Re: Locating already drilled holes

CNC:

At 02:29 PM 10/11/00 -0500, Jon wrote:

>It works, but if you put the drill rod in a Jacob's chuck, it will
>likely be a little off center, therefore the hole will also not
>be exactly under the center of rotation of the spindle.
>
>A dial test indicator held in a mechanism that clamps around the
>spindle can read off the inside of the hole. As you rotate the
>spindle by hand, you can see the change in indicator reading,
>and adjust the table until the hole is exactly under the
>spindle's center of rotation.

I have had for a long time what is called a Co-Axial Indicator.
This mounts in the spindle of a mill and shows deviations from
center in both X and Y. A little hard to describe but any
machinist supply (Enco, Rutland, MSC) will have a picture of one.
With the spindle running at slow speed one moves the X and Y
handles for minimum dial reading. When the spindle is directly
over the hole the dial reading is constant. Much quicker to use
than a test indicator. A marvelous magical mechanical
measuring meter. :-)

I also use a dowl pin to quickly locate holes, but I'm sure
it isn't as acurate as the Co-Ax.

Hugh Currin