On Thursday, February 23, 2012 11:44:50 PM Kent A. Reed did opine:
> On 2/22/2012 9:35 PM, gene heskett wrote:
> > On Wednesday, February 22, 2012 09:14:52 PM R.L. Wurdack did opine:
> >> Whatever you use, beware of reflections from the sides of the slots
> >> themselves.
> > Precisely my concern. The front& rear faces of the disk are
> > basically a never mind. Its the walls of the slots I am concerned
> > with.
> >> i.e. The surface of the disk may not be the only reflection
> >> problem. Will lampblack with a coat of clear flat Krylon work, or
> >> just flat black Krylon.?
> > 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. Hence the search for something that would leave
> > a truly non- glossy surface. I, after thinking about it, may just
> > clean it up with Tarnex to dull& degrease the surface, and after
> > much rinsing, try the vinegar dip and ammonia fumes route. After
> > adjusting a few more params in the gcode, just made another,
> > considerably neater cut one I am quite a bit happier with, if I can
> > get it suitable blackened inside the slots. Low res .jpg attached
> > Actually Dick, this is a case where a roughing bit might have been an
> > advantage. :-) But I don't know as I've ever seen a 1/16" diameter
> > rougher. That doesn't mean they don't exist, just that I never
> > thought of it till a couple minutes ago.
> > Hindsight, always 20/05 or better you know. :)
> Back when Jimmy Carter was President, I was engaged in some high-end
> optical physics work that included measuring the specular and diffuse
> reflectance of a large number of materials as a function of wavelength
> and of angle of incidence. I could tell you what it was for but then I'd
> have to...well, you know the saying.
> I never found anything better than lampblack smoked right onto the test
> coupon. It became our reference material. Of course, it lasted only as
> long as we didn't touch it.
> One technique that can help mitigate the reflectance from the sides of
> the slots is to collimate the light source and use baffles before and
> Simple pencil-and-paper raytracings of prospective geometries can reveal
> a lot. So can a test rig with a scope.
Which is what I am using since I have a dual trace 100 mhz Hitachi V-1065.
I found another glitch in the gcode this evening & squished that, turns out
that the main code to carve the slots diddled its own constants when
carving the index slot, so pass 2 was carving 20 thou wider slots. So I
added a couple more vars to save the original math & restored from those at
the top of each loop. Then, using LinuxCNC as a tape measure, I looked at
the path it was going to carve, and adjusted the number of slots downward
one at a time until I could move Y, starting centered on a slot about 2
below the centerline of the Y axis, put it in the .1" at a time jog mode
and tapped the up arrow 8 times to see where the other opto was, and
adjusted the number of slots until a .8" separation, which is this PCB's
mounting distance, with Z in the middle so it catches the index slot, until
it was dead between the slots when up .800". That turned out to be 39
slots/360 degrees. Scan attached & I don't think it will need blacking as
the duty cycle now is about 52%/48%. I was out touring the local
pharmacies (well, 4 out of 5) and they, nor Jerry's nor Wallies had
anything that could be construed to be a brass black solution, so if I want
any, its off the net & pay the (&#^ hazmat fees, except for the K2S on
With rigid enough mounting of the opto's, I should be good to go.
I don't have any bypassing on this test board, so I can see the crosstalk
glitch of the index pulse too, and its rather well centered, either on the
/A|B or on the A|/B condition depending on which edge.
Is hal's ability to track this instant, or in the case of a quadrature
signal source, actually based on the running average of the last 4 edges?
That latter would seem to be the best compromise between instant control,
and noise reduction in the signal timing over one full 4 edge cycle, if I
understand how it works at all. That, in my mind, should do a good job of
averaging out any duty cycle errors.
> Good luck.
Its looking better, see scan attached. This one I will actually use, at
least till I know better. :)
I assume the missus was taken care of while you were in the shop. How are
both she and you doing now?
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* CosmicRay wishes he had some strippers here....
<CosmicRay> err, wire strippers