Alternative Wahl Eversharp Doric Plunger Filler Repair.

[fountainbel]

Hi all,

Just finished the repair of a beautiful 2end generation Doric plunjer filler.

This is a rather difficult repair since the rod seal cartridge is screwed in the barrel with left hand threads and sealed with a kind of sealing kit which does not soften easily by applying heat.

I’ve already repaired several of these pens and only succeeded on approximately half of them to get the cartridge out after hours of frustrating work

On some of the ones I did not succeed the part of the cartridge sticking out behind the barrel broke partly off.

1- The rod seal alternative :

Given these frustrating experiences I decided to leave the cartridge in the barrel and install a 7mm long complementary cartridge inside in the barrel.

This special cartridge features an O ring on its outside which seals in the barrel bore and two internal O rings which seal on the plunjer rod

In between the two inner O rings is a spacer ring which is internally filled with silicone grease ensuring a long problem free movement of the rod.

The front of the new cartridge is tapped with an M3 thread,so using a long M3 bolt one can easily push or pull the cartridge in or out the barrel whenever neccesary.

Only drawback of the complementary cartridge is that one looses 7mm stroke,

However given the high ink intake of these pens this looks not a big problem to me.

2- The piston alternative:

The original flat piston seal features 3 small bypass holes which back-up against the back flange of the piston rod, aiming to create a check valve function hence avoid back-up pressure when pulling the rod out.

This proved however to be a borderline system in my experience : when pushing the rod in one sometimes gets leakage over one of the there bypass holes and one can’t obtain a full vacuum.

Not providing these 3 bypass holes is not an alternative since the back-up pressure becomes extremely high in this case , so one can hardly pull the rod out.

So I decided to install my “shifting O ring” piston instead.

The O ring sits on a conical seat between two collars , and the O ring outside diameter has 0.20 mm radial pretension in the barrel bore.

Outside diameter of the O ring being 8 mm, barrel bore being 7.8 mm

When pulling the rod out the plunger piston head first shifts 2mm inside the then "static” O ring, and axially contacts the O ring against the front collar at the smaller diameter of the cone.

Arriving on this smaller seat diameter there is a radial gap of 0.25mm between the inside diameter of the O ring and its seat, so when pulling further the ink or air behind the piston easily escapes.

Doing so there is hardly any restriction when pulling the rod out.

When pushing the rod in the piston seat first moves axially in the static ring, arriving at the back seat collar.

At that moment the inner diameter of the O ring fully contacts the larger diameter of its conical seat and vacuum is created.

In fact the shifting O ring features a perfect " check valve” function

Note the new piston head is also equipped with the original pin at the front to push the rod off center when the piston arrives at its down position

This pin ensures easy filling and a fluent ink transfer during writing

Only drawback being one has to install a 5mm shorter plunjer rod,

Since the original steel celluloid covered plunger rods often show cracks and pitting due to rust formation a solid stainless rod is however far superior.

3-The results :

Tests revealed a perfect vacuum, when pushing the rod in for 25 mm it jumps fully out as it was spring loaded !

The big advantage off the "shifting O ring" design is the piston centers itself automatically in the barrel bore when pushing the piston down. On the classical designs one can push the rod in slightly skewed which results in vacuum loss since the piston seal will easily deform in this situation & slightly leak.

And the ink intake is 1.5/1.6 ml , which looks not a bad result in my opinion.

Note the same repair approach can be used on the larger size of the second generation Doric's , although logically larger size parts are needed.

Some off you - the purists - may rightfully say thie pen is not as original after doing the repair as such, but note that I've not adapted anything on the pen itself, so the pen can still be re-build to its original filler design.

On the attached picture you can see the new parts, with the old rod on top of the picture.

Regards,

Francis

http://i62.photobucket.com/albums/h89/fountainbel/Repair%20suggestions%20to%20forum/2018-05-182011.30.31.jpg

I've just added the sketch of the system, hope it makes it more clear !

http://i62.photobucket.com/albums/h89/fountainbel/Repair%20suggestions%20to%20forum/2018-05-192017.23.51.jpg

[siamackz]

Well done Francis, as always! I hope that someday I will understand what exactly you mean in your explanation above, haha!

[fountainbel]

Well done Francis, as always! I hope that someday I will understand what exactly you mean in your explanation above, haha!

 

Thanks Sia,

BTW, I've just added a sketch of the system making it easier to understand !

Francis

[lcoldfield]

This is a great improvement for plunger fillers, but it requires some expertise and time on the lathe. I have a prototype Onoto of my own using this system, but I never used it on customer repairs because it did not seem cost effective.

Laurence

[penjog]

Hi Laurence

that's certainly not wrong.

But from my point of view fountainbel is an enthusiast for whom cost considerations step back behind smart solutions - just a committed engineer.

I am happy that there are still such experts with this attitude - fortunately for enthusiasts who do not have this skills and possibilities.

Hansjürgen

[praxim]

Very interesting, thank you for the thoughts, Francis, and it is also interesting that Laurence has tested the same option. It essentially removes dependence on sourcing precise cup washers provided one is equipped to make the O-ring carrier. In the case of Onotos, most use one of two cup washer sizes so it is routine to buy them, but this certainly can solve the Random Magna problem as well as unusual pens.

[fountainbel]

Thank you all for your comments !

I fact I've designed & prototyped this system already 11 years ago, see :

https://www.fountainpennetwork.com/forum/topic/75081-fountainbel-plunger-filler-head-gasket-design/?hl=%2Bfloating+%2Bring

And Conid used the system on their first series of pens, which were plunger fillers.

Francis