In 2009-2010, I used Laney College's machine shop in between classes to work on projects. One of my favorite projects made during this time period were my stainless and titanium rings.
Initially unsure about what to expect, I started with 303 stainless, which is the softer, and more machinable of the austenitic stainless steels (300 series). That way, despite any mistakes, early attempts would remain wearable or at least, giftable.
I first built a little fixture to hold rings in a convenient position on the lathe. Additionally, it can be transferred back and forth between secondary operations on the mill without any trouble.
I turned down an aluminum bar to be just smaller than the ID of the ring. A 1/4" NPT hole is drilled and tapped down the center. The fixture is then carefully slit with a hack saw so that it will expand when a short piece of pipe is driven into the tapped hole. Basically, it is a homemade expanding mandrel.
The first two 303 SS rings turned out well. I found an efficient process which I used later on:
1. Crudely rough the ring out of bar stock and part off.
2. Mount the ring on the fixture.
3. Completely shape the outside of the ring, including any mill work.
4. Hold by OD in a 5C collet, and completely shape and polish the inside.
5. Remount on the ring fixture and polish the OD.
Next, I moved on to titanium. A friend from work had given me a bar to play with. I knew I had to use low surface speeds, but didn't realize quite how low! After toasting a couple tools, I found that my HSS cutters were happy around 30-40 SFM (surface feet per minute, across the material).
The titanium rings were a pleasure to machine. They turned easily and filed nicely and the chips were attractive, if not on the unruly side. Of notice, titanium doesn't seem to take to polishing, and is always at its shiniest following a cut.
I made two Ti rings with turned finishes (shinier) and two which were sanded with fine sand paper. My friend claims the stock was Ti 6AL4V, although, based on the color code, it was 99% commercially pure. I am still not sure which it was.
I set out to anodize the Ti rings. I chose Cola for its phosphoric acid content, and a series of AA batteries for a power supply. Setting the Titanium ring as the anode, and a piece of scrap aluminum as the cathode, I immersed the objects in the Cola bath.
With lower voltages, around 10V (approx 6 AA batteries in series), I was able to create a bronze-brown color. With higher voltages, like 35V (all 20-something of my AA batteries), I found a nice bluish purple. Other colors, like green, are out of my reach.
Immersing the jewelry in the soda for different amount of time, or in different places gives different effects. I dipped only the edges of a couple rings, and found a rainbow effect.
Anodizing produces titanium oxide on the surface. It is a fairly durable finish but can be scratched up by other metals. Titanium does not corrode, and it is hypoallergenic, so there is not much need for anodizing besides for the colors. A similar process is available for aluminum, but requires a more serious setup.