Re: [CAD_CAM_EDM_DRO] Re: Creating long straight edges

"Ian W. Wright" wrote:

> The laser idea won't work just with pinholes. The beam on these cheap lasers
> diverges by a couple of degrees so, as you have found out, the spot gets
> bigger the further away you are. Putting a pinhole at the detector will
> certainly seem to cut down the diameter but how will you know where the
> centre of the spot is? To use this method you would really have to add
> lenses to the system to tighten up the beam (oh, and another problem with it
> is that, as the laser beam is derived directly from a chip like a LED, the
> beam is oval, not round - i.e. it starts off as basically the width of the
> contact on the chip by the thickness of the top layer of the chip). You
> would also have to ensure that the beam is travelling directly down the part
> to be measured - the pocket lasers rarely send the beam out parallel to, or
> central with, the body of the laser tube - and you would then have to
> measure to each side of the spot at the far end and take the mean. Modern
> methods look good but they are rarely as accurate as the older, tried and
> tested methods unless you spend a lot of money on super accurate equipment!

The best way to do this optically is with a target and a transit? Theodolite?
Alignment telescope? I've heard them called different things, I'm not sure
which is the correct term. Anyway, you mount the target on a block that can
ride the ways, and you read the height with the optical instrument. They can
read height variations of a few thousandths of an inch fairly easily.

Jon