File:Design of a universal portable electric drill (1920) (14594781029).jpg

Identifier: designofuniversa00conn (find matches)
Title: Design of a universal portable electric drill
Year: 1920 (1920s)
Authors: Connell, Edwin Lewis
Subjects: Electric drills Theses
Publisher:
Contributing Library: University of Illinois Urbana-Champaign
Digitizing Sponsor: University of Illinois Urbana-Champaign

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thegear according to stiructural requirements. Workmanship is anotherimportant item. The total ratio of 16 to 1 required must be divided betweenthe armature pinion and conpound gear and the compound pinion andspindle gear; about 4 to 1 fo r each r^tio. It is desirpble tokeep the outline of the lower head within the diameter of themotor housing for several reasons. A layout shows that 43 teethof 24/26 pitch meshing with the armature pinion and 54 teethof 20/22 pitch on the spindle ger.x meshing with a compound pinionof 12 teeth will meet this requirement ani give us a ratio of 16to 1. The material and treatment required to carry the load withthese gears can be determined by calculation of the stress obtainedafter assuming the face desirable from the standpoint of space andother structural requirements. See i^igure 20. Assuming a normal load of .4 HP at 5500 RPM on the armaturepinion the working stress in the pinion and compound gear v/ill beas follows: V/ _ HP X 33000s - and w p f y V
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41 w - Load transmitted in poimds.p r GirGula.r pitchf - iiaoe y - iactoi- for different number and fornsof teeth. See hn.nd books. s - Safe working stress of material. V = Velocity in feet per minute.V = .0417 X 5500 - 721w = .4 X 33000 s 18,3 lbs. 72118.3 s = 4780 Dinion .1309 X .375 X .078 18 .3 = 2960 gear .1309 X .375 X .1E6 At a speed of 721 feet per minute these stresses ^re v/ell withinthe safe limits for mild steel but the pinion v>fould be the fiistto fail. Repeating this calculation for the compound pinion andspindle gear: 5500 V - .05~Tr X ■ 3.58 .4 X 33000w = = 54.5 lbs. 242 54.5 s - ■ - 7920 pinion .157 X .5625 X .078 s - 54.5 - 4630 gear .157 X .5625 X .132ihese stresses ^re ?,lso srfe for mild steel but in the pinion 42 is very close to the iisiis,! limit. It hes been found advisableto use 3-;/o nickel .19 ci.rbon steel for both armature snd com-pound pinions. These parts would be case hardened l/64 deepto test about 80 in the scleroscope. Nickel steel will show

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