The Drop Spindle Whorl: A Mass Rule That Balances Spin Time Against the Drafter's Arm

A drop spindle costs almost nothing, yet its one shaped part, the whorl, decides how the tool behaves for every metre of yarn it ever makes. Spinners choose whorls by habit, by what came with the spindle, or by copying a teacher, and trade descriptions ('a fast whorl', 'a long-spinning whorl') circulate without numbers attached. This paper replaces the adjectives with arithmetic. Given a stated flick energy, a stated drag torque, and the plain geometry of a disc, it computes how long each whorl size spins, how much yarn one spin can twist, and how much yarn a spinner finishes in an hour once the fixed handling time of drafting and winding on is charged against every cycle. In the computed results, the best mass g is 40; the best metres per hour is 35.84; the best grams per hour is 1.43; the best spin time s is 36.2; the light metres per hour is 32.39. Choose the lightest whorl that reaches the output plateau. The study is simulated, not measured; all inputs are stated assumptions, printed in the accompanying computation, which readers may replace with their own values and re-run.