Vintage "Pilot Watanabe" plunger filler repair

[Fountainbel]

Hi all !
I've just finished the repair of a vintage Pilot "Watanabe" plunger filler dating from around 1939.
The pen leaked at the filling knob side and the piston washer was cracked
I made a new cartridge for the rod equipped with an O-ring on the rod and one in the barrel bore.
Instead of making a special rubber piston washer and the inherent special punching tool , I've opted to use an O ring mounted in a small Delrin washer which features a radial groove for the O-ring.
The washer is flat polished on both sides to achieve a perfect sealing closure contact on the back-up collar on the rod.
The radial pretension of the piston O-ring being 0.15 mm, pushing the plunger down the axial friction is just perfect to ensure a leak free flat sealing contact on the backup collar.
Ensuring easy entrance of the piston Oring in the vacuum chamber, the diameter transfer between the expansion chamber end the barrel bore was chamfered on 60°.
The advantage of using standard "off the shelf" O-rings is that future repairs will be easy.
I am sure that Pilot would have opted for O-rings also, but unfortunately these were only invented late 1945!
The pen takes 1.1 ml of ink, which is in effectively the maximum possible volume the pen can hold
Attached a sketch showing the repair approach and the original patent drawing.
Note the fixation of the rod in the filling knob was different to the patent drawing.
The bore point in the filling knob is made 0.3mm off center, resulting in the fact that when tightening the rod enclosures screw the filling knob slightly stands skewed.
This was surely done to improve ink entrance and ink feeding to the nib , similar as Sheaffer did with the extended tale on the feeds of their plunger fillers

Francis