Intro: Machining Titanium and Stainless Steel Jewelry
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.
Step 2: Facing Off the Bar Stock
The first step is to cut the end of the bar stock so it's square to the length. This gives a nice clean, smooth surface for drilling. Decide how long you want the bar to be, then add maybe a mm or two and cut it off. A jewelers saw works delightfully for this.
Chuck up the piece of bar in the lathe and take some light cuts to clean up the end. I'm using a carbide insert cutting tool, fairly moderate cutting speed, and no coolant.
Step 3: Turn the Bar
The next step is to turn the bar down to the diameter you want. You'll need to know what gauge piercing you want. In the US we use a bizarre system of measurement, of course. It's based on the Brown and Sharpe wire gauge measurements. I'm making an 10 gauge barbell, which comes out to 0.102 inches or 2.6 mm.
Take light cuts until you get down to the diameter you want. I like to make the last cut very light- just a couple of thousandths of an inch- at higher rpms. This leaves a smoother finish which is means less polishing. I finished this step with a diameterof 0.106, which leaves something to take off when polishing.
Step 4: Center Drill the End
Use a center drill to 'spot' the end of the piece. This leaves a little dimple right in the middle which will keep the drill bit in the right place in the next step. It's the same idea as center punching a piece of material before drilling it with a hand drill.
Step 5: Drill the Bar
Drill a hole through the bar. This should be the right size for the tap we'll use to cut the threads. I'm using a 1-72 tap, so it's a #53 drill bit which is 0.059 inch or 1.511 mm. As an interesting trivia point, number drill bits are measured using American Wire Gauge (AWG), which is completely different from the B&S wire gauge for piercing sizes.
I drill the hole all the way through the bar, drilling half the depth from each end. I think this lets me do a better job of cleaning out cutting oil, chips, and general muck from the threads. Make sure to use some kind of lubricant on the drill bit and back it out frequently to clear out metal shavings.
Step 6: Tap the Bar
Using a tap, cut threads inside the bar. This is where the balls will screw on. Tapping small holes like this can be difficult- it doesn't take a lot of force to break the tap. If the tap is not perfectly lined up with the hole it will jam and break. I use the chuck in the tailstock to loosely hold the end of the tap while I turn the tap wrench by hand. Use lots of cutting lube, go slowly, and back the tap out more often than you think is necessary. I get into a rhythm of 1/2 turn forward, 1/4 turn back and then completely removing the tap every few turns. If you break the tap, you get to buy a new one and throw away the piece.
One fun trick though, in case you're working on a piece you don't want to throw away. The bar here is titanium and the tap is steel. This means that if the tap broke, you could put the whole mess in a bath of nitric acid, which would dissolve the broken tap piece but not the titanium part. Of course, when you were done you'd still have to deal with whatever problem made the tap break...
Step 7: Drill Your Balls
Chuck up one of the ball bearings in the lathe and use the center drill to start drilling it. The center drill does a good job of breaking through the ball's crunchy outer shell to the gooey center. Usually, ball bearings are pretty hard and difficult to drill without annealing. Stainless doesn't harden very well and I haven't had any problems with drilling them.
Step 8: Drill, Countersink, and Tap the Balls
Next, drill, countersink, and tap the balls. Drill a hole 2/3 of the way through the ball using the same bit you used for the bar. Then use a bit the same size as the diameter of the bar to put a short countersink into the ball. This will allow the bar to seat into the ball slightly when they're screwed together. This is the trickiest part of the whole thing. If the hole is too small, the barbell won't fit together right. Too big and there's a gap perfect for all kinds of biological nasties to live in. To make it more difficult, the bar is probably machined to some wierd size where you can't get a drill bit to match it (and drilling usually make the hole a little bigger than the bit anyway.
Once everything's drilled, tap the hole the same way you tapped the bar. Then screw one of the screws tightly into the ball and cut its head off. Leave enough threads sticking out of the ball that it can securely attach to the bar. I like to leave them longer than most commercial barbells.
Step 9: Rough Fit
At this point, we've machined two balls and a bar. All the components are done and it's time to check if they fit. Screw everything together- the threads should work smoothly. Check that the bar fits tightly into the countersinks. If it doesn't, you'll probably have to redo that ball. If everything looks good, then we're done with machining and ready to start finishing- in other words, we're about halfway.
Step 10: Polishing Fun!
Now it's time to make it all shiny. I use some 600 grit wet/dry sandpaper to remove any tool marks from machining. Don't overdo it- you don't want to change the dimensions too much. Then use a rotary tool with a felt pad and polishing compound to get a mirror shine. In the picture below, the bar is screwed onto a brass fixture to hold it in the lathe while it's polished.
I finish off with an ultrasonic bath to remove polishing compound and and residue from cutting oils, then passivate in a citric acid solution for 10 minutes. Passivation is a process of using an acid bath to remove any little bits of iron that might have rubbed off from the cutting tools. For the stainless bits, it also helps to remove iron from the surface layer of the part and make a good corrosion-resistant surface. Finally, it gets washed again and it's done!
Step 11: And We're Done
Here's a picture of the finished product, showing a couple of common problems. First, it's hard to tell from the photo but the surface isn't quite where I'd want it. It's smooth and shiny, but not quite there. So it goes back for some more polishing- not a big deal. Second, and more seriously, the ball on the left has too big of a countersink. This shows well what I was warning about earlier. Nasty gunk can get caught in there and it gives a great place for bacteria to grow. This might be good enough for a healed piercing, but I still redid it.
I put a picture of my 'shop' at the bottom. The point I want to make is that you don't need a lot of space or massive machine tools to do this kind of work. The lathe is the biggest investment, and that was about $300 from harbor freight. It takes me an hour or so to make one of these. The first one took more like three hours, but I made 4 or 5 balls before I was happy with them.