On 7/13/2010 3:18 PM, Jon Elson wrote:

Well, you need a CNC machine to do that! The problem is that without
accurate measuring of table travel, it is hard to do. You can use a
boring head to bore the central hole, and any centering boss or recess
at your (0,0) coordinate. but, then you need to spot and drill 4 holes
at the corners. A machine with worn Acme screws and no DRO will give you
fits as there is differential wear on the screws, so even relative
movements are wrong. (My old manual Bridgeport had this disease, nothing
would ever fit no matter how careful I was.)

Yoiu can try scribing marks with calipers, or even surface plates and
height gauges, but it all comes down to how accurate you can dial in the
drill bit over the mark. I was never very good at this.

Jon

With some indicators set up you should be able to figure out what your
backlash is like and get to within .01 easy enough. Might be a pain in
the ass moving the indicator every time your close to travel limits, but
it would at least get you there.