📐 Equal Spacing Gear Bench: step-by-step build

Two independent gear pairs fit the same spacing, but their outputs turn differently.

Two gear pairs share a three-hole-spacing gap, yet one speeds up fivefold and the other stays one-to-one. Build independent 40/8 and 24/24 pairs on opposite edges of one rigid frame. Their tooth sums match; their tooth ratios do not. This original controlled comparison is inspired by ssugawara1955’s gear-combination display, not a replica of that dense motor-driven array.

  • Level 2 of 5 (easy)
  • About 20 minutes
  • 13 steps, 37 parts
  • Powered by: Hand-crank
  • Series: Starter Builds

What you will learn

  • Gears: Gears are wheels with teeth that push each other round.
  • Gear Ratio: Fast or Slow: A big gear turning a small gear makes it spin faster.
  • Axles: An axle is a cross-shaped rod — anything on it turns together.
  • Bushes & Spacers: Bushes stop things sliding off an axle.
  • Frames: A frame is a ready-made strong rectangle.
  • Pins: Grippy or Smooth: Pins join beams together — some hold tight, some let things swing.

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 × Axle 3
  • 12 × Bush
  • 4 × Axle 6
  • 12 × Half bush
  • 1 × Giant gear (40 teeth)
  • 1 × Tiny gear (8 teeth)
  • 2 × Medium gear (24 teeth)

Steps

  1. Lay the 5×11 frame flat on a level table. The first and last holes on each long edge will carry retained feet. Count axle spacing by gaps between hole centres, not the number of holes.
  2. Fit a 3-module axle through this corner, with a full bush immediately underneath and another immediately above. Hold the axle while seating both bushes. Repeat at all four corners; the feet must sit level.
  3. Fit a 3-module axle through this corner, with a full bush immediately underneath and another immediately above. Hold the axle while seating both bushes. Repeat at all four corners; the feet must sit level.
  4. Fit a 3-module axle through this corner, with a full bush immediately underneath and another immediately above. Hold the axle while seating both bushes. Repeat at all four corners; the feet must sit level.
  5. Fit a 3-module axle through this corner, with a full bush immediately underneath and another immediately above. Hold the axle while seating both bushes. Repeat at all four corners; the feet must sit level.
  6. Fit the large input 6-module axle through the third hole along one long edge. Hold it while adding a half bush immediately below the frame and another immediately above. These stop the whole shaft escaping in either direction while its round bearing permits rotation. Add a full bush onto the upper half bush. Fit all four shafts and these spacers before adding any gear.
  7. Fit the small output 6-module axle through the sixth hole along one long edge. Hold it while adding a half bush immediately below the frame and another immediately above. These stop the whole shaft escaping in either direction while its round bearing permits rotation. Add a full bush onto the upper half bush. Fit all four shafts and these spacers before adding any gear.
  8. Fit the equal input 6-module axle through the sixth hole along the opposite long edge. Hold it while adding a half bush immediately below the frame and another immediately above. These stop the whole shaft escaping in either direction while its round bearing permits rotation. Add a full bush onto the upper half bush. Fit all four shafts and these spacers before adding any gear.
  9. Fit the equal output 6-module axle through the ninth hole along the opposite long edge. Hold it while adding a half bush immediately below the frame and another immediately above. These stop the whole shaft escaping in either direction while its round bearing permits rotation. Add a full bush onto the upper half bush. Fit all four shafts and these spacers before adding any gear.
  10. Slide the 40-tooth gear onto that spacer and a half bush immediately above the gear. This is this pair’s input; leave space for its output. Red top bushes identify inputs; blue identify outputs. All four gears sit at the same height. The two shafts in each pair are three hole spacings apart; the pairs are independent.
  11. Slide the 8-tooth gear onto that spacer and a half bush immediately above the gear. Turn the entire keyed shaft gently to seat its teeth in the neighbouring input’s gaps. Red top bushes identify inputs; blue identify outputs. All four gears sit at the same height. The two shafts in each pair are three hole spacings apart; the pairs are independent.
  12. Slide the 24-tooth gear onto that spacer and a half bush immediately above the gear. This is this pair’s input; leave space for its output. Red top bushes identify inputs; blue identify outputs. All four gears sit at the same height. The two shafts in each pair are three hole spacings apart; the pairs are independent.
  13. Slide the 24-tooth gear onto that spacer and a half bush immediately above the gear. Turn the entire keyed shaft gently to seat its teeth in the neighbouring input’s gaps. Red top bushes identify inputs; blue identify outputs. All four gears sit at the same height. The two shafts in each pair are three hole spacings apart; the pairs are independent.

Play time

Hold the stationary frame on a level table. Mark an input and its output with removable dots. Gently turn the 40-tooth input once: predict five opposite output turns. Separately turn the 24-tooth input once: predict one opposite output turn. Repeat slowly in reverse. Do not brake an output, add a motor or force binding teeth; check height, spacing and seated retainers first. We have not physically tested this model.

Credited demonstrations and component sources