This historic book may have numerous typos and missing text.
Purchasers can download a free scanned copy of the original book
(without typos) from the publisher. Not indexed. Not illustrated.
1918 Excerpt: ...angle less than 90) it will generate a cone and
the curve made by the moving point will be a "conical helix." When
the angle becomes 90 degrees the helix degenerates into a spiral.
To Draw the Projection of a Helix.--Fig. 305. Divide the circle of
the end view of the cylinder into a number of equal parts, Fio.
305.--The helix and its development. and the lead into the same
number. As the point moves around through one division it will
advance a proportional distance of the lead; when half way around
the cylinder it will have advanced one-half the lead. Thus the
curve may be found by projecting the elements represented by
divisions of the circle to intersect lines drawn through
corresponding divisions of the lead. If the cylinder be developed
the helix will appear on it as a straight line inclined at an angle
whose tangent is v The conical helix ITU is drawn similarly, the
lead being measured along the axis. Screw Threads.--Threads are
always understood to be single and right hand unless otherwise
specified. A single thread has one thread of whatever section cut
on the cylinder. When it is desired to give a more rapid advance
without using a coarser thread two or more threads are cut side by
side, giving double, triple, etc., threads, as illustrated in Fig.
306. A right-hand thread advances away from the body when turned
clockwise. A left-hand thread is always marked plainly "L.H." and
may be recognized also by the direction of the slant. The pitch of
a thread is the distance from center to center of consecutive
threads. The lead has already been defined as the distance advanced
in one revolution. In a single thread therefore the pitch and lead
are equal, in a double thread the lead is twice the pitch,
similarly for other multiple threads...
|Country of origin:
Thomas Ewing French
||246 x 189 x 4mm (L x W x T)
||Paperback - Trade
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