The Keystone Model 4 Skimmer, introduced in 1921, was somewhat longer and about 5-tons heavier than the original series built in 1916.
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 8x8 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.