and the average number of foot pounds of torque applied at the time the spindle failed is as shown in the table.

By comparing the data, for the spindles having a drive shank with a dimension A of A of an inch in diameter, it can be seen that increasing the diameter N of the adjoining cylindrical portion 22 about 10 percent streiigth by about 3 percent from il.34 to 3f4s foot lbs-.

Of greater significance is that spindles with dimension l A of A; of an inch in diameter increasing diameter N about 18 percent from .05 8/057 t0 .068/.067 increased the torque strength by about 16 percent from .337 to .392 foot lbs. WW Additional tests have been performed on mounted points to compare the increase in strength between identical swaged and turned prior art spindles made according to the dimensions for the prior art spindle shown in the table wherein dimension A of the drive shank is A of an inch. Applying the force with a 6 inch lever arm the turned spindles failed at an average of 2.6 foot lbs. of torque while the swaged spindles failed at an average of 3.3 foot lbs. of torque.

Mathematically comparing turned spindles only, increasing the diameter N .013 of an inch from .125 to .138 of an inch increases the cross sectional area from .0123 to .0149 ofa square inch by the amount of .0022

of a square inch or approximately 19 percent and inherently the calculated torque strength by about /3. Similarly increasing the diameter N .010 of an inch from'.058 to .068 of an inch increases the cross sectional area from .0026 to .0035 ofa square.inch,'by the amount of .0009 of a square inch or approximately 34 TORQUE STRENGTH TEST Ft. lbs. of torque at failure Dimensions of spindle in inches Knurl Lever Average Type of spindle A B C D E L N PD '1 pitch length ft. lbs

Swaged prior art $6 068/. 065 916 $52 /23 1 352 058/. 057 058/. 057 361 4 337 Turned invention $6 068/. 065 340 $62 Zg 1 068/. 067 058/. 057 3GP 4" 392 swaged prior art 5/ 138/. 135 %2 3a: 1% 125/. 124 .125/.124 3GP 6" 3. 34

Turned invention 54 138/. 135 $62 as 1% $4 361 6 3.

The swaged spindles were made out of 410 stainless steel which has substantially the same tensile strength but not the machinability as does the 416 stainless steel from which the turned spindles of the invention were made. Comparable spindles have also been preformed out ofAlSl-l lLl7 cold finished, rolled, or drawn steel and thereafter nickel plated to prevent oxidation or rust forming thereon. The nickel plated spindles were bonded to identical abrasive points which upon being tested in the same manner gave substantially the same results as shown in the above table for those turned out of 416 stainless steel. Thus non-stainless AlS1-llLl7 cold finished steel available from Republic Steel Corp. with a tensile strength, of about 102,000 p.s.i., equivalent to 416 stainless steel, can be substituted for the relatively higher priced 416 stainless steel. The cost of each spindle made ofAlSl-l lLl7, including the nickel plating, was found to be less than one made of 416 stainless steel.

The strength test was performed on a plurality of tapercent and the calculated torque strength by about Thus swaging increased the strength by almost 25 percent. Hence it is obvious that a similar spindle of the instant invention can be further strengthened by at least 20 percent by swaging it to form rather than turning. However, the individual cost of a swaged spindle is considerably more than that of an identical spindle. Therefore, a mounted abrasive point with a swaged spindle could be provided only for the most critical applications, for example mounted points with exceptionally small diameter spindles with a drive shank dimension A of less than A; of an inch and in applications where the safety factor must be increased because the applied grinding force is greater than that at which a turned spindle would fail.

While knurling as illustrated herein is the most practical, it is to be understood that the mounting portion 18 may be serrated in any other suitable fashion so long as the serrated mounting end portion includes an adjoining portion 22 of the same maximum cross sectional size or diameter as the serrated, roughened or knurled portion but of greater cross sectional area and strength. The invention is also applicable to mounted points other than those which as disclosed, are first preformed and then cemented onto the mounting portion, but includes those made in any suitable manner such as by molding a conventional mixture, including at least abrasives particles, and bonding material, to the desired size and shape about the mounting portion of the spindle so that the inner side of the abrasive point lies in a plane passing through the plain adjoining portion 22 where the maximum shear strength is desired.

Further, the invention is also applicable to spindles which are known conventionally in the art as straight, shouldered, or the tapered spindles and is descriptive of the drive shank portion, that projects from the inner side of the abrasive point.

it is to be understood that the disclosure hereinabove is for the purpose of illustration only and that the invention includes all modification and equivalents which fall within the scope of the appended claims.

What is claimed is:

1. A mounted abrasive point comprising: a preformed spindle including a drive shank portion of predetermined shape, size and length extending axially from one end of the spindle, a mounting end portion of predetermined length extending axially from an opposite end of the spindle inwardly toward the drive shank portion, and having a serrated portion with a substantially uniform maximum cross sectional dimension extending axially a predetermined distance from the opposite end, a plain portion, adjoining the serrated portion, having a uniform cross sectional shape with a maximum cross sectional dimension substantially equal to the maximum cross sectional dimension of the serrated portion, a greater'cross sectional area than the serrated portion, and greater strength than the serrated portion; and a rigid bonded abrasive point of predetermined size, shape and grade rigidly fixed about and bonded to ..r -m st s..v r ieni and avi an inner side situated in a plane passing through the plain portion of the mounting portion of greater strength whereby the mounted point has improved strength, more resistance to breakage and a higher factor of safety during use.

2. A mounted abrasive point according to claim 1 wherein the plain portion has a cylindrical shape of predetermined diameter and the serrated portion has a knurled surface with a plurality of valleys and peaks formed by knurling and displacing material of a preformed cylindrical portion of smaller diameter to a maximum diameter substantially equal to the diameter of the plain cylindrical portion.

3. A mounted abrasive point according to claim 2 wherein the abrasive point comprises:

a preformed abrasive structure bonded, with bonding material, to the mounting portion and having an inner side, a cylindrical hole therein with an entrance at the inner side of a diameter slightly larger than the diameter of the plain cylindrical portion and an axial depth measured from the inner'side greater than the axial length of the serrated portion, whereby inserting the mounting portion into the abrasive point, the full axial depth of the hole, and curing the bonding material places the inner side of the abrasive point in a plane passing through the plain cylindrical portion of greater strength.

4. A mounted abrasive point according to claim 3 wherein the preformed spindle further comprises:

a tapered portion of predetermined axial length extending from a large diameter adjoining the drive shank portion to a relatively smaller diameter ad- 5. A mounted abrasive point according to claim wherein the drive shank portion is no greater than onequarter of an inch in diameter, and the plain cylindrical portion has a diameter less than one-quarter ofan inch, andan axial length less than the serrated portion but no less than 1/32 of an inch.

Claims

1. A mounted abrasive point comprising: a preformed spindle including a drive shank portion of predetermined shape, size and length extending axially from one end of the spindle, a mounting end portion of predetermined length extending axially from an opposite end of the spindle inwardly toward the drive shank portion, and having a serrated portion with a substantially uniform maximum cross sectional dimension extending axially a predetermined distance from the opposite end, a plain portion, adjoining the serrated portion, having a uniform cross sectional shape with a maximum cross sectional dimension substantially equal to the maximum cross sectional dimension of the serrated portion, a greater cross sectional area than the serrated portion, and greater strength than the serrated portion; and a rigid bonded abrasive point of predetermined size, shape and grade rigidly fixed about and bonded to the mounting portion, and having an inner side situated in a plane passing through the plain portion of the mounting portion of greater strength whereby the mounted point has improved strength, more resistance to breakage and a higher factor of safety during use.

3. A mounted abrasive point according to claim 2 wherein the abrasive point comprises: a preformed abrasive structure bonded, with bonding material, to the mounting portion and having an inner side, a cylindrical hole therein with an entrance at the inner side of a diameter slightly larger than the diameter of the plain cylindrical portion and an axial depth measured from the inner side greater than the axial length of the serrated portion, whereby inserting the mounting portion into the abrasive point, the full axial depth of the hole, and curing the bonding material places the inner side of the abrasive point in a plane passing through the plain cylindrical portion of greater strength.

4. A mounted abrasive point according to claim 3 wherein the preformed spindle further comprises: a tapered portion of predetermined axial length extending from a large diameter adjoining the drive shank portion to a relatively smaller diameter adjoining the plain cylindrical portion of the mounting portion; and the preformed spindle is made of a metal selected from a group consisting of stainless steel and carbon steel having a tensile strength of at least 100,000 pounds per square inch.

5. A mounted abrasive point according to claim 4 wherein the drive shank portion is no greater than one-quarter of an inch in diameter, and the plain cylindrical portion has a diameter less than one-quarter of an inch, and an axial length less than the serrated portion but no less than 1/32 of an inch.