Machine key structure

BACKGROUND OF THE INVENTION

There is a basic theoretical and practical fault in the standard commercial straight-sided, square-seated, rec- 35 tangular key, square type or flat, straight or tapered. Such a key, however well fitted, is not tight enough, and is not uniformly pressured on the lateral surfaces where it must carry the load. Therefore, it soon works loose under heavy reversing loads. This deficiency has been well recognized, 40 even in public records, for many decades. The language, viewpoints and proposed remedies of the commentators vary, but the essence of the cited difficulty is the same. It is set forth in U.S. Patent No. 408,835 to Grafton, issued Aug. 13, 1889; in the patent to De Bechtolsheim, French 45 Patent No. 357,967, of Jan. 22, 1906; in U.S. Patent No. 867,468 to Von Bechtolsheim, issued Oct. 1, 1907; and in “Handbook for Machine Designers and Draftsmen” by F. A. Halsey. Quoting from this manual (1st ed., 1913, p. 47, “Keys and Keyways”): 50 “The common driven key . . . is a poorly designed thing at best; and under heavy duty, especially when the stresses alternate in direction, . . . (it is) the source of much trouble. They seldom fail by shearing, but frequently fail from deformation due to the turning over tendency of 55 the forces to which they are subjected. Calculations of dimensions based on shearing stress are, therefore, largely futile.”

In the standard tapered rectangular key, and in the straight key also, if fitted to bear at top and bottom as 60 recommended by some handbooks, there are three independent pairings of six elemental contact or pressure areas of the key: (1) the radial, i.e. between the floors of the two keyseats, with the pressure being certain and heavy in the case of the driven or tapered key; (2) between the 65 two walls of the shaft keyseat, with the pressure being light, incomplete, and uncertain; (3) between the two walls of the hub keyseat, which is also light, incomplete, and uncertain. Moreover, there is no communication of pressure among the three pairs of areas, nor between any two 70 of them. Thus the vertical or wedging pressure may be very great and the lateral pressures in the hub and shaft keyseats very light, or one of these may be heavy and the other have wide clearance, but without either affecting the other or affecting the vertical pressure in any degree.

_ Practical considerations which add to the above-men_g tioned problems, inherent in the case of the rectangular key, are: that the key seat walls are of only rough to ordinary finish by reason of the cutting actions of the tools commercially usable, preventing continuous and durable fitted contact unless heavily pressured; that the spacing IO of the parallel walls is set by a cutter dimension which is subject to some gradual reduction by abrasion and redressing; that the wall spacing may have further variation according to the dull or sharp condition of the cutting edges; that the keyseats in shaft and hub are cut by two different tools which have slight casual variation from each other both in cutting width and finish produced; and that a single key, which is itself subject to variations in dimensions must be fitted in the opposed keyways. Under these circumstances, only very imperfect results are obtainable, and then often only after laborious hand labor.

With square and flat keys, both tapered and straight, some actual relative motion of the key and the keyed members occurs from the start, usually with the first sharp direct reversal of loading. This results from lack of ade25 quate pressure of the major working surfaces. With that initial motion, deformation and wear inevitably occur. Therefore, the motion can only increase. The lateral contact gaps can never be compensated nor the play eliminated; it can only progress until the accumulated damage renders the key unusable. For want of preloading, the standard rectangular key is destroyed by a key duty which is well within the actual shear capacity of the key.

The machine key structure of this invention distinguishes patentably over the key structures disclosed by the Grafton and Von Bechtolsheim patents mentioned above. In Grafton, the hexagonal key is longitudinally tapered on all six sides and thus has the shape of the lower part of a regular hexahedral pyramid. Because of its configuration, such a key cannot possibly fit a shaft keyway of uniform depth. It might be contended that, in the light of the Von Bechtolsheim patent referred to above, which does show a key having a lower non-pressure face lying in a plane parallel to the bottom of a keyway of uniform depth, it would be dbvious to modify Grafton in accordance with Von Bechtolsheim and thereby produce a machine key system which is anticipatory of the present invention. Such a contention entirely overlooks, however, another crucial distinction between the key of this invention and the prior art. Thus, according to the present invention, the hub key and keyway surfaces are not all tapered as in Grafton but are instead longitudinally parallel while, at the same time, being inclined longitudinally in a direction parallel to the median plane of the key. And, although Von Bechtolsheim may disclose longitudinal inclination of the key hub faces, that reference does not show that the key hub pressure faces are planar, and, as will be shown hereinafter, a true wedging of the key in the keyway is impossible when the hub pressure faces on both key and keyway comprised curved surfaces as in Von Bechtolsheim.

SUMMARY OF THE INVENTION

The machine key structure of the present invention is designed to remedy the above-described deficiency. Basically, the machine key structure of this invention employs a key which is of generally hexagonal cross-section. The shaft and hub keyways are designed to provide a clearance over the entire length of the key between its top and bottom surfaces and the corresponding keyway surfaces. The remaining key surfaces are, in general, pressure surfaces all of which are planar. The shaft keyway pressure faces are longitudinally parallel as are also the corresponding

3,428,343 ³ key pressure faces, and the shaft keyway is of uniform depth and width over its entire length. The hub keyway pressure faces are also longitudinally parallel, but they, together with the associated non-pressure surface, are longitudinally inclined to provide a keyway of varying depth over its length. The corresponding key pressure faces and associated non-pressure surface are similarly inclined.

Deformation and wear of the key and the keyway faces are avoided or greatly reduced by pre-stressing the working faces which carry the combined loadings, the primary, two-way, tangential power load and the lighter, secondary, radial pressure for gripping the hub against casual axial displacement, in the basically hexagonal key of my invention, equalization or proration of all initial working face pressures is inherent in the principle. Installation requires no selective adaptation or surface reductions for fit. The driving of the key compensates and adjusts automatically for the flattening of any surface irregularities and/or depth-and-width deviations in the key itself and in either or both keyseats. Any loss of pressure which may result from gradual accommodation of surfaces in operation is fully compensatable by drive-tightening of the key.

The initial normal force on each of the four working faces may be considered as the combination or resultant of two elemental forces, a radial and a tangential, the latter having the same direction and point (or area) of application as the active power force exerted in the operation of the machine. Of these initial component forces, each is balanced against a corresponding force on another face, the radial forces opposing each other, the tangential likewise. There are four pairings of forces, but they are not segregated or isolated in their oppositions; no increase or decrease of pressure can occur in one pair alone as all pressure change occurs simultaneously in all four.

The theory then of the construction herein shown and described is that a driving force imposed upon any given face, from either steady or impact torque and of a magnitude less than the initial pressure, will never entirely relieve the effective pressure of the corresponding, inactive face circumferentially opposite to the given power-loaded face; that, because of this residual pressure, both relative shift and rotative motion of the key (upon its own axis) are prevented; and that thus a rigid and simultaneous twoway fixity of the keyed members is obtained. The fixity is maintained up to, or nearly to, the shear-yield value of the key, thus preventing the destruction of the keyage by forces representing a minor fraction of its actual shear capacity and so meeting the weakness of standard keys as observed by Halsey.

The pre-loading does not in any degree reduce or limit the useful net power-transmitting capacity of the key as it does in certain dual keyages. The static or pre-load forces, being a balanced system, do not exert any shear upon the key, but only compression. It is only as the circumferentially balancing pressure is reduced at one side of the key that actual shear develops, and this can only come from relative displacement forces in the keyed members.

In the accompanying drawings, wherein reference letters are used to indicate parts generally and numerals particular points, lines, surfaces and areas, and wherein all key taper angles are exaggerated for clarity of exposition:

FIGURE 1 is a side elevation view of a headless machine key made in accordance with this invention and having triangular or transition areas at the sides, with adjacent portions of a shaft grooved for use of the key;

FIGURE 2 is an end view of the key in FIGURE 1, at the left-hand, larger end;

FIGURE 3 is an enlarged elevation of the key of FIGURE 1 viewed from the right-hand, smaller end, at 3—3 in FIGURE 1;

FIGURE 4 is a plan view of the key and shaft keyway of FIGURE 1;

FIGURE 5 is a side elevation of a headed key made in accordance with this invention but without triangular transition areas at the sides, such as are shown in FIGURE 1;

FIGURE 6 is a left-hand end view of the key of FIGURE 5;

FIGURE 7 is an enlarged view of the key of FIGURE 5 from the smaller, right-hand end;

FIGURE 8 is a top plan view of the key and shaft key way of FIGURE 5;

FIGURE 9 is a side elevation of a key made in accordance with this invention but of basically square cross section;

FIGURE 10 is an end view of the left-hand, larger end of the key of FIGURE 9;

FIGURE 11 is an enlarged end view at the right or smaller end of the key of FIGURE 9;

FIGURE 12 is a top plan view of the key and shaft key way of FIGURE 9;

FIGURE 13 is an elevational view of a crank arm provided with an alternative embodiment of the machine key structure of this invention;

FIGURE 14 is an end elevation of the parts shown in FIGURE 13;

FIGURE 15 is an enlarged elevation of the block key of FIGURES 13 and 14;

FIGURE 16 is a side elevational view of a key of the present invention illustrating in combination certain optional features, including a shim or liner for key positioning;

FIGURE 17 is a right-hand end view, enlarged, of the key and shim of FIGURE 16;

FIGURE 18 is a top plan view of the key and shim of FIGURE 16 with an outline of a portion of the keyway as formed by end milling;

FIGURE 19 diagrammatically illustrates the result obtainable with a key having curved pressure faces as in the prior art; and

FIGURE 20 diagrammatically illustrates the result obtainable with a key having planar pressure faces as in the present invention.

FIGURES 1-12, and 16-18, are illustrative of the use of the key of this invention in various adaptive combinations of features for holding machine members having cylindrical surfaces of contact. FIGURES 13, 14 and 15 illustrate an adaptation of the key for holding members having flat surfaces of contact.

In the embodiment of the invention shown in FIGURES 1—4 the key A has top and bottom surfaces 1 and 2, respectively. Surfaces 1 and 2 are planar, as shown, and top surface 1 slopes or converges toward bottom surface 2 at one end of the key. Upwardly convergent planar side faces 3 engage corresponding faces in the keyway of the hub C, and downwardly convergent planar side faces 4 engage the shaft B on sloping walls 6 as shown in FIGURE 4. Side triangular faces 5 are vertical, planar, and parallel, extending longitudinally of the key and are cleared slightly by the corresponding hub keyway surfaces 25 (FIGURE 3). The shaft and hub keyway floors 7 and 8, respectively, have substantial clearances from the top and bottom faces of the key, and thus only the four flank faces 3 and 4 of the key have contact in the keyways. Arc 9 (FIGURES 2 and 3) is the line of exterior shaft surface. The narrow flat shoulders or relief areas 10 formed at the sides of the shaft keyway lower the actual shaft keyway lip line from the normal position 24 (FIGURE 1) to the level of the shoulder. The transition face 5 of the key A is accordingly extended down to the level of the shoulder. This shouldering or relief area feature is optional and may be used also with the keys of FIGURES 5-8, 9-12, and 16-18. Its advantage is two-fold, first, strengthening the flank of the keyway lip and the wall itself, even beyond the basic strength improvement inherent in the key form, and second, the provision of a small, appropriately-shaped space for the accommodation of any lip swelling which may occur at very high loading of the key, thus avoiding or minimizing shaft lip impaction against the bore lip and consequent difficulty in disassembly due to shaft seizure in the hub.

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In the headed key D of FIGURES 5-8 the top and bottom surfaces 11 and 12, respectively, and also the upper and lower pairs of pressure faces 13 and 14, are all planar. Arc 21 indicates the exterior surface of shaft E, and F represents the hub. A gib or head piece G having _ga face 15 may be arc or resistance-welded to an extension of the key body to facilitate extraction in the manner usual with gib keys. In this key, which may be cut from regular hexagonal stock, the planes of the faces 13 directly intersect those of faces 14 along the lines 20. Each ₁₀line 20 slopes downwardly, as shown in FIGURE 5, with reference to shaft keyway lip line 17. The end or runout of the slope of the upper three faces 13, 11, 13 is shown at 23. The lower three faces 14, 12, 14 may be used as drawn, with no machining. The line 20 may be placed 15 entirely above lip line 17 or entirely below it; but, for the purpose of minimizing and dividing the voids, line 20 is here placed to cross 17 at the midlength 16 of the key body. This disposition produces, at each side of the key, two small voids 19—19 (FIGURE 7) in the hub keyway 20 at the larger end of the key, and 18—18 in the shaft key way at the smaller end.

In the key H of FIGURES 9-12, the upper pressure faces 28 converge at a right angle at the top 26 and, lower faces 29 similarly at the bottom 27. At the sides, 25 are elongated, triangular connective faces 30 modifying the generally square cross-section of the key. Faces 30 are planar and parallel. The shape, purpose, clearance and options as to location of these side faces with reference to the lip line 31 of shaft keyway 33 are generally 30 similar to the case of key A (FIGURES 1-4) and so need not be described again. Arc 32 (FIGURES 10 and 11) is the surface line of the shaft J, while K designates the hub. In the use of this form of key, it is recommended as a practical matter that the pressure faces should not be 35 extended to a literally sharp comer. Both strength of hub and maintenance of key and keyway cutting tools are greatly served by a small rounding or flat area at these points, with the key slightly clearing the keyway in order to ensure against a false bearing of the key in driving. 4.0

In the key of FIGURES 13-15 the body of the key L is essentially the same as that of FIGURE 1 except in relative length, and so need not be described again. Clearances are the same or proportional. The plane 41 of keyed contact of the crank arm S and block R, corresponding 45 to the curved surfaces of shafts in the other constructions, intersects at its edges the keyway pressure faces in crank arm S. Alternative key positions 36, 37, and 38 are shown which permit shifting of the block R and the pivot of reciprocating bar Q in the recess of the arm S and hence 50 in angular reference to the shaft P, thus relocating the swing or oscillating range of arm S and shaft P. A pocket 40 is formed incidentally in the floor of the recess in milling the wall key ways. An extension of the body of the key L shown at 43, passes through one of three holes 39 55 which are drilled in line with the keyways and carries compression spring M, which may be seated in a counterbore 42 at the back of the arm S. The nuts N, threaded on the end of key extension 43, are turned to set up a full and some reserve spring pressure and key tension, and 60 then locked. If, then, in the course of operation, the initial fit of the key L yields, due to seating or settling of faces, occasional severe overload, or spring of the members, the expansion force of the spring M pulls the key into tighter setting, preventing play from developing. This 65 adjustment occurs automatically during operation of the machine, without the attention and regardless of the inattention of the operator.

In the construction of FIGURES 16, 17, 18, which combines lateral transition areas (as in FIGURE 1) with 70 the direct lateral intersection of pressure faces (as in FIGURE 5), T designates a key having top and bottom surfaces 50 and 51, respectively, mounted in a shaft U and bolstered in true position by a shim V, partially broken away at the forward end. The shimming may be either in tegral or laminated. The thickness of the single-face shim here shown is here exaggerated for distinctness. The upper and lower pairs of pressure faces 52 and 53 are joined, through a rearward portion of their length, by lateral transition area 54 (FIGURE 16) of which sloping line 55 is the upper edge and 65 the lower, the latter located at the level of the shaft keyway lip line. Broken line 56 is for reference and is located at the end point of area 54. Line 57, extending from 56 to the end of the key is the direct intersection of faces 52 and 53. It is not aligned with either 55 or 65 and, as may be seen in FIGURE 18, recedes slightly from the plane of area 54. Point 58 (FIGURE 17), represents the intersection of arc 63, the line of shaft surface, with face 52 at the forward extremity of the key. Small triangular space 59 is a void resulting from the descent line 57 below the level of the lip line. This void tapers backward along the key to a point at line 56. Broken lines 61 are extensions of the lower flank faces of the key, which may intersect as far down as point 60, the axis of shaft U. The wall of the shaft keyway is shown at 62. Broken line 64 is for reference, to indicate an intermediate length of key.

This construction illustrates four things: a method of correlating the draft in this general key type with the practical object of a keyage system having a relatively great range of key lengths; a lesser proportionate basic height of key than that shown in the preceding figures; a dispostion of lower flank faces approximately radially to the shaft; and the use of shimming.

FIGURES 19 and 20 illustrate diagrammatically highly significant difference between a key having hub having curved pressure faces as in FIGURE 19 and one having planar pressure faces as in FIGURE 20. Curved pressure faces are disclosed, for example, in the Von Bechtolsheim patent referred to above, whereas planar pressure faces in as FIGURE 20 are in accordance with the teachings of the present invention.

In FIGURE 19, the key having the curved pressure faces 7ft and 71 and the planar top non-pressure faces 72 is shown as being fitted within the shaft keyway 73. The clearance between the pressure faces 7ft and 71 of the key and the corresponding keyway pressure faces 74 and 75 has been greatly exaggerated for purposes of illustration. In FIGURE 20, the key has planar pressure faces 76 and 77 and also a planar non-pressure face 78. The respectively opposed hub keyway pressure faces are designated as 79 and 80, respectively. Here again the clearance between opposed pressure faces has been illustrated in an exaggerated manner for clarity.

In each case, i.e. in both FIGURES 19 and 20, the driving of the key into the keyway results in forces being exerted between the key and keyway hub pressure faces in a direction normal to the contacting surfaces of the hub and shaft at the medium plane of the key. Referring first to FIGURE 20, it can readily be seen that the driving of the key into the key way results in a uniform pressure over the respective pairs of pressure faces which comes about because of the equal distances between the opposed pressure faces in the effective direction of movement of the key. In other words, the distances d_u d₂, d_s, and are all equal so that driving the key into the keyway results in uniform contact between opposed pressure faces over their entire surface. In contrast to this, in FIGURE 19, it can readily be seen that the limit of movement of the key relative to the keyway is determined by the distances d_s and since when these are reduced to zero, the key will be in tight contact with the keyway. At such time, however, the pressure faces of the key will not be in uniform contact with the hub keyway pressure faces since the distances d. and d_s are substantially greater than the distances d_s and d^, and thus a gap will remain adjacent each lip of the key of FIGURE 19. Because of this, it is impossible to secure a true wedging action of a key when, as in FIGURE 19, it is provided with pressure faces which are not planar.

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I desire it to be understood that I may practice the invention with such variations of construction as may fall within the scope of the appended claims. Examples of such variations which I consider to be within the spirit of the invention are: extension of the key more deeply into one machine member than into the other, in order to reduce relatively the unit pressure in the one member which may be made of softer material than the other; use of different angles of convergence of working faces than those here shown, so varying the relative magnitudes of the radial and circumferential components of the forces on the working faces of the key; and other variations of width to height of key, of the tape or wedge angle, and of the form of key head.