A friend gave me this pen in kit form. She included the bushings for holding the barrel on the mandrel, but not a mandrel. I do not have a mandrel. I decided to make my own precision mandrel and do a good job of turning the acrylic barrel blank. That means it had to be correctly centered while turning and with no vibration.
Step 1: The Parts
This pen is from Woodcraft. The barrel features a cylindrical circuit board in clear acrylic. In addition to the various parts, you see a 1/4 inch steel rod from my workshop. The barrel blank shows the two bushings for mounting the barrel blank on a mandrel. I inserted the bushings into the ends of the barrel blank so I could determine how long to cut the 1/4 inch steel rod I will use to make a mandrel. The holes in the bushings are just a little too small for the 1/4 inch rod. I suspect the holes are 6 mm, which would be just a tiny bit smaller than 1/4 inch. My finger marks the length I want to cut for the mandrel.
Step 2: File the Rod to Make a Mandrel
The plan is to chuck the 1/4 inch rod in my drill press and lightly file the rod while the drill press is running at its slowest speed of about 500 rpm. In the photo you can see I began near the bottom of the rod and filed until one of the bushings would just slide onto the 1/4 inch rod. Then file a bit above where the bushing stopped until the bushing will slide farther onto the rod. There is a lot of stopping the drill press, checking the fit, and starting again to file more. But, in very little time I had resized the 1/4 inch rod for the mandrel bushings. Since I was removing only a little material from the rod and the filing is done at slow rpm's, there was little danger the rod would go out of round.
Step 3: Thread the End of the Rod
Here I am taking a measurement to determine how much threading I need to do. You can see the rod is firmly held by the drill chuck on its upper end. Next comes one of the pen barrel bushings. Then comes the barrel blank. At the bottom is the other barrel blank bushing. A self-locking nut will compress the assembly to keep the barrel blank from slipping on the mandrel. If it does slip a little during operations, just tighten the self-locking nut a little more.
Step 4: Cutting the Threads
Since I removed so little material from the 1/4 inch rod to fit it to the bushings, I decided I could thread the rod for a 1/4 inch nut. I usually hold a rod in my vise while cutting threads, but there was too much of a chance I might damage the end of the rod. Then the chuck would not hold it properly, and I would have too much wobble on the mandrel. I decided to put the mandrel rod into the drill chuck and use the drill press in cutting the threads, but without power to the motor. The table of the drill press holds the die in the right alignment. I placed the chuck wrench into the chuck holes for it and used the wrench to turn the drill press shaft by hand. With my stomach I kept tension on the feed control levers. That was a problem only until the threads got a good start at cutting. An adjustable wrench held the die. After cutting a couple of turns, I would raise the drill press table to provide a resting place for the adjustable wrench. When I finished, there was a burr at the top of the threads that I had to remove so the bushings would still slide onto the mandrel.
Step 5: Anchor the Bottom Bushing
I drilled a hole in the wood that is just a little larger than the outside diameter of the bottom bushing. I raised the drill press table so the hole in the wood comes up over most of the bushing. Depending on how the mandrel is held in the chuck, there could be some oscillation and vibration at the bottom of the mandrel. I lightly pulled the piece of wood against the mandrel to plant it firmly and eliminate any vibration. I clamped the wood against the drill press table to hold it in place. The letters in yellow say, "Bottom Bushing--Add drops of oil to reduce heat." The mandrel ran without chatter or vibration and the blank turned very nicely on center.
Step 6: Rough Cutting With a Dremel
Step 7: Check With a Caliper
I wanted to keep my cutting even top to bottom. I checked my work often with a caliper. I have turned a couple of wooden pens, but never one with acrylic as the barrel. I erred on the side of removing too little material with rough cutting tools, like a Dremel, so I would be certain to have enough material to polish at the end without undercutting.
Step 8: Finishing
I used what I had to finish the barrel blank. I used a couple of files, some 60 grit sandpaper, and some 320 grit sandpaper. The final tool was rubbing the barrel blank with an cotton old "T"-shirt while it spun at 3000 rpm. It worked quite well, although there is a slight matte surface rather than a very high gloss finish. Through use the pen will develop a slight matte finish, anyway. I added some extra shine to the finished acrylic by touching some wax for finishing pens to it while spinning and buffing it with my old "T"-shirt. That made a difference and added gloss.
In the process of finishing the barrel blank, the sand paper took the black finish from the bushings.
The alternative would have been to buy a micro-mesh sanding kit. This has progressive grit gradations up to 12,000. But, a sanding kit would have cost as much as the pen kit.
Step 9: Assembly
My mandrel worked pretty well, as did my improvised polishing method. Woodcraft has a fountain pen I just might make.