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Doc's Merkur Steam Shovel Excavator

Hi folks, Doc here, with another Merkur model. This one is the M8 Shovel Excavator ("Lopatove Rypadlo" in Czech). Like my Trolley Bus model, it is based on a color illustration (shown below) from what I assume to be an older Merkur manual. You can see a full-size version of this illustration along with a parts list on my G-Files page. And, just as with the Trolley Bus before it, this great-looking model was fun to build and makes a fine display piece.

INTRODUCTION
Once again I tried to replicate the original Merkur design as closely as possible. Fortunately, this time around there were several detail illustrations to help me, including (thankfully!) a cable rigging diagram. Still, I was forced to make a few part substitutions owing to some minor differences between my M8 set and the set that the original model was designed to be built with. Lastly, I made the usual handful of technical adjustments in order to enhance model assembly and operation. Each of these items are detailed in the discussion below.

BACKGROUND
The shovel excavator, or revolving power shovel, is one of the most interesting of all the earth moving machines. Excavators come in all shapes and sizes, from small personal mini-cats and backhoes to the building size monsters designed for use in mines and quarries. All excavators share the same general purpose: moving earth or other materials from one place to another. Though it was designed to do brute force work, with all of its various mechanisms working in unison and with a skilled operator at the controls it can exhibit an elegant, coordinated motion matched by few other machines.

The first shovel excavator, powered by steam, was invented by William Otis in 1836 and patented by him three years later. Many of these early "steam shovels," as they were commonly called, took the form of partial-swing dipper shovels mounted on railroad trucks. Later types were fully revolving, and were mounted on traction wheels. The image at right shows a 1920's era steam shovel, as designed by A.C. Gilbert to be built with his Erector sets. He even gave this particular design its very own set, the Classic Period No. 7 Steam Shovel Set. To see this model in detail, check out my Complete Model Pictorial in the Model Gallery.

In 1904, Benjamin Holt, one of the pioneers in the development of steam powered tractors in the late 19th century, successfully tested one of his tractors using caterpillar-tracks instead of wheels. Between 1910 and 1920, excavators began to be mounted on caterpillar-tracks instead of wheels, and internal combustion engines and electric motors began to replace the steam engines. Originally, steam shovels used a system of pulleys and chains or belts to move their arms and bucket. Much later, hydraulic systems replaced the tried and true older technology, but the operating principles of the excavator remained the same. By the late 1940's, most steam shovels had been scrapped, but some survived as pile drivers because they could furnish steam for the hammer. Today, diesel or electric powered shovel excavators continue to be the workhorses of the construction industry.

THE MODEL
As the photos below will attest, my final version is a nearly exact replica of the original design shown in the first image on this page. I did offset the two cranks on the left side of the cab a bit in order to provide for smoother operation. I also widened the stance of the caterpillar treads by about ½" to prevent them from rubbing on the screw heads along the edges of the base unit. The original Merkur design for the base unit (underside) is shown in the small image above. The final result, shown in several photos farther down in this page, will work great as a generic mounting base for almost any tread-driven model you would care to build.