Part 1: Cutting Angles for Lathe Work, Methods of Mounting and Types of Holders
by Paul Grodinski
This article first appeared in the Volume 4, Number 41 (March, 1942) issue of Aircraft Production magazine, and is presented here through the kind permission of Flight International. Thanks also to Bruce Vander Mark for furnishing volumes of Aircraft Production for scanning.
Diamond tools play an exceptionally important part in the quantity production manufacture o f aircraft engines. Owing to the extreme hardness of the cutting edges it is possible to use these tools for periods as long as two years without relapping, a valuable feature for repetition work. In general, the use o f diamond tools is restricted to lathe and boring machine work, but there are other applications. Very little information concerning cutting angles and the choice o f tools has hitherto been available for publication, but we are able to publish the first of two articles written by an authority on the subject.
There are certain features that make the diamond a high-class precision finishing tool with a performance which has not yet been equaled by any other tool. The single-crystal structure is so dense that it enables the production of absolutely keen and durable cutting edges which appear, even under a high-powered microscope, as a straight line. These cutting edges and surfaces are very smooth, and offer the minimum friction resistance to the flow of chips. At the same time, they are a good conductor of heat, and, consequently, heat generated during cutting is quickly dissipated, the tool edges remaining quite cool. This is assisted by the fact that the chips are very fine and minute, and the cutting resistance they offer is small.
The hardness of the diamond enables it to cut completely through the structure of the material, i.e., soft and hard parts are cut without the tool either “digging in“ or being forced back. Composite materials, such as commutators composed of copper and mica segments, as well as interrupted surfaces such as bearing shells with oil grooves, slotted skirts of pistons, etc., do not affect the smooth action of the tool. Also, the edge is so keen that it will remove the minute imperfections caused by the dullness of tools used in previous operations. With the diamond tool finer cuts may be taken than with any other type, and the high wear-resistance properties ensure maintenance of the edge for exceptionally long periods. Consequently, the tool can be used for long runs without the need for resetting, and there have been instances where tools have remained in use for two years or more without inspection or adjustment. As no scientific data regarding the durability of diamond cutting edges are available, it has been suggested that durability could be measured in terms of “cutting length,” i.e., the total length or path of the tool edge along the surface of the workpiece before the tool has to be removed for relapping. For facet diamonds the cutting length values are usually in the region of 1,500 to 2,000 miles, the corresponding values for single-point carbide-tipped tools ranging from 20 to 30 miles.
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