Saturday, April 26, 2008

Geneva Mechanism, Maltese Cross or Geneva Stop

The Geneva Drive is also called the Maltese Cross or the Geneva Stop.
Animated Geneva mechanismThe Geneva mechanism was originally invented by a watch maker from Geneva to prevent the spring of a watch from being over-wound.

The most common use of the mechanism is to convert a continuous rotary motion into an intermittent rotary motion. In operation, a drive wheel with a pin enters into one of several slots on the driven wheel and thus advances it by one step (or "station"). The drive wheel also has a raised circular disc that serves to lock the driven wheel in a fixed position between steps.
Steps in motion of a Geneva mechanismHistorically, this mechanism is was often used in movie film cameras and projectors to increment the film one frame at a time. Many automata use the Geneva mechanism for various purposes. In my own piece, The Birthing Engine, I used a 4-station Geneva wheel to control the appearance of the four babies that emerge from the mother.

Here is an 3-D animation of a shifter system that uses a Geneva mechanism:The mechanism in the animation above is patented by Barloworld CVT Technologies and is used in their positive drive CVT as a ratio shifting mechanism.

Here are some books that show various forms of Geneva mechanisms:

Five Hundred and Seven Mechanical Movements
Mechanisms and Mechanical Devices Sourcebook
1800 Mechanical Movements, Devices and Appliances
Pictorial Handbook of Technical Devices
Machine Devices and Components Illustrated Sourcebook
Cam Design and Manufacturing Handbook

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Friday, April 11, 2008

Making Mechanical Marvels In Wood - DIY Book

Making Mechanical Marvels In Wood - DIY BookHere's a book that should interest you makers out there. Making Mechanical Marvels In Wood

This book is not unlike Making Wooden Mechanical Models which I reviewed here. There are, however, some important differences between the two books.

Like Making Wooden Mechanical Models, this book isn't specifically written for automaton makers. Both books feature basic wooden machines as finished projects in themselves.

Making Mechanical Marvels differs in that many of the projects in this book are key building blocks to making contemporary wooden automata. For example, projects such as the cam and follower, the Scotch yoke, the fast-return actuator, and the Geneva wheel are all elements often found in an automaton.

The projects in this book are very handsome and would make nice gifts. There's something inexpressibly classy about machines made of wood.

I bought Making Mechanical Marvels bundled with Making Wooden Models from Amazon.com and I'm glad I did. The two books really compliment each other. I consider this book to be Volume 1. This book has very clear instructions and drawings to get you up to speed making wooden mechanisms. Making Wooden Models is equivalent to Volume 2 in which you tackle some more complicated projects.

The book has well-drawn line diagrams and a series of color pages in the center. The instructions are very well written; I would feel good about giving this book to a new woodworker or youngster looking for a science fair project.

The book concludes with some handy shop tips and jigs -- a nice bonus. I have learned a great deal from this book. Don't overlook it as a resource for building wooden mechanism.

Here is where you can order Making Mechanical Marvels In Wood.

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