This machine has a hollow piston, the drill-holder being a screw passing
through the piston, moving with it, and fed through it, by means of a
nut on the end of the piston-rod. This nut is held by means of a cap or
union nut, as it is called, the union nut being screwed on to the
coupling, and the coupling nut screwed to the piston-rod. The feed-nut
protrudes through the union nut, and is allowed to turn round in it. On
the end of this feed-nut is a ratchet gear covered by a ratchet-band
with an arm upon it, all moving with the piston. The ratchet arm moves
up and down in a spiral groove, the groove being in a shield attached by
screws to the cylinder; on the ratchet-band there is a pall and two
springs, one under the other. One of the springs holds the pall in gear,
the other holds it out of gear. As the piston moves down, the outer
spring comes in contact with a trip which is on the shield and is lifted
up, allowing the under spring to throw the pall into the ratchet, and as
the piston is moved back, turns the nut round, thereby feeding the screw
forward. At the extremity of its backward stroke, the pall comes in
contact with another trip on the shield which lifts it out of gear, the
outer spring having a catch upon it which holds the pall when thus
lifted out. The rotary motion is given by a ratchet on the coupling-nut,
covered by a ratchet-band the arm of which moves in a spiral groove in
the shield similar to the other, only having a spring to hold the pall
in the ratchet; this rotates all the parts on the piston except the
ratchet-bands and cross-head. The latter is held between two check-nuts
on the coupling-nut. To this cross-head is attached a bar which
communicates with a valve which opens the port when the piston moves
back, and shuts it when it moves forward; the air is always on during
its backward stroke. The piston having a greater area on the forward
than on the backward stroke, overcomes the backward pressure and moves
the piston ahead, and when cut off, the continued pressure forces the
piston back.
This machine is automatic; generally running until some portion of it is
destroyed. No part of the machine has been found strong enough to
withstand the friction upon it for any considerable portion of time. The
union nut has proved its weakest point, and the breaking of this
generally destroys that part of the piston to which it is attached.
Another point of weakness is the feed ratchet-band, the springs of which
are almost continually breaking.
The machine consists of eighty pieces; twenty-three of which are screws,
fifteen pins, and seven pieces of cast iron. It weighs 240 pounds, runs
about 200 strokes per minute, and costs about $400. Its longest run
without breaking has been five days. The run of one of them two days
without breaking during the time, is considered fortunate. The average
breaking is more than one a day. A table showing the list of breakages
will follow this description.
The piston-head of this machine has a diameter of 4-5/8 inches. The
diameter of the piston-rod is 4 inches at the large end and 2-1/4 at the
small end.
So there are 12-87/100 square inches of air area to drive the drill
ahead into the rock, and 4-23/100 to draw it out; but as the air is not
taken off from the front end, the actual pressure is upon an area of the
difference between the two, or 8-64/100 square inches.
Table showing Number of Drilling-Machines Broken, &c.
Column Headers
A. No. Machines Broken.
B. Cross Heads
C. Cylinder Flanges.
D. Coupling Nuts.
E. Feed Springs.
F. Feed Palls.
G. Ratchet Covers.
H. Valve Stems.
I. New Packing.
J. Tapper Bars.
K. Screw Spindles.
L. Union Coupling Nuts.
M. Feed Nuts.
N. Shields.
O. Piston Heads.
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1866. [A] [B] [C] [D] [E] [F] [G] [H] [I] [J] [K] [L] [M] [N] [O]
----------------------------------------------------------------------
July 21, 32 5 2 4 3 2 2 1 10 7 - - - - -
31, 67 7 2 1 10 4 5 2 18 14 2 3 - - -
Aug. 7, 75 4 1 - 18 15 8 4 39 6 4 - - - -
14, 76 6 - 5 25 17 11 3 - 10 1 6 1 1 -
21, 65 7 1 3 28 15 13 7 - 12 - 1 2 - -
31, 102 1 1 9 64 7 18 2 - 10 2 4 5 1 -
Sept. 7, 65 1 1 - 27 4 24 - - 5 2 1 1 - -
14, 60 2 5 - 23 2 12 2 - 10 - 3 2 1 1
21, 56 1 1 1 28 6 13 - - 3 - 1 2 2 -
30, 56 3 2 1 31 3 16 2 - 4 - 1 9 1 -
Oct. 7, 54 7 - - 39 2 7 1 - 9 3 - 1 2 -
14, 53 5 1 2 28 5 10 1 - 9 1 4 6 2 -
21, 58 3 - - 28 4 13 - - 9 3 - 4 2 -
31, 77 7 1 2 63 4 11 2 - 12 1 2 6 2 -
Nov. 7, 38 2 - 2 19 3 13 - - 8 2 - 3 4 -
14, 40 1 1 - 17 2 9 - - 8 3 2 4 - -
21, 44 - 1 - 32 1 4 - - 7 - 1 1 1 -
31, 66 - - - 34 2 11 - 13 8 1 1 - 1 -
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1,084 62 20 30 517 98 200 27 80 151 25 30 47 20 1
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About forty of the Brooks, Burleigh and Gates machines have been used at
the tunnel; of these eight or ten were originally vertical, and intended
for use at the Central Shaft. At the commencement of their use, the
machines were new and had their best wear in them; there were from
twenty to twenty-four at the beginning. In a short time they began to
break down, but by putting on a large repair force and converting the
vertical machines into horizontal ones, a fair supply was kept up for
from two to three months, at the end of which time the greatest machine
progress was attained, viz., fifty-four feet and six inches, in
September. After that the progress diminished very much, and in
proportion to the giving out of the machines. It is the opinion of the
engineer that if a constant supply of machines could have been
furnished, that the progress would have reached a point much beyond that
obtained by hand labor; but with the stoppage of the supply, the number
of machines that could be kept in working order was daily reduced, and
at last it fell down to two or three, and finally, at times, none were
in condition to work. The frames were, however, kept in the tunnel to
await the completion of the Burleigh machine, the reception of which was
retarded till late in October; much beyond the time anticipated by the
commissioners, although the work of their construction was carried on
continuously night and day. They came at intervals of several weeks, two
at a time; the first of which were put into the tunnel on the
thirty-first day of October. Through the month of December, four of
these machines were at work.