# Tool Finds Middle of Wheel

When developing homemade robot wheels, drilling a hole in the correct place for the motor shaft can be tricky. Even a slight error causes the wheel to wobble or at least rotate off center enough to reduce performance.

Tool and box for 1 1/2-inch center square

## Center Square Tool

MicroMark sells a metal tool (\$17.45 #82285) that helps locate the center of any small circle, square, or octagon.

## Step 1

Place the circle firmly against the inside of the tool. The tool has sides that are at a right angle (90 degrees).

(The picture above shows the tool under the circle. Actually, you'll need the circle to be underneath the tool -- flipped over -- in order to draw the line in the next step.)

## Step 2

Draw a line using the straight edge as a guide.

The straight edge bisects the right angle. In other words, the straight edge is 45 degrees from each side of the circle.

## Step 3

Rotate the circle 90 degrees or whatever and draw a second line.

The second line intersects the first line at the center of the circle no matter what angle is chosen.

## All Done!

The center of the circle is where the lines cross.

You don’t really need the tool. A ruler and a protractor will work just fine. The tool is just a little easier and precise.

Now if you could only drill straight.