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Re: [Emc-users] Brass finish question? gene heskett Thu Feb 23 00:00:52 2012

On Thursday, February 23, 2012 02:31:08 AM Jon Elson did opine:

> gene heskett wrote:
> > Lampblack would be fine IF one could find a binder as effective as the
> > krylon that wasn't glossy at low incident angles.  A case where thin
> > is good, but I expect trying to mill the outside 1/3" of it down to
> > the point where knife edge diffraction was the major effect, would be
> > pretty frustrating.
> 
> Might be possible to mill it with a ball-end mill so that the
> sides were not parallel to the light path.
> 
> Looks cool, anyway!
> 
> Jon

Thanks Jon.  I thought of that, but by the time I had it clamped down on a 
sacrificial slab of HDPE, it was bowed up in the middle by 13 thou or so.  
Unless I mapped the cut depth carefully, the slot width would have been the 
largest variable.  To get fully thru a 32 thou thick sheet, I actually had 
to carve 47 thou deep on the final pass.  Theoretically I imagine there is 
a timing error from that, but it should get lost in the noise in spite of 
it.  I thought about reducing the slot count from 45 to 36, but that would 
stretch the edges to 2.5 degrees apart.  If I can't get a good duty cycle 
and quadrature pattern out of this one after its blacked, then I supposed 
I'll make another with fewer slots just to widen the dark bars, but we'll 
see how close to ideal this one is first.  I sure wish I had more diameter 
available though.  That would make things a lot easier.

Cheers, Gene
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
My web page: <http://coyoteden.dyndns-free.com:85/gene>
Mankind is poised midway between the gods and the beasts.
                -- Plotinus

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