Full resolution (JPEG) - On this page / på denna sida - Screws - Cutting multiple-threaded screws and nuts by the engine lathe - U. S. Standard screws
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41
8
SCREWS.
The most practical way to move the tool from one thread
to another, when cutting double-threaded screws or nuts, is
to select a gear for the stud or spindle of the lathe having a
number of teeth which is divisible by two, and when one thread is
cut make a chalk mark across a tooth in this gear onto the rim of
the intermediate gear ; count half way around the gear on the stud
and make a chalk mark across that tooth; drop the swing plate
enough to separate the gears, pull the belt by hand until the oppo-
site mark on the gear on the stud comes in position to match the
chalk mark on the intermediate gear; clamp the swing plate again
and the tool is in proper position to cut the second thread.
When triple threads are to be cut, select a gear for the
spindle or stud whose number of teeth is divisible by three,
and in changing the tool from one thread to the next, only turn
the lathe enough so that the gear on the stud moves one-third
of one revolution.
If, for any reason, it should be inconvenient to make this
change by the gear on the stud, the change may be made by the
lead-screw gear. The intermediate gear is first released from the
gear on the lead-screw, which is then moved ahead the proper
number of teeth, and again connected with the intermediate gear.
The proper number of teeth to move the gear on the lead-screw
is obtained by the following rule
:
Multiply the number of teeth in the gear on the lead-screw
by the number of threads per inch of the lead-screw ; divide this
product by the number of threads per inch of the screw to be
cut, and the quotient is the number of teeth that the gear on the
lead-screw must be moved ahead.
Example.
A square-threaded screw is to have ^-inch lead and triple
thread. The lead-screw in the lathe has two threads per inch,
and the gear on the lead screw has ninety-six teeth. How many
teeth must the gear on the lead-screw be moved, when changing
from one thread to the next ?
Solution
:
A screw of >^-inch lead with triple thread has six threads
2 X 96
per inch, therefore the gear must be moved —^—- = 32 teeth,
in order to change the tool from one thread to the next.
_60 ^ U. S. Standard Screws.
/JUk /JH^ ^£* * shows the shape of
_^^^^k_^^^[ thread on United States stand-
^^^^^^^^^P ard screws. The sides are
^^^^^^^^^ straight and form an angle of
^^w^^^^ sixty degrees, and the thread is
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