Worm gearing . thehollow and the straight worm. This point must be insistedupon. Here, however, there comes a difference. The straightworm perpetually re-generates the surface of the wheel toothmaintaining the correct involute outline to the end of its life,and in the other type, as the pressure is always along thecentral plane, it follows that the greatest wear takes place alongthis line and the tendency is to finally reduce the worm wheelto the form of Fig. 11. The word tendency is used advisedlybecause the rate of wear on any perfectly made worm gear isalmost inappreciable so that the diffe
Worm gearing . thehollow and the straight worm. This point must be insistedupon. Here, however, there comes a difference. The straightworm perpetually re-generates the surface of the wheel toothmaintaining the correct involute outline to the end of its life,and in the other type, as the pressure is always along thecentral plane, it follows that the greatest wear takes place alongthis line and the tendency is to finally reduce the worm wheelto the form of Fig. 11. The word tendency is used advisedlybecause the rate of wear on any perfectly made worm gear isalmost inappreciable so that the difference between the two israther an academic one. One advantage the side of theLanchester worm; since the sides of the wheel never touch the 32 WORM GEARS worm, they can be cut away altogether and the wheel con-siderably reduced in width and weight thereby. Its disadvan-tage is that the worm cannot by any mechanical device beground on any of its finished working surfaces, so less accuratefinish must Fig. 11. Another argument presents itself against the use of this type:it is that it is harder to assemble and adjust, since the wormmust be truly located on the wheel in three planes, while thestraight one requires adjustment in only two. This necessityfor exact location in the axial direction of the worm demands PRESSURE ANGLE AND FORM OF THREAD 33 much more care of the thrust bearings and further when theworm becomes warm under use expansion must take placeendways and the contact be impaired. The fact remains,however, that this form of gear is entirely satisfactory if per-fectly made and in point of efficiency, the experiments ofthe Brown & Sharpe Manufactiu-ing Company^ referred to inChapter X show that the efficiency of the hollow worm ap-proaches that of the straight so nearly that the difference maybe said to be negligible and it is extremely doubtful if a suffi-cient number of examples were taken whether this differencewould as an average exist at all. ^ The Bro
Size: 1501px × 1664px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookpublishernewyo, bookyear1916
