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DESIGN FEATURES
THE BED AND SADDLE
The bed has a longitudinal form that is completely self-contained and stiff in itself, and therefore needs no outside support whatever. This Drummond cantilever design is unique in that it enables the lathe to be bolted down on any floor, no matter how uneven, without distorting or affecting its accuracy in any way; it is the only form by which a small table lathe can be made or guaranteed to remain accurate wherever placed.
The bed is a complete box section casting, stiffened internally, and is of the same general design as our new toolroom and manufacturing lathe beds. Although the top surface of the bed is flat, it is not the ordinary so-called "flat English bed". The Drummond form of lathe bed combines the accuracy of the long narrow guides of the "American" type with the long wearing qualities consequent on the large wearing surfaces of the "English" type.
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Referring to Fig.2, it will be seen that the design gives a 90 degree vee saddle guide at the front of the bed, the centre line of which coincides approximately with the average line of cutting thrust. The vertical downward component of this thrust is taken on the top surface of the front way, A; the horizontal forward component of the cutting thrust is met squarely by the back face of this way. The rear way C is seperated from the saddle by clearance D, and the saddle is firmly held to the top face of this way by the stiff gib strip shown. Thus the cut itself holds the saddle to a long narrow guide at the front of the bed.
The leadscrew B is brought close in under this saddle guide, thus reducing to a minimum the unavoidable "wringing" action between these two elements, and ensuring a clean, steady saddle movement. |
Fig.2.
The bed and saddle design.
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THE HEADSTOCK
This is positively and permanently clamped against the flat vertical face of the front way of the bed, thus ensuring alignment of the spindle with the ways. In earlier designs an overhead arm joined the two main bearing bosses of the headstock casting, but the modern design is provided with a heavy cast beam on base, which ensures absolute rigidity and great strength with fully adequate support for spindle bearings.
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