US3022569A - Form-cutting tool - Google Patents

Description

Feb. 27, 1962 E. WILDHABER 3,022,569

FORM-CUTTING TOOL Filed April 27, 1956 4 Sheets-Sheet 1 G INVENTOR.

Feb. 27, 1962 E. WILDHABER 3,022,569

FORM-CUTTING TOOL Filed April 27, 1956 4 Sheets-Sheet 2 IN VEN TOR.

Feb. 27, 1962 E. WILDHABER 3,022,569

FORM-CUTTING TOOL Filed April 27, 1956 4 Sheets-Sheet 3 14 FIG. 23

\ INVENTOR.

Enmt' Feb. 27, 1962 E. WILDHABER FORM-CUTTING TOOL 4 Sheets-Sheet 4 Filed April 27, 1956 IN V EN TOR.

United States Patent 3,022,569 FORM-CUTTING TOGL Ernest Wildhaber, Brighton, N-.Y. (124 Summit Drive, Rochester 29, N.Y.) Filed Apr. 27, 1956, Ser. No. 581,088 13 Claims. (Cl. 29-102) The present invention relates to form-cutting tools for cutting teeth in gears, worms and other articles in a process of reciprocation.

Form-cutting tools differ from generating tools in that they do not require a rollingenerating motion, and in that they do not cut the tooth surfaces by envelopment with a large number of cuts. The shape to be produced is built directly into the form-cutting tool.

In applying the finishing cut a cutting edge of a formcutting tool sweeps an entire tooth side in a single pass. For roughing prior to finish-cutting a feed may be effected between the tool and Work piece depthwise of the teeth to be cut. Or the depthwise feed may be built into a tool that has a plurality of cutting teeth differing in the radial position of their end-cutting edges.

One object of the invention is to devise an improved tool having a plurality of cutting teeth that are sharpened by regrinding their cutting faces, and whose cutting faces remain at a constant distance from a common axis throughout the life of the tool.

A further aim is to devise an improved form-cutting tool having a plurality of cutting teeth spaced about an axis and disposed at an angle to the direction of said axis, for cutting without turning on said axis, the side surfaces and end surfaces of said cutting teeth extending at a constant distance from said axis, cutting clearance being obtained by the position of the tool.

Another object is to devise a reciprocatory form-cutting tool having a plurality of cutting teeth or blades spaced about an axis, in which the cutting teeth follow one another in a circle about said axis, and in which the side surfaces of all said teeth are different portions of a common surface of revolution, on each of the two sides of the cutting teeth.

A further aim is to adapt the last-named tool to longitudinally curved teeth of tapered gears, by inclining the center-line of the cutting teeth to a plane perpendicular to the tool axis.

Another aim is to devise a tool having helical cutting teeth of such design that they approximately match the twist at various radial distances of the tooth spaces to be cut, and a tool whose helical cutting teeth have the same hand as the teeth to be cut.

The invention is particularly important for form-cutting spiral teeth of bevel gears and of hypoid gears, where cutting clearances vary materially in the length of each stroke. It is a main object of the invention to solve this clearance problem.

Further objects are to devise novel tools for the process of cutting cylindrical gears described in my application Serial No. 510,468, filed May 23, 1955, now Patent No. 2,975,681 issued March 21, 1961, and for the processes of form-cutting tapered gears and other toothed articles described in my applications Serial No. 557,151, filed January 3, 1956, and Serial No. 573,034, filed March 21, 1956, now Patent No. 2,976,773 issued March 28, 1961.

Other objects will appear in the course of the specification and in the recital of the appended claims.

The objects may be attained singly or in any com bination.

In the drawings:

FIG. 1 is an end view taken along its axis of a reciprocatory form-cutting tool constructed according to the ice present invention. It is shown in cutting engagement with a nearly completed spur gear.

FIG. 2 is a side view corresponding to FIG. 1, looking upwardly in FIG. 1.

FIG. 3 is an end view similar to FIG. 1, showing a modified tool.

FIG. 4 is a diagram showing the superimposed cutting profiles of the difierent cutting teeth of the tool of FIG. 3.

FIG. 5 is a diagram similar to FIG. 4, showing a slightly modified embodiment.

FIG. 6 is an axial section of a cutting tool constructed according to a further modification.

PEG. 7 is a diagram showing the superimposed cutting profil s of the different cutting teeth of the tool of FIG. 6.

FIG. 8 and FIG. 9 are diagrams explanatory of a principle underlying the design of a helical cutting tool, in accordance with the present invention. FIG. 8 shows a helical gear in mesh with an unrelieved tool, in a view along the gear axis. FIG. 9 shows the same helical gear and tool in a view perpendicular to both axes; and it also shows the construction of the helix angles at various radii.

FiG. 10 is a side view and axial section of a cutting tool with helical cutting teeth, constructed according to my invention, and shown in engagement with a nearly finished gear also shown in FIG. 8 and FIG. 9.

FIG. 11 is an end view of the tool shown in FIG. 10, looking at the front of the tool along its axis.

PEG. 12 is an end view similar to FIG. 11, showing a tool whose cutting teeth have a progressively increasing height.

FIG. 13 is a diagram illustrative of one use of the tools of FIG. 11 and of those shown in FIG. 12.

FiG. 14 is a diagram referring to tapered gears and particularly to spiral bevel gears. It illustrates the problems and the principles used in applying the invention to this field.

FIGURES l5 and 16 are fragmentary cylindrical sections, developed into a plane, of a pair of tools for cutting opposite ides of spiral teeth.

FIGURES 17, 18 and 19 are enlarged views of simplifiecl tool profiles, showing the treatment of tool relief in cutting spiral teeth.

FIGURES 20 and 21 are diagrams referring to tapered gears and specifically to hypoid gears, showing in section a pair of cutting teeth for cutting opposite sides respectively of spiral teeth. The cutting teeth form part of tools constructed according to the present invention and contain spherical cutting faces.

FIG. 22 is an axial section of a tool, illustrating a further embodiment of my invention, and intended especially for use on the larger member of a pair of spiral bevel or hypoid gears.

FIG. 23 is an end view of the tool shown in FIG. 22, taken in the direction of arrow 23 of FIG. 22.

FIG. 24 is an end view of a tool similar to the one of FIG. 23, but having cutting teeth of progressively increasing height.

FIG. 25 is a fragmentary axial section of a machine for cutting spiral teeth on tapered pinions, with tools constructed according to the present invention.

Tool 30, shown in FIGURES 1 and 2, contains a plurality of cutting teeth 31 spaced about the tool axis 32. The tool 30 is a reciprocatory tool, and is shown in the middle of a cutting stroke, in engagement with a nearly completed spur gear 33. It does not turn during the cutting stroke, which is in the direction of the axis 34 of gear 33. The stroke may be performed either by the tool 30 or by the work piece 33.

Tool 30 contains side-cutting edges 35 which lie in and are part of the side surfaces of the teeth 36 to be produced. They are tooth profiles in a section taken along the cutting face 37 when the latter is in cutting position.

In the final finishing cut aside-cutting edge (35) completely describes and cuts a tooth side in a single pass.

The plurality of cutting teeth 31 of tool 30 serve to confine tool wear, and to keep the tool sharp for a long time. The tool 3%) is preferably indexed after every cut ting stroke, during the return stroke, while clear of the gear blank. The latter may also be indexed after every cutting stroke, if desired. The tool then has to completely clear the outside periphery of the work piece, as is readily understood.

Tool wear is caused chiefly by high temperatures occurring locally onthe cutting face adjacent the cutting edge. These temperatures can be kept down by changing cutting teeth and cutting faces with each stroke. In this way either a much longer tool life and cleaner cutting is attained, than when cutting with a single blade, or a higher cutting speed is feasible with a good cutter life, or a combination of both.

Reciprocatory tools with a plurality of cutting teeth following one another in a circle have been proposed before. However these were designed like a milling cutter, with radial relief. After sharpening, by regrinding the cutting faces, their cutting profiles are displaced towards the axis of the tool. Radial or depthwise tool adjustment is then required to set the cutting profiles to the original position. This in addition to a turning displacement about the tool axis.

Tool 30 needs no radial adjustment after sharpening. Also the configuration of its cutting teeth is simpler. The side surfaces 49, 40' of its cutting teeth 31 lie in a common surface of revolution, that has here a concave profile. That is, the side surfaces 40 (or 40') are different portions of a common surface of revolution coaxial with the tool axis 32.

The cutting teeth 31 cut one at a time, and are spaced apart an angle 'suflicient to avoid interference between the work piece and a cutting tooth other than the one in the cut.

At any point of the cutting edge, as for instance point 41 (FIG. 1), an angle 42 is included by its radial line (41-32) with the direction 43 perpendicular to the cutting stroke. This angle could be called the relief angle. Another angle 44 is included between radial line 45 with direction 43, where the outer end of line 45 has the same distance from the tool axis 32 as point 41, and lies on the rear end of the adjacent cutting tooth. Angle 44 should be substantially larger than angle 42, to avoid interference.

Tool 30 may be rigidly secured to its spindle by a toothed face coupling 46 of known construction. However other connections can also be used, if desired. For simplicity of illustration 1 have shown a keyway on many of the tools shown.

' Other tools with circular cutting teeth FIG. 3 shows a'tool 50 of similar design as tool 30. Its cutting teeth 51 are however not identical. They have a gradually increasing height, and their outside surfaces 53 have a gradually increasing distance from the tool axis 52. Cutting tooth 51' is the lowest and the first one to cut. Cutting tooth 51" is the highest, and cuts last. The superimposed cutting profiles of the several cutting teeth are best seen in FIG. 4.

Tool 50 is not indexed after every cutting stroke. It takes at leastone cut in every tooth space of the work piece, before it is indexed by one cutting tooth. The work piece may be indexed after every stroke.

The merit of this tool lies in the wide and simple chips it removes. It cuts practically only with the end-cutting edges, in the roughing operation. As there is essentially only one chip per stroke, the chips do not get into each others way. Except for a slight amount of stock left for finishing, the chips extend through the whole width of 4 the tooth space cut. This is the most efilcient way of removing stock.

Except for the different height of its cutting teeth, and a possible gap 54 left between the first and last cutting teeth 51' and 51", the structure of the tool or cutter 50 is identical with the structure of tool 30; Here also the side surfaces 55 of all the cutting teeth 51 are portions of a common surface of revolution, that is coaxial with the cutter axis.

Here also the cutting stroke is at right angles to the cutter axis or tool axis 52. V

In the slightly modified embodiment indicated in FIG. 5 the end-cutting edges and outside surfaces 53' of tool 56 are the same as the surfaces 53 shown in FIGURES 3 and 4, but the side edges 57 of the cutting teeth do not lie in a common surface of revolution. To avoid crowding the drawing, the edges 57 are shown only on one cutting tooth. They reach the profile to be cut attheir outer end portions, but recede from said profile further down on the cutting tooth.

Tools 56 and 56 can be used with or without depthwise feed motion. Feed motion is' used if each cutting tooth is to apply a plurality of cuts in each tooth space of the workpiece. The feed is then through the depthwise distance between the first and last cut of a cutting tooth. The feed thus repeats with each cutting tooth.

No feed motion is required when each cutting tooth is to apply only a single cut per tooth space. This occurs when the tool has a number of cutting teeth large enough to cut the whole depth of the teeth without feed. It also occurs when a plurality of tools are provided for simultaneous operation on a work piece, so that together they have enough cutting teeth to cut without depth feed.

A process of this kind is completely described in my aforesaid application Serial No. 510,468.

The tool 60 shown in FIGURES 6 and 7 is like tool 50 or tool 56, except for the radial position of the cutting teeth. Here the outside edges 61, that is the end-cutting edges, are all at a constant distance from the tool axis 62. Thus edge 61' and edge 61" (FIG. 6) have the same radial distance 63 from axis 62. The outside surfaces of the tool 60 contain the edges 61 and are parts of a common surface of revolution, of a common cylindrical surface coaxial with axis 62. Tool 60 is designed for use with a conventional depth feed, such as used also on tool 30 of FIG. 1. The depth feed is stepwise or continuous, and extends through the whole cutting depth.

7 Helical cutting teeth An important application of the invention is to form= cutting tools containing a plurality of helical cutting teeth, and to helical cutting teeth in general. Such tools differ from a tool shown in my application Serial No. 510,468 by the hand of the helical cutting teeth and by the position of the tool in the cutting machine. One purpose of this difference will now be described with FIGURES 8 and 9.

In FIG. 8 the helical gear 64 is shown in a fragmentary mid-section taken at right angles to its axis 65. Instead of a relieved tool an unrelieved helicalmember 66 with axis 67 is shown, as such an unrelieved member illustrates the problem more simply and more directly. Line 68 is radial to both axes 65 and 67, and intersects both axes at right angles. It is the shortest connecting line therof. Point 70 of line 68 lies midway in the tooth zone, and can be considered the pitch point in the mesh of gear 64 and member 66. At this point then the tooth direction is the same on gear 64 and on member 66.

Let us now consider another point 71 of line 68, at a larger distance from the gear axis 65. The tooth direction of gear 64 is the direction of the helix at the considered point 71. This helix has the same lead as the helix passing through pitch point 70 and a larger radius. Accordingly the helix angle is larger than at point 70.

A geometrical construction of the helix angle is indicated in FIG. 9. First the known helix angle at the pitch point 70 is plotted, that is the inclination of the teeth to the direction of the gear Line -72 is drawn inclined at the given helix angle at the pitch point. Then the pitch radius (65-70 in E16. 8) is spaced from 0 on a line 73 perpendicular to the gear axis 65 to obtain a point 70 thereon. A line 70-72 drawn through point 70 parallel to the gear axis intersects the inclined line 0-72 at point 72. It is well known that the trigonometric tangent or the helix angle is proportional to the radius of the nelix, at a given constant lead, The proportion of the distances 0-70 and 70'-72 is the trigonometric tangent of the helix angle at point 70, where 0-70 is equal to the pitch radius, the distance of pitch point 70 from axis 65. When 0-71 is equal to the radial distance of point 71 from axis 65, then the proportion of the distances 0-71 and "70-72 is the trigonometric tangent of the helix angle at point 71. Accordingly we locate the point 75 which has an axial distance 70-72 from point 71', and has the same radial distance from axis 65 as point 71'. In other words we plot the distance 70-71 on the vertical through point 72 to obtain point 75. 0-75 is then the sought helix direction at point 71.

The determination of the helix angle is analogous on the helical member 66, allowing for the dilferent direction of its axis 67, and keeping in mind that point 71 is at a smaller radial distance from axis 67 than pitch point 70.

The tooth direction at the pitch point is the same as on gear 64 and as defined by line 0-72 of FIG. 9. We now plot the pitch radius of member 66 from 0 on the radial line 76 of member 66, to obtain point 70". A line is drawn through point 70" parallel to the axis of member 66. It intersects line 0-72 at point 77.

The radial distance of point 71 from axis 67 is now plotted on line 76, to obtain point 71" thereon. A line is drawn through point 77 parallel to line 76, and distance 70-71 is plotted thereon from point 77. In this Way point 80 is obtained. 0-80 is the helix tangent and tooth direction at point 71 of the helical member 66. This direction practically coincides with the direction 0-75 of gear 64 in the instance illustrated.

With the dimensions assumed in the drawings the helical tooth surfaces of the gear 64 and of the member 66 are about equally warped, and warped in the same direction. The tooth directions are not only matched at the pitch point (70), but are also approximately matched at other points lying to one side or the other of the pitch point. p

This condition is retained essentially when relief is added. Cutting interference with the rear end of the cutting teeth is readily avoided therewith.

While the shown geometrical construction refers to a right angle arrangement of the axes 65 and 67, it is also applicable to other than right angles.

When expressed in mathematical terms, the following formula can be derived for best matching of the tooth directions in a wide range of radii:

sin 2(s-l- Ap) sin 28 Herein R and R, denote the pitch radii of the gear and member, that is the distances of pitch point 70 from 'axes 65 and 67 respectively.

s denotes the helix angle of the gear, at pitch point 70, that is the angle between line 0-72 and the direction of axis 65.

Ap denotes the departure of the shaft angle from a right angle, if it increases the lead angle of the helical member that represents an unrelieved tool. The lead angle is understood to be the complement of the helix angle of any one member, that is 90 deg. minus the helix angle. (s-l-Ap) is the lead angle of the helical member.

6. An for axes 65 and 67 at right angles, Ap=0, the above formula can be transformed into When one or the other of these two formulas is fulfilled, then the rate of change of the tooth direction is matched best on the two members. While at diilerent radial distances the tooth direction changes from the direction at the pitch radius, the rate of change is the same on both members.

Preferably the tool axis is kept at right angles to the direction of the axis of the work piece.

When the axes are parallel, the tooth direction changes oppositely on the work piece and member. The changes add to each other instead of subtracting. To subtract from each other an internal helical member would have to be used, when the axes are parallel. But complete matching of the rate of change of the tooth directions is then obtained only when the internal member is the direct counterpart of the helical gear.

The external helical member 66 with crossed axis 67 has approximately the same twist and balance of tooth directions as said internal counterpart, but difiers from it by getting clear of the gear teeth rapidly and increasingly with increasing distance from the line of engagement. This property is made good use of, especially in cutting spiral teeth on tapered gears, Where tool clearance is a major problem. This will be further described. Also an external tool is desired Whose cutting teeth are in selective engagement with the work piece, and which permits simultaneous use of a plurality of tools on a work piece.

Member 66 represents an unrelieved tool. Relief could be obtained by using a slightly tapered tool rather than a cylindrical member, and retaining the position of axis 67. The tool would then look somewhat like a helical gear-shaper cutter, except for the usually concave or straight form-cutting profiles and the larger distance of the cutting teeth.

Preferably relief is provided by changing the tool position and retaininga cylindrical tool with helical cutting teeth coaxial with the tool axis. This is indicated in FIG. 10. The axis 82 of tool 83 passes through the same point 84 of line 68 as axis 67 of member 66 (FIG. 8), but has a difierent direction.

The direction of the helical cutting teeth 85 and their lead can be described by their helix tangent at pitch point 70. Consider the projection of this helix tangent to a plane 86 tangent to the cylindrical pitch surface of gear 64 at 70. This projection should be identical with the helix tangent of gear 64 at its pitch point 70. This requirement permits to determine the lead of the helical cutting teeth 35. I When the axis 82 lies in a plane perpendicular to the gear axis 65, as shown, the lead angle s of the tool at point 70 can be shown to have the following mathematical relation to the helix angle s of the gear at point 70, and to the angle a between the tool axis 82 and plane 86:

Tan s=tan s/cos a An end view of tool 83 is aiiorded by FIG. 11. The end-cutting edge 87 lies in or is tangent to the tangent plane 88 of the tooth bottom of gear 64 (FIG. 10). Plane 88 is parallel to plane 86 and inclined to the tool axis 82. The end-cutting edge of tool 83 therefore is inclined to a cylindrical surface 00 coaxial with the tool axis 82. Also the helical surface 01 at the outer end of each cutting tooth 85 is inclined to said cylindrical surface. The profile of its axial section is at an angle to the straight-line element of the cylindrical surface 90 (FIG. 10). Similarly the profiles 92, 93 of the helical side surfaces of the cutting teeth 85 are unequally inclined to the radial direction 94 of tool 83.

The inclination of the side-cutting edges 87', 87" in the 7 end view of the tool, FIG. 11, depends on the inclination or front rake of the cutting face 95.

The tool 96 shown in FIG. 12 also contains helical cutting teeth (97) coaxial with the tool axis (98). These teeth have a gradually increasing height. Tool 96 bears the same relation to tool 33 as toolSd does to tool 30 (FIGURES l and 3).

FIG. 13 diagrammatically illustrates a way of using tools 99 on a helical gear blank 100. The tools are equally or unequally spaced about the axis of gear 100, depending on its tooth number. The tools 99 may be of the type of tool 83 or of tool 96.

Tools 83 are preferably indexed with each cutting stroke, during the return stroke, and depthwise feed is used towards the axis of the work piece. Tools 96 may each be indexed after a cutting tooth has taken one cut in every tooth space. A pair of opposite finish-cutting edges may be provided on one tool or split up on two tools, so that a single cutting edge applies the final cut on each'side of all teeth. The procedure may be the same as described for a difierent kind of tool in my application Serial No. 510,468.

Tools for cutting spiral teeth An important application are tools for cutting spiral teeth on bevel gears and hypoid gears. On bevel gears with intersecting axes conical pitch surfaces rigid with the two gears of a pair can be considered rolling on each other without sliding. The tooth surfaces extend along pitch lines, which are the intersection lines of the tooth side surfaces with the respective pitch surface. The pitch lines of a pair of gears are related to each other as if printed from one pitch surface to the other.

The preferred pitch lines are uniform-motion spirals. They can be described by moving a point at a uniform rate along the straight contact line of the pitch surfaces, while the pair of bevel gears turn uniformly on their axes at a ratio corresponding to their tooth numbers.

The so produced spirals are known as Archimedean spirals, when the conical pitch surfaces are developed into a plane. a

FIG. 14 shows one such pitch spiral 110 on the pitch surface 111. 112 is the line of contact of the pitch surfaces. It passes through the apex 113 where the gear axes intersect. The describing point is shown in a mean position 114. The normal 115 to pitch spiral 110 at this point 114 passes through a point 116 of straight line 117. Line 117 passes through apex 113 and is perpendicular to the path 112 of the describing point. It is a known property of the Archimedean spiral that its normal at any point of the radial path 112 passes through the same point 116. Thus when the describing point is at 114',

and the pitch spiral intersects line 112 at that point, the a normal 115' passes through the same point 116 as normal 115. Likewise the normal 115" at point 114" passes through point 116.

The tooth direction 124) at point 114' and 120" at point 114" is tangent to the pitch spiral. It is perpendicular to the respective normal 115' and 115", and changes along line 112.

A cutting tooth or blade 121 moved along line 112 in parallel relationship will therefore have a varying side clearance. The cutting teeth or blades used on spiral teeth have preferably one side-cutting edge only, a pair of tools, or several pairs, being provided for cutting opposite sides of the teeth.

Blade 121 has its side-cutting edge passing through point 114'. The blade is shown in the position of minimum clearance, which should be still sufficient for cutting with out drag. As it moves to the dotted position 121" at the opposite end, its side-clearance is increased over the minimum angle by the angle included between the two tangents 120' and 120", that is by the angle 114--116114" between the normals 115', 115". The cutting tooth or blade'122 for cutting the opposite side of the teeth has its minimum side' clearance .when its side-cutting edge passes through point 114". .The side clearance is increased by the angle 114116-114'T in the opposite end position 122' indicated in dotted lines.

This variation of side clearance during the cut makes it imperative to use tool clearance angles much larger than required for helical teeth They are kept within bounds according to the invention by providing tools whose relief angle increases towards the rear of the cutting teeth, and by providing a side-clearance component favoring the side-cutting edge of the respective tool of the pair. This side-clearance component is feasible because of the increase of the clearance angle towards the rear of the cutting tooth or blade.

A pair of tools 124, 125 are shown in development in FIGS. 15 and 16. These tools have helical cutting teeth 126, 127 respectively, all of whose surfaces are helical surfaces coaxial with the tool axis. The tools are like the tools 83 and 96 (FIGS. 11 and 12), except that their cutting teeth are intended to cut on one side or the other side only. The side-cutting edges of tool 124 pass through the points 130. Those of tool 125 pass through the points 130. The cutting faces 131 and 132 of the ,two tools are inclined to effect a keen side-cutting edge.- Each of the tools 124, 125 may be set up so that its axis projects as a dotted line 129 in FIG. 14, in the middle position of the cutting stroke.

FIGURES 17 to 19 further illustrate the clearance problem and the solution on tools for cutting spiral teeth on bevel and hypoid gears. For simplicity straight cutting edges are shown.

FIG. 17 shows in heavy lines a cutting tooth or blade that completely fills the tooth space of the work piece at its narrow or small end. This blade is shown for comparison and contains side-cutting edges 141, 142 and an end-cutting edge 143 extending between points 144, 145. The view is in the direction of the cut. Lighter lines 141, 142', 143' show the cutting edges of the blade as they appear after many sharpenings, assuming a constant relief all along the blade. The side-cutting edges 141, 142 are a given distance inwardly of the respective edges 141, 142, to provide the required cutting clearance at the edges 141, 142. The two side clearances also determine the clearance at the end-cutting edge 143, because endcutting edge 143' should have the same length as edge 143. Accordingly the two points 144, are projected to the side edges 141, 142 with parallel lines, to obtain points 144', 145' thereon, whereby line 143'=144145 is parallel to line 143. This results in a relatively large distance between the lines 143 and 143', indicative of a large clearance angle at the end-cutting edge 143.

Excessive clearance angles should be avoided as they shorten tool life. A cutting edge not sufiiciently backed up is apt to break down under repeated load.

FIG. 18 shows in heavy lines 142, 143, 151 the profile of a blade designed to cut with the edges 142, 143, but not with edge 151. The profile does not fill the tooth space completely. Edge 151 has a small distance from profile 141, which is shown in dotted lines and'is the same as in FIG. 17. Lighter lines 151', 143", 142 show the edges of the blade as they appear after many sharpenings, assuming a constant relief all along the blade. Edge 142' is in the same position as in FIG. 17. But edge 143" appears closer to edge 143 than edge 143' of FIG. 17, indicative of a decreased clearance angle at the end-cutting edge 143. This edge is now backed up better.

This showing is obtained by an oblique projection of the points 145, 154, to obtain the points 145", 154" of edge 143". In other words side clearance is added on the side of edge 142. The clearance added on this side is clearance subtracted on the opposite side. But as edge 151 is at a distance from profile 141, and as furthermore in accordance with the invention the relief or clearance increases rapidly towards the rear of the blade or cutting tooth, there is no interference with edge 151" at the 9 rear of the blade. The actual profile stands back further from profile 141 than profile 151 because of the rapid increase in clearance. In this way the relief angle or clearance angle at the end edge 143 can be kept within practical limits.

Diagrams FIGURES 20 and 21 refer to cutting opposite sides of spiral teeth and have two purposes. They specifically illustrate a procedure for hypoid gears. And they also illustrate a way of varying the tooth-profile curvature lengthwise of the teeth on tapered gears in general.

7 The preferred pitch surfaces on hypoid gears are hyperboloids of revolution, described in detail in my app'ication Serial No. 557,151. A portion of the pitch surface of the gear member is indicated at 156 in FIG. 20, and a pitch spiral at 157. Dotted lines 153 denote the pitch surface of the mating pinion.

These pitch surfaces of a gear pair contact each other along a straight line, and as they turn with their gears they roll and slide on each other. The pitch surfaces preferably used differ from the kinematic pitch hyperboloids, where sliding is in the direction of the straight line of contact (160) of the pitch surfaces. The pitch surface of the pinion is larger. When a larger pitch hyperboloid is used on the pinion, and a matching hyperboloid on the gear, the direction of relative sliding is inclined to the straight line of contact (160) of the pitch surfaces.

The drawing plane of FIGURES 20 and 21 contains the straight line of contact 160 of the pitch hyperboloids and the line of centers 161. This line intersects both axes of the gear pair at right angles. It intersects the projected pinion axis 162 at 163, and the projected gear axis 164 at 165. 166 is its intersection with contact element 169.

The inclination angles p and p of the pinion and gear axis to the plane of the drawing, and the distances E- 163'-166 and E=163165 are related to each other, as described in the last-named application. When the axes 162 and 164 of the gear pair are at right angles to each other, the relation is:

On hypoid gears the assumed shape of the pitch surfaces also determines the shape of the pitch lines. They are determined by the requirement that they extend in the direction of relative sliding at their intersection with contact element 160.

The pitch spirals are found to be uniform-motion spirals, that can be described on the uniformly rotating pitch hyperboloids by a point moving uniformly along the contact element 160. The rate of this motion can be determined from the known direction of relative sliding. At its intersection with element 169 the pitch spiral extends at right angles to a normal that lies in the drawing plane of FIGS. 20 and 21. Normal 175 at mean point 174 intersects the line of centers 161 at a point 176. All other normals at points of element 169 also pass through that point 176. Thus the normals 175', 175" at points 174', 174" respectively intersect there.

It is seen that this showing is analogous to the showing illustrated in FIG. 14 for spiral bevel gears with intersecting axes, except for the offset position of the contact element 169. The same form-cutting procedures can be used in both cases, that is on tapered gear pairs with offset and with intersecting axes. The same types of tools are applicable in both cases.

The cutting edges for cutting mating gears should have the same direction at their intersection with the contact element 160. along which they are moved while the respective gears turn on their axes in proportion thereto. They are however dilferently curved. The cutting edge used on one member is concavely curved. The cutting edge used on the mating member may be either concavely curved or straight. or in principle even convex. In all cases there is a difference in curvature of said two edges 10 when these are moved in parallel position along the contact element 160. I

Similarly the produced tooth profiles of plane sections perpendicular to the pitch spirals have different curvatures. They are curved relatively to each other. This difference or relative curvature should change lengthwise of the teeth, that is at difier'ent points of the contact element 160.

In accordance with a procedure described and claimed in my application Serial No. 557,151 the change of relative curvature is controlled with the position of the curvature plane of the cutting edge, at its point of intersection with the contact element. The curvature plane contains the cutting-edge tangent and is otherwise open to choice. To afford a wide enough selection of the positions of the curvature plane, without impractical cutting angles, cutting faces are used that are portions of spherical surfaces. Thus the cutting face of blade or cutting portion 181 is a convex spherical surface centered at 182. It has a radius 183. The cutting face 184 of blade or cutting portion 185 is a concave spherical surface centered at 186. It has a radius 187.

This control of the profile change applies to spiral teeth of tapered gears in general, of bevel gears with intersecting axes and of hypoid gears with offset axes.

The single blade shown in FIGS. 20 and 21 is the blade that is in the cut. It may be part of a tool having a plurality of cutting teeth spaced about an axis. These cutting teeth may be all alike, like those of FIG. 11 and of FIG. 23 to be described. Or the cutting teeth of a tool may have end-cutting edges of gradually changing width, like those of FIG. 12 and of FIG. 24.

On tapered pinions and gears the twist of the teeth depends to a large extent on the normal radius of the member rather than on its actual radius. This normal radius is measured on the pitch-surface normal. It is the distance between the mean point (174) and the intersection of said normal with the axis of the member.

On tapered pinions I preferably use cutters with helical cutting teeth. They may be designedfor operation With their axes at right angles to the axis of the work piece, or at other angles, but preferably with a hand of their helical cutting teeth equal to the hand of the teeth of the completed gear. Thus a right hand tool cuts a right hand gear or pinion, as also shown in FIG. 10, and a left hand tool cuts a left hand gear.

On relatively fiat tapered gears the twist of the teeth is small, and I may use a tool with circular cutting teeth, as will now be described with FIGURES 22 to 24.

Tool 290 contains circular arcuate cutting teeth 201 that extend at a constant distance from its axis 202. It is one of a pair of tools for cutting opposite sides of spiral teeth on tapered gears. Each cutting tooth 201 contains a side-cutting edge 203 and an end-cutting edge 264 formed thereon by a cutting face 212. The endcutting edge 204 joins the side-cutting edge 263 with an arcuate port'on 205, best seen in the enlargement at the right of FIG. 22. It has a chamfered portion 286 at the opposite side. The edge 207 of the cutting tooth 201 is not intended to cut.

Tool 200 has its cutting teeth 281 inclined to one side. It can be considered tapered. The purpose of this taper is to approximately match the curvature of the spiral pitch lnes of the teeth to be cut, that is the lengthwise curvature of these teeth. For best matching it should be so tapered that its ax's 2132 seems to pass through the mean curvature center 208 of the pitch spiral 157, in a view taken in the direction of the pitch-line tangent, see FIGS. 20 and 21. v

The other tool of the pair differs from tool 290 merely by the opposite position of the side-cutting edge, as shown at the left in FIG. 22. Its side-cutting edge 207' joins the end-cutting edge 204' with an arcuate portion 205' The chamfer 296' is at the opposite side of the end-cutting edge 204'.

Because of the similarity of the tools further description or illustratlon of said other tool of the pair is unnecessary.

The surfaces 210, 211 back of said cutting edges and of cutting face 212 are surfaces of revolution coaxial with the tool axis 202; The surface back of the endcutting edges204 follows a cylindrical surface 213 coaxial with axis 202, and is inclined to said cylindrical surface. The latter is indicated by its straight line element in FIG. 22.

The profiles 215, 216 of the side surfaces of each cutting tooth 201 are differently inclined to the tool axis 202. Straight or curved profiles may be used.

The tool 200 contains identical cutting teeth 201 equally spaced about the tool axis 202.

The tool 200' of FIG. 24 contains cutting teeth 201' of gradually increasing height. They have end cutting edges 204 of gradually changing width. The'r width decreases with increasing height of the cutting teeth.

The two tools of a pair are set up so that the dotted lines 202, 202" of FIGS. 20 and 21 are their projected axes respectively.

The cutting teeth of all the tools described are inclined to the direction of the tool axis, at an acute or at a r'ght angle. And they are convex lengthwise, as they extend outwardly of a circle or helix. All the tools are form-cutting tools, with a large enough spacing of their cutting teeth that each has only one cutting face in the cut at a time. Helical teeth of cutting tools are preferably spaced apart enough so that the normal distance of adjacent portions at the root is larger than the normal width of said cutting teeth at the r root.

Cutting tapered pinians Procedures and structure for cutting cylindrical gears and for cutting tapered gears have been described in the aforesaid applications, using different tools. These disclosures also suggest procedures and structure for the present tools.

A procedure and structure for cutt'ng tapered pinions in quantity will now be described with FIG. 25.

The pinion 300 specifically illustrated is a hypoid pinion. This requires moving each ,tool 301 along a line (302) offset from the axis 303 of the work piece 300 and d sposed at an angle thereto. Line 302 is the aforesaid contact element (160) or a line close to it. The diagrammatically indicated tool 301 is of the general type shown in FIG. 11 or FIG. 12, each tool cutting on one side only, as described with FIGS. and 16. And it may have the spherical cutting faces shown inFIGS. and 21. V

According to my invention the work piece 300is made to perform a helical reciprocation along itsaxis 303. In order to achieve a relative path 302 in space, the tool 301'also moves. It is mounted on a slide 304 and moves in a straight path. When the work piece moves up during the cut the slide 304 recedes in proportion thereto. In other words, the stroke along line 302 is resolved into a component parallel to the work axis 303, performed by the work piece, and into a component perpendicular to line 302 and lying in a plane parallel tothe work axis.

The tool 301 is preferably designed for arrangement with its axis 305 in a plane perpendicular to the.

Work axis. This axis is shown perpendicular to the drawing plane on tool 301. The path of slide 304 may or may not be parallel to the drawing plane. If the offset of path 302 from the pinion axis 303 is large enough to result in a cylindrical tool of sufiic'ent cutting clearance, then the motion of slide 304 and line 302 may both be parallel to the drawing plane. Otherwise said path and line 302 are inclined to the drawing plane when the too] axis is perpendicular thereto. Or else the tool axis is not perpendicular to the drawing plane when path 302 is parallel to said plane.

' The same tool slide 304 also performs the clapping motion, that is it keeps its tool clear of the work piece during the return stroke, and thus permits indexing the work piece. Tool slide 304 performs a depthwise mo: tion which during the cut is part of the cutting stroke and outside of the cutting engagement is used to get the tool clear of the work piece, to keep it clear during the return stroke, and to advance it aga'n to'cutting position just before cutting starts. Tool 301 follows a ta pered surface of the pinion blank in each cut. This tapered surface coincides with the'root surface of the pinion when full depth is reached.

A plurality of tools 301, 301' etc. are provided, each mounted on its own tool slide. No add tional depthwise feeding motion is needed when the several tools together have a number of cutting teeth at least equal to the num ber of cuts required in any one tooth space, tocut to full depth. The cutter slides then perform the same motion during all cutting cycles, and each tool is indexed by one tooth after a cutting tooth has taken a chip from every tooth space of the work piece. The means for indexing and locking a tool represent known art and are not shown in this figure.

The work piece 300 is secured to a chuck 310, that is in turn secured to. the work spindle 311. It is locked against turning by one or more pins 312, and is shown held axially by a bolt 313. The head 314 of said bolt seats against the end of sp ndle 311, and its opposite end engages a thread 315 provided on the work piece. Of course more elaborate forms of chucking may also be used.

Secured to spindle 311 are the end races of a thrust bearing 316 whose middle race 317 contains coaxial pivot portions 318, 318'. These project outwardly in a direction radial of the axis 303 of the work spindle. P'ece 317 is maintained angularly stationary by guide means not visible in this view. It is reciprocated axially of the work piece by means of a pair of cranks 320, 320' and connecting rods 319, 319'. The cranks are shown near the middle position of the stroke. They form part of a member 321 rotatably mounted in bearings 322,322 of stationary machine portion 323. An opening 324 is provided to permit admission and removal of bolt 313. The drive is through a dagrammatically indicated Wormgear 325 rigid with member 321. 7

As member 321 rotates, it reciprocates piece 317, and the work spindle 311 with it.

The work spindle contains a helical guide portion 326 rigidly secured to it and here shown integral with it. It is in engagement with a counterpart internal guide portion provided in the hub 327 of a Geneva wheel 328, that has as many slots 330 as there are teeth in the pinion 300. Wheel 328 is rotatably mounted in an axially fixed position in bearings 331, 332 held by stationary portion 323. It may be clamped during the cut, if desired. The Geneva wheel 328 is intermittently turned, during each return stroke, by a pin or roller'333 mounted eccentrically of a continuously rotating shaft 334. This shaft is offset from the plane of the drawing and has been turned into it for illustration.

In operation the work spindle performs a helical reciprocation in the hub of the Geneva wheel, which is stationary during the cut. During the return strokes the Geneva wheel and work spindle are indexed, so that a new tooth space is presented to each tool with each cutting stroke.

If desired, antifriction means may be used at the helical guide portion 326.

The motion of the tool slides 304 is effected by a member 335 that reciprocates axially'of the work spindle in a guide portion 336. Member 335 comprises an upper part 335 and a lower part 335", which are rigidly secured together or formed'integral with each other. Inclined bars 338 extending between the parts 335', 335" are secured thereto, and engage slots or openings provided in the slides 304 to move said slides. The bars 338 are preferably disposed parallel to the tool path 302. It can be shown that the axial motion of member 335 and of 13 a the rksp fiflfa'mthe im dt t naflii ui i'i engagement. They ditfer durin'g the retufn'stroke because of t e ppi s o i aq t sl de t i.

Member 335 is reciprocated by nieans ofashaft whose 341 is parallel to the ai n's o'f me be sgn and which is rotated at the same rate as said member. They are a d, together et =1I i i s ra Pai t e m with vertical axes, engaging wormg'ea'rs32 5 and 3'45, and a pair of cylindrical gears. A pair of cams 346 are rigidly secured to the shaft with axis 341, and engage rollers 347 rotatably mounted on pins or rods 348 secured to member 335.

A pair of bars 350 are secured to the pivot portions 318, 318' of piece 317 at their outer ends, Bars 350. extend vertically through o enings of the machine frame 352mm engagement with a shim 353 secured to the lower, end of part 335". This engagement exists only during the cutting stroke while the axial or vertical motion of the spindle 311 and of member 335 are equal. Engagement under pressure is maintained by using a shim 353 at suitable thickness. Between cutting engagements the bars 350 and shim 353 separate. 7 A,

This contact under load; duringthe cut, is n'ijadeto insure perfect timing between the axial motions of spindle 311 and of mernber 335; to fu'rtheraccuracy.

For loading and unloading; the cutter unit including guide portion 336 and the shaft with axis 341 is raised. This is' done without disturbing the timing between the wormgears 325 and 345 by providing a sliding-spline connection with the vertical shaft of the timing train. The drive is applied to the vertical shaft in any suitable known manner.

While the invention has been described in connection with several different embodiments thereof, it will be understood that it is capable of further modification, and this application is intended to cover any variations, uses, or adaptations of the invention, following, in general, the principles of the invention and including such departures from the present disclosure as come within the known or customary practice in the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth, and as fall within the scope of the invention or the limits of the appended claims.

I claim:

1. A reciprocatory form-cutting tool having a plurality of cutting teeth equi-angularly spaced about an axis and projecting outwardly therefrom, for cutting without turning on said axis, each of said cutting teeth having a sidecutting edge and an adjacent end-cutting edge formed thereon at the junctures of the front end face of the tooth with one side and with the top of the tooth, respectively, the surfaces formed on each cutting tooth back of said cutting edges being helical surfaces of constant lead that are coaxial with said axis, said lead being the same on both of said surfaces.

2. A reciprocatory form-cutting tool having a plurality of cutting teeth spaced about an axis, for cutting without turning on said axis, each of said cutting teeth being inclined from its front end to its rear end with reference to a plane perpendicular to the tool axis and being so directed as to permit setting said axis in a plane perpendicular to the axis of a gear blank to be cut therewith, at least one side-cutting edge and an end-cutting edge being formed on each of said cutting teeth at the junctures of the front end face of the tooth with one side and with the top of the tooth, respectively, the surfaces formed on each of said cutting teeth back of said cutting edges extending along a line of constant distance from said axis, said line being directed at a constant angle along its length to a plane perpendicular to said axis.

3. A reciprocatory form-cutting tool having a plurality of cutting teeth equi-angularly spaced about an axis and projecting outwardly therefrom, for cutting without turning on said axis, each of said cutting teeth having at least one side-cutting edge and an end-cutting edge formed thereon; at the junctures of the front end face of the tooth with one side and with the top of the tooth, respectively, the surfaces formed on each cutting tooth back of said cutting edges being helical surfaces of constant and equal lead thatare coaxial with said axis, the helical surface back of said end-cutting edge being inclined to a cylindricar surface coaxial with said axis.

4. A reciprocatory form-cutting tool having a plurality of cutting teeth et'q'ui-angul'arly spaced about an axis and projecting outwardly therefrom, for cutting without turning on said axis, each of said cutting teeth having at least one side-cutting edge and an end-cutting edge formed thereon at the junctures of the front end face of the tooth with one side and with the top of the tooth, respectively, the surfaces formed on each cutting tooth back of said cutting edges and oh the other side of each cutting tooth being helical surfaces of constant lead that are coaxial with said axis, the helical side-surfaces being differently inclined to the radial direction of said tool in sections containing the tool axis.

5. A reciprocatory form-cutting tool having a plurality of cutting teeth spaced about an axis, for cutting without turning on said axis, each of said cutting teeth being inclined from its front end to its rear end with reference to a plane perpendicular to the tool axis, said cutting teeth being all alike and being uniformly spaced about said axis and allha'vin g the same axial position, at least one sidecutting edge and an end-cutting edge being formed on each of said cutting teeth at the junctures of the front face of the tooth and a side and the top of the tooth, respectively, the surfaces formed on each cutting tooth back of said cutting edges extending along a helix which is at a constant distance from said axis.

6. A reciprocatory form-cutting tool having a plurality of cutting teeth spaced about an axis, for cutting without turning on said axis, each of said cutting teeth being inclined from its front end to its rear end with reference to a plane perpendicular to the tool axis and having at least one side-cutting edge and an end-cutting edge formed thereon at the junctures of the front face of the tooth and one side and the top of the tooth, respectively, successive cutting teeth having, respectively, end-cutting edges of gradually changing width, the surfaces back of said sideand end-cutting edges extending along a helix which is at a constant distance from said axis.

7. A reciprocatory form-cutting tool having a plurality of cutting teeth spaced about an axis, for cutting without turning on said axis, each of said cutting teeth being inclined from front to rear with reference to a plane perpendicular to the tool axis, successive cutting teeth having end-cutting edges disposed at gradually increasing distances from said axis, the end-cutting edges of the different cutting teeth decreasing in width with increasing distance from said axis, the surfaces back of said end-cutting edges extending along a helix which is at a constant distance from said axis on each cutting tooth.

8. A reciprocatory form-cutting tool having a plurality of cutting teeth spaced from one another about an axis, for cutting without turning on said axis, each of said cutting teeth having at least one side-cutting edge and an end-cutting edge formed thereon at the junctures of the front face of the tooth and of one side and the top of the tooth, respectively, the surfaces formed on each cutting tooth back of said cutting edges being helical surfaces of constant lead that are coaxial with said axis, the spaces between successive cutting teeth being wider at the bottoms of the spaces than the thickness of the cutting teeth themselves at their bases.

9. A reciprocatory form-cutting tool having a plurality of cutting teeth spaced in a circle about an axis, for cutting without turning on said axis, each of said cutting teeth having a concavely curved side-cutting edge and an adjacent end-cutting edge formed thereon at the junctures of the front face of the tooth and of a side and the top of the tooth, respectively, the surfaces formed on each cut- 1 5 ting tooth back of said cutting edges extending at a constant distance from said axis along lines inclined to'a plane perpendicular to said axis.

10. A reciprocatory form-cutting tool having a plurality of cutting teeth with curved side-cutting edges spaced about an axis, said cutting teeth being inclined to a plane perpendicular to the axis of said tool and having approximately equal'positions lengthwise of said axis, and the side surfaces and top surfaces of each of said cutting teeth extending at a constant distance from said axis from front to back, said side surfaces of each cutting tooth being 7 coaxial helical surfaces of the same lead extending about said axis. 7

11. A reciprocatory form-cutting tool having a plurality of cutting teeth spaced about an axis, said cutting teeth being inclined to a plane perpendicular to said axis and having approximately equal positions lengthwise of said axis, each cutting tooth containing a pair of opposite sidecutting edges and an end-cutting edge'formed at its top, the surfaces back of said side-cutting edges being coaxial helical surfacescof the same lead but, of different profile inclination, and the surface back of each end-cutting edge also lying in a helical surface which is of the same lead from front to back as said coaxial helical surfaces.

12. A reciprocatory form-cutting tool having a plurality of cutting teeth spaced about and projectingoutwardly from an axis, for cutting gear tooth sides without turning on said axis, each of said cutting teeth being inclined to a plane perpendicular to the tool axis and having a sidecutting edge and an adjacent end-cutting edge joined thereto at the junctures of the front end face of the tooth with one side and with the top of the tooth respectively,

the surfaces formed on said one side and the top of each cuttingtooth back of said front face extending along a helix of constant distance fromthe tool axis, and said front face including a smaller angle with said one side surface back of said side-cutting edge than with the opposite side surface of said cutting tooth, to effect a keen side-cutting edge.

13. A form-cutting tool according to claim 12, wherein the front face of each cutting tooth is part of a spherical surface.

References Cited in the file of this patent UNITED STATES PATENTS 41,818 Libby Mar. 1, 1864 1,299,712 Halstead Apr. 8, 1919 1,740,604 Kienzl Dec. 24, 1929 7 2,126,990 Graves Aug. 16, 1938 2,267,182 Wildhaber Dec. 23, 1941 2,302,783 Luers Nov. 24, 1942 2,348,759 Sneed May 16, 1944 2,357,153 Wildhaber Aug. 29, 1944 2,374,890 Pelphrey May 1, 1945 2,413,406 Dooling Dec. 31, 1946 2,414,283 Aeppli Jan. 14, 1947 2,479,287 Aeppli Aug. 16, 1949 2,674,030 Wildhaber Apr. 6, 1954 2,698,988 Klomp Jan. 11, 1955 FOREIGN PATENTS 590,978 Great Britain Aug. 1, 1947 France Oct. 14, 1953

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