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THE
LATHE
The sizes
of turning lathes are given as 10", 12", etc. These figures denote
the diameter, or size, of the largest piece of work that can be
turned on them. The measurement is taken from the center point of
the live center to the bed of the lathe (usually 5" or 6") and is
one-half the diameter of the entire circle. The length of a lathe
is determined by the length of a piece of work that can be turned.
This measurement is taken from the points of the live and dead centers
when the tail stock is drawn back the full extent of the lathe bed.
Fig. 1 shows a turning lathe with sixteen principal parts named.
The student should learn the names of these parts and familiarize
himself with the particular function of each.
CARE
OF THE LATHE
The lathe
should be oiled every day before starting. At the end of the period
the lathe should be brushed clean of all chips and shavings, after
which it should be rubbed off with a piece of waste or cloth to
remove all surplus oil. All tools should be wiped clean and put
in their proper places. If a student finds that his lathe is not
running as it should, he should first call the attention of the
instructor to that fact before attempting to adjust it; and then
only such adjustments should be made as the instructor directs.
SPEED
OF THE LATHE
The speed
of the lathe should range from 2400 to 3000 revolutions per minute
when the belt is on the smallest step of the cone pulley. At this
speed stock up to 3" in diameter can be turned with safety. Stock
from 3" to 6" in diameter should be turned on the second or third
step, and all stock over 6" on the last step. The speed at which
a lathe should run depends entirely upon the nature of the work
to be done and the kind of material used. Pieces that cannot be
centered accurately and all glued-up work with rough corners should
be run slowly until all corners are taken off and the stock runs
true. At high speed the centrificial force on such pieces is very
great, causing the lathe to vibrate, and there is a
possibility of the piece being thrown from the lathe thus endangering
the worker as well as those around him. After the stock is running
true the speed may be increased.
Fig. 1. - Wood Turning Lathe
TO
FIGURE THE DIAMETER OF PULLEYS
Suppose
a motor runs 1500 R.P.M. and is fitted with a 4" pulley. Suppose
also, a main shaft should run 300 R.P.M.
Then,
1500 : 300 :: x : 4;
Or, 300x = 6000,
x = 20, or the diameter of the large
pulley on the main shaft.
Suppose
again that a line shaft runs 300 R.P.M., and a counter shaft 600
R.P.M. The counter shaft has a pulley 4" in diameter. The pulley
on the line shaft must then have a diameter of 8".
300
: 600 :: 4 : x;
Or, 300x = 2400,
x = 8"
Suppose
the cone pulley on the counter shaft runs 600 R.P.M.; a lathe spindle
runs 2200 R.P.M., when connected with the small cone pulley which
has a diameter of 3". The large cone pulley has then a diameter
of 11".
600
: 2200 :: 3 : x
Or, 600x = 6600;
x = 11"
RULES FOR FINDING THE SPEEDS AND SIZES OF PULLEYS
1. To
find the diameter of the driving pulley:
Multiply
the diameter of the driven by the number of revolutions it should
make and divide the product by the number of revolutions of the
driver. (20 x 300 = 6000; 6000 ÷ 1500 = 4"--diameter of motor pulley.)
2. To
find the diameter of the driven pulley:
Multiply
the diameter of the driver by its number of revolutions and divide
the product by the number of revolutions of the driven. (4 x 1500
= 6000; 6000 ÷ 300 = 20"--diameter of the driven pulley.)
3. To
find the number of revolutions of the driven pulley:
Multiply
the diameter of the driver by its number of revolutions and divide
by the diameter of the driven. (4 x 1500 = 6000; 6000 ÷ 20 = 300--revolutions
of driven pulley.)
POINTS
ON SETTING UP LATHE AND SHAFTING
The counter
shaft should be about 7' above the lathe. A distance of 6' from
the center of the shaft to the center of the spindle is sufficient.
In setting a lathe or hanging a counter shaft it is necessary that
both be level. The counter shaft must be parallel to the line shaft.
When the counter shaft is in position a plumb bob should be hung
from the counter shaft cone to the spindle cone; the lathe should
be adjusted so that the belt will track between the two cone pulleys.
The axis of the lathe must be parallel to that of the counter shaft.
The lathe, however, need not be directly beneath the counter shaft
as the belt will run on an angle as well as perpendicular.
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