This page keeps the documented pump-drill topology while removing unsupported operating speeds, forces, materials, tolerances and craft advice. The connected view shows a sliding crossbar, two cord legs, spindle, flywheel and reversible motion; the calculator is only a declared cord-travel ledger.
Pump Drill Declared Cord-Travel Ledger
Enter declared spindle diameter, available wound cord travel per direction and used cord travel per half-cycle. The calculator divides declared cord travel by circumference; it does not predict crossbar stroke, RPM, torque, cutting or flywheel dynamics.
Equation Used
- D is the declared effective diameter at the cord-wrap surface.
- L is declared available wound cord travel for one direction, not total cord length.
- s is declared cord travel used in one half-cycle; u=min(s,L).
- Ideal shaft turns equal cord travel divided by pi D.
- The animation is a connected qualitative topology; it does not solve cord helix geometry or flywheel dynamics.
- Slip, cord stretch, cord diameter, crossing, tension, inertia, RPM, torque, thrust, cutting, wear, tolerances, materials, maintenance and safe operation are excluded.
Replaces an unsupported crossbar-stroke/RPM model and prescriptive craft advice with an exact declared cord-travel ledger and source-grounded qualitative topology.
A sliding crossbar and cord reverse a weighted spindle
The British Museum describes a wooden shaft with a circular weight near the bottom, a top hole carrying fibre string and a perforated crossbar attached to the string ends. A Queensland State Library guide likewise shows the push board sliding over the drill stick while a flywheel maintains momentum.
The connected animation shows that documented topology and reversible motion qualitatively. Its numeric ledger does not solve the physical crossbar position or flywheel response.
Use this page only as a cord-travel identity
The worksheet reports declared circumference, available ideal turns, used ideal turns and unused declared travel.
It cannot select dimensions or materials, predict RPM, torque, thrust, runout, cutting, cord life or safe use.
Divide declared tangential travel by circumference
The identity is exact for an ideal no-slip cord moving tangentially on a cylinder. The page does not infer cord travel from crossbar stroke.
A transparent declared-travel example
For D=6 mm, L=300 mm and s=250 mm, circumference is 18.85 mm, available ideal turns are 15.92, used ideal turns are 13.26 and unused declared travel is 50.00 mm.
No rotational speed or drilling performance follows.
A travel ledger is not a working-tool design
A real pump drill couples changing straight cord legs, helical winding, a sliding board, spindle inertia, cord tension and a workpiece load. Those effects require measured geometry and dynamics absent here.
The former specific RPM, force, flywheel mass, dimensions, life, tolerances, pearl-drilling, material-selection, maintenance and troubleshooting claims are removed.
Pump-drill ledger questions
Is used cord travel the crossbar stroke?
No. It is a separately declared tangential travel quantity.
Does the turns output predict RPM?
No; time and dynamics are absent.
Does the model calculate flywheel rewind?
No.
Can this specify a drill or bit?
No.
Pump-drill topology references
- British Museum, pump drill Am1962,01.174: shaft, circular wooden weight, top cord hole, fibre string and perforated crossbar.
- Zhenjing Traditional Woodwork Museum, Pump Drill with Flywheel: drill bit, shaft, narrow board, flywheel and cord.
- State Library of Queensland, The Pump Drill: perforated push board, cord through the shaft and flywheel-assisted reciprocal operation.
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