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BULLETIN 300, U. S. DEPAKTMENT OF AGRICULTUKE. 



machines. Although caterpillar tractors require no track, they have 

 not given complete satisfaction when working under all the different 

 conditions usually met with in operation. The wear on the chains 

 is very great in sandy soil, and the expense of repairs and the time 

 lost through breakdowns are likely to be considerable. 



VARIATIONS IN ROTARY TYPE. 



For the purpose of eliminating some of the weaknesses in the ordi- 

 nary moving devices a novel design of walking scraper excavator of 

 the rotary type has been put on the market. (See PL II.) Attached 

 to the upper platform and extending through the machine in a direc- 

 tion at right angles to that of the boom is a heavy steel shaft, on each 

 end of which is a wheel segment. The shaft also carries a large gear 

 wheel, which meshes with a pinion on the loading-drum shaft of the 

 main engine. Suspended from the middle arm of each segment by 

 means of a carrying beam and chains is a long shoe which affords a 

 bearing for the segment as it rotates and propels the machine for- 

 ward. The machine can be made to move in any desired direction 

 by first swinging the upper platform. The excavator is moved 

 ahead 8 feet during each complete revolution of the segment. The 

 great advantage of this type of machine, as well as of the excavator 

 mounted on caterpillar tractors, is the reduction in the necessary 

 working force from four to two men, the trackmen being unnecessary. 

 It is claimed that five men can take this type of machine down in a 

 week and erect it in about two weeks. The machine weighs about 

 60 tons and costs $7,000. Three cars are required for shipping it. 



Another form of the rotary type is the so-called boom-guided 

 bucket excavator. The entire machine rests on two steel rails spaced 

 12 feet apart and laid on short wooden ties. Either steam or gaso- 

 line may be used as power. The unique feature of this machine is 

 the boom on which the scraper bucket travels. (PL III, fig. 1.) It is 

 the purpose of this guide boom to overcome the difficulty of holding 

 the ordinary bucket in place in passing from stiff to loose material. 



The bucket, which is a rectangular steel box open at the end 

 toward the machine, travels upon the guide boom on steel rollers. 

 To fill, the bucket is first pulled outward by the back-haul cable, 

 which leads from the bucket to the head of the main boom and back 

 to the engine. The guide boom is then lowered and I he bucket pulled 

 toward the machine. The bucket is dumped by being pulled up on 

 the vertical end of the guide boom, the boom having first been swung 

 around to the location at which the material is to be deposited. 



This machine is made with three different lengths of boom, a 30- 

 foot adjustable boom which can be increased to 40 feet, a 40-foot, 

 and a 65-foot boom. Buckets of 1$, 1J, and 2 cubic yards are used 

 on these machines, it is claimed that 5 men can take down ihe 



