US2989354A - Bushings - Google Patents

Description

June 20, 1961 H. H. MERRIMAN BUSHINGS Filed Nov. 25, 1952 IN V EN TOR.

/Z BY Mevrnmm um-widow United States Patent C 2,989,354 BUSHINGS HenryH. Merriman, 751 W. WashingtonAve,

Jackson, Mich. Filed Nov. 25,- 1952, Ser. No. 3223477" 2 Claims. (Cl. 308;-237):

The presentinvention relates toimprovements in bush ings of the type disclosed in my co-pending application Serial No. 200,855, filed December 14, 1950, now abandoned.

Bushings of the conventional design which are press fitted into position require a very accurately reamed hole into which the bushing is inserted plus the necessity of holding the outside diameter of the; bushing slightly oversize with respect to the inside diameter of the. hole and the oversize of the bushing must be held to close limitations. This practice will often resultin the fracture of the material in which the hole is reamed, especially in the case of fragile material such as cast iron. Also,,the conventional type of press-fitted bushing will collapse sufliciently to require grinding or reaming after insertion where close tolerances upon the hole size of the bushing must be maintained.

Whereas it was one of the purposes of the invention described in the aforesaid application to provide bushings which could be fabricated from standard bar stock without a shaving operation upon the outer diameter of the stock, the present invention is concerned with high precision bushings which may be inexpensively manufactured and inserted without any appreciable collapse of the bushing hole or danger of fracture of the material in which the bushing is inserted.

I have found that in the employment of bushings as disclosed in the aforesaid application which may be described as self-broaching or stacking, variations of standard stock size, inadequate provision for chip disposal resulting from the broaching operation and the amount of dilferential in size between the reamed hole and the outer diameter of the broaching surface of the bushing all contribute to the amount of collapse of the bushing at the time of insertion.

According to the present invention, in the manufacture of my improved bushing of the type described, I preferably perform a shaving operation upon the outside of the bushing stock to reduce the diameter of the bushing along its inserted length to slightly less than the diameter of the reamed hole into which the bushing is to be inserted. The knurling operation is then performed upon the bushing stock to provide the longitudinal broaching ribs or splines upon the surface thereof. This knurling operation 7 will increase the diameter of the bushing stock or blank to something greater than that of the reamed hole. Thereafter, the bushing stock or blank is ground, preferably in steps of varying diameter, to accurately provide the desired broaching operation within the reamed hole at the time the bushing is inserted. By regulating the shaving, knurling and grinding operations, I am able to provide proper chip disposal in a multi-step broaching operation which results in the manufacture of precision bushings characterized by their substantial freedom from hole collapse and insertion fracture.

Thus, the principal object of the invention is to provide an improved bushing of the type described having stepped diameters with provision for chip clearance and chip accumulation all of which reduce collapse of the bushing to a minimum yet provide adequate self-staking characteristics.

Other objects and advantages of the present invention residing in the construction, arrangement and combination of parts will more fully appear from the following specification and the appended claims.

In the drawings,

1 isan elevational view of a, bushing involving the present invention.

FIG; 2 is;an,enl arged fragmentary cross-sectional view taken on line; I;L-II, of FIG. 1, and

FIGS, 3. and 4 are views similar tov FIG. 1 of other forms of bushings, embodying the present invention.

Referring to FIGS. 1 and 2, the; metallic bushing 10 is preferably fabricated from bar stock, in. automatic screw machines. iqholdconcentricity in size a shaving opera.- tion ofthe entire bushing blank is v first performed upon that portionofthe, bar stock located in the machining position. For example, if the bushing is to be inserted in a. .750 reamed hole the blank.- would be accurately shaved to .750," which would be the approximate outside diameter of the pilot portion 12gof the finished bushing. Following the shaving; operation and prior to cut-01f, the annular chippedgrooves 14 are provided and. the stepped broaching portions 16 and 18 are knurled to form the longitudinal teeth or splines 20; the'broaching operation increasing the diameter of the shaved bushing blank across the splines 20 in the order of .003 to .005" with the diameter of the blank across the recess 22 being slightlg less than the original shaved diameter. In practice, the blank will be drilled and reamed in the bar and following cut off the bushing blank is centerless ground to accurately provide the desired differential in diameter between the pilot 12 and the portions 16 and 18. In the example given above, the portion 16 would preferably be ground to the order of .7515" and the step 18 to the order of .753".

It is to be understood that the diiferential in diameter of the stepping broaching portions of the bushing Will vary depending upon the size of the bushing and the tolerances of the reamed holes in which the bushings are to be inserted. Where minimum collapse of the bushing hole is of principal concern, the diiferential in diameter of the portions 16 and 18 in the example given above should be in the order of .001". By increasing the fineness of the knurl any tendency to collapse the bushing hole is reduced. Also, by having the recesses 22 of greater cross-sectional area than the splines 20 and the diameter across the recesses 22 of less diameter than the reamed hole in which the bushing is to be inserted, the forces tending to collapse the bushing hole are held to a minimum.

The pilot 12 performs two important functions by holding its diameter to that of the reamed hole into which it is inserted, or slightly less, and providing it with adequate longitudinal extent, the pilot 12 will accurately align the bushing with the reamed hole and thus prevent the tendency to cock the bushing experienced in conventional designs. It also provides a retaining wall for the chips resulting from the broaching operation of the splines 20 by the portion 16 whereby a wedging accumulation of chips is provided by the pilot 12 and the wall of the reamed hole for assisting in the self-staking of the bushing 10 in the hole of its insertion.

In FIG. 3, the bushing 10" is shown with stepped knurled portions 24, 26 and 28 separated by chipped clearance grooves 14'. By way of example, if the bushing 10' is to be inserted as a drilled bushing into a .750" reamed hole, the pilot 12' should have a diameter of .749", the portion 24 a diameter of .751", the portion 26 a diameter of .752" and the portion 28 a diameter of .753". In the machine operation of the bushing 10, the blanks below the flange 30 could all be shaved to the diameter of the pilot 12', namely, to .749" and then following knurling and cut off the diameter of the portions 24, 26 and 28 across the splines 20' ceiiter ground to the diameter given by way of example.

A modification is shown in FIG. 4 inv which the bushing 10" is provided with a helical chip groove 14". With this arrangement, the number of individual spline lengths making up the surface of the bushing may be conveniently varied by altering the pitch of the helix. By center grinding the diameter of the knurled portion of the bushing 10" above the pilot 12 may be provided in one or more steps.

Having thus described my invention what I claim is novel and desire to protect by Letters Patent is:

l. A self-staking bushing comprising at one end a leading pilot portion of a diameter approximating the hole in which the bushing is to be inserted, a hole broaching portion adjacent said pilot portion and having an external surface defined by longitudinal splines separated by longitudinal recesses with the leading ends of said splines defining cutting teeth adjacent said pilot portion, said broaching portion constituting the major portion of the longitudinal length of the bushing, an annular chip groove of lesser diameter than said pilot portion and disposed between said pilot and broaching portion adjacent the cutting teeth defined by the leading ends of said splines, and a helical groove defined in the surface of said broaching portion.

2. A self-staking bushing comprising at one end a leading pilot portion of a diameter approximating the hole in which the bushing is to be inserted, a hole broaching portion adjacent said pilot portion and having an external surface defined by longitudinal splines separated by longitudinal recesses with the leading ends of said splines defining cutting teeth adjacent said pilot portion, said broaching portion constituting the major portion of the longitudinal length of the bushing, an annular chip groove of lesser diameter than said pilot portion and disposed between said pilot and broaching portion adjacent the cutting teeth defined by the leading ends of said splines, said broaching portion being in the form of a series of cylindrical-like surfaces of slightly increasing diameter.

References Cited in the file of this patent UNITED STATES PATENTS 1,686,468 Rosenberg Oct. 2, 1928 2,320,787 Mentley June 1, 1943 2,372,485 Grifiin Mar. 27, 1945 2,376,406 Weingart May 22, 1945 2,392,172 Markstrum Jan. 1, 1946 2,436,325 Penny Feb. 17, 1948 2,685,320 Rosan Aug. 3, 1954

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