US1956407A

US1956407A - Method of and means for abrading gears

Info

Publication number: US1956407A
Application number: US479481A
Authority: US
Inventors: Wildhaber Ernest
Original assignee: Individual
Current assignee: Individual
Priority date: 1930-09-03
Filing date: 1930-09-03
Publication date: 1934-04-24
Anticipated expiration: 1951-04-24

Description

April E. WILDHABER 1,956,407

METHOD OF AND MEANS F01 ABRADI-NG GEARS Filed Sept. 5. 1930 v 4 Sheets-Sheet l INVENTOR EIVAME'WLZJZW April 24, 1934. 5-. WILDHABER 1,956,407

METHOD OF AND MEANS FOR ABRADING GEARS Filed Sept. 5. 1930 4 Sheets-Sheet 2 125' I INVENTOR April 24, 1934. WILDHABER 1,956,407

' METHOD OF AND MEANS' FOR ABRADING GEARS Filed Sept. 3, 1930 4 Sheets-Sheet 5 l 9 i 144 k.

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INVENTOR April 1. E. WILDHABER 1,956,407

METHOD 0F AND MEANS FOR ABRADING GEARS luvsmoR Patented Apr. 24, 1934 UNITED STATES PATENT OFFICE E-r1101) or AND MEANS FOR ABRADING GEARS Ernest .Wildhaber, Rochester, N. Y. Application September 3, 1930, Serial No. 479,481 14 Claims. (Cl. 51-278) The present invention relates to a method of and means for abrading gears in a process of continuous rotation of a gear blank. In processes of the character referred to, an abrading member is provided, which contains teeth or threads, or at least one tooth or thread, and which is rotated in abrasive engagement with a rotating, gear blank. l

The said abrading member is devised for the 19 express purpose of abrading and difiers from the mating gear, or mating gears, of a finished gear blank through its shape, its position. and usually also through its material.

Processes of the character referred to are known for their capacity of turning out gear teeth with very high accuracy of tooth spacing. However difliculties are experienced in continuously producing accurate tooth profiles. These difliculties are caused by the uneven wear of the g0 abrading member, and can only be partly counteracted by frequent truing operations, which in the cases referred to require much time and skill.

' One object of the present invention is to attack the evil at its root and to prevent uneven wear of the abrading member. Another object of the present invention to to devise a method of and means for abrading gears in a process of continuous rotation of a gear, wherein the abrading member is subjected to a self-correction. A further object is to devise self-correction of the abrading member by shifting mesh in a manner that a point. of the abrading member successively engages points of various heights on the tooth profile of a gear blank or of another toothed member, as will be fully described? A further object of thepresent invention is to provide a machine having means for .rotatably mounting three toothed or threaded elements, ineluding a gear blank and an abrading member, means for rotating said elements so that one of said elements is in abrasive engagement with the two others in the manner that the same side of its teeth are engaged by'said two elements, and means to efiect reciprocating feeding motions between said elements along two straight lines angularly disposed to each other in a manner as to effect self-correction of the abrading member.

A still further object is to provide a toothed abrading member fully conjugate to a gear blank,- or to a gear to be produced from a gear blank, and suited to mesh with line contact with said gear.

Also an abrading member for gears having straight orv helical teeth shall be provided, which contains tooth portionsinclinedto its peripheral direction and conjugate to said straight or helical teeth, .and which is suited to contact simultaneously with a larger number of teeth of a gear blank than the rack corresponding to said gear. A further object of the present application is to claim the shape of abrading members disclosed in my pending application entitled Rotary member for forming gears, filed June 1, 1927, Serial No. 195,716, now Patent No. 1,877,104, and of my Patent No. 1,759,333 entitled Method of forming gear Another aim of the present invention is to provide an abrading member for worm gears and worms of hour glass form, said abrading member having one or inore teeth or threads and having 7 a constant tooth profile in parallel planes perpendicular to its axis, and an abrading member of the aforesaid character containing a truly helical thread or tooth, or a plurality of helical threads or teeth. 7

A further aim is to provide a tapered abrading member for tapered gears, such as spiral bevel gears and hypoid gears, said abrading member having one thread or a. plurality of threads or teeth, the side surfaces of said threads or teeth being portions of helical surfaces, and preferably portions of involute helical surfaces.

A still further aim is to provide a machine for abrading gears, in which a gear blank and a toothed abrading member especially constructed for said purpose are mounted on angularly disposed and offset axes, and in which the timed relation between the rotation of the gear blank and said brading member is obtained through their abrasive engagement without the use of an additional positive operative connection between the gear blank and said abrading member. Elimination of such positive operative connection is made possible without sacrific of accuracy with the use of an abrading member constructed in accordance with the present invention, namely of an abrading member capable of simultaneously contacting with a large number of teeth of the gear blank.

A further object in view is to provide a machine in which a gear blank having helical teeth is rotated in abrasive engagement with an abrading member of hour glass form, said abrasive engagement being the only positive operative connection between said gear blank and said abrading member, and wherein means are provided for imparting to said gear blank a helicoidal reciprocation on its axis in a manner as to leave the pressure of abrading engagement unaffected.

Various other objects will appear in the course of the specification and from recital of the ap pended claims.

My invention will be explained with reference to the accompanying drawings, in which Fig. 1, Fig. 2 and Fig. 3 illustrate one simple embodiment of the present invention.

Fig. 1 is a plain view, partly an axial section of an abrading member, and a section of simplified means for mounting said abrading member and imparting motion to it.

Fig. 2 is a front elevational view of the abrading member shown in Fig. 1, partly a section along lines 22 of Fig. l, and of a gear blank shown in engagement with said abrading member.

Fig. 3 is a partial end view of the abrading member shown in Fig. 1 and Fig. 2, and partly a section along a tooth bottom.

Fig. 4 is a diagram explanatory of one of the principles underlying the self-correction of abrading members, in accordance with the present invention.

Fig. 5 and Fig. 6 illustrate a modified form of the present invention.

Fig. 5 is a plan View of an abrading member and a truing member meshing with each other in varying bodily positions and constructed in accordance with the present invention, and partly in axial section of said abrading member. A gear blank meshing with said abrading member is also diagrammatically indicated in two different bodily positions.

Fig. 6 is a partial and diagrammatic front elevation corresponding to Fig. 5, and partly a section of the abrading member along lines 6-6 of Fig. 5.

Fig. '7 is a view of a spur gear and of an abrading member conjugate to said spur gear and constructed in accordance with the present invention, and a diagrammatic view of a truing member engaging said abrading member, and of a second abrading member engaging said spur gear.

Fig. 8 is a view similar to Fig. 7 but referring to a gear containing helical teeth. Fig. 8 can also be considered as a view of a worm of hour glass form and of an abrading member in the form of a helical gear.

Fig. 9 is a partial and simplified plan view of a device for abrading worms of hour glass form and worm gears, in accordance with the present invention.

Fig. 9a is a diagrammatic plan view in reduced scale, similar to Fig. 9 and illustrative of the disposition of the slides.

Fig. 10 is a partial front elevation corresponding to Fig. 9, and a section along lines 10-10 of Fig. 9.

Fig. 11 is a simplified plan view of a machine for abrading gears in accordance with the present invention, namely spur gears, helical gears and other gears, the machine being shown in position for abrading spur gears.

Fig. 12 is a partial front elevation corresponding to Fig. 11.

Fig. 13 is an individual view, partly a section, of a detail used in the machine illustrated in Fig. 11 and Fig. 12.

Fig. 14 is an individual view and an axial section of another detail used in the machine shown in Fig. 11 and Fig. 12, namely of an abrading member and adjacent parts.

Fig. 15 is a partial plan view similar to Fig. 11 and showing the machine illustrated in Fig. 11 in a setting for abrading gears containing helical teeth.

The novel principles underlying the method of abrading gear teeth in accordance with the present invention will first be introduced with reference to the simple embodiment illustrated in Fig. 1, Fig. 2 and Fig. 3. In these figures, numeral 11 denotes a gear blank containing straight teeth 12, which extend parallel to the gear axis 13. The tooth profiles 14 are here preferably involutes of a circle 15, which is com monly known as a base circle. Abrading member 16 contains threads or teeth 17, which are fully conjugate to the teeth 12 of gear blank 11 and which are suited to mesh with line contact with said teeth. In other words a tooth 17 is so shaped that it is capable of contacting with a tooth 12 along a line, which during roation of gear blank 11 and abrading member 16 sweeps over a side surface of tooth 12.

In the instance illustrated, member 16 is provided with helical teeth 1'7, which extend along helices about its axis 18, and which have a constant profile in parallel planes perpendicular to its axis 18. A helix is commonly understood to'be a line extending on a cylindrical surface and having a constant lead, so that in development of said cylindrical surface to a plane the helix appears as a straight line.

Axis 18 of abrading member 16 and axis 13 of gear blank 11 are ofiset from each other and angularly disposed to each other.

Ordinarily helical tooth surfaces or thread surfaces cannot mesh with line contact with a gear (11) having straight teeth (12) or helical teeth, but contact only at a point or at a plurality of separate points at a time.

Line contact may be effected however in the case, where the tooth surfaces 20 of member 16 are involute helicoidal surfaces capable of meshing with the teeth 12, provided that axis 18 is offset from gear axis 13 a distance equal to the sum of the radii of the base circles of gear 11 and member 16. In other words line contact may be effected between teeth 12 and helical teeth 1'7, when the teeth 1'? correspond to a position of contact of the cylindrical base surfaces of the

involute elements

11 and 16.

Gearing of this character is known as Beale gearing, and it can be demonstrated mathematically, that the aforesaid structure is the only one possible, which permits of line contact between straight or helical teeth 12 of a gear and truly helical teeth 17 of an abrading member.

The base circle 21 of abrading member 16 is best seen in Fig. 3. The active tooth profile of member 16, in a plane perpendicular to its axis 18, is an involute 22, which starts at the base circle and extends outwardly. The profile of an axial section of teeth 17 is also curved. It is well known, that an involute helicoidal surface (20) is composed of straight lines 23 tangent to the cylindrical base surface (21), and that gear contact takes place along a line 23 or a plurality of such lines at a time. The

mesh between gear blank 11 and member 16 3 takes place in a plane 24 (Fig. 2) tangent to the cylindrical base surfaces of gear blank 11 and of member 16. A

Member 16 contains a body portion of cup form, which is rigidly secured toa shaft 18' by means of a nut 19 engaging a screw thread formed on shaft 18. Shaft 18' contains helical teeth or threads 25 and is journalled in a large bearing 26, contact with the bearing being made by the outside ends of teeth 25. Bearing 26 forms part of a'slide, which is adjustable in known manner along guides 27 of a column 28,

Threads 25 of shaft 18' mesh with a worm gear 30, which is rotatably mounted on an axis 31. When abrading member 16 and gear blank 11' are positively geared up with each other, as is common practice in gear grinding, worm gear 30 also'forms part of the gear train provided to that effect. to worm gear 30 or to any other member of said gear train in any suitable known manner.

The abrading member (16) may be made of conventional abrasive material, consisting of hard ,grains of abrasive proper embedded in a less hard carrying or connecting substance. The action of such abrasive members depends much on the grade of said grains and on. the nature of the carrying substance, which should be carefully selected for the specific purpose, to obtain best results.

At the present time I preferably provide abrading members (16) of gear form, made of uniform material which is less hard than the hardened gears to be abraded. The hard abrasive material proper is then added as a paste or fluid, which contains the hard and fine abrasive grains suspended in a fluid or semi fluid in the nature of an emulsion. One way of applying the abrasive is.

to provide a supply of abrasive paste or fluid ad- J'acent the lower end of abrading member 16, so that said member dips into said paste or fluid and covers each of its teeth with abrasive at every revolution. Another way of applying abrasi've is to direct abrasive fluid in the form of a jet to the teeth of the abrading member or the gear blank, and by efl'ecting the'required fluid pressure with a pump.

The abrading member (16) may be made for instance of cast iron, or of aluminum, or of other metallic or non metallic materials. This holds true alike for all the embodiments of the present invention. I

In operation, gear blank 11 and abrading member 16 are turned on their

axes

13 and 18 at the inverse ratio of their numbers of teeth. In addition gear blank 11 is slowly reciprocated lengthwise of its axis 13, so that any point of the surface of the abrading member successively operates upon axially displaced points-of the gear teeth.

Numeral 11' denotes-diagrammatically another gearposition thus arrived at.

Furthermore abrading member 16 is also given a slow reciprocation in the direction of its axis 18, and an additional turning motion on its axis so that the total motion added to the continuous rotation of member 16 amounts to a helical reciprocation. The lead of said helical reciprocation equals the lead of the teeth (17) of the abrading member; so that its teeth (17) are displaced in their own direction. To eifect this lead of the helical reciprocation, the lead of threads 25 is made equal to the lead of the teeth or threads 17 of the abrading member 16. Re-

ciprocation of member 16 and shaft 18 lengthwise of axis. 18 is efifected in any suitable known manner, for instance by means of a lever 32, whose one end is indicated in Fig. l, and which contains rollers 33 which contact with a disk 34 fastened to the end of shaft 18. A spring attached 'on one end to lever 32, at point 35, and

on its other end to the inside of hollow shaft 18,

keeps disk 34 and rollers 33 in contact witheach' other.

One of the positions through which member Motion may be-imparted 16 passes in its helical reciprocation is indicated While wear is unavoidable to a certain extent, it

may be controlled in accordance with the present invention in such a manner, that it is harmless. Abrading members formed, positioned and moved as disclosed here are bound to wearso that the resulting worn tooth surfaces .of the abrading member are identical in form to its initial correct tooth surfaces, and only displaced angularly about the axis of said abrading member, as compared with said initial tooth surfaces.

Further, it will be seen that even when the initial tooth surfacesof the abrading member are imperfect, the self-correction provided in accordancewith the present inventionimproves them in the abrading operation.

The principle here used for abrading gears and for maintaining a true tooth shape of the abrading members is in its broadest aspect at present used in an altogether different art, namely for abrading or grinding optical lenses. Optical lenses require the production of truly spherical surfaces of extreme accuracy. It is well known. that they are ground on rather primitive machines with spherical forms or laps, and that the reason for the high accuracy obtained lies in each point of the lap surface successively contacts with all thefpoints of a large portion of the spherical lens surface. With this provision protruding points ofthe lap surface are worn off immediately after theymight occur, and a high accuracy results.

Fig, 4 can be considered as an enlarged section taken along plane of action 24 of Fig. 2. The active profile lines 36 of teeth 17, in a plane tangent to the base surface of the abrading member, are straight lines as already pointed out. Contact between the gear teeth 12 and teeth 17 takes place along said straight lines or along portions of them. The above described reciprocating feeding motion of the gear blank lengthwise of its axis 13 effects positions of the gear teeth such as indicated in dotted lines 12'. It amounts to a displacement of the straight lines 37 of gear teeth 12 on the straight lines 36 of teeth 17 of the abrading member. When

lines

37 and 36 are not accurately straight, the portions protruding from the true straight line form contact more than other portions and are rapidly worn off.

The portions of one straight line successively contact with various portions of the mating straight line, and a portion disposed midway between the ends of a straight line successively engages portions adjacent both ends of the mating straight line. The said displacement assures even Wear of the straight profiles 36 of the abrading member. The profiles 36 necessarily remain straight, and in correct shape. And if through some inadvertence they would have some, inaccurate shape, as'indicated in dotted lines 38, they would finally wear to the correct straight form. Self-correction of lines (36) of the abrading member" requires provision of a displacement as described,and it"also requires. that the gear blank and the abrading member mesh with line con tact. It is clear from consideration of Fig. 3 that this latter condition is also fulfilled in the example just described.

The aforesaid self-correction of lines 36 alone of the abrading member is however not sufficient to insure a continuous correct shape of the entire active tooth surfaces of the abrading mem-- her. The tooth surfaces (20) might nevertheless wear out of shape in a manner that their lead would change as a whole or change lengthwise of the teeth. In order to further insure the same correct lead of teeth 1'1 at all times, a helical reciprocation along axis 18 of the abrading member is provided, as has been already described. This helical reciprocation at a lead equal to the correct lead of the abrading member causes the abrading member to maintain its correct lead, provided again, that the gear teeth and the teeth of the abrading member are suited to mesh with line contact with each other, so that any portion of the abrading member remains in a position of mesh not only in one axial position of abrading member 16, but in a whole range of such positions. Any portion of the active surface of the abrading member then successively contacts with portions disposed on teeth 12 at various profile heights. A portion of the tip of a tooth 1'7 successively contacts with tip portions as well as flank portions of the conjugate teeth 12.

The aforesaid two displacements between two fully conjugate elements, which are suited to mesh with line contact with each other, insure constant profiles 36 as well as a constant lead of the abrading member. The said profiles and lead fully determine the tooth surfaces of the abrading member. Through provision of the aforesaid two displacements between the gear blank (11) and the abrading member (16), the tooth shape of the latter is automatically corrected and is prevented from wearing out of its correct form.

It should be noted that the two different displacements provided are in the direction of two straight lines angularly disposed to each other, and extending in a plane parallel to the axes of the gear blank and the abrading member, or also in a plane parallel to the axisof the gear blank and containing a line of action of said gear blank.

In the example illustrated in Fig. 5 and Fig. 6 an abrading member 40 is provided and shown in engagement with spur gear blank 41. The sides of the threads or teeth 42 of abrading member 40 are portions of helical surfaces, and particularly of involute helical surfaces, like the sides of teeth 1'1 of abrading member 16 shown in the previous figures. The outside contour (43, Fig. 5) of abrading member 40 is however concavely curved and fdllows substantially the tooth bottoms of gear blank 41. Larger active tooth surfaces may herewith be obtained on'abrading member 40, than on abrading member 16 referred to above, especially on the tooth portions 42' which engage with the tips of the gear teeth 44.

Abrading member 40 and gear blank 41 may be given the same relative motions as described with reference to abrading member 16 and gear blank 11, if so desired.

In the embodiment shown another arrangement is made. The self-correction of the lead of the abrading member is here obtained by means of another element 45, which may be called a truing member, and which contains helical teeth 46 fully conjugate to the helical side surfaces 4'? of teeth 42 and suited to mesh with line contact with the same, when mounted on an axis 48 parallel to axis 50 of abrading member 40.

Abrading member 40 and element 45 mesh with each other in the manner of helical gears mounted on parallel axes. Preferably the pitch circles of said gears are chosen to extend outside or inside of the tooth zones, with the object in view of introducing a certain amount of profile sliding at all points of tooth contact of abrading member 40 and element 45.

A helical reciprocation is imparted to element 45 in the manner described with reference to member 16, Fig. 1, so that said element reaches at one time a position as indicated in dotted lines 45', Fig. 5. The lead of said helical reciprocation is equal to the lead of teeth 46 of element 45. This helical motion secures a constant and correct lead of abrading member 40 as well as of element 45, and in this respect it is equivalent to the helical reciprocation of member 16 of the embodiment described before.

Gear blank 41 is slowly reciprocated in the direction of its axis 51, as described with respect to gear blank 11 and with the same effect. Gear blank 41 thereby passes through various axial positions, such as indicated also through lines 41.

In this manner complete self-correction of the active tooth surfaces of abrading member 40 may be obtained, with the added advantage of securing an increased area of abrasive engagement between the abrading member and the gear blank, a maximum number of teeth contacting at all times.

The embodiment described with reference to Fig. 5 and Fig. 6 may be characterized as follows:

Three elements are provided, comprising a gear blank (41), an abrading member (40), and another element (45) which may be called a truing member. One of said three elements (40) is set in mesh with the other two elements (41, 45). The abrading member (40) and the gear blank (41) are mounted on angularly disposed and oftset axes (50, 51) and are fully conjugate to each other, so as to mesh with line contact with each other. Feeding motions are provided along two straight lines, which are angularly disposed to each other, namely alongthe axes (51 and 48) of the gear blank (41) and of said other element (45) which contains helical teeth.

The helical reciprocation of element 45 along its axis, in engagement with abrading member 40 may be effected continuously during the gear abrasion itself; or if so or before gear abrasion. Element 45 may be made of the same material as abrading member '40, or of a different, preferably metallic, material less hard than the case of case hardened gears. Another form of abrading member will now be described with reference to Fig. '7 and Fig. 8. This general form is usually preferred for abrading straight teeth and helical teeth, by reason of the large number of simultaneously contacting teeth and of the large area of tooth engagement, which insures a very fast abrading operation.

In Fig. '7 numeral 54 denotes an abrading member meshing with a spur gear blank 55. Abrading member 54 and gear blank 55 have offset desired periodically after axes 56, 5'7 angularly disposed to each other.

The teeth or threads 58 of member 54 are fully conjugate to the teeth 59 of spur gear blank 55, or to the teeth of the gear intended to be formed from said spur gear blank. The tooth surfaces of gear blank 55 and of the gear to be produced from blank 55 are identical or practically identical, it is understood, and their respective teeth differ only The side in their thickness and their accuracy.

60 of spur gear teeth 59 is engaged by the side 61 of theteeth 58 of abrading member produced in many ways.

'sists in providing a tool of the form of gear 55,

54. In the view lengthwise of gear teeth 59, the outlines of the teeth 58 are curved. Likewise the profiles of an axial section of teeth 58 are curved, and have a changing inclination with respect to the axis (56) contained in said section.

Reference is also made to my application Serial No. 195,716, mentioned above, to my application entitled Method of forming gears filed May 4, 1928, Serial No. 275,142, now Patent No. 1,797,460, and to my Patent No. 1,759,333 for further information concerning the tooth form of abrading members of the general character now referred to.

Frequently member 54 is made of larger diameter than indicated in the drawing, where the diameter has been kept small to save space.

The teeth or threads 58 of member 54 may be One simple way conwhose cutting edges lie on the tooth surfaces of gear 55, and whose cutting teeth are preferably relieved back of the cutting edges. A tool of this kind is similar to well known gear shaper tools. The tool is then mounted on the work spindle of a hobbing machine of known character, and a blank of the contour of member 54 is mounted on the hob spindle. The hob spindle is set at the same angle to the work spindle as the angle included between the directions of

axes

56, 57. Furthermore the axes of the work spindle and of the hob spindle are oiTset the same amount as

axes

56, 57. The tool of gear form and the blank mounted on the hob spindle are then rotated in timed relation to each other, at the inverse ratio of the numbers of

teeth

59 and 58, while a feeding motion is provided between the tool and the blank in the direction of the work spindle, that is to say ofthe tool axis (57). In this operation, the cutting edges of the tool successively describe the entire tooth sides of gear 54 with respect to the abrading member blank, and thereby. generate the exact tooth surfaces of said abrading member.

This process of generation is equally well applicable where the gear blank is provided with helical teeth, as indicated in Fig. 8. In this case the tool is provided with relieved helical teeth, and the feeding motion consists of a helical motion about the axis of the work spindle, or the equivalent thereof, as well known in hobbing practice.

The teeth 58 of member 54 contact simultaneously with a large number of teeth 59 of spur gear 55. The average number of teeth 59 which are simultaneously engaged by member 54 is larger than three, and larger than the number of teeth simultaneously engaged by the rack corresponding'to gear 54. The said rack, as well known, would mesh with gear 54 in the manner that the pitch circle of the latter which rolls on the pitch circle of the mating gear, also rolls on the pitch line of the rack.

In the usual known methods of gear grinding by means of a continuously rotating gear shaped member, which is made for the purpose of abrading and which differs from a mating gear of the gear being abraded, the gear blank and the abrading member are operatively connected by means of a gear train. In other words in addition 10 their direct mesh another positive operative connection is provided between a gear blank and its abrading member.

The aforesaf'd large number of simultaneously.

contacting teeth (58, 59) insure a steady motion of the rotating elements engaged in abrasion also cated and provided with helical teeth.

without said operative connection, so that preferably said operativeconnection is omitted, when abrading members of the general character indicated in Fig. 7 and Fig; 8 are used.

The abrading members are then provided preferably with a plurality of .teeth or threads, as shown.

Fig. 8 illustrates an abrading member 62 meshing with a gear blank 63 containing helical teeth 64. Again the abrading member (62) is fully conjugate to the gear blank and suited to mesh with line contact with its teeth. A large number of teeth are simultaneously in contact, namely a number much larger than the number of teeth simultaneously engaged by the rack corresponding to gear 63.

In the instance particularly shown, the axis 65 of the abrading member is contained in the plane of the drawing, and inclined at a right angle to the direction of axis 66 of gear blank 63. Other angular positions of the axes may however also be used. In Fig. 7

axes

56 and 57 are disposed at an acute angle with respect to each other.

Abrading member 54 (Fig. 7) is indicated in engagement with another element 67, which may be called a truing member, and which is only diagrammatically indicated. Element 67 contains helical teeth or threads and serves for the same general purpose as element (Fig. 5), namely for maintaining the abrading member (54) true in one direction. In operation it performs a helical reciprocation along its axis 68. Abrading member 54 may be maintained true in another direction through reciprocating the gear blank along its axis, as described above.

To obtain the desired effect of complete selfcorrection, element 67 is so chosen that it contacts along different lines with the tooth surfaces of the abrading member (54) than gear 55. Element 67 should therefore differ materially from gear 55, as it does when positioned as indi- It is further important that element 67 meshes with line contact with abrading member 54, or practically with line contact.

The problem of determining helical threads in such a manner as to mesh with line contact or practically with line contact with a member of the character of member 54, has been fully disclosed in my application Method of forming gears, filed May 4, 1928, Serial No. 275,142, now Patent No. 1,797,460, and reference is made to it.

The said problem might also be solved experimentally, if so desired. In this case helical worms or pinions of various diameters are provided, which contain all the same pitch along the tooth normal as gear 55. Of these worms the one is selected, whose mesh extends over a maximum A portion of the tooth surfaces of abrading member 54.

- Element 69, shown in Fig.8, serves to maintain abrading member 62 true in one direction. Like element 67, it also contains helical teeth suited to mesh with line contact with its abrading member, or practically with line contact. It also performs a helical reciprocation in the direction of its axis 70, with a lead equal to the lead of its teeth or threads.

Elements

67 and 69 contain constant tooth profiles in parallel planes perpendicular to their respective axes, that is to say the profiles of a member 67'or 69 in a plane perpendicular to the axis of rotation extend along identical lines as the profiles in a parallel plane.

Element 69 may in some cases be provided with straight teeth, like a spur gear, if so desired.

In quantity production, the two sides of the gear teeth may be simultaneously abraded or ground by means of two abrading members, which operate on the two sides of the teeth respectively. In Fig. '7 and Fig. 8 such abrading members 54' and 62' are indicated in dotted lines. Abrading

members

54 and 62 are mounted on axes parallel to the axes of

members

54 and 62 respectively. Member 54 is symmetrical to member 54 and of opposite hand. It has the character of a left hand worm or pinion, whereas member 54 has the character of a righthand worm or pinion. The opposite hands of members 54 and 54' are readily understood to be the result of the parallel arrangement of their axes, which are inclined to the plane of spur gear 55. Members 62 and 62' are of equal hand.

Members of the general character of

members

54 and 62, Fig. '7 and Fig. 8, may be used also as worms of hour glass type, or as worm wheels. Worms and worm wheels will be jointly referred to as worm gears. Fig. '7 and Fig. 8 serve therefore also for illustrating ways of grinding worm gears. In this case element 55 (Fig. 7) is an abrading member of spur gear form. Element 63 (Fig. 8) is an abrading member having helical teeth meshing with element 62. Element 69 is then another abrading member having helical teeth and meshing in a different manner with the same tooth sides of element 62. To obtain self-correction, helical reciprocations are provided in the directions of axes 66 and '70, as described.

In successively abrading a plurality of equal gears, the gear axis and the axis of the abrading member are preferably kept at a constant oifset from each other and in a constant angular position. In other words the bodily positions of the abrading member and of a gear blank are maintained the same, when said gears are successively abraded. The abrading operations may continue until the abrading member is nearly used up. A new abrading member is then provided and mounted in the same settings.

A somewhat simplified machine for abrading worm gears and especially worms of hour glass form will now be described with reference to Fig. 9, Fig. 10 and Fig. 9a.

In these and subsequent figures, Ihave omitted many conventional parts, whose presence is self evident, and confined description and disclosure as much as possible to the characteristic novel features provided in accordance with the present invention. So for instance screws or other connecting means are usually omitted. Also protecting guards are omitted, which would serve the conventional purpose of preventing the abrasive from reaching the bearings.

Numeral '71 denotes a worm gear having a concave outline, which is shown in dotted lines in Fig. 9 and in full lines in Fig. 10, the threads or teeth being omitted in the drawings. Worm gear '71 may be either a worm or a worm wheel. Element 71 is mounted in any suitable known manner not further shown, and meshes with an abrading member '72 containing helical teeth 73,

namely preferably involute helical teeth, which contain involute profiles in planes perpendicular to axis '74. Axis '74 of member '72 is offset from and angularly disposed to the direction of axis '75 of element '71. Worm gear '71 and helical abrading member '72 are interrelated ina manner that they are fully conjugate to each other and suited to mesh with line contact with each other.

Abrading member '72 is rotatably mounted on a slide '76 by means of two bearings '77, 7'7, and meshes with another element '78, which will be referred to hereafter as a truing'member. Truing member '78 is mounted on another slide '79 by means of bearings 80, which are diagrammatically indicated.

Abrading member '72 as well as truing member '78 contain bodies of cup form, and are provided with teeth or threads which project outwardly from said bodies. Members '72 and '78 may be secured to their

respective shafts

81, 82 from the outside, without dismounting their

shafts

81, 82;

The arrangement of the aforesaid slides is best shown in Fig. 9a. Slide '76 is movable on the machine frame 83 in the direction of shaft 81, along slot 84 of said frame. Slide '76 is of U-form and contains slide '79 inside of the two projections of said U-form, so that slide '79 is moved along with slide '76. Slide '79 is movable relatively to slide '76 in a directionperpendicular to shaft 81. Its relative position is controlled by a roller 85 rotatably secured to slide '79 and contacting with a straight templet 86, which is secured to the machine frame. A spring 8'7 maintains roller 85 of slide '79 in continuous contact with templet 86.

Slide '76 is slowly reciprocatecl in the direction of slot 84 by a roller 88 which is rotatably and, adjustably mounted on a disk forming part of a shaft 89, see Fig. 9 and Fig. 10. The center of roller 88 is offset from the center of shaft 89. Roller 88 engages a slot 90 provided on a part rigidly secured to slide '76.

A brake drum 91 is slidably keyed to shaft 81, and engages stationary braking means diagrammatically indicated by a brake shoe 92, which is maintained in engagement with drum 91 by spring pressure. Drum 91 is maintained in a constant and stationary axial position by means of a fork 99, which engages a slot 93 provided in the hub of drum 91, and which forms part of a member which also holds the brake shoe and which is secured to the machine frame.

A helical gear 94 is tightly secured to shaft 81 and meshes with another helical gear 95 loosely mounted on shaft 82. In the instance illustrated shaft 82 is disposed parallel to shaft 81. Gear 95 is adjustably connected with a disk 96 of shaft 82,'so that it may be adjusted to various turning positions with respect to said disk. This adjustment, which may be carried out with known means, serves to compensate for the wear of the elements '72, '78.

Truing member '78 and abrading member '72 mesh with each other in the manner of gears having helical teeth. Their pitch circles 9'7, 98 are disposed outside of the tooth zones, to secure 1,

profile sliding at all points of tooth engagement.

Truing member '78 serves to maintain true profiles on the helical teeth '73 of abrading member '72. Tothis effect, a' reciprocating feeding motion is provided between elements '72, '78 in a 1 direction perpendicular to the

shafts

81, 82, so as to move shaft 82 successively away from and towards shaft 81. As already pointed out, shaft 82 is mounted on slide '79, which moves shaft 82 towards or away from shaft 81 in relation to l ber. Superimposed to its uniform turning momerit when the masses are the masses is in a constant relation to and the tooth profiles are parts of the same curves as the tooth profiles of

elements

72, 78. Often these curves are. involutes of a circle. In this case element 72 and gear 94 are provided with equal base circles; likewiseelement 78and gear 95 also contain equal base circles.

In Fig. 9 and Fig. 10 the

shafts

81, 82 are shown in a position of closest approach, and slide 76 is indicated in a position closest to shaft 89.

On the teeth of element 78, the lower portions or flank portions may be removed. The tip portions of its teeth successively contact with the flank portions and with the tip portions of the teeth of abrading member 72, in the various positions of slide 79. Gear 95 contacts with the same side of its teeth with gear 94, as element 78 contacts with element 72. In order to effect a suitable pressure of engagement a known brake may be provided on shaft 82 or on a drum connected thereto. In the drawing I have indicated in dotted lines 100 a pa'rtwhich may serve this purpose, namely a worm meshing with gear 95. The sliding mesh between worm 100 and gear 95 furnishes a. certain amount of friction, which can be artificially increased in known manner, namely by braking the shaft with which worm 100 is connected.

From the foregoing it is seen, that the profile control of abrading member 72 is effected in a positive manner and with comparatively simpie means.

The reciprocating feeding motion of slide 76 along shaft 81 of helical abrading member 72 serves to maintain or to establish an accurate and constant lead of the teeth 73 of said memtion, abrading member 72 ismade to perform a helical reciprocation along its axis with a lead equal to the lead of its teeth 73. i

The two motions provided between the three

elements

71, 72, 78 effect the full self-correction of abrading member 72.

Turning motion is imparted-to worm gear blank 71 in any suitable known manner. Abrading member 72 is rotated through its mesh with worm gear blank 71, in which a comparatively large number of teeth are in simultaneous tooth contact. Preferably no other positive operative connection is provided between

elements

71 and 72.

In accordance with the present invention care is taken that the described additional helical motion of abrasive member 72 does not affect or not materially affect the pressure of abrasive engagement between

elements

71 and 72. Ordinarily the turning component of the aforesaid .additional helical motion would be effected through said abrasive engagement, and the inertia of the rotating masses would much increase the pressures when the masses are accelerated, and reduce the pressures of abrasive engageretarded or decelerated. Inasmuch as the acceleration and retardation of the position of slide 76, it would mean that the teeth 73 of the abrading member would be subject to more wear adjacent their one end than adjacent their other end, and that they would not maintain their constant and accurate lead.

This difliculty is overcome by a dispositionin which'thekinetic energy stored up in the rotating masses is unaffected by the additional turning motion of said helical reciprocation. It has already been pointed out, that brake drum 91 does not participate in the motion of slide 76 lengthwise of shaft 81, and that it is held axially 5 It is clear to those familiar with kinematics that provision of a larger lead on splines 102, or provision of straight splines, would cause drum 91 to be accelerated through said helical motion of shaft 81. In other words the additional rota.- tion of drum 91 would then be in the same direction as the additional rotation of shaft 81 and the masses it carries.

Helical splines 102 (Fig. 9) are provided with a smaller lead than the lead of teeth 73. The smaller lead causes drum 91 to be. decelerated or retarded, when rotation of shaft 81 is accelerated through said helical reciprocation. Similarly, when shaft 81 and the masses secured to it or operatively connected with it are retarded through said helical motion, then brake drum 91 will be accelerated.

Briefly the rotation superimposed to brake drum 91 through said helical motion is opposite to the rotation superimposed to shaft 81 and shaft 82. On account of its opposite motion drum91 is suited to balance the influence of the other rotating masses. The relations to be observed between the moments of inertia of the masses secured to

shafts

81, 82, and of drum 91, and the lead of splines 102, for effecting complete compensation and maintaining constant pressures of abrasive engagement may be determined with the known methods of kinematics.

A machine for abrading straight and helical gear teeth will now be described with reference to Fig. 11, Fig. 12, Fig. 15, and detail views Fig. 13 and Fig. 14.

A spur gear blank 110 is secured to shaft 111, which is rotatably mounted in two bearings 112 113 of a support 114. Support 114 is angularly adjustable on the machine frame 115 about a center or axis 116. A brake drum 117 is slidably keyed to shaft 111, and is engaged by stationary and adjustable braking means, diagrammatically indicated as a brake shoe 118. Reciprocating feeding motion in the direction of shaft 111 may be imparted to said shaft with any suitable known.

means of a rod 121, which contains a ball end engaging the center of shaft 111 and forming one part of a known ball joint. Lever 120 may be oscillated in any suitable known manner.

The term gear blank is used here throughoutto designate an unfinished gear, that is to say a gear which has not yet passed through the final process of abrasion, and which usually contains cut teeth.

An abrading member 124 of the general character of member 54 of Fig. 7 is secured to a shaft 125, which is mounted on a slide 126 which is vertically adjustable, that is to say adjustable in the direction of pivot axis 116, along guides 130v providedv on the machine frame; It contains a body of cup form, and is provided with teeth pro see Fig. 14. A

jecting outwardly from said body, truing member 127 is secured to a shaft 128, which is also mounted on slide 126. Trtiing member 127' contains helical teeth or threads, and is of the character described with reference to member 67 of Fig. 7.

Shafts

125 and 128 are operativeiy connected by means of a pair of hypoid gears 132',

133 of known structure, whose tooth'numbers have the same ratio as the tooth numbers of

elements

124 and 127.

Reciprocating feeding motion may be imparted to shaft 128 by means of a lever 134 and rod of the character of lever 120 and rod 121. Hypoid gear 133 is mounted on bearings 135 (see Fig. 13) secured to slide 126, and contains an internal spur gear 136 or clutch member rigidly secured to it or forming part of it. Internal gear 136 engages an external spur gear 137 or other clutch member which is slidably keyed t0 shaft 128. The one end of shaft 128 contains namely helical splines 140 having a hand and lead equal to the hand and lead of truing member 127, and which engage the hub of external gear 137.

The-axial position of external gear 137 is determined by a nut 141 of cup form, which engages a thread 142 provided on the outside of internal gear 136. External gear 137 is maintained in contact with nut 141 by a spring 143. Adjustment of nut 141 changes the axial position of the external gear 137, and on account of the engagement of said external gear 137 with the helical splines 140 also changes the angular position of said shaft. Such change is desirable for compensating for the wear of the truing member 127 and abrading member 124.

Nut 141 is so adjusted as to secure a desirable pressure of engagement between

elements

124 and 127.

Uniform motion is imparted with a belt to a pulley 144, which is secured to shaft 125. Spur gear blank 110 is rotated through its abrasive engagement with abrading member 124, which is fully conjugate to gear blank 110 and suited to contact simultaneously with a large number of its teeth. The said number of teeth is larger than the number of teeth simultaneously engaged by the rack corresponding to gear blank 110.

Truing member 127 is rotated in the manner already described.

Self-correction of the abrading member 124 is obtained through provision of a slow reciprocation of the spur gear blank 110 in the direction of its axis, and through the helical reciprocation of truing member 127, with a lead equal to the lead of its teeth.

If so desired, the last said reciprocation may be effected before or after the abrading operation proper. Also the machine may be fitted with an additional slide similar to slide 126, for mounting an additional abrading member on an axis parallel to shaft 125, and a truing member, for the purpose of abrading both sides of the teeth simultaneously, as described with reference to Fig. 7.

Member 124 may be made of abrasive material, or preferably of a uniform material to which abrasive is separately added, as described.

The machine described withreference to Fig. 11 and Fig. 12 may also be used for abrading gears having helical teeth.

One way of abrading helical teeth on this machine is illustrated in Fig. 15, where numeral 145 denotes a helical gear blank. Gear blank 145 meshes with an abrading member 146 which engages it with line contact and is suited to contact simultaneously with a large number of its teeth. Abrading member 146 is secured to shaft 125 described with reference to Fig 11 and Fig. 12, and is also engaged by a truing member of the general character of truing member 69, Fig. 8, and omitted in Fig. 15.

It is noted that support 114, on which helical gear blank 145 is rotatably mounted, is set to a different angle about center 116, than in the instance illustrated in Fig. 11, namely for instance so that the axis of the gear blank 145 and the axis of abrading member 146 are disposed at right angles to each other. The said two axes are offset from each other a distance corresponding to the diameters of gear blank 145 and abrading member 146, by adjusting slide 126.

The process of abrading helical gears is analogous to the process of abrading spur gears. The three elements provided, namely the helical gear blank 145, the abrading member 146 and the truing member are rotated in abrasive engagement with each other. Turning motion is imparted to abrading member 146, and a moderate braking load is applied to brake drum 117. Feeding motions are provided in such manner that a tip portion of one of said elements, namely of the truing member, successively engages portions of various height on the profile of another of said elements, namely of the abrading member. Moreover feeding motion is provided in a manner that a portion disposed midway between the ends of the teeth of one element (146) successively engages portions adjacent both ends of the teeth of another element (145). As described, such feeding motions may consist in slow reciprocations along two straight lines angularly disposed to each other, and particularly in a helical reciprocation. about the axis of the truing member and in another helical reciprocation about the axis of the helical gear blank 145.

In accordance with the present invention means are provided for maintaining the pressure of abrasive engagement constant and independent of the helical reciprocation of gear blank 145, in a machine which contains no operative connection between

elements

145 and 146 outside of their direct mesh. Shaft 111, Fig. 11, is here replaced by a shaft 150 of the same diameter as shaft 111, and which contains helical splines 151. These splines engage the hub of brake drum-117, which is shaped to receive selectively

shafts

150, 111, containing helical splines and straight splines respectively.

When helical splines 151 have a lead equal to the lead of the helical teeth 153 of gear blank 145, then the turning motion of drum 117 is left entirely unaffected by the helical reciprocation of the blank, which is superimposed t0 the'continuous rotation of the latter. The helical reciprocation then changes the speed of rotation of gear blank 145 and of shaft 150 only.

Often the moment of inertia of brake drum 117 is much larger than the moment of inertia of the other parts rotating on axis 152.

In this case the effect of the helical reciprocation is nearly compensated by splines having a lead equal to the lead of teeth 153.

Preferably the lead of splines 151 is made smaller than the lead of teeth 153. In this case rotation of brake drum 117 is accelerated through said helical reciprocation, when rotation of shaft 150 and blank 145 is decelerated. And rotation of brake drum 117 is decelerated when rotation of shaft 150 and blank 145 is accelerated. A complete compensation of the effects of the helical reciprocation may thus be obtained. The interrelations to be observed between the moments of inertia and the exact lead of splines, for effecting complete compensation, may be determined with the known methods of kinematics.

If so desired a similar compensation may be made for the helical reciprocation of the truing member, or the latter reciprocation may be made What I claim is:

1. The method of abrading gear teeth in a continuous process of rotation of a gear blank and of an abrading member other than its mating gear, which consists in providing at least two elements including a gear blank and an abrading member suited to mesh with said gear blank, one of said elements having equal tooth profiles in parallel planes perpendicular to its axis, in

mounting said gear blank and said abrading member on angularly disposed and offset axes in' engagement with each other, in rotating said elements in abrasive engagement, and in displacing one of said elements in a manner that a tip portion of the tooth sides of said abrading member successively engages portions of various positions of tooth height of another of said elements.

2. The method of abrading gear teeth in a continuous process of rotation of a gear blank and of an abrading member other than its mating gear, which consists in providing at least two elements including a gear blank and an abrad ing member, said elements containing teeth or threads having side surfaces suited to mesh with each other, in-mounting said gear blank and said abrading member on angularly disposed and offset axes, in rotating said elements in abrasive enagement with each other, and in effecting two 'difierent bodily displacements between said elements, namely a displacement such that a tip portion of the side surfaces of one of said elements successively engages portions of various positions of tooth height of the side surfaces of another of said elements, and another displacement such that a portion midway on the length of the side surfaces ofone of said elements successively engages portions of various lengthwise positions on the side surfaces of another of said elements.

3. The method of abrading gear teethin a continuous process ofrotation of a gear blank and of an abrading member other than its mat-.

ing gear, which consists in providing at least two elements including a gear blank and an abrading member, at least two of said elements being provided with teeth or threads having side surfaces fully conjugate to each other and suited to mesh with line contact with each other, in mounting said gear blank and said abrading member on angularly disposed and offset axes, in rotating said elements in abrasive engagement with each other, and in effecting two different bodily displacements between said elements while in engagement with each other.

4. The method of abrading gear teeth of constant profiles in parallel planes perpendicular to the gear axis, which consists in providing a gear blank and an abrading member containing at leastone helicoidal thread, the profile of an axial section of said thread being curved and being 9 of teeth or threads, and in providing feeding motions between said gear blank .and said abrading member along the axis of said gear blank and along a straight line angularly disposed to said axis, said straight line being contained in a plane parallel to the axes of said gear blank and said abrading member.

5. The method of abrading gear teeth, which ing" motions between said elements along two straight lines angularly disposed to each other, so that a tip portion of the. side surfaces of one of said elements successively engages portions of various positions of tooth height of another, of said elements.

6. The method of abrading a plurality of equal gears, which consists in mounting two rotary elements suited to engage in gear mesh with each other on angularly disposed and offset axes, said elements comprising a gear blank and an abrading member differently related to each other than said gear and its mating gear, one of said elements containing constant tooth profiles in parallel planes perpendicular to its axis, the other of said elements having differing tooth profiles in parallel planes perpendicular to its axis, in'

amount from the axis of said abrading member as the axis of the first said gear blank, and in successively rotating said gears in abrasive engagement with said member until the tooth thickness of said member is reduced at least ten percent.

7. The method of abrading gear teeth, which consists in providing two elements, namely a gear blank and an abrading member, both of said elements containing a plurality of teeth and being suited to mesh with line contact with each other, one of said elements having equal tooth profiles in parallel planes perpendicular to its axis, in mounting said elements on angularly disposed and offset axes, in rotating said elements in abrasive engagement with each other at the inverse ratio of their numbers of teeth, said ratio being effected through said engagement alone, and in providing reciprocatory feeding motions between said elements along-two straight lines angularly disposed to each other. V

8. The method of abrading gear teeth of constant profile in parallel planes perpendicular to the gear axis, which consists in providing at least two toothed elements including a gear blank and an abrading'member other than a mating gear,'said abrading member being conjugate to inclined to a radius at an angle smaller thanthe gear to be produced from Said gear blank and the normal pressure angle of said gear blank, in mounting said gear blank and said abrading member on angularly disposed and offset axes, in rotating said gear blank and said abrading member in abrasive engagement with each other at the inverse ratio oftheir respective numbers suited to contact simultaneously with a number of its teeth at least fifty percent larger than the rackconjugate to said gear, in mounting said elements-on angularly disposed and offset axes, in rotating said elements in abrasive engagement with each other atthe inverse ratio of their numbers of teeth, and in providing reciprocatory feeding motion between said elements.

9. The method of abrading gear teeth of substantially constant profile in parallel planes perpendicular to the gear axis, which consists in providing at least two toothed elements includ ing a gear blank and an abrading member other thana mating gear, said abrading member being conjugate to the gear to be produced from said gear blank and suited to contact simultaneously with a number of its teeth at least fifty percent larger than the rack conjugate to said gear, in mounting said elements on angularly disposed and oifset axes, in rotating'said elements in abrasive engagement with each other at the inverse ratio of their numbers of teeth, said ratio being effected through' said engagement alone, and in providing reciprocatory feeding motion between said elements.

10. The method of abrading gear teeth, which consists in providing threetoothed elements including a gear blank and an abrading member,

said elements being interrelated inya manner that one element is suited to engage in difierent gear mesh with the other two elements, in mounting said elements so that the axes of said other elements are angularly disposed to and offset from the axis of said one element, in rotating said one element in abrasive engagement with said other elements so that the same side of its teeth contacts with both of said other elements, and in providing reciprocatory feedingmotions between said elements along two straight lines angularly disposed to each other.

11. The method of abrading gear teeth, which consists in providing three toothed elements, namely a gear blank, an abrading member and a truing member, said elements being interrelated in a manner that said abrading member is suited to engage in difierent gear mesh with said gear blank and said truing member, two of said elements having constant tooth profiles in parallel planes perpendicular to their respective axes, in mounting said three elements on three difierent and offset axes so that axes of the gear blank and a process of continuous rotation of a gear blank, means for rotatably mounting three intermeshing elements, said elements including a gear blank and at least one abrading member, the axes of two of said elements other than said gear blank being parallel and angularly disposed to and offset from the axis of said gear blank, means for rotating said elements on their axes at a speed inversely proportional to their respective numbers of teeth, and means for efiecting reciprocatory feeding motions between said elements along two straight lines angularly disposed to each other.

13. In a machine for abrading gear teeth in a process of continuous rotation of a gear blank, means for rotatably mounting at least two intermeshing elements, said elements including a gear blank and an abrading member, means for applying power to one of said elements for rotating said intermeshing elements through their abrasive engagement, braking means operatively con nected with another of said elements for effecting pressure of abrasive engagement, means for superimposing a helical reciprocation to the motion of one of said elements, and means for maintaining the pressure of abrasive engagement independent of said helical reciprocation.

14. In a machine for abrading gears, the combination of two rotary members fully conjugate to each other and suited to mesh with line contact with each other in the manner of a pair of gears, said members comprising an abrading member and a truing member representing a gear other than the gear to be abraded, one of said members having constant tooth profiles in parallel planes perpendicular to its axis.

ERNEST