Mechanical drawing self-taught: comprising instructions in the selection and preparation of drawing instruments, elementary instruction in practical mechanical drawing together with examples in simple geometry and elementary mechanism, including screw threads, gear wheels, mechanical motions, engines and boilers (1883)
Fig. 250. ?A2 MECHANICAL DRAWING SELF-TAUGHT. divided with great facility and accuracy by a verysimple process, which we take from Prof. RankinesMachinery and Mill Work, and is illustrated in Fig-ure 252. Let O B be tangent at O to the arc O D,of which C is the centre. Draw the chord D O, bisectit… … Fig. 252. exceed about 60 degrees; if it be 60 degrees, theerror is theoretically about ^00 of the length of the arc,O B being so much too short; but this error varies withthe fourth power of the angle subtended by the arc,so that for 30 degrees it is reduced to ^u of thatamount, that is, to ttIod.…
Mechanical drawing
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