very black anodizing

Hi,

Have your anodizer deep etch the material before Type II black. That will give a matte surface. The only trade off is loose threads etc as the deep etch will eat at the tapped holes a little.

dave

snipped-for-privacy@krl.org wrote:

Yes, Bill, a post to sci.materials or sci.physics.research might disclose a way to determine the RMS finish resulting in optimum blacking. For a noncontact surface, I might recommed 'Luma-Black, for a contact surface, an appropriate alloy selection, and conventional black anodizing, not hard anodizing.. But there are choices to be made. Too coarse a grit and you get speckles; too fine and there's no effect.

Cylindrical interiors can be turned to a finish that will capture light even better than a grit blast. It all has to do with wavelenths of light. Have they considered using a near-monochrome source and an finish wavelength very close to that value? That is, a trap?

If the x-ray company calls me I can do the research and make a recommendation.

Is that Don's email there in the quote header?

Doug Goncz Replikon Research Seven Corners, VA 22044-0394

I was hoping that someone here would know something about Ball

Good idea but not for this application. The part actually has two light bulbs so that when one bulb burns out, the operater can just push a button and the part is moved back and up so the second light source is used. No problem with one of the light sources, but the other lamp is located in a pocket and the reflections are from two adjacent sides.

I guess it is time to start calling to get more information on Ball Black.

Dan

Has this problem been looked at by a OPTICAL engineer? We often design systems to minimize stray light and put it where it is not a problem.

If this is not a sliding contact surface, how about having the CNC shop milling the parts use a fine thread mill when profiling the affected sections of the part so that you end up with scatter lines rather than a mirror finish? Something between 20 and 40 TPI, maybe? --Glenn Lyford

It has not been looked at by an Optical engineer, but has been looked at by some ordinary engineers. And the design can be changed to fix the problem.

One definition of an engineer is someone who can do what any damn fool can do, but can do it so it is cheaper. And that is what this is about. Not fixing the problem, but fixing it for the least cost. In this case it looks as if the cost effective solution is going to be changing the shape of the part to keep the light from hitting the two surfaces.

Dan

FWIW, Dan, that doesn't sound to me to be the problem. If you're having a problem with contrast, then the usual suspect is diffused light bouncing around between the elements, not direct light hitting them. In that case it's just as important for the surface to absorb light as it is to avoid direct reflection.

But you'll be able to tell with some experiments.

-- Ed Huntress

In this case the problem is light from the filament of a lamp hitting a surface at a low angle and reflecting in the same general direction as the light directly from the filament. There are no lens elements. | x | |_____________________ ooooooooo

The light comes from the light bulb at x and reflects off the surface above the oooooo's. It is kind of a trivial problem which can be solved in several ways. I was hoping that there might be a better black anodize that would eliminate the reflection at essentially no additional cost and no change to the machining.

Dan

Not a contact surface and this is likely to be the solution. It will require a change in the program as the surface is currently machined with the spindle perpendicular to the surface.

Dan

Hmm. If that angle of incidence is in approximate scale, and if the target is to the right, that's going to be interesting. You probably know this but even quite black surfaces can reflect some light at such a low angle of incidence.

Good luck. It will be interesting to hear what you come up with.

-- Ed Huntress

is it possible to put a short tube around x extending a little way out into the cavity. or maybe even a tube with an annular end to totally eclipse/shade the sides?