Wednesday, 16 April 2014

Casting Custom C Ring Tools for Obscure Fountain Pens (II)

Just a short update on the 'casting bespoke C rings from obscure fountain pens using metal epoxy' trials today; the epoxy has done a good job of taking an impression of the plastic football air pump adaptor, despite the shallow plastic threads, and the big ugly injection line across them. This is an encouraging development, and gives me confidence for the risky business ahead!

The plastic valve adaptor after a smear of RRG and a wrap of teflon tape.

The red rubber grease & teflon tape have prevented the epoxy from adhering in every test so far, so that aspect of these experiments is performing well enough to consider low risk. I'm comfortable with the idea of applying the epoxy to the Japanese eyedropper mentioned in the previous post, and don't think the epoxy will stick to its boss based on experience thus far.

The C ring has taken a good impression of the valve's threads.

The epoxy coped very well with the plastic valve adaptor's injection molded, indistinct threads! This is really good news, as it should do even better with the pen's well defined, die cut threads.

So where to from here? The major unanswered question is this; If the eyedropper's boss its threaded in, will it withstand the clamping pressure necessary to grip the thing and rotate it? I'm 90% sure the boss is made of BHR (black hard rubber). Who knows?

Till next time,



  1. What exactly is Red Rubber grease, and in what sort of store is it found? (Hardware? Plumbing? Automotive?)

    I managed to break a bit of the threads on an old plastic pen and have toyed with the idea of repairing it by fitting a reinforcement in there and then replacing the threads with black epoxy. My perhaps a better idea in my head than in actuality idea is to use some black epoxy, smooth it as best as possible and then grease the threads of the cap, screw the cap on and take it off, hopefully forming the missing parts of the thread as I do. Since the red rubber grease worked for you I thought it might be something to try...

    Scrivelry from FPN and FPG

    1. Hi Scrivelry! Red rubber grease is a grease derived from vegetable oils rather than hydrocarbons, specifically for lubricating and protecting natural and synthetic rubber seals. I *think* it was first formulated a long time before silicon grease was developed.

      According to Castrol, one of its manufacturers, it is suitable for "applications where the lubrication of natural or SBR rubber components is required". eBay is the best place to pick up small quantities, as the 500g tubs common in auto stores would take a lifetime to get through.

      It's mostly used in brake caliper rebuilds, being compatible both with rubber seals and the hydraulic fluid they seal in. TBH the last 3 bad calipers I had, I just bought a reconditioned caliper and traded in my manky old one rather than spend all day cleaning it up and regreasing.

      Here's a Material Safety Sheet for Castrol's formulation.

      I've uploaded a new youtube video, embedded in the post following this one, which includes the C ring screwing on and off the pen. Hope it helps you out, your idea sounds promising!


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