On Tuesday, December 13, 2016 at 10:53:51 AM UTC-5, rangerssuck wrote:
I am making prototypes of a new product. The case is made of aluminum plate, approximately 4" x 1" x 3/16". I have engraved a test piece and it worked very well, but:

* Due to the complexity and fine detail of the engraving, I can only go to about .0005" depth with a .1mm x 10° bit.

* Doing this on bare aluminum, it has all the detail, but very little contrast. I would like to color either the whole piece and then etch through to bare aluminum OR color the design after engraving.

* All I have read about coloring after engraving recommends a minimum depth of .005", preferably .010 - .012". That would not work well for this design. I tried rubbing in some acrylic paint, waiting for tit to dry and rubbing it off, but it also removed most of the paint from the design. I also tried squeegeeing off the paint, with similar results.

* I'm not even sure that black anodizing beforehand would work, as (I think) the anodize layer is thicker than I am engraving.

So, I started looking at other coloring methods for aluminum. The one that keeps coming up is Birchwood Casey Aluminum Black Metal Finish https://goo.gl/zfC1eo . The reviews are mixed for this. Some say it's great, others say it comes out blotchy and still others say it barely colors the metal. Brownells also sells it.

I'm thinking that I could either color the entire piece and engrave through it OR spray a coat of paint on the whole piece, engrave through the paint and then use the Birchwood stuff (or something else) to color the logo, and then strip off the paint.

I welcome any suggestions and experiences.

BTW, I'm doing this with a newly acquired Taig cnc mill. Very cool, fits my needs well. From this engraving test, I see no reason why it won't work fine for making prototype pc boards. Sp many toys, so little time.

JPB

Regarding the reviews on the Birchwood stuff, different grades of aluminum respond very differently to anodizing and chemical treatments. That could be the issue.

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Ed Huntress