COMPARING MAKERS' SPARE PARTS AND THEIR SUBSTITUTES.
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WE ARE asked by the Associated Equipment Co., Ltd., of Waltham stow, Landon, E.17, to state that spare parts,. not of their manufacture, f reofently fail to give satisfaction because of the use of Very inferior material, imperfectly heat-treated and liable to cause much trouble.
The following reptart demonstrates clearly the danger which users incur by using such substitute spare parts in the belief that they are effecting 'economy.
A driving shaft 'purchased in the open market was compared with shafts of the company's manufacture, with the results set out in the tables.
Micro-examination shows the middle of the substitute shaft to he hardened and tempered, and the splined end to be hardened and at a temperature exceeding its correct hardening temperature. Apparently heat-treated 3 per eent, nickel-steel bar has been used, and the splinecl • end again hardened off after machining to obtain an additional hard neSs on the splines, and no tempering has been carried out alter this secondary heating, kloweVer well a part may he made so far as actual machming limits are. con-c cerned, material and heat treatment are the real factors.