Project ForgeA conventional lathe's incomplete schematic shows the speed gearbox Uv placed between locations P and Q on the spindle drive (Motor-P-Uv-Q-R-S-Workpiece), and the feed gearbox Us is to be placed to drive the lead screw via a takeoff point E and a half-nut. Changes in Uv should NOT affect the pitch of the thread being cut, and changes in Us should NOT affect the cutting speed. The correct connections and placement of Us are given by
- AQ and E are connected. Us is placed between P and Q.
- BS and E are connected. Us is placed between R and S.
- Q and E are connected. Us is placed between Q and E.
- DS and E are connected. Us is placed between S and E.
Explanation
The lead-screw drive must be tapped off AFTER Uv (at Q), so that any Uv change scales both the spindle speed (Q-R-S-workpiece) and the lead-screw drive by the same factor, leaving their ratio (and hence pitch) unchanged. Us must then sit between that takeoff (Q) and E, in the separate branch to the lead screw only — so changing Us alters the lead-screw speed (and thus feed/pitch) without touching the spindle line at all (cutting speed unaffected). This matches 'Q and E connected, Us between Q and E'.
Source: GATE ME 2008 (2008)
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