Source For Piston Cork

[Ron Z]

Ironic that you should ask this as I'm working on replacing the seal on a Wahl safety, and a Kaweco Dia to come later this week.

 

You can buy Flor corks for wine bottles at wine making supply places.  They aren't cheap.   I would assume that you can slice them to the right thickness.  Not sure how you do that without power tools though.  Corks are rather small for slicing with a power tool with fingers really close.  Maybe one of the chain mail gloves that my son used when working in a sub shop.  Take that slice of cork and punch with that.  Do expect to go through a couple of corks or slices - there are often voids hidden in the middle of the cork even when the outside looks really good.

 

I do my work on a lathe. Mount the cork in the chuck, drill the center hole slightly smaller than the shaft and leave the drill in the cork.  Spin at really high speed with multiple show, shallow cuts with a sharp bit until you're close.  Finish to the right diameter with sandpaper backed by a wood block so it's straight.  Then run the lathe backwards and at slow speed, and cut the cork to length using an Xacto knife.  You may need to sand the cork down a bit once mounted.

[FarmBoy]

Sharp knife, small round file and sand paper. 
 

or just use a few orings. 

[Paul-in-SF]

I think I'm going for the o-rings, sanded down slightly to roughen them up to accept more silicone grease. But while I'm waiting for those to arrive, maybe I'll try again your way.

[OMASsimo]

I’d strongly discourage you to use O-rings, they might cause more trouble than anything. It’s really not that difficult to make a cork piston seal by hand without specialized tools. I make them from wine corks, which I collect whenever I get one of excellent quality. As Ron said, there might be little holes or cracks in it, which are not seen from the outside. So, it might take a couple attempts to find the right piece that doesn’t break during the making. All I need to make a seal is a sharp drill bit smaller that the required hole, an Xactor knife, sandpaper boards of different grit, and two tea lights plus a bit of time and patience.

[Karmachanic]

Member Eric Wilson recomends woodwind cork, which is flor. Presumably of a high quality.

[OMASsimo]

Might be a good source. It’s brass rather than woodwinds, though. You can buy cylindrical rods of different diameters, which are used to make the bumpers in the valves.

[Paul-in-SF]

So I did try again with the Flor cork that I bought. First try, using @FarmBoy's simple tools (sharp knife, small round file, and sandpaper) actually worked. I just needed to think about it differently. I also got the little tiny rod in place that guides the piston shaft up and down. So, the pen is completed, and inked up and writing. Here's a quick writing sample. Thanks everyone!

 

[Paul-in-SF]

A note on other materials to substitute for cork: I finally took a close look at the old seal from the above pen, it was still in there when I got the pen and I had just assumed that it was worn out cork. But no, it was in fact twine, blue twine, wrapped around the spindle until it was thick enough to scrape along the inside of the barrel. I don't know if it ever worked well as a seal, but there was a fair amount of old ink impregnating the outer layer of twine, so maybe it held its own for a while. 

[DvdRiet]

1 hour ago, Paul-in-SF said:

A note on other materials to substitute for cork: I finally took a close look at the old seal from the above pen, it was still in there when I got the pen and I had just assumed that it was worn out cork. But no, it was in fact twine, blue twine, wrapped around the spindle until it was thick enough to scrape along the inside of the barrel. I don't know if it ever worked well as a seal, but there was a fair amount of old ink impregnating the outer layer of twine, so maybe it held its own for a while. 

props for such a creative solution (attempt)! 😁

[Karmachanic]

On 6/24/2022 at 11:20 AM, OMASsimo said:

I'd strongly discourage you to use O-rings

 

There are those who feel this way about silicon, but recommend Viton O-rings

[OMASsimo]

This was a recommendation for a seal of a safety filler, not for a replacement of a piston ring. I’d say that’s something very different. But it’s only my two cents as a hobby collector and restorer of European piston fillers. I’m always happy to learn. Is the Viton material considerably compressible? I’d be surprised. The problem with old piston fillers, particularly when made of celluloid, is that the barrel usually is tapered inside. The seal has to be sufficiently flexible to compensate for that.

[Ron Z]

It is true that you sometimes find deformation in the barrel wall caused by the long term pressure of the piston seals, with the  ID being a bit larger where the seal usually sits.  It can make fitting a seal "entertaining" because the seal has to hold no matter where it is in the barrel.

 

I don't think that there is a universal yes or no on materials to be used.  The earlier piston seals used in pens after the 1950s are not soft and elastic, and neither are the replacements.  Modern Pelikan seals are somewhat soft, modern  MB aren't though the way the seal is molded allows for some flex. Even so, I prefer the after market seal replacements with their 0-ring seal built in. 

 

There are arguments going both ways, and what gets used depends on the pen.  Aurora 88s for example used stacked rubber sheet for the piston seal.  In that case 0-rings make sense, and are a heck of a lot easier to install because you don't have to try to sand to fit.  The way that the piston on a Conklin Nozac is made, you really can't use cork, so finding the right diameter and material 0-ring is important.  The cork seals in safety pens often benefit from the use of 0-rings because the cork itself is often very thin, and stacked 0-rings make for a better and more durable seal.  In other cases, I use cork both because that is what was used, and also because the diameter of the seal doesn't match a standard 0-ring size.  If I have to shave it down to fit, I may as well use cork.  Note that if the 0-ring is too tight it can cause problems and damage the pen.  You can't just jam the things in the pen.

 

The material that is used to make the 0-ring, size and durometer (hardness) of the material count.  The 0-rings used as seals in touchdown Sheaffers for instance, were a specific material and durometer.  I have the specs that were in the bag that we got from Sheaffer.  Viton is both chemical and wear resistant.  The seals were a little larger, and a little softer than what we had been using, so sealed better and the pen filled better.  So a lower duometer could be as flexible or "elastic" as cork, but have a longer life.  I do not like, and will not use silicone 0-rings.  You can't use silicone grease with silicone 0-rings.

 

David Nishimura has suggested scuffing up the surface of 0-rings so that the silicone grease stays in place and provides lubrication.  That seems to work.  Fail to do that and the silicone grease gets displaced and the 0-ring can stick to the barrel wall.

[Paul-in-SF]

How is nitrile as a material for piston o-rings? The o-rings I sent for arrived today (although I no longer need them) and both sizes I got are nitrile (one says it is "buna-nitrile"). They both have a durometer of 70. 

[Ron Z]

The question is how much nitrile is in the rubber.  I don't remember details about percentages, but they don't have to have a lot of it in the rubber to be called nitrile rubber.  But buna-N is good.

 

A durometer of 70 is likely OK.  That's what the durometer of our head gasket rubber is.  I had to look in my notes.  The durometer of the 0-rings (snorkel and PFM/Fat TD) from Sheaffer is 60, and is what I would be looking for.  I passed the data sheet information on to David Nishimura and Martin Ferguson/Sam Marshall 15 years ago since they were selling 0-rings for the pens.  I wanted them to have the Sheaffer specs for the rubber parts that they were selling.

 

To give you an idea of the scale for durometer,  hard rubber/ebonite is 100.  A rubber band is IIRC, is down somewhere around 30 or 40.  If someone has better data on the lower I am willing to be corrected.  We went for 70 on the head gaskets so that it wouldn't pull off over the head gasket nut when you pulled the plunger back, but wanted to have something that would still flex and press against the barrel wall and seal without sticking.

 

 

[Paul-in-SF]

Thanks, all very useful information. 

[GeoffMartin]

I wrote a couple of blog postings about this

https://www.pm-pens.com/2018/05/29/harvesting-cork-for-gaskets/

and 

https://www.pm-pens.com/2018/05/29/making-a-new-cork-gasket/

using the instructions on this page

https://goldfinkberlin.wordpress.com/2021/02/10/cutting-cork-seals-for-piston-filler-repairs/