Have you ever needed to find the center of a circular object? This project required milling a circular piece of Lexan to the correct thickness and then drilling a 1/4 inch hole through the center of a Lexan spacer. Fortunately you can use the the Digital ReadOut (DRO) device to find the center of the part. The DRO that I used was a Anilam Wizard 411 but other DRO's should have similar functionality. By using a 0.200 inch diameter touch probe, I was able to touch 3 points on the circular part and the DRO would calculate the diameter of the part and determine the center of the part. After touching the probe to the 12:00, 4:00 and 8:00 O'Clock positions, I was able to drive to the 0,0 coordinate and drill the center point. It worked well. Here is how I did it.

## Step 1: Select the Tool Tab

Select the tool button which looks like a drill on the hard keys keypad and input the diameter of the probe. Using the blue buttons, make sure to select the correct tool and ensure that the tool is selected in the status bar. In this case it should be T:1. This is an important step. Accurately measuring the diameter of the touch probe and ensuring the tool is selected in the status bar (see T:1 in figure) will assure the center point is calculated correctly.

## Step 2: Select the Datum Button

Select the datum button shown above. This will open a menu across the bottom that can be selected using the blue keys.

## Step 3: Select the Probe on the Menu

Select the probe button. This creates a secondary menu that allows you to determine the coordinate system via detecting an edge, a center line or a circle center.

## Step 4: Select the Circular Center

Select the circular center button and the DRO will ask you to probe three points. To minimize error, it seems best to probe the 12:00 o'clock position, the 4:00 o'clock position and the 8:00 o'clock position on the part. Press the train button after hitting each location.

## Step 5: Select Enter

After completing the 3 points, select enter. The DRO will calculate the diameter of the part and will make the center of the part be at the 0,0 position. If the diameter of the part is known, it is useful to compare the known diameter to the calculated diameter. My results had less than 0.002 inch error.

## Step 6: Conclusion

That's it. It is that simple. I was able to simply replace the the touch tool with the 1/4 drill bit and go to the 0,0 position and drill the hole. The second figure above shows the finished parts and the raw Lexan starting material.