If the number of sidewalk spectators is any indication, the most
fascinating phase of any new construction is the hole in the
ground. In any case, this crowd of curious watchers usually seems
to diminish in a kind of inverse ratio to the progress of the
building. The first act, that of excavation, has always been the
feature attraction. And it was thus that I came to know the various
Steam Shovels; these stars of the show, who would change their
make-up to return as Clamshells, Draglines, or Pile-Drivers, like
headline performers, down in the big arena rimmed by an audience of
‘standing room only’.
Aside from deep cellar excavations, another appeal to the
passing pedestrian was any project of street grading in preparation
for repaying. How we watched with mingled emotions as the finest
red brick pavement of years before was ripped out and carted off;
how the long-ago trolley tracks, since hidden by asphalt, again
came to light; or how those stately old shade trees surrendered to
a wider roadway and rows of parking meters. In this work, the
digging was often done by a second cousin of the Steam Shovel,
which was variously known as a KEYSTONE TRACTION EXCAVATOR or
SKIMMER. Although they lasted for many years, most of the
steam-driven Keystones were built from 1916 to 1922, by the
Keystone Driller Company of Beaver Falls, Pennsylvania.
On this machine, a twin-cylinder horizontal engine was mounted
on a long rigid frame which was carried on small wide-tread
traction wheels in front, and large 48-inch diameter steel wheels
in the rear. A vertical boiler was mounted just aft of the rear
wheels, and was fired from a back platform equipped with water tank
and coal hopper.
In place of the familiar dipper and shipper-rack of the
conventional type shovels, the Keystone employed a sliding scoop
equipped with rollers guided along a simple girder-type boom that
was horizontal when digging, or was raised approximately 45-degrees
for loading wagons. The base of the boom was pivoted, and rotated
by means of a large cable-driven bull wheel which could turn
90-degrees to the right or left. On either side of the front wheels
there were adjustable outriggers to stabilize the machine during
extended radial movements.
One constant-speed steam engine drove three separate cable drums
through a planetary transmission which was manually operated. On
the left-side operator’s deck, the big hand levers were each
provided with a ratchet and pawl to relieve the operator while
holding certain positions. Since the lateral and vertical movements
of digging were governed by two of these large hand brakes, which
demanded the operator’s firm grip at all times, the rotation of
the boom was controlled by an ingenious foot-operated toggle
clutch. In fact, the operator’s hands and feet were so
constantly occupied as to require a second workman on the ground
whose sole duty was to trip the latch for dumping the load. After
the scoop was emptied, its hinged bottom was re-latched by a sudden
braking action as the scoop descended the boom.
By rearrangement of the sheave blocks, and with a ditcher
attachment added to the end of the boom, the Keystone Excavator
could be converted for trenching work (to a depth of 20-ft) in the
manner of a present-day Back-Hoe. But in its principal role as a
‘Skimmer’, the scoop (of cu yd capacity) was crowded
(traveled) 11-ft of the 16-ft boom. The engine provided 8×8 inch
Cylinders and a link reverse, designed primarily for maneuvering
the machine, which was self-propelled. The machine itself was 7-ft
in extreme width, by 18-ft in length (without boom); and weighed 9
tons complete.
Compared to the hoisting motion of a conventional type Steam
Shovel, the unique crowding action, or long lateral thrust, of the
Skimmer’s scoop gave it a peculiar prying leverage that was
well adapted for ripping up old asphalt or lifting large slabs of
broken concrete; hence the name ‘Skimmer’, However, as
though to disprove this nomenclature, the steam Keystones were
sometimes found in high-bank excavations where the going was
anything but skimming. Unlike the familiar Steam Shovel which digs
by means of a circular upward thrust, the Skimmer would just bite
‘at’ the bank. In the parlance of the trade, its method was
to ‘notch’ rather than to ”shave’ the face of
the cut. And depending upon the type of soil, this could lead to
under-cutting with resultant slides; whereupon the old Skimmer,
incrusted with sand and grit in every bearing, would back off and
start again.
But the unsung heroes of earthwork were not always earthbound.
Like the time an old Skimmer was grading a strip along the
railroad’s right of way which approached a high trestle
crossing a deep gorge. As work finished on the near side, the
prospects involved some rather tedious travel over nearly two miles
of winding highway down through the town and up again in order to
reach the opposite shore. This would entail all the usual loss of
time and labor, until someone discovered that the span of the old
Keystone’s wide traction wheels closely matched the spacing
between each inner rail of the double track on the bridge. Then
with advance clearance from the Trainmaster, the old Skimmer inched
her way above the tree tops, as something of an innovation in
travel by rail.
Another version of the Skimmer principle was a gasoline-driven
Excavator built by the Bay City Dredge Works of Bay City, Michigan.
Their Model 16-B, introduced around 1922, was a 5/8 cubic yard
machine mounted on small traction wheels in the rear; with the
stress of digging supported in front on a short caterpillar
mounting, whose wide base precluded the need for outriggers. Later
variations of the gasoline models were also turned out by Keystone,
as well as Pawling & Harnischfeger (P & H) of
Milwaukee.
The canvass you see is over the drive belt to keep the rain off
and the wind from blowing on it. Number of engine is 7943.
While the Skimmers might be found on almost any type of job,
they were best suited for shallow grading on street work. In this
role they apparently offered some advantages, for a present-day
model of the Bay City is still manufactured. It retains the same
basic design of a horizontal boom and scoop, now powered by a
Diesel plant set on a revolving turntable.
