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Angular
Measuring Rack (AMR) on G. A. Gray VTM
G. A. Gray , now Giddings &
Lewis, build large vertical turning machines. The VTM is
essentially a milling and boring machine with the workpiece held on a
rotary table capable of two modes of operation - milling and turning.
In the milling mode, the table
serves as one of the axes of the machine moving slowly during milling
and intermittently between drilling, tapping and boring operations.
The second mode is turning with fixed single
point tooling and for this the workpiece is rotated at relatively high
speed on a vertical axis. Angular measurement at the table is not
required in this mode. In some cases, it may be that both modes are
needed at the same component and then a quick change from one mode to
another is helpful. Two drive systems are used to obtain the large
speed range (over 1000:1) needed to serve the two modes.
The AMR is
fitted to the G. A. Gray machine. It consists of 12 modular sections of
curved rack clamped inside the base of the table. The pinion which
drives an encoder is aligned to the radius of the table and is spring
loaded into mesh to remove backlash. The rack and pinion act as a
step-up gearbox with a 180:1 ratio. Individual rack sections are
adjusted to minimize errors.
In the low speed milling mode, the pinion is
engaged for normal measuring. In the high speed turning mode, when
angular measurement is not required, the pinion is disengaged to prevent
overspeeding and is "parked" on stationary length of dummy rack. It is
held there until it is needed again for the milling mode when it can be
returned by vernier adjustment to true datum. There is a safety
interlock to prevent the table starting on its high speed with the
pinion engaged.
All components are serviceable without
dismantling the table. |
