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Anodising red

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  • Anodising red

    Don, a long term customer of ours, sent me this email. I thought it would be helpful to pass on his experiences.

    "My good friends and neighbors at the lake like to play cribbage. They brought their cribbage board, shaped and decorated to resemble a largemouth bass, to our cabin for games.
    It has plastic pegs, two blue ones and two red ones. They’re quite happy with the campy board but not so much with the plastic pegs.

    I suppose turned pegs made of some exotic woods of different colors would be more in keeping with a cabin motif, but I’m not a wood guy. I do metal. So I decided to make aluminum pegs, anodized and then dyed red and blue.

    First iteration was a flop. The red ones came out pretty good but the blue ones were awful. WTF, over? I’ve made other stuff that I anodized and then dyed blue that was freakin’ gorgeous!

    I finally tumbled: anodize films do NOT like sharp corners. Mil specs call for minimum radius of .030 on anodized corners. I’d knurled the handle part of my aluminum pegs and the failure occurred in the knurled regions. Don’t know why it worked OK on the red ones, maybe just because the knurls weren’t quite as aggressive.

    OK, so knurled pegs hit the can, new design. Now I’m making them with round grooves. I make the grooves .030 deep with a round-nosed lathe bit, and then smooth the outer edges with the smallest round file from my recently-acquired Oregon Chain Saw Blade sharpening kit. The peg part is tapered like the originals, 3 degree taper going from 0.098” dia to 0.130” dia in a distance of 0.3” because that’s what I measured the plastic pegs to be. The top part is about .187 dia. Photos when I get them made if successful. I got two made today, then had to clean up for dinner out with friends tonight. I’ll make two more tomorrow (about an hour), anodize them (2 hours while I do something else), dye them (30 minutes) and seal them (30 minutes).

    Mike Caswell did a genius job of putting together kits with instructions that make it possible for amateurs to accomplish professional-grade plating on small projects like guns and car parts. I’ve used his stuff for a couple of decades now. Haven’t sent him a penny for as long as I can remember; the stuff just keeps working. I do zinc, nickel, tin and copper plating, and black oxide for shop-made tooling and gun parts. Don’t do chrome because chromic acid is seriously nasty stuff.

    Anodize films are electrical insulators, but they have pores that electrolytes (acid) can permeate. Those pores are what later receive and hold dye. As the anodizing process progresses, if done with constant voltage then current will decrease as the film builds until a point is reached where the rate of dissolution of the film by the acid equals or exceeds the rate of deposition, then current starts to increase. I prefer to use a constant- current regulator I designed and made that I can set precisely with a 10-turn pot to deliver a set current regardless of load resistance from dead short to where supply voltage is insufficient to deliver set current to a given load. That saves a lot of blown current meter fuses. I anodize at about 30 mA per square inch of work surface. Voltage is whatever it turns out to be. As the process progresses at constant current, the voltage rises as the film builds until it reaches a point where it levels out and then starts to decrease. That’s when it’s “done”. I have this process highly automated with a clipboard and pencil, recording voltage every once in a while when I think of it.


    Last edited by mcaswell; 06-22-2021, 05:52 AM.
    Mike Caswell
    Caswell Inc
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