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HORSE-POWER. 319
Power of Man.
A man may be able to do work at a rate of 4000 foot-
pounds per minute ; for instance, in turning a crank on a crane
or derrick, a force of 15 pounds may be exerted on a crank, 18
inches long and, with 30 turns per minute, the work would be
4228 foot-pounds per minute.
Note.—In derricks, pulley blocks, jack-screws, etc., a large
part of the expended power is consumed in overcoming friction.
Power Required to Drive Various Kinds of Machinery.
In the nature of the thing it is impossible from experiments
on one machine to tell exactly what power it takes to run an-
other similar machine, as there are so many different factors
entering into the problem ; for instance, the speed and feed on
the machine, the hardness of the stock it works on, the quality
of the tools used, the kind of lubrication, etc. Therefore, such
assertions are only approximations at the best.
16-inch engine lathe, back geared, % horse-power.
26-inch engine lathe, back geared, 1 % horse-power.
Planer, 22" x 22" x 6 feet, % horse-power.
Planer, 32" x 32" x 10 feet, U horse-power.
Shaping machine, 10-inch stroke, % horse-power.
20-inch drill press, y
2 horse-power.
26-inch drill press, back gear, boring
a 3-inch hole, using boring bar, 1 horse-power.
Plain milling machines (Lincoln
pattern, No. 2), 1 %. horse-power.
Small Universal milling machines, X horse-power.
Circular saws (for wood), 24" di-
ameter (light work), 3>£ horse-power.
Circular saws (for wood), 36" di-
ameter (light work), 6 horse-power.
Fan blower for cupola, melting four
tons of iron per hour, 10 horse-power.
Fan blower for five blacksmith fires, 1 horse-power.
Drop hammer, 800 pounds, 8 horse-power.
In machine shops and similar places, from 40% to 70% of
the total power required is consumed in running the line shaft-
ing and counter-shafts. An average of from 55% to 60% is
probably the most common ratio.
In exceptionally well-arranged establishments, under favor-
able conditions, in light. manufacturing it may be possible that
only 30% of the power is consumed in driving line and counter
shafting, and that 70% is used for actual work.
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