A car gearbox you can see into. Turn the crank and the input shaft drives the countershaft, which turns every gear on the main shaft at once, each at its own speed: they all run free on bushings until you pick one. Move the lever into a gear and its fork slides a dog collar against that gear, its six dogs drop in, and from then on that gear turns the main shaft and the output flange. Fourth locks the input straight to the output, fifth is an overdrive, and for reverse an idler gear under the shafts turns the output the other way. The lever works like the one in a car: sideways to pick a rail (1-2, 3-4 or 5-R), then forwards or back. Pins between the rails let only one of them leave neutral at a time, and a printed spring clicks each rail into place. The case is open on both long sides, so you see all of it happen.
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Floor, front wall and rear wall in one piece, open on both long sides. The walls carry the shafts, the three rails, the interlock bore across the rails (front) and the three click springs (rear); the cheeks on the floor carry the reverse idler.
Spans the two walls over the rails and holds the ball of the lever in a cup. It sits on four pegs on the walls.
Closes the cup over the lever's ball, so the lever can tilt every way but not lift out.
The H pattern the lever moves in: 1, 3 and 5 forward, 2, 4 and R back, with the numbers cut into the top. The ends of the slots are the stops for the lever.
The lever is split down its length so it prints flat: glue two halves together, lined up by two short pieces of filament in the ball. The finger at the bottom sits in the slot of a selector.
Glued onto the top of the lever, after the gate is on.
On the hex end of the input shaft. Turn it clockwise, seen from the front.
20 teeth, in constant mesh with the 34 on the countershaft, and a ring of dogs at the back for 4th. The main shaft's nose turns in the bore at its back.
Hexagonal, so the hubs and bushings turn with it. The round nose turns inside the input shaft; the hex stub at the back takes the output flange.
Hexagonal: the six countershaft gears are keyed to it and turn together.
A bearing for the front of the countershaft. The hole in the wall is big enough to thread the hexagon through; the sleeve then closes it up.
36 teeth, driven by the 18 on the countershaft: 3.40 : 1 overall. Dogs on its front face.
30 teeth, driven by the 24: 2.13 : 1. Dogs at the back.
24 teeth, driven by the 30: 1.36 : 1. Dogs in front.
18 teeth, driven by the 36: 0.85 : 1, an overdrive. Its dogs sit on a disc in front.
32 teeth. It does not touch the 16 on the countershaft: the idler under them joins the two, so the main shaft turns the other way. 3.40 : 1.
Driven by the input shaft. Its long hub spaces it from the next gear.
Drives 3rd.
Drives 2nd.
Drives 1st.
Drives the reverse idler.
Drives 5th; the last one at the back.
20 teeth, on its pin between the two cheeks on the floor, below the shafts.
Ø5 mm, pushed through the cheeks and the idler.
Slides on a hexagonal hub, so it always turns with the main shaft. Six dogs on each face; pushed against a gear, they drop between that gear's dogs and lock it to the shaft. The fork rides in the groove.
Hexagonal inside and out: keyed to the main shaft, with the collar sliding on it.
Two free gears turn on it, with a washer between them.
5th gear turns on it.
Between two free gears.
Slides through both walls. The notch on its inner face is for the interlock pin, the three grooves at the back are the click positions: back, neutral, forward.
The middle rail: notches on both faces and a cross hole for the short interlock pin.
Like the 1-2 rail, mirrored.
Rides in the groove of the 1-2 collar. A piece of filament through the sleeve pins it to its rail.
For the 3-4 collar.
For the 5-R collar.
Pinned to its rail under the lever. In neutral the slots of the three selectors line up, so the lever's finger can move across from one to the next.
The middle one.
Like the 1-2 selector, mirrored.
Ø3 × 7.3 mm with pointed ends, in the bore across the rails in the front wall: one between each two rails.
Ø3 × 4.4 mm, through the middle rail.
On the hex stub at the back of the main shaft: watch it to see the speed and the direction.
For a 0.4 mm nozzle. Filament amounts are estimates for these settings.
Nothing needs supports. The case stands on its floor. Clean any elephant's foot off the hexagons, the bores and the gear teeth, and check that the gears turn freely on the bushings and that the collars slide on the hubs.
Hold the six countershaft gears in the case in a row, from the front: 34, 30, 24, 18, 16, 36, every hub pointing to the back. Push the countershaft in through the front wall and through all of them until its shoulder stops at the rear wall. Glue the sleeve into the front hole, over the shaft.
Put the idler between the two cheeks on the floor and push the pin through.
Lay out the main shaft parts from the front: hub with collar (3-4), 3rd gear and 2nd gear on a long bushing with a washer between them, hub with collar (1-2), 1st gear and the reverse gear on the other long bushing with a washer, hub with collar (5-R), 5th gear on the short bushing. The dogs of every gear face its collar. Set them in the case, in mesh with the countershaft, and push the main shaft in through the big front hole and through all of them until its back end comes out of the rear wall. Glue the output flange on the hex stub.
Push the input shaft in through the front hole, its bore over the main shaft's nose. Glue the crank on its hex stub.
Push the 5-R rail in through the front wall, through its fork (in the groove of the 5-R collar) and its selector, into the rear wall, and set it in neutral. Through the empty middle hole, push a long interlock pin into the bore until it sits in the 5-R rail's notch. Put the short pin into the 3-4 rail's cross hole and fit that rail the same way, then the second long pin and the 1-2 rail. Line up each fork and selector with the holes in its rail and pin it with a piece of filament.
Glue the two lever halves together, with two pieces of filament in the holes in the ball. Drop the ball into the bridge's cup from above and glue the socket cap over it. Set the bridge on the wall pegs, guiding the finger into the slot of the middle selector. Put the gate on, its posts in the bridge, and glue the knob on top of the lever.
Turn the crank and pull the lever into 1st: the output flange turns slowly. Go through the gears, 2-3-4-5, and watch the flange speed up. For reverse, stop turning, shift and turn again: the flange turns the other way. If a gear does not go in, turn the crank a little while you push the lever.
Small parts and gears that can pinch: keep them away from young children.
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