Dug’s Automata Tips, Techniques and Tricks No.3
March 15, 2011 by Dug North
Pinwheels – Gears for the Masses
Gears are very useful to the automata-maker, but they can be tricky to make depending on your knowledge, skills, tools, and patience. Enter pinwheels: gears almost anyone can make! In a previous installment of this column, we looked at a number of methods to make wooden circles. This time around, let’s divide some circles into equal segments to make pinwheel patterns.
The Cabaret Mechanical Movement Method
One method of designing printable pinwheel templates is provided for free by Cabaret Mechanical Theatre as a supplement to their excellent book Cabaret Mechanical Movement. The instructions show you how to create patterns for pinwheels with 36 and 12 pins — a 3:1 gear ratio. The technique requires a computer drawing program such as Adobe Illustrator. The method was first published several years ago, but I’ve tested it in the latest version of the program (Illustrator CS5) and the instructions still work beautifully! If you have access to Illustrator, this is a great method.
Note: The ‘Paint Style’ window mentioned in Step 1 may be hard to find these days. You can apply the fill and stroke settings as instructed using either the ‘Control’ bar at the top of the screen, or by opening up the ‘Appearance’ window, under the ‘View’ menu.
Making Pinwheel Templates with the Online Gear Template Generator
What if you don’t have Adobe Illustrator? How else can you make a paper template? Fortunately, woodworking mastermind Matthias Wandel has created an amazing online Gear Template Generator. He offers a feature-rich version for purchase, but for our purposes the free version will do. Let’s use the Gear Template Generator to recreate the pinwheel patterns made with the Illustrator technique mentioned above.
Getting Acquainted with the Gear Template Generator
The Gear Template Generator is designed to generate paper templates for cutting wood gears. When you first arrive at the page, you are presented with a default gear and the settings that were used to produce it. The generator has a number of fields into which you can enter numerical values or enable and disable features.
First, check the box for ‘Show pitch diameter’ on the right-hand side of the screen. On a gear, this is the point where the meshing teeth make contact. For pinwheels, this is the circle on which the pins will be placed. Next, check the ‘Show center’ box. This produces a pair of lines showing the exact center of the pinwheel. Finally, check the ‘Dividing plate mode’ box. This changes the gear teeth into line segments representing even divisions of the circle. It is starting to resemble a pinwheel template already! The pins will be located where these line segments intersect with the pitch circle. I also changed the value for ‘Shaft hole dia.’ to 6.25mm to create a hole at the center of the circle that is a bit smaller than 1/4 of an inch.
Making the Large Pinwheel Template
To replicate the large pinwheel template, we’ll need to adjust a few settings. First, we know the large wheel has 36 teeth. Find the input box for ‘Gear 1 teeth’, type in 36, and then hit ‘Enter’ on your keyboard. The pinwheel template should now have 36 teeth. Great! But, if you printed it out now, the pinwheel would be very large. Why is that? Notice the first box in the upper left-hand corner labeled ‘Tooth spacing’. This value defines the distance between each tooth and is set to 15 millimeters by default. That’s an appropriate number for robust wooden gear teeth, but a bit big for an automaton pinwheel. The distance between pins for the large pinwheel generated with the Illustrator method was about 5.25mm, so go ahead and type 5.25 into the ‘Tooth spacing’ box and hit ‘Enter’. That’s all you need to do for now. Use the ‘Print gears’ button below the Gear Template Generator to print the template.
Making the Small Pinwheel Template
To replicate the small pinwheel template, we’ll need to modify some values again. We know the smaller wheel has 12 teeth, so type that number into the ‘Gear 1 teeth’ box, and hit ‘Enter’. Done! So why didn’t we change the ‘Tooth spacing’ value? Here’s something very important to remember about pinwheels: regardless of their size, the number of pins per inch must be same for pinwheels to mesh together properly. The ‘Tooth spacing’ field effectively sets the number of pins per inch. Therefore, the value we set for the larger pinwheel is also the value required for the smaller pinwheel. Go ahead and print this template out, making sure to use the big ‘Print gears’ button on the screen. This ensures that the two templates will be drawn to the same scale.
Tweaking the Templates
If you would prefer a different sized hole in the center of your pinwheel template, change the “Shaft hole dia.’ value accordingly. Entering a value of 0.5mm will give you a small dark point at the center of your circle.
The one thing that is not drawn by the Gear Template Generator is the outside diameter of the pinwheel. The pins must sit in some distance from the edge of your wooden circle, so you’ll need to draw a larger outside circle by hand. Take a drawing compass and place the point at the intersection of the template’s center lines. Open up the compass so that it extends beyond the drawn pitch circle by about 5mm. This isn’t a critical dimension; you just want to be sure there is enough wood around the pins to hold them securely without splitting the edge.
The pin spacing on pinwheels can be wider than the 5.25mm used in these examples. They can up to 9 or 10mm apart and still work. Make a few sets of your own to find out what spacing works best for you.
Creating pinwheel templates just scratches the surface of what the Gear Template Generator can do. If you would like to make some wooden gears, this tool is great for creating the patterns. Give it a try!
A quarterly column by automata-maker and enthusiast Dug North
Copyright 2011 Dug North
Warning: The topics covered in this column include the use of tools and materials that have the potential to cause damage to property and/or bodily injury. Your safety is important and it is your sole responsibility. Always read and follow the safety instructions that come with tools and materials you use. Wear safety glasses, use guards and other forms of safety equipment, follow safety precautions, and use good judgment. Seek the guidance of experienced outside sources whenever required.