Abstract
Since the presentation of the last paper on excavator practice to the Institution by F. H. Livens, M.I.Mech.E., and W. Barnes, M.I.Mech.E., in 1920,† a great many changes have taken place in both the application and design of excavating machinery. The application of this type of machinery has been dealt with on several occasions during the intervening years, and as recently as December 1934, Sir Henry Japp dealt very fully with “Modern Methods and Plant for Excavations” in a comprehensive paper read before the Institution of Civil Engineers.‡ This paper therefore deals more particularly with the progress in design of the excavator itself rather than its application.
Attention may first be drawn to the extension of the range of sizes available in both directions. In 1920 machines carrying dippers of 6 cu. yards capacity and weighing about 250,000 lb. represented the upper limit in size, whilst machines carrying dippers of 
cu. yard capacity were the smallest available. In 1937 machines having dipper capacities of as much as 33 cu. yards and weighing 2,500,000 lb., or as little as 
cu. yard and weighing 15,000 lb., were manufactured.
A greater number of distinct types have also been developed. Twenty years ago types in common use were the shovel and the grab or clamshell. To-day, drag-line, drag-shovel, and skimmer-scoop equipments are largely used, and these have been developed to meet the growth of application of the single-bucket excavator, enabling it to do work for which it was originally unsuited.
In 1920 steam was practically the universal motive power, but this has given way to the internal combustion engine and electricity, and is now virtually obsolete for this purpose.
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