Thanks guys. [
] Jake, I need to take a few pics of the shop and the lathe. I was thinking that as I was drilling the holes, and coolant was blasting like Niagara Falls, but I was too nervous to leave the machine while it ran for the first time.
Here's the detailed version of how I made it:
I started with the pen cap and turned it cantilevered out of the spindle from 5/8" solid titanium stock. I had to dial in speeds and feeds to keep it from hitting a resonance and making chatter marks on the outside. I parted it off, so now I have a nicely turned surface that is curved and can't be clamped on.
I made a special collet that had the inside bore that matched the outside of the surface. I tried one out of plastic, but found that the hydraulic chuck squashed it out of shape when it was drilled out. I made another in aluminum and milled some lines to divide the collet into 3 jaws. The collet was made with a 1" outside diameter to match the bore of my chuck jaws. Since the pen cap goes over center a little bit and starts curving back inward, I realized that it would be tough to get the part in and out of the stiff collet, so I added a threaded hole to the bottom so I could put in a bolt and use that to jack the part out of the collet after it was drilled. I used a milling vise to push the part into the collet at the start. It was snug as a bug when the part was in the collet and because the curve precisely match the outside curve of the collet, I wasn't worried about the hydraulic chuck jaws clamping down on the collet and crushing the part.
I drilled a double hole and bored a little bit of a taper on the inside of the cap that matched the pen body. When the turned part was complete, I chucked the part in my milling vise to drill the holes for the clip. I made a plastic nosecone for the pointy part so I wouldn't crush it while champing the part in the front to back orientation. I used a tiny endmill to drill the holes for the clip using XY coordinates for location. I had to be extremely careful because the clip holes are way on the rounded outside of the part and would easily deflect and snap the small endmill.
I made a plastic mandrel for the clip on my machining center. This gave the theoretical elliptical curve that I was shooting for. Since the titanium wire I used for the clip was so springy, I couldn't simply bend the metal to the mandrel, but had to overbend it by quite a bit in order to hold the shape. I could bend it by hand and used needlenosed pliers to bend it. I used the mandrel to check my progress.
I cleaned up the surface and anodized the clip in a homemade anodizer. I increased the voltage from around 26 volts to around 40 volts while pulling the clip out of the bath. This made the anodized color fade.
The main body was a bit more challenging to make. I first drilled the stock with two very deep holes while the 5/8" barstock was short in the lathe chuck. There is an inside step that was bored then too. I tapped the threads for the nib by hand. I then pulled the bar out to full length and brought in my tailstock. I turned the outside of the part leaving it attached by a 1/8" stalk at the tip end. I snapped the finish turned part off by hand and had to hand grind the tip to the normal point.
The mokume material was slit to proper width and rolled by hand around a metal piece to the approximate diameter needed. I sheared it to length and proceeded to hammer it into the undercut groove. The part was soldered with as small a seam as possible and any remaining stock was hammered to as low a position as possible. The Mokume was hand ground down to flush with sanding discs. The pen was then hand finished with fine sanding discs and micromesh until around an 8000 grit. I then polished it out with hard cotton buffs and a large buffing wheel. Assembly consisted of pressing in the clip and screwing in the nib.