. Canadian machinery and metalworking (January-June 1919). ight emerg-ing fv >v\ the lens Apass through thehelix angle. This to be the casewhen the fringe pat-tern which is formedabout the image ofthe screw due to im-perfect focus is sym-DESIGNED BY the metrical. The screw-is then brought intofocus by a slow mo-and the adjustments tion arrangementare complete. The examination of the thread angleis made with the aid of a device shownin Fig. 2. The standard angle M knownto be 60° is supported by three columnson the stand T, on which rests a pro-tractor ring P carrying the standardang
. Canadian machinery and metalworking (January-June 1919). ight emerg-ing fv >v\ the lens Apass through thehelix angle. This to be the casewhen the fringe pat-tern which is formedabout the image ofthe screw due to im-perfect focus is sym-DESIGNED BY the metrical. The screw-is then brought intofocus by a slow mo-and the adjustments tion arrangementare complete. The examination of the thread angleis made with the aid of a device shownin Fig. 2. The standard angle M knownto be 60° is supported by three columnson the stand T, on which rests a pro-tractor ring P carrying the standardangle and the straight-edge E. Duringthe examination of the thread angle thestandard angle is adjusted so that its 114 CANADIAN M A C III N E R Y Volume XXI. shadow occupies the light space of theprojected image on the surface of thetable below. The standard angle is re-volved so that one side exactly matchesthe shadow of the thread and the read-ing of the graduated head is done bymeans of the magnifying glass R. Thestandard angle is then revolved until it. PIG. 2—BEVEL PROTRACTOR USED IN coincides with the other side of thethread and a reading is again difference between the two readingsgives the error of the thread protractor can be further used todetermine whether the thread is sym-metrical with D, a line perpendicular tothe axis of the gauge being tested. The use of the protractor results ina very high degree of accuracy being-maintained. The eye is viewing two ob-jects of similar character, two shadowsand these can be made to approach untila faint, even thread of light remainsbetween the two—an inaccuracy of onlya few minutes can be easily paper may be used wheiea permanent record is desired. Equipments of this kind are made toprovide for obtaining a magnification ofeither 44, 65, or 115 times actual sizebetween the work and the face of themirror; then by regulating the distancebetween the mirror and the stage Nupon which the
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectmachinery, bookyear19
