Page 229 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

Chapter 7 Bearings, Couplers, Gears, Screws, and Springs 207

WM Berg (www.wmberg.com) is another good place to find hubs, shaft adapters, and
other components in convenient sizes. (The product search on the WM Berg site
doesn’t have pictures at the time of this printing, so it may be easier to order the
company’s free print catalog.)

Increasing Shaft Size
Since motor shafts are often smaller than the components you need to attach to
them, there are a few handy tricks you can use to fill the gap. One way is to use a
shim. Shim is a general term for a thin thing that fills a gap, and can be made of
wood, metal, or plastic. If you’ve ever tried wrapping duct tape around a shaft to
make it fit tightly to a component, you were shimming the shaft. You can certainly
stick with duct tape if that works, but a more professional approach is to get a roll of
shim stock—basically thick tin foil—and cut a piece that wraps around your motor
shaft.

You can find shim stock sheets and rolls at most hardware stores (and McMaster, of
course). Soda and beer cans are also readily available sources of metal shims if you
have some tin snips to cut off the ends. Shim stock comes as thin as 0.001 in, so if
your component fits on your motor just a little too loosely, you can jam some layers of
shim stock in that gap until you get a snug fit.

You can also use aluminum or brass tubes as a kind of shim to create a new uniform
surface on the motor shaft. These are available from McMaster and most hardware
and craft stores, and they come in many diameters. The walls can be almost as thin as
plastic drinking straws, so you can layer one size on top of another if necessary.

Attaching the Motor Shaft to Another Shaft
Sometimes you need to extend a motor shaft to reach a wheel or rotate a long shaft.
For example, if you are trying to automate your window shades, you might want to
connect your motor to a rod that runs the width of your window and rolls up the
window shade when you turn on the motor. There are three main options here,
depending on the relative sizes of the shafts:

• Insert a smaller shaft into a bigger shaft Make a hole in the bigger shaft,
stick the smaller one into it, and secure it with a set screw if necessary. See
Project 9-2 in Chapter 9 for an example of how to drill a hole in the center of
something without a lathe.