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. :) > > Gene: > > 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 > after. > > 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 ebay. 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. :) > > Regards, > Kent > I assume the missus was taken care of while you were in the shop. How are both she and you doing now? > > ------------------------------------------------------------------------ > ------ Virtualization & Cloud Management Using Capacity Planning > Cloud computing makes use of virtualization - but cloud computing > also focuses on allowing computing to be delivered as a service. > http://www.accelacomm.com/jaw/sfnl/114/51521223/ > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users 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> * CosmicRay wishes he had some strippers here.... <CosmicRay> err, wire strippers
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------------------------------------------------------------------------------ Virtualization & Cloud Management Using Capacity Planning Cloud computing makes use of virtualization - but cloud computing also focuses on allowing computing to be delivered as a service. http://www.accelacomm.com/jaw/sfnl/114/51521223/
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