A traditional cone-pulley lathe back gear uses a pulley-mounted pinion, a bull gear keyed to the spindle, and a compound gear cluster carried on an eccentric shaft. The animation demonstrates the cluster moving into both meshes after the direct-drive pin is withdrawn.
Lathe Speed-motion Engagement Interactive Calculator
Explore logarithmically spaced speed steps and the result of an entered back-gear reduction.
Equation Used
- Positive endpoints and equal logarithmic spacing.
- The entered reduction is exact arithmetic, not a ratio derived from illustrated gears.
- The animation demonstrates the stopped-machine engagement sequence; it does not model tooth phasing, forces, interlocks, wear or safe operating procedure.
The two illustrated pairs each use 16 and 44 teeth with a common pitch; their engagement sequence is separate from the entered speed-series reduction.
Direct drive and back gear
In direct drive, a pin joins the cone pulley to the spindle-mounted bull gear. For the low range, the machine is stopped, that pin is withdrawn, and a compound back-gear cluster is moved into mesh by rotating its eccentric shaft. Drive then runs from the pulley pinion through the compound cluster to the bull gear.
Scope
The calculator compares an ideal schedule. The animation identifies the traditional components and power path but does not design a gearbox or authorize a shift procedure. The gear pairs are separated into two end views; the dashed green link represents their common compound shaft.
Progression
r=(Nmax/Nmin)^(1/(S−1)). The selected ideal speed is divided by the entered reduction B.
Interpretation
The first and last selector detents equal the entered endpoints. The animated engagement state is independent of those calculated detents.
Limitations
The illustrated 16/44 tooth pairs share a common pitch and center distance. Tooth phasing during engagement, shaft and bearing loads, shift forces, losses, wear, lubrication, guards and machine-specific interlocks are not calculated.
Questions
Are these actual lathe speeds?
No. They are an ideal geometric series.
Should a back gear be shifted while the spindle turns?
No. The animation is a slowed explanatory sequence and explicitly begins by stopping the drive; follow the machine maker's instructions.
References
The component topology follows educational descriptions of a cone pulley, pulley pinion, spindle bull gear and compound back gear on an eccentric shaft, including the machine-tool archive at Lathes.co.uk and the historical patent US1028095A. The paired-gear layout is also shown in US3109319A, figure 3. The displayed 16/44 tooth pairs are illustrative, not dimensions taken from that patent.
Building or designing a mechanism like this?
Explore the precision-engineered motion control hardware used by mechanical engineers, makers, and product designers.
