doesn't matter. Next, divide the base circle line into 12 equal sections as shown. Each section corresponds to 30° of cam rotation, from 0° to 360°.
Next, determine the distance of follower movement you want, and mark off this actual distance from the base line. On the example shown, the high point of cam travel occurs at 180° of rotation (point F on the drawing).
Now draw a smooth curve from the 0° point to the high point and back again to the 360° point. The shape of the curve determines the follower velocity, and you might want to experiment with different-shaped curves—both symmetrical and asymmetrical—to see what type of follower movement they produce.
Next, draw a small base circle as shown. This circle corresponds to the base circle line. Divide the base circle into 30a segments as shown. With the cam follower positioned at 0. plot points A. B. C, etc., plotting against the rotation of the cam.
Finally, connect the points with a French curve to form the cam profile.
The same procedure can be used to lay out more complicated cams with multiple-follower cycles per rotation. You'll find more detailed information about cam development in any good mechanical-drawing textbook. — David Sloan
This mechanism is commonly used in industry when items need to be distributed one at a time. I've used marbles to illustrate the parts-feed process. The marbles are loaded in the column and delivered down the chute one bv one as you turn the crank. Each full turn of the crankshaft delivers a marble to the next station. Sliding plates with staggered holes prevent the marbles from being delivered all at once.
Variations of this device are used in processing and assembling equipment, for example, in an automatic riveter. You hardly need to think of a way to employ this mechanism —it is fun to play with on its own —but don't hesitate to devise creative ways of incorporating this mechanism into a larger wooden assembly like a complicated marble roll.
The Scotch Yoke is a mechanism in which a rotating crank pin slides hack and forth within a rectangular slot, resulting in the uniform reciprocating up-and-down motion of a rod. It makes a very compact assembly. The Scotch Yoke was used in small steam engines in place of a more traditional connecting rod. saving about a third of the space. It is also used in piston pumps, where a compact design is required. It is frequently used in textile and food processing machinery today, but is almost always referred to as a pin and slot actuator. The Scotch Yoke might be used to animate a wary groundhog poking her head in and out of her burrow.
The fast-return actuator is also known as the swinging block linkage. This device is used in machines that require a slow working stroke and a rapid return stroke. The motion traces an arc. In this particular example, the arm's return stroke is a little more than twice as fast as the initial stroke. The specific ratio of working and return stroke is dependent 011 the dimensions of the mechanism. The fast-return actuator is used in metal shapcrs and industrial sewing machines. You might use such a device to animate a toy Grandpa nodding off to sleep, then jerking back his head to stav awake.
This mechanism does just what its name says: it circulates parts in a continuous rotary manner. Like the parts-feed escapement, the rotary-parts circulator is a self-contained device—and lots of fun to play with by itself. Once people get to cranking this one. it's hard to pull them away.
Turning the crank drives the elevator disk by means of a floating idler wheel which compensates for wear and seasonal dimensional changes. The idler is coated with a thin layer of General Electric Clear Silicone Sealant, which assures positive friction under all conditions. The rotating elevator disk picks up a marble from the feed chute at the bottom. The marble is carried up and released, at the top. into a chute behind the elevator disk. The marble rolls down a sloped horizontal chute to a vertical chute and back into the feed chute at the bottom of the device. The marbles continue to circulate without interruption.
Such devices arc used in industry to circulate parts through different temperature or moisture zones for heating and cooling, wetting and drying, or chemical processing.
The rotary parts circulator is lots of fun to play with, but it's also the most difficult to make of all the mechanisms shown here. The holes in the disk are both angled and tapered, and the slots in the disk taper from shallow to deep. Making one from scratch will challenge you. I've developed several complicated production router jigs to produce the device more easily. A
Raymond Levy is a designer of physics apparatuses in Soquel, California. For more detailed information about his mechanisms, send a business-size, stamped envelope to him at: P.O. Box 804. Soquel. CA. 95073.
ood craftsmanship not only requires good tools, it also requires a good tool cabinet. A cabinet is an important tool in itself for both practical and aesthetic reasons.
On the practical side, a cabinet provides the organization you need to work efficiently. With all your important tools arranged in a single cabinet, it's easy to find a tool when you need it. Aesthetically, it's a pleasure to have a finished example of your craftsmanship in the shop, where you can enjoy it as you work. Sometimes, especially during a difficult operation, it settles your mind to be reminded of what can be accomplished with a little care and patience.
This tool cabinet provides three types of storage-shelves, drawers, and racks—to accommodate all kinds of hand-held woodworking tools. It opens to display your tools, holding each item at a comfortable height, so you can reach a tool without stretching. It closes into a simple, elegant chest on a stand, letting you appreciate the form as well as the function.
Although the cabinet looks complex, the joinery is very simple. Dovetails hold the case and the door sides together. All the other joints are either mortise and tenon or some sort of tongue-and-groove.
I joined the case and door parts with through dovetails for two reasons—one practical, and the other, as you might have guessed, aesthetic. Aesthetically, dovetails look nice, and nothing exemplifies good craftsmanship more than a well-made dovetail joint. For practicality, nothing does a better job of keeping a case square, and this particular cabinet case must withstand unusually high loads. Without strong joinery, the case may become distorted, or the doors may droop after the first few months of use.
As you build the cabinet, you'll run up against some specific construction problems. Here are some possible solutions:
Making dovetails—There are several different ways to make dovetails, both by machine and hand. I routed mine with the help of a dovetail template. There are two templates on the market that make through dovetails—the Leigh Dovetail Jig and Keller Dovetail Templates. The Keller is the simplest to set up, but the Leigh allows you to adjust the width and the position of the dovetails (see March/April, 1988 AW).
Making raised panels—There are also several ways to shape the edges of the door panels. Panel-raising cutters are available for both routers and shapers. You also can bevel the edges of the panels on a tablesaw (sec May/June. 1989 AW).
Routing stopped grooves and dadoes —The door panels and cabinet back all float in 'A-in. grooves. These grooves are stopped grooves, and because of this, it's easiest to guide the router against a fence. I mark the beginning and end of each groove by drilling a '/-»-in. dia., /«-in. deep hole at the ends of the groove. Mount a 'A-in. straight bit in the router, and place it in
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