Making Pulleys and Belts for Automata – Dug’s Tips 9
Pulleys and belts are incredibly useful to the automaton maker. They can transfer power from one axle to another and change the speed, direction or plane of rotation! Check out Cabaret Mechanical Movement for more information about pulleys.
In this article, we will use a simple approach to make a pair of pulleys and make a belt from O-ring gasket material.
1/8�?� thick Baltic birch plywood sheet – roughly 12�?� by 12�?� (about 30cm by 30cm)
1/4�?� diameter dowel – about 4 inches (10cm)
Tools and Materials
Hole saw, or other means for cutting circles of different size
O-Ring Splicing Kit
or the following:
- 1/8�?� Buna-N O-ring gasket material – 16�?� or more (about 40cm)
- Single-edged razor blade
- Cyanoacrylate glue (Super Glue)
Sandpaper – 150 grit or similar
Drill and drill bits – size 1/4�?� and 17/64�?�
White Stabilo All-Surface Marking Pencil
Saw for making straight cuts
Cut Some Circles
The two pulleys are made up of six circles total. The four larger ones form the sides of the pulleys while the two smaller ones make up the center sections. I used a hole saw set mounted in pillar drill (drill press). If you don�??t have a hole saw or pillar drill, refer to my previous article, Wooden Circles for Your Automata.
Place a piece of scrap wood under the 1/8�?� plywood and clamp both securely to the pillar drill table. Cut the four larger circles using a 2 1/2�?� diameter hole saw. Cut the two smaller circles with a 2 1/4�?� saw. Use 150 grit sandpaper to smooth the edges of the circles.
Cut and Drill the Test Board
From the remaining plywood, cut a rectangle measuring about 4�?� by 6�?� (or 10cm by 15cm). Drill two 17/64�?� holes through the board. Locate the holes 1�?� (2.5cm) from the top edge and 1�?� from each of the sides. Sand any ragged edges around the holes smooth. We�??ll use this board to test the pulleys.
Mount the Pulleys to the Axles and Testing Board
Press each of the pulleys on to a 2�?� (5cm) length of 1/4�?� dowel. The dowels will serve as axles for the pulleys. Apply a drop of glue at the seam where the axle passes into the pulley.Insert the pulley axles into the holes in the test board. Keep the board horizontal while testing or cut pieces of wood with 1/4�?� holes in the middle and press them on to the dowels from the back to keep the pulleys in place.
O-ring material is made from Buna-N, also known as Nitrile rubber. I used an O-ring splicing kit to make the belt. The splicing kit is convenient, but not required. You can get by with the O-ring material itself, cyanoacrylate glue, and a single-edged razor blade.
Using the Splicing Jig
Pick one end of the O-ring belt material and push it through the 1/8�?� hole in the splicing jig. Place the razor in the slot at the top of the jig and push down to cut the belt material. If you do not have the splicing kit, simply place the belt material on a suitable cutting surface, and use a razor blade to cut it.
Cut the Belt to Length
Wrap the belt material around both pulleys until it forms a loop. Hold both strands between the thumb and first finger of your left hand. With your right hand, pull the long, uncut end of the belt material while holding the previously cut end in place. Pull until you feel the material start to stretch a little. Make a mark with a white pencil on the uncut section where the cut piece ends. Cut the belt material at this mark.
Glue the Belt into a Loop
The top side of the jig has a series of U-shaped channels to aid in gluing the belts together. Apply a very small drop of cyanoacrylate glue to one end of the belt. Rest the end with the glue within the U-shaped channel designated for 1/8�?� material. Slide the other end into the opposite side of the channel until it meets the glued end. Gently press the two ends together for 30 seconds.If you don�??t have a splicing jig, no problem! Once glue has been applied, hold one end in each hand, and press them together. Keep the ends lined up so the belt doesn�??t form with a bump in it.Once the glue has dried, gently try to pull the two ends apart. If they come apart easily, try again using less glue and give it more time to dry.
Take It for a Spin!
Stretch the belt around both pulleys, then turn one of the pulleys by hand. If the tension is right, turning one pulley will cause the other to turn. If the belt is too loose, cut a very small section out of the belt around the glue joint, then re-glue it. The belt, now smaller, should cause the second pulley to spin. If the belt is far too tight, it will have too much friction to turn. You will need to add belt material or start over.
Make a Working Model and Experiment
There should be enough plywood left over to make a stand for the testing board. Add a crank to the back of one of the axles and you�??ve got a nice desktop demonstration model like the one shown at the beginning of this article. There is also enough plywood left to make some pulleys of different sizes. Make both large and small pulleys to see how different combinations affect the speed of the rotating axles.