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SPEED OF MACHINERY. 32]
about 40 feet per minute. Oil is used for lubrication. Cast-
iron is milled without oil.
Grindstones.
When grindstones are used to grind steel and iron in manu-
facturing, they work at a surface speed of 2000 to 2500 feet per
minute, but grindstones for common shop use, to grind tools,
chisels, etc., run at much slower speed.
Emery Wheels and Emery Straps.
Emery wheels and straps do good work at a speed of 5000
to 6000 feet per minute, but all such high-speed machinery,
especially grindstones and emery wheels, must be used very
carefully and special attention paid to the strength, so that they
will not break under the stress of centrifugal force.
Calculating Size of Pulleys.
TO FIND SIZE OF PULLEY ON MAIN SHAFT.
Multiply the diameter of pulley on counter-shaft by its
number of revolutions per minute, and divide this product by
the number of revolutions of the main shaft, and the quotient is
the diameter of the pulley on the main shaft.
Example.
A main shaft makes 150 revolutions per minute ; the counter-
shaft has a pulley 9 inches in diameter and is to make 400 revolu-
tions per minute. What size of pulley is required on the main
shaft?
Solution :
Diameter of pulley = 400 X 9
= 24 inches.
150
to find size of pulley on counter-shaft.
Rule.
Multiply the diameter of pulley on the main shaft by its
number of revolutions per minute, and divide this product by
the number of revolutions of the counter-shaft; the quotient is
the diameter of the pulley on the counter-shaft.
Example.
The pulley on a main shaft is 36 inches in diameter and it
makes 150 revolutions per minute ; the counter-shaft is to make
450 revolutions per minute. What size of pulley is required ?
Solution:
Diameter of pulley = 36 X 150
= 12 inches.
450
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