Re: Creating long straight edges

Doug,

Thanks for the lab experiment. Reading your results along with Les'
insightful comments made me yearn for more info. [by the way Les, I
think your signature line should read: L M Watts Furniture and
Physics lab :<) ].

I dug into the newsgroup archives and found an interesting thread on
collimating light. One author suggested using an ordinary camera
lense to collimate the light by placing the laser at the focal point
of the lense.

So, I dug out my 35mm camera and tried a rough test of shining the
laser through the lens. I couldn't really ascertain if the lense
made a difference because I didn't have a good rig to hold my lense
(I didn't want to scratch an expensive lense...I may rip apart a
cheapie disposable camera though.)

Anyway, I saw my circular polarizer in the bag and tried it. I
shined the light through it and after manipulating the lense I was
able to obtain a nice tight spot free of glare and thus limited
diffraction. If you have your test rig still set up and a polarizing
filter for a camera, maybe you could see what kind of results that
would provide.

My college physics is really rusty but I believe this could be a
suitable technique for obtaining a suitable reference device. It may
not provide the .00001 (or smaller) reference needed by machinists,
but with some tinkering do you think one could obtain a reference
of .001? Like Dave, I too am looking for a technique to create a
suitable mounting surface for a large router table for wood. I
realize I don't need a great deal of precision, but I like tinkering
and shooting for the best precision I can.

Also, in this same newsgroup thread, for the aperture, the guys
created a hole in aluminum foil using the point of a pin. One guy
claimed he could create a hole smaller than 20um(.00079 in) by
placing the aluminum foil on a hard surface like glass and then
piercing the foil. For those interested in the thread, do a search
on deja (The thread started on Jan 7, 1995 and was still alive
through Apr 14, 2002)

Regards,

David

--- In CAD_CAM_EDM_DRO@y..., "Doug Harrison" <prototype@c...> wrote:
> >> The variabiltly of the rail would
> > > be the width of the hole in the placards.
> > > Any thoughts or suggestions?
>
> I just tried a #70 (that's small) carburetor jet for the hole. It
gets the
> spot down to about .010" as long as the hole is close to the spot.
With the
> hole two feet from the wall the spot grows to about .050" and gets
worse as
> the pinhole to spot separation increases. I think its that
diffusion thing.
>
> Doug