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The Department of Production and Industrial Administration of
The College of Aeronautics has made a detailed analysis into the
performance of numerically controlled machine tools, and this shows
that when these machines are operating under light cutting loads, the
total envelope tolerance is about 0.003 ins. Further investigation
into the source of the errors showed that about 80 per cent of this
error was due to mechanical mechanisms in the machine tool. The
electronic equipment operated inside a total band of 0.0004 ins. over
small distances, and 0.0006 ins. over 10 inches. This situation
appeared to justify a comprehensive survey into the methods which may
be used to improve the mechanical performance of these machines.
After due consideration had been given to a number of possible
alternatives, it was decided to fit hydrostatic lubrication to the
slides, nut and screw arrangement, and the thrust bearings used on
the X and Y axes of an existing No. 3 Archdale Milling Machine.
The Z axis was not included in the redesign, because analysis showed
that a new head casting would have been necessary. It was thought
that this additional expense was not justified and that the data
obtained from an examination of the performance given by the X and
Y axes would show whether the system could be used with advantage
in the design of new machines. The paper gives details of the
calculations used to establish the dimensions of the new features
fitted to the machine to satisfy the target performance conditions
which appeared to be possible and are given in the introduction.
The authors would like to express their appreciation to James
Archdale and Co. for making a machine available for this investigation,
to the Staveley Research Department, and in particular to Mr. Graham,
Mr. Harris, Mr. Huntley) M r. Cummings and Mr. Hayward. |
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