Interesting Machines-3 Steam Tractor

                          Videos: Steam Tractor replica built by Don Hunter. Took him nine years to build it

Rumely Steam Tractor

    History: Steam powered tractors moving on 4 large metal wheels were a common sight in the US of A from around 1890s to a few decades into the 20th century. It all started with Daniel Best, and his creation of his own company – Best Agricultural Works – and the development of the Best Harvester, which led him to creating the stream traction engine. Daniel Best sold his first steam traction engine for $4,500 in February 1899. They had one major flaw, the metal wheels easily sunk into the wet ground and the weight of these machines would make it very difficult to get them out. Benjamin Holt hit upon the idea of having "tracks" fitted onto the tractors so that the weight was evenly spread. In fact, the first commercial success for crawler tracks was by American Alvin Lombard. He assembled and patented the first steam log hauler track system in 1901. By 1917 he had produced 83 Lombard Log Haulers. Meanwhile, Lombard was selling licenses to other manufacturers to sell similar machines. Benjamin Holt purchased a license in 1903. Holt had established his own company, Holt Manufacturing Co., which would eventually become Caterpillar. He began designing his own crawler tracks based on Lombard’s.

Meanwhile a British company called Richard Hornsby & Sons was also designing. Chief engineer David Roberts patented his own design in 1904. His crawler tracks were steered by alternating the speed of the left or right track, whereas the Lombard system was equipped with a pivoting wheel for steering.

Eventually Holt’s company bought Hornsby & Sons' patent and basically controlled the crawler track market and their development. A merger between Best and Holt marked the beginning of the legendary Caterpillar construction equipment company.

Construction: The steam traction engine and the "tracks" were the main systems in the steam tractors. 

Crawler tracks, sometimes called caterpillar tracks, aid in the transportation of a vehicle. They serve the same purpose as wheels, except they distribute weight more evenly over a larger surface area, decreasing ground pressure and thereby keeping them from sinking in moist terrain. They are also more resistant to shrapnel, such as nails or broken glass, and sharp fluctuations in the ground.

The tracks are constructed from modular chain links, which, when put together, compose a closed chain. These links are broad and made of durable metal. Between every two pieces of chain, there is a joint that enables them to change the angle between themselves. This allows the track to be flexible and maintain an elliptical shape.

Crawler track assembly

Holt patent application for Track type tractor

 Steam Traction Engine: The first steam traction engines used a chain drive. However, it was more typical for larger gears to be used to transfer the drive from the crankshaft to the rear axle. Two different approaches were taken in the construction of steam traction engines. The first was to use the boiler as the central structure and then attach all the other parts such as the engine, drive gears, steering gear, and main truck to it. The other approach was to provide a separate framework on to which the boiler was mounted and the rest of the parts attached. In earlier models, the engine was usually top-mounted, placed on the boiler and the boiler, then mounted on the truck. In road locomotives, it was common to mount the engine under the boiler. In some models, engines were also side mounted or rear mounted. To preserve the engine from damage, heavy shocks and jars or heavy coil springs were placed between the boiler and the front and rear axles. Springs in the steering gear also assisted the front wheels from breaking when an obstruction was hit.

Power of steam traction engines was transmitted to the traction wheels by a simple train of spur gears made of cast iron. Most machines had two large powered wheels at the back and two smaller wheels positioned at the front for steering. These wheels were often made of steel. A collar on the front wheels helped to prevent slippage. The drive wheels had steel tires, either round or flat spokes and a cast-iron hub.

The first traction engines were geared only to travel at speeds of two to three miles (3.2 to 4.8 km) an hour on the road. Later engines were modified with two forward speeds—one slow and one fast.

Steam traction engines were very heavy and often weighed 45,000 pounds (20,412 kg) and, when operating, generated steam pressure of 150 to 200 pounds per square inch (1,034 to 1,379 kPa)

One of the most popular Steam Traction Engines in the US of A was the JI Case Steam Traction engine. Give below is a video and schematic of the same.