£2.50
Worm Gear / Cam
Turn the handle on the Worm Gear / Cam box and the gear inside advances one turn for each turn of the handle, a speed reduction of 12:1. Inside the box is a snail cam and cam follower which slowly lift as the gear turns and then suddenly drop at the end of the twelve turn cycle.
Use the Worm Gear / Cam as an interesting exercise in pure mechanism or as the starting point for your own character based paper automata.
Members can download this model for free at the link. Thanks for signing up! Non-members can download the project file for £2.50.
Print out the parts onto three sheets of thin card. 230gsm / 67lb is ideal. I have printed the parts onto coloured card to make a colourful model.
Score along all the dotted and dashes line and cut out the cross-hatched holes before carefully cutting out the model.
Fold over the gear to make double thickness card then card carefully cut it out.
Fold over the cam to make double thickness card as well. Once the glue is dry carefully cut it out.
Roll up the three tubes and glue them down lining up the ends with the points of the arrows.
Thread the gear and the snail cam onto the square shaft lining them up with the grey lines. Make sure the cam is the correct way round.
Assemble the cam follower.
Glue on the tab…
…then the short section of tube.
Roll the tab round and glue it into position between the two triangular tubes.
Take a penny piece (20mm diameter 4gram weight) Wrap an off-cut of card tightly round the coin and glue it down. Glue the coin to the cam follower just behind the tube.
Fit the wider tube into the worm axle Line it up with the grey lines.
Start at one end of the spiral grey line, glue a section of worm to the shaft. Try and keep it as perpendicular to the shaft as possible.
Glue the next one in place overlapping the first by one face width of the hexagon tube.
Work your way down the tube in the same way gluing each piece down with a full face overlap.
Once complete glue the five pieces of worm gear together.
Assemble the handle in three steps.
Fold up and glue the triangle tubes on the box ends.
Fold up and glue the right angle triangles on the box top and base.
Glue the sides to the top as shown.
Thread the gear into position and glue in the base. The gear should turn freely in the box holes. If it does not, remove the shaft and expand the holes very gently with a pencil.
Glue in the two box side stiffeners next to the cam shaft but not so close that they stop it turning.
Fit the worm gear into position.
Close the box front locating the worm shaft into position. Glue the handle to the shaft.
Glue the end of the push rod to the cam follower.
From the back of the box, thread the push rod up through the hole in the box top then glue the cam follower to the back of the box. Once the glue is dry turn the handle and the cam will inch round incredibly slowly.
Perfect for making a tortoise that peeps out of her shell? Or a snail creep along or perhaps a sloth in a tree?
Whatever you create with this useful mechanism be sure to share photographs with the rest of the website visitors by emailing them in!
