Re: [CAD_CAM_EDM_DRO] Re: Creating long straight edges

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!

Best wishes,
Ian
--

Ian W. Wright
Sheffield, UK

----- Original Message -----
From: "Doug Harrison" <prototype@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Sunday, July 07, 2002 5:31 AM
Subject: Re: [CAD_CAM_EDM_DRO] Re: Creating long straight edges


> ----- Original Message -----
> From: drking777 <david.king@...>
>
> > I've been thinking about a method that is a variation on your
> > method. What do you think about it? ...
> >
> > Place the rails on the support beam. At one end of the rail, place a
> > cheap laser pointer and at the other end, place a detector ciruit
> > with some audible feedback. Make three identical (relatively)
> > placards and create the smallest hole possible (end of needle?) in
> > each of the placards. Place one of the placards in front of the
> > laser and one in front of the detector. Securely affix the third to
> > the bearing surface that rides on the rail.
>
> I think it's possible if you could control diffusion in the holes.
>
> >
> > Move the bearing along the rail and shim wherever the light is
> > blocked. Now, if there exists a material that could be injected (or
> > more like oozed) between the rail and the support beam, then it seems
> > like this method would be a piece of cake.
>
> Any 100% solids marine epoxy filled with powdered metal and fumed silica
> should work.
>
> >Also, it would compensate
> > for variations in the rail itself. The variabiltly of the rail would
> > be the width of the hole in the placards.
> >
> > Any thoughts or suggestions?
> >
> I must have overdone the caffiene today because I just set a construction
> laser up on my desk and tried it. The pin hole held about one foot from
the
> laser makes a 1/8" spot on the wall 12 feet away. With the pin hole one
> foot from the wall and the laser about 30 feet away I get a fairly round
> spot about .030" diameter.
>
> Of course one might get better results with a precision drilled hole than
I
> get with a mylar granola bar wrapper and a safety pin.
>
> OK, darnit! Now I'm curious. I have some carburetor jets somewhere. I'll
> report back.
>
> Doug
>
>
>
>
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