In spite of what I said earlier about the lack of precision of the Jacobs Chuck, we will be using one of them for turning this pen, and we will make a special mandrel for it. It is easier this way, and the Chuck provides the adjustability in length that we need. Any run-out and eccentricity will never be noticed because the pen is used in a holder, and the point is always extended. If it is never twisted, nobody will ever notice any mismatch between the barrels.
The collet adapter from Woodcraft would be a better option, but its cost is almost that of the Jacobs Chuck.
The best rod to modify is another mandrel rod. They are readily available in a size that fits the ID of the brass pen tubes. 1/4" diameter commercial drill rod (0.250" diameter) is too large unless we can find it that is slightly undersized or the pen tubes are larger than 0.250. It is easier to spend the price of a mandrel rod that is threaded, and cut the threads off. Woodcraft has a mandrel rod that is threaded on only one end.
Grind one end of the rod with the profile shown.
Remove the threads if necessary.
Drive the pointed end of the rod down through the glue in the bottom of the brass tube, and into solid wood.
Don't overdo it with the hammer. It doesn't take much to drive the rod through the glue foam in the bottomof the hole.
Place the center bushing on the rod, followed by the lower pan blank and two (2) "Slim-Line" bushings.
Mark and cut the rod at 1" above the bushings. Try to make this as close to 1" as possible. If it any longer, there may be a problem with taking up the slack with the chuck when the center bushing is removed
