Abstract
The accuracy of the gears cut by a gear-hobbing machine is extremely influenced by the error of the master worm gearing. This paper presents : 1. A measuring method of the accumulative pitch error of the master worm wheel applying the scratch marking method similar to "smoked-glass test" of J.M. Newton, and a seismograph method for the worm cyclic error measurement and their results. 2. Three kinds of the error compensating equipments applying the analog- and digital-programming systems for compensation of the accumulative pitch error and the worm cyclic error, and their results. The scratch marking method is proved to have good repeatability in the accumulative pitch error measurement of the work table in running condition with high accuracy and handy operation. The seismograph method is proved to have high sensitivity and reliability in measurement of the worm cyclic error on the machine table. In the error compensator, the compensating instructions corresponding to the error measurement records are programmed on a disc cam or on a perforated tape digitally. Following these instructions, a hydraulic servo-system or an electronic-hydraulic servo-system adds the error compensating motion to the rotation of the master worm shaft of the hobbing machine. In the preliminary experiment of the 24"-gear hobbing machine, the maximum accumulative pitch error of the cut gear is reduced from 85 seconds in angle at the non-compensated condition, to 25 seconds in angle by the error compensator. The practical test record on the 5 meters master gear hobbing machine with a pitch error compensator shows the satisfactory result that the maximum accumulative pitch error of the cut gear reduces to 2 seconds in angle from 4 seconds in the case of not compensating. In fabrication of big gear hobbing machines of high accuracy, the benefit of the application of the pitch error compensator for the purpose of reduction of the painstaking skilled work in the finishing of the accurate master worm gearing is emphasized. Finally a plan of the numerically controlled pitch error compensator is described.
