Patent GB-544556-A (GB)
Title: Method of producing gears
IPC: B23F9/10
Filed: 1940-10-16
Abstract: 544,556. Gear-cutting. GLEESON WORKS. Oct. 16, 1940, No. 15346. Convention date, Nov. 21, 1939. [Class 83 (iii)] In a method of generating curved tooth tapered gears such as bevels or hypoids, the ratio of the generating rolling movement between the tool and blank is varied during the generation of each tooth surface, a different variation being employed in generating the opposite sides of the teeth. By this method gears of widely varying spiral angles, cone angles and cone distance, may be cut on the same machine particularly where gear pairs of the " formate" type, i.e. those in which the gear is form-cut and only the pinion is generated are to be produced. A formate pinion 20, Fig. 1, may be generated by a face mill cutter C. According to prior practice such a pinion, if forming part of "rightangle bevel gearing was generated conjugate to the mate gear having an axis 27 at right angles to the pinion axis. In order to eliminate bias bearing the cone distance of the generating gear was modified, being smaller than that of the mating gear for generating the concave tooth sides and larger for generating the convex tooth sides. The axes of these modified generating gears are shown at 28, Fig. 1, and 37, Fig. 3, and the generating movement of the cutter C was performed about these axes. The cutter axis has therefore to be inclined to the generating or cradle axes. According to the invention the pinion is generated by a cutter C which represents a nominal crown wheel, having an axis 30 passing through the point 29 'for the concave tooth sides or an axis 35 passing through point 36 for the convex sides. In forming the concave sides the cutter C rotates on its axis 24 while the pinion blank rotates on its axis 21, in unison with a movement of the cutter about the axis 30 the ratio between the latter movements being continuously varied. The profile 42, Fig. 5, represents the theoretical profile conjugate to the non-generated mating gear and 43 represents the involute profile produced by the usual constant-ratio rolling motions. The cutter positions required to form the profile 42 are shown at 25<SP>11</SP>, 25, and 25<SP>1</SP> and the corresponding cutter positions for the involute profile are shown at 25 2 , 25, 25 1 . The distance between the edges 251, 25, is less than the distance between the edges 25, 2511. Thus the crown wheel movement of the cutter requires to be accelerated during the roll from positions 251 to 2511. Similarly it is shown that for cutting the convex tooth sides, the crown wheel movement of the cutter requires to be retarded during the roll from positions corresponding to those shown in Fig. 5. The invention is equally applicable to cases where either the work or the tool has the entire rolling movement. In the application to hypoid gears, Fig. 10, the axis 54 of the nominal crown gear is offset from the axis 51 of the pinion 50, the cutter axis being displaced along the arc 55, 55<SP>11</SP> in steps which are not equal for equal turning movements of the pinion. Face mill gears of standard pressure angle may be used to generate gears of larger or smaller pressure angle by rolling the blank as though its pitch cone were smaller or larger respectively than its actual pitch cone. The invention may also be applied to spiral bevel or hypoid gear generators having tilt and swivel adjustments of the cutter but where the tilt angle adjustment is not sufficient to allow the cutter to represent the mate gear and where the radial adjustment is not sufficient for the cutter to be positioned to represent a crown gear. Thus if 83, Fig. 9, represents the axis of the mating gear of the pinion 80 the cutter may be set so that it represents a gear whose axis 87 is inclined at an angle which is within the range of adjustment of the machine, the ratio of the rolling movements being suitably varied. The non-generated gear may have either conical or spherical tooth surfaces according as a straight sided or arcuate profile face mill is employed for cutting it. In some cases the invention may be applied to cutting the gear member of a pair whereof both gear and pinion are generated. In the case of gears of low or zero spiral angle, Fig. 12, the cutter centre 95 may require to be located at a distance from gear cone apex 93 which is beyond the range of the machine. This distance may be reduced by arranging the cutter to represent a tapered gear other than the mate gear, the rolling ratio being suitably modified. In a similar way the settings for generating the pinion may be brought within the range of the machine. In the application to the cutting of gear pairs of large cone distance, Fig. 15, the basic crown wheel represented by the cutter would normally have its centre at 121 and a large machine would be required. In this case the gear and pinion are both generated conjugate to a basic gear whose axis is at 130 the cutter being swung about this centre at a non- uniform speed while the blank is uniformly rotated. If the points 1271, 127<SP>11</SP> on the theoretical arc of cutter movement are equidistant from 127 the corresponding points on the arc 129<SP>1</SP> concentric with the new centre 130 are obtained by drawing lines 132, 133 parallel to the tangent 126 to the tooth curve. In a modification of this method the centre 130 need not be located on the line 121, 127. Grinding-wheels or other tools may be used instead of face-mill cutters.