Building the World's Smallest Working Dragline
By: Walter Bennett
I have always had the ambition to some day operate a dragline. Driven by this ambition, but not being able to find an employer, I decided to build and operate my own miniature dragline.
Work on the dragline started in early 1967. The first step was finding a suitable machine to copy. After a two year search I chose a Bucyrus Monighan lOW because of its style, size and antiquity. The original machine was used for strip mining anthracite near Shenandoah, Pennsylvania, from about 1931 until 1961 when it was taken out of service.
After finding the lOW abandoned in a field, I started photographing it and recording measurements. This process took nearly four years and resulted in my acquiring nearly 5,000 different photographs, and more than an equal amount of measurements. The photographs and measurements were then utilized for laying out to scale the many components of the dragline. Actual fabrication of parts for the model began about 1969.
Initially I made patterns of the many forged parts found on the original machine. These included the walking cam mechanism, sheaves fairleàd and bucket hardware. Patterns were generated from aircraft aluminum and or Plexiglass with the aid of an endmill, lathe, drillpress and an assortment of hand tools. These patterns were later shipped to Florida where they were cast in brass. Finally the castings were returned to me for final machining and assembly.
Erection of the boom began in late 1972 using custom made brass shapes and a jewelers acetylene welding torch. Each member of the boom was sized and fitted to exactly match that of the original machine. Brass rivets were later soldered to the members simulating actual joint construction.
The boom is equipped with twenty-one working spotlights. Each bulb measures 1/8" long and 3/32" in diameter. The point sheave rotates on ball bearings and is mounted on pillow blocks, allowing it to swivel. The boom took four years. to construct and weighs a mere five pounds. A 1/32" diameter 7 x 7 stainless steel cable serves as the main hoist line for the boom. In addition a second such cable serves as a safety cable. The main cable has 18 parts, while the safety cable consists of a six part line.
The house is constructed of solid brass plates and weighs about 125 pounds. Two 1/8" brass plates form the main deck, while 1/16" reinforced brass sheets form the sides. All doors and windows are individually hung and fully operable. The window panes are replaceable. Brass shim stock measuring .003 inch thick forms the outside skin of the house and gives it a realistic delicate appearance. The house is lighted by ten outside and nine inside miniature bulbs. All are replaceable. Basic component parts of the house were individually machined to fit and then fastened together using miniature brass angle iron and number 4-40 machine screws.
A corrugated metal roof consisting of individual sheets is cemented to two 1/8" thick brass plates. The "A" frame is a integral part of the roof and together with it can be removed for easy access to the engine and other internal mechanisms. The house measures 20" wide, 21" long, and 24" high. Three cooling fans are located to the rear of the house and are driven by a miniature "boxer" fan. The stacks, miniature jib crane, hookshoes and other miscellaneous components of the house are for the most part brass castings.
The operators cab is an exact replica of the original and includes foot pedals, hand levers, a Johnson bar, pot bellied stove, and of course an operator. The operator, if standing fully erect, would measure 2 1/8" tall. In addition, the cab has individual windows, an adjustable operators seat, and is lighted. Work on the cab was started in 1977 and was completed along with the house in late 1980.
The model lOW walks on two miniature shoes each weighing about five pounds. The step of the machine measures 2.75 inches and it can move a distance of 27 feet in one hour. Fabrication of the shoes started in 1978 paralleling construction of the house and tub. Each shoe is made from 1/4" thick brass plate machined to fit and then bolted together. Brass shimstock measuring .015" thick was silver soldered to the plate and simulates the actual 1/2" plate found on the original.
The cam mechanism consists of five separate castings each of which was mechanically carved early in the project. These castings represent the most difficult part of the model building process and required the largest single block of construction time. For example, the large cam wheel represents one year of parttime work generating its pattern. All parts of the cam mechanism can be disassembled for repair and or replacement. Bolts used for fastening
the mechanism together are a number 00-90, equipped with miniature lock washers. Both shoes can be removed from the main house by simply loosening two small set screws. The shoes are fitted with three cleats each and, when walking, the machine leaves tracks identical to that of the original.
The tub consists of two 1/8" brass plates machined to a diameter of 13 1/2 inches. It is 1 1/8" high. The main ring gear has a pitch diameter of 8" with a 1/2" face. The roller races are an integral part of the tub being machined into the top plate. Miniature brass rails were added to simulate the actual rails found on the original lOW. The 76 tub rollers were turned on an automatic screw machine and are set in two concentric retainer rings machined from a single 1/4" brass plate. All rollers rotate on individual 3/32" brass shafts.
The tub contains a set of 17 slip rings, each of which represents a conductor, powering a specific function of the model. The ring system is made of alternate layers of brass and bakelite. The center of the ring system is hollow, allowing for the attachment of the trail cable. A 15 foot trail cable was made by placing the 17 various gauge conductors in a 1/8" diameter plastic tube. The diameter of this cable was held to scale by running high voltage circuits to the machine and then using on board transformers. These high voltage, low amperage circuits allowed the use of finer gauge wires, resulting in the thinnest possible trail cable. In all, the model runs on one 22 gauge, four 26 gauge, and twelve 30 gauge conductors.
The bucket exclusive of its many cast parts, represents three months work. It is composed of numerous weldments similar to the real "red arch" of the 30s. The teeth are replaceable. Both the sides and bottom were milled from 1/8" solid brass plate. In addition, components of the bucket are dovetailed, assuring a good solid joint after brazing. The drag chains were individually cast, cut, and then brazed back together. The arch of the bucket is made from four separate brass plates, and is filled with lead to add weight for better digging. Finally, both sheaves on the bucket were individually cast and are fitted with ball bearings. The bucket is manipulated by means of a 1/16" 6 x 19 stainless steel drag cable and a two part 3/64" 7 x 7 stainless steel hoist cable. All cables are terminated in sockets identical to original equipment.
The original lOW was a diesel machine, while the model is electrically powered. At the heart of the machine are three D.C. motors. The first powers the swing by varying voltage and reversing polarity. The second is for propel, it too is a variable speed, reversible D.C. motor. The third powers the bucket. Its speed is variable depend-ing on load demands. The drive system for the bucket includes two electric clutches, two electric brakes, emergency brakes, a variable speed drive in both hoist and drag, and is equipped with torque overrides which eliminate any chance of damage due to stalling. The drive motors are linked to individual flywheels which govern accelerations. When running the models speed and accelera-tion are identical to the original lOW. An additional slip clutch is located within the swing gear train. This device eliminates any overloads, should the boom point or part of the house come in contact with an immovable object. A boom hoist motor and drum is powered from the swing motor circuit by manually throwing a double pole double throw switch.
The model control panel measures four feet in length, two feet in width, and eight inches deep. It represents three years of part-time work. All motors and lights of the model are controlled remotely from this panel. At present, the panel can operate the model from a distance of up to 18 feet, although lengthening the 17 conductor trail cable would extend this distance without limitation.
The controls for the dragline largely consist of variacs and rectifiers. In addition, variable resistors are located in the control circuits allowing for fine adjustments and trimming of actual control levers. The relaying of signals and direct current flip-flops are accomplished through the use of both conventional and mercury wetted relays. The mercury relays provide for both quiet operation and high dependability. The panel weighs well over one hundred pounds.
The swing, hoist, and drag motions are controlled entirely from two levers. No foot pedals are involved. _ Both the hoist and swing are on a single joy stick, stick. while the drag control is on a lever by itself. All levers and their motions are transferable, enabling me to duplicate the lever formats of various makes of machines. The system of controls was thoroughly tested for more than 200 running hours prior to its final assembly. This shakedown period eliminated nearly all bugs and has proven very worthwhile, in that the machine now has nearly 500 running hours on it with no major problems.
The control panel, in addition to being the heart of the model control system, is also a monitoring panel. From it, all circuits to the machine can be accessed for testing. In addition, all circuits are equipped with circuit breakers and current limiting resistors.
Having completed the model on December 14, 1980, it was put to work at a miniature stripmine located in the basement of my home. Since then the model has moved well over two tons of earth, while affording me the opportunity to do what I have always wanted; operating a dragline.
Attached to this brief history is a list of facts about the model, its size, construction, and ability to duplicate the original machines s motions.