Introduction: Rotating Knob/wheel/crankhandle
About a year or four back I made this “Do nothing machine” or a “Trammel of Archimedes” as you would also find it called on the internet (image 1). It’s a fun mechanical device which actually does nothing functional as you crank the lever. There are these parts (shuttles) that move criss cross from each other through perpendicular channels, while the outer handle makes a nice elliptical movement.
Sawing the basic parts and glueing everything together was pretty straightforward – although the accuracy of my sloppy woodworking style was quite challenged. The last part I needed was a handle or a knob to rotate the crank. The instructions called for a knob that you could buy in the store or maybe some construction of nuts, washers and bolts. I didn’t feel like making some nice thing out of “wood” (MDF in this case) and then finishing it up with nuts and bolts or something ready bought from the store, so I figured out this turning knob construction which is very simple to put together but in some way really appealing visually. And in wood style of course (exploded view in image 2).
Now I don’t know whether this is a frequently used construction, or that perhaps it’s been here on instructables for a million times already, but I just figured it’s such a nice and simple movement that I would make an instructable on how to make one. Perhaps someone out there hasn’t seen one of these and would enjoy making one or is – like me some time back – trying to finish some woodworking project without any metal screws, bolts or nuts. This particular construction is quite versatile and can also be used for other things like wheels on a wooden toy , a rattle, a propellor - probably anything that needs to rotate on an axle. You can decorate the outside of it as you please, the options are endless (image 3). In this instructable I'll be using the construction to make a knob.
The tools you'll be needing:
- Tenon saw
- Sharp knife
And the materials:
- Wood glue
- Sanding paper
- Some scrap pieces of wood
- A dowel or a stick of wood
When working with saws, sanders or knives take care not to cut (or sand) your fingers off. Also, with all the dust flying around, prevent from inhaling sawdust and wear some breathing protection. Oh and be sure not to impale yourself on the dowel or stick.
Step 1: How It Works
Having a look at the exploded view, here's the way it works: there's a static axle (5) on top of which a wheel (2) is mounted. The wheel is encased in a ring (3), bottom lid (4) and a top lid (1). The hole in the bottom lid is just large enough to provide easy rotation around the axle. Depending on what size and area of materials you have, you can decide on what size knob/wheel you want to make.
Step 2: The Axle
Start out by getting a wooden stick or a dowel. The thickness doesn't really matter, as sloppy woodworking goes, just work with or around what you have. You can cut the stick to the length you want or maybe wait a step or two. If you got a square stick, round off the outer ends - either cut it with a knife or sand it down a bit, or do both (images 2 to 4). I used a piece of leftover round stick about 1 cm thick (image 1).
Step 3: Bottom Lid
Bottom lid first, since when you've already made a knob/wheel at the other end of the axle, you will need to slide the bottom lid first over the end of the stick you're working on now. Cut out a piece of wood the size of the knob/wheel you want and make a hole in the center where the axle will fit through loosely. Slide the bottom lid on the axle. In my case, I've made a more or less circular bottom lid.
Step 4: Wheel
Cut out a circle from another piece of leftover wood - the thickness of the piece I'm using in this instructable is about 7 mm. Sand it down just some 0.25-0.5 mm at each side. In the center make a hole where the stick will fit in. Glue the wheel on the end of the axle you're working on.
Step 5: Top Lid
Cut out a piece of wood the size of the bottom lid. Since we’re making a knob, no hole in this one.
Step 6: Ring
Cut a hole just a little bit bigger than the size of the wheel you cut in step 4 in yet another piece of wood - make sure it's the thickness you used for the wheel. Check whether the ring revolves loosely around the wheel. It does? Glue it to the top lid, making sure that the wheel has space to move. I'm going for a round knob in this instructable, so I've made a ring shaped ring. Could also have been a square shaped ring. Or a star shape, or whatever shape you like. Clamp and let dry.
Step 7: More Glueing
Glue the top lid and ring construction over the wheel to the bottom lid (image 1 and 2). Make sure not to get glue on the wheel! Clamp tightly (image 3). I've added image 2 to show how you should glue the pieces together - don't get any glue within the black dashed circle.
Step 8: Finish
Now you have a stick on which a lump of wood rotates (image 1). In order to make the knob look like a knob, I sanded off the sharp edges a bit (image 2). Then I took the knob and fastened the axle to my old trammel, which had it's knob broken off (image 3).
Step 9: Variations on a Theme
- Instead of just glueing the wheel at one of the outer ends of the stick, slide it to another position on the stick, glue it there and put on a top lid with a hole in it (like the bottom lid). You'll have a spinning wheel in the middle of an axle and the wheel won't budge from it's place.
- Instead of making a nice round wheel piece, why not make some kind of a cog with pointy teeth (Dracula cog!). When you prepare the ring to go around it, insert some nice and flexible pieces of wood (popsicle sticks work nicely) on the edge that will center the wheel and rattle across the cog when the contraption is rotated (image 1).
- In the instructable I've made a knob that's just a knob that rotates. Why not make a see through knob: cut openings or spokes in your top and bottom lid so people can see your magnificent handywork as it rotates along (image 2).
That's about it. I hope you have some use to this contraption or just have fun while making it.