Jewelry for body piercing is expensive and can be hard to find, particularly if you need an unusual or large size. I go through the steps of machining a barbell style piece from scratch. This project includes many operations typical of small scale machining on a lathe including facing, turning down, drilling, tapping, and polishing.
Step 1: Gather materials
The first step, as in most projects, is to track down all the materials you'll need. For this barbell, we'll use titanium and 316L stainless steel. The titanium bar stock is 1/8 inch (3.2mm) diameter, and we'll only use a small amount of it. The screws are 18/8 stainless- still corrosion resistant, but stronger than 300 series. The balls are 316L ball bearings. All of this is pretty easy to find online. smallparts.com and onlinemetals.com are good sources.
Alternatively, you could use 316L for the bar. I've made quite a bit of stuff from titanium and in small sizes it's pretty much like working 316- I don't see much reason not to use the titanium and some people may have reactions to the small amount of nickel in 316.
I love using recycled materials for projects. I'm always grabbing scrap metal out of trash and my basement is, well, let's say it's full. This is one place where scrap materials are a really bad idea. For piercing jewelry I would only use 316L stainless, titanium, or gold. Use new materials from sources that know their stock. 'Stainless steel' rod from the hobby store or home center won't cut it, and is probably more expensive than buying good stock from a metal supplier. Anything else is risking nasty metal reactions and infections. The right stuff is not very expensive- all these materials should run under $10 and give enough for 5 or 10 pieces of jewelry.