Tumble gears are used to set up which parameter?

• A. Lead screw ratio
• B. Spindle speed
• C. Thread pitch
• D. Feed rate

Answer: (A)

Tumble gears set the drive ratio between the spindle and the leadscrew. By selecting different gear combinations, you change how fast the leadscrew turns for each spindle revolution. That relationship is the lead screw ratio, and it directly controls how far the carriage moves with each spindle turn—i.e., the feed per revolution. This is essential when threading or when you need a specific controlled feed.

Spindle speed, on the other hand, comes from the belt/pulley setup rather than the tumble gears. Thread pitch is determined by the leadscrew and the gear ratio you select, but the gears exist to establish that ratio. Feed rate is the result of both spindle speed and the leadscrew ratio, not a direct setting of the tumbler gears. So the parameter being set by tumble gears is the lead screw ratio.