Has a solid piston (so called,) which has a hole in its back end to
allow the feed-screw to pass in without touching; the drill is secured
to this piston. On the back end of the piston is a section of a ball
used as a cam, which works the valve and the feed-motion. The valve is
rotated by a rod lying on the band of the cylinder; upon this rod are
two cams which perforate the band of the cylinder. The action of the
piston brings the ball on its end in contact with these cams, rocking
them up and down; the rod to which they are secured being connected with
the valve, imparts to that its motion. This machine is fed altogether on
ways, or a bed-piece, upon which is the feed-screw; the feed-nut is upon
the end of the cylinder-band. To this feed-nut is attached a
feed-ratchet, which is held between two collars, allowing it to turn
round. Upon the cylinder-band is a lever, one end of which passes
through the band; upon the other end is a pall. The motion of the piston
raises the lever up, pressing the end containing the pall against the
ratchet which turns the nut on the feed-screw, thus moving the machine
forward. The rotating ratchet is in the band of the cylinder and has a
spline in it, and a pall on its outside. The piston having a spiral
groove is turned by this ratchet as it moves down. On the return of the
piston, the pall drops into the ratchet and then the piston is turned.
The piston is not encumbered with any machinery, and moves alone; its
area of air is greater on the forward than on the backward stroke; the
alternation of the valve admits the air. The machine, like the one last
described, contains eighty pieces; it has the same number of screws and
pins, and weighs 372 pounds including the ways or bed-piece; without the
ways its weight is 212 pounds. Its number of strokes is about 300 per
minute, and its blow somewhat lighter than that of the other. This
machine is not entirely automatic; the feed-motion not working regular;
when it does not, it is fed by hand, which is a simple process.
These machines stand the work much better than those first made at
Fitchburg. Their average time in the tunnel without repairs in the
interval, is about five days; they have needed repairs in two days; one
remained at work fourteen days. They accomplish double the work without
repairs that those do which were made after the previous pattern. There
is a further advantage in using the Burleigh machines; their breaking,
when it occurs, is not very serious, the injured parts consisting mainly
of cams, can generally be replaced at the tunnel; whereas for the
repairs on the Brooks, Burleigh and Gates machine, the dependence to a
very great extent has been upon the machine shop at Fitchburg.
The piston-head of this machine has a diameter of 4-25/100 inches. The
diameter of the piston-rod is at the large end, 3 inches, at the small
end, 2-75/100 inches.
So the number of inches of air area, is 8-20/800 when the drill is
propelled upon the rock, and 7-7/100 when returning from it.
A full complement of men to work the machines first used, would be,
perhaps, thirteen. Mr. Gates, who superintended their operation in the
first instance, began with fourteen, but they were reduced to thirteen.
The Burleigh machine practically requires feeding, and a full set at
work would probably demand fifteen men for their successful operation.
The value of these machines has not yet been ascertained. The Committee
are of opinion that when a full complement shall have been obtained, so
that the workmen can have at all times a full supply upon the frames,
that greater progress can be obtained by them than by hand drilling; and
after a few months operation, the cost of using them, in comparison with
hand labor, can be fairly tested. But as the Brooks, Burleigh and Gates
machine has been abandoned, no useful results would be obtained by
comparing the expenses within the tunnel during the months of July,
August and September, with three corresponding months when hand
drilling was carried on, and no satisfactory comparison can be made
between the working of the Burleigh machine and hand drilling, until a
sufficient number of machines has been introduced into the tunnel to
keep the men fully employed. It is to be hoped that machines sufficient
to make the test may be soon obtained, and that this desirable
information may be made known.
The introduction of the first machine into the tunnel, before its
capacity, strength, and expense of working had been fully tested, was
unfortunate, inasmuch as its use there delayed the progress of the work.
The second machine gives such promise of success, that it will be
continued in use in the tunnel until a fair test has been made. But
should the Burleigh machine prove unsuccessful, and further attempts
with machines be attempted, the Committee recommend that their
usefulness be tested outside of the tunnel, and meanwhile the excavation
with hand drills be resumed.