🐌 Worm Counting Bench: step-by-step build

Count 24 input turns for one output turn, with both shafts retained.

A screw-like input advances a toothed output one tooth at a time. This original unloaded bench places the input between two bearings and the output between two towers, so you can count the reduction without a crane load. Slow motion explains the ratio; it does not establish self-locking or lifting safety.

  • Level 3 of 5 (medium)
  • About 35 minutes
  • 16 steps, 48 parts
  • Powered by: Hand-crank
  • Series: Mechanical Wonders

What you will learn

Build these first

  • ⚙️ Gear Friends: Three gears holding hands — spin one and they all dance. (level 1 of 5, about 8 minutes, 6 steps)

Parts you need

  • 1 × Open frame 5×11
  • 4 × Blue long pin
  • 4 × Split pin block
  • 1 × Axle 10
  • 13 × Half bush
  • 2 × Axle 3
  • 10 × Bush
  • 3 × Axle 8
  • 1 × Medium gear (24 teeth)
  • 3 × Beam 5
  • 4 × Red axle-pin
  • 1 × Worm gear
  • 1 × Hand crank

Steps

  1. Lay the 5×11 frame flat. This is the bench's base.
  2. Push two blue long pins up into the 8th and 10th holes of the left long side. Press two split pin blocks onto them, one on top of the other.
  3. The same on the right long side: two blue long pins and two split pin blocks.
  4. Fit a 10-module input axle in the middle short-edge hole, extending half a module below the frame. Fit half bushes directly below and above the frame.
  5. Give the bench two more feet at the other end: push a 3-axle into each corner hole so it pokes out underneath, and slide a bush on below.
  6. Lock the two feet with a bush on top of each.
  7. Fit two stationary 8-module support poles into the corner holes beside the input. Retain each beneath the frame with a full bush; these stationary bushes also support the front of the bench.
  8. Retain the support poles above the frame with half bushes, then position full bushes four modules above the frame as shelf stops.
  9. Output module: take the 8-module shaft and preload a half bush, the 24-tooth gear and the second half bush so they touch both gear faces.
  10. Output module: slide one upright bearing tower over the shaft end. The mounting pins are inserted after the module is seated.
  11. Lower the output module into place, then engage both tower mounting pins in the split blocks. Keep the input shaft clear: the worm is fitted in a later step.
  12. Fit the two red axle-pins on the opposite side and slide the second tower over the shaft end. Both tower bearings support the output; neither may tilt.
  13. Retain the whole output shaft outside both towers with half bushes.
  14. Slide a full-bush spacer onto the input, then fit the worm, gently aligning its groove with the output gear teeth. Fit a half bush directly above the worm; it prevents upward sliding.
  15. Slide a 5-hole upper bearing beam over both support poles and the input. It rests on the two shelf stops. Retain the shelf ends with half bushes.
  16. Retain the input above the upper bearing with a half bush. Stack a full bush, the hand crank and a top half bush. Check the crank clears the output gear.

Play time

Hold the stationary frame. Add a removable mark to the output and count 24 slow crank turns for one output turn. Reverse gently and observe backlash. Do not press the output against a load, lever the axles or infer that this bench is a lifting brake.

Real-world inspiration

S. L. Froden demonstrates a worm mechanism with deliberate axial sliding. This bench instead captures the worm axially; its frame and assembly are original.

Credited demonstrations and component sources