fibergeek, thanks for the comments!
As I’ve replied to neilfj, I will better control the parameters next time and post new pictures of the results.
The test pieces I’m using are cut from an old 1/8” plate which I’ve had for a number of years, not recently machined at all. After polishing it with the “wadding” polish, I had sprayed & rubbed it off w/simple green, rinsed it and left it to soak in hot SP degreaser for 15 minutes. Since it passed the water break test, I presumed it was good to go. But perhaps not? Will SP degreaser not get at embedded polishing compounds? What's better to use?
Notably, the reverse side was only brushed and blasted, so there was no polishing compound/chemical there, yet it shows the streaked finish. A different effect than the polished side though.
Whatever I’ve done wrong will hopefully be resolved w/tighter temp & rinse control next time.
Regarding my DMM resolution, you are right. I have my decimal point off by one. My bad, I should have checked the numbers more carefully before posting. The resolution is 0.1 ohm, and I use that AFTER taking test lead resistance out of the equation.
With test leads clipped together, the meter reads steady 0.9 ohm. With the leads about 1 cm. apart, w/in the connection area, the meter fluctuates between 0.9 and 1.0 ohm. With leads about 3 cm. apart, on either side of the connector area, the meter fluctuates between 1.0 & 1.1 ohm. So I had presumed this is the natural resistance of the aluminum. Is it possible that even this low a resistance is interfering w/anodize current flow?
With one test lead on the anodized area, continuity goes open circuit, so I know I’ve got SOME degree of growth there. I don’t have any means of actually measuring thickness, but I’ll try a crude scratch test later, and see how hard it is to break through.
As a trivia after thought, I wonder how the “big boys” do their anodizing to get 100% coverage. Until I started to learn about anodizing, I never knew that it was an insulator. But I’ve got a few pieces in my scrap pile that are 100% covered. These are some @ 1/16” plates, 3x10”, some dyed red, some black, which I picked up from an aerospace surplus place, just for possible project use. They appear to have been from a production test, since they are stamped w/alloy identification, e.g.. 7075-T6 & 6061-T6. I just took a closer look at them, and there is nowhere that I can find any spot where a mechanical or electrical connection was made. Even the edges appear 100% anodized. Is this possible? How’d they do that?
Thanks for your help!
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