🛗 Scissor Lift: step-by-step build

Turn the crank and the platform climbs straight up on criss-cross legs.

Builders and window cleaners ride up buildings on scissor lifts. The legs cross like a pair of scissors, and when you squeeze their feet together, the top shoots up! You will squeeze the feet with a crank, a worm gear and a toothed rack. Moving the feet a tiny bit makes the platform rise a LOT — that is the magic of a scissor linkage. And because a worm gear can't be pushed backwards, the platform stays up when you let go.

Level 3 of 5 (medium)
About 45 minutes
29 steps, 81 parts
Powered by: Hand-crank
Series: Mechanical Wonders

What you will learn

Linkages: Beams joined by pins change one motion into another.
Rack & Pinion Steering: A gear rolling on a straight rack slides it sideways.
Worm Gear: The Lock: A worm gear turns a gear super slowly — and never slips back.
Triangles Are Strong: A triangle cannot be squished — a square can.

Build these first

🏗️ Worm-Gear Crane: Crank the worm gear to lift the boom — then let go. It stays up by itself! (level 3 of 5, about 30 minutes, 15 steps)
🏎️ Steering Go-Kart: Turn the steering wheel and the front wheels really turn — just like a real car. (level 3 of 5, about 30 minutes, 25 steps)

Parts you need

2 × Open frame 5×11
1 × Beam 7
12 × Black pin (grippy)
8 × Blue long pin
6 × Split pin block
2 × Axle 3
2 × Cross block
2 × Axle 5
5 × Bush
1 × Tiny gear (8 teeth)
1 × Medium gear (24 teeth)
3 × Long pin-axle block
1 × Axle 4
2 × Beam 5
5 × Half bush
1 × Worm gear
1 × Axle 10
1 × Hand crank
1 × Steering rack
1 × Axle 8
8 × Beam 11
8 × Grey pin (smooth)
2 × Beam 3
2 × Red axle-pin
1 × Axle 9
2 × Beam 9

Steps

Lay the white 5×11 frame flat. It is the base of the lift.
Pin a 7-hole beam flat across the frame at the 5th holes of the long sides, sticking out on both sides. The rack will slide on it.
Foot blocks: push blue long pins up into the 1st and 3rd holes of the back long side. Slide two split pin blocks down onto them, one on top of the other.
Do the same on the front long side: two blue long pins and two split pin blocks.
Push black pins up into the 1st, 3rd, 5th and 7th holes of the cross beam.
Press a split pin block onto each pair of pins, and push a 3-long axle into each block's cross hole, pointing right.
Slide a cross block onto the end of each axle, its round side hole on top. These are the bearings for the gear axle.
Hold the bush, the tiny 8-tooth gear and the 24-tooth gear in a row between the bearings, and push a 5-long axle through the back bearing, the gears and the front bearing.
Foot axles: hold a long pin-axle block standing up in front of the front foot blocks and push a 5-long axle through it and the top front foot block. Push a 4-long axle into the top back foot block, pointing back.
Hold a 5-hole beam upright on each side of the long block and push blue long pins through beam, block and beam, in the bottom and top holes of the block. Two worm towers!
Hold a half bush (against the right tower), a bush and the worm gear in a row just above the 24-tooth gear, and push a 10-long axle from the left through the tops of both towers, the half bush, the bush and the worm.
Push another bush onto the right end of the worm axle, snug against the worm, and put the red hand crank on the left end. The half bush against the tower and the crank against the other tower stop the axle sliding; the bushes keep the worm in place.
Lay the steering rack on the cross beam, teeth up under the tiny gear, and push the long slider axle through its back hole.
Left legs: cross two 11-hole beams and join them at the middle hole with a grey pin.
Pin the next leg to the top of the inner beam.
Pin the last leg on, then join the second cross in the middle.
Slide the left legs onto the back foot axle and the slider axle.
Right legs: build the same X again.
Pin on the next leg.
Finish the second X.
Slide the right legs onto the front foot axle and the slider axle.
Push a half bush onto the outer end of each foot axle and each end of the slider axle, so the feet cannot slide off.
Push a blue long pin into the top of each inner leg, pointing in, and slide a 3-hole beam onto each by its last hole, sticking out to the front. These arms ride up with the platform.
Push a black pin into the front hole of each 3-hole beam, pointing in. Press a long pin-axle block onto each beam: its end holes go onto the black pin and the blue pin, so each beam is held by two pins.
Push a red axle-pin into the cross hole of each block, axle end down and pin end pointing up.
Push an axle through the tops of the outer legs and put two bushes on it as rollers.
Press the second 5×11 frame onto the two red axle-pins: the platform! It rides up and down on the legs.
Push two black pins up into the left side of the platform and press a red 9-hole beam flat onto them as a safety edge.
Do the same on the right side.

Play time

Crank it up and down. Count how many crank turns it takes to go all the way up. Put a toy on the platform — does it stay up when you let go of the crank?

Real-world inspiration

Scissor lift / aerial work platform — https://en.wikipedia.org/wiki/Aerial_work_platform#Scissor_lift