Many WWII British aircraft incorporated stopwatches held by either rubber (6A/269) or a device with prongs (6A/1475). They could be found on the pilot’s instrument panels, bomb aimers or navigator’s stations.
As one component in the restoration of a Lancaster Instrument panel, I was able to purchase an old rubber stopwatch holder. The rubber had deteriorated significantly and the original AM etc. impression was weak (photo). It was also very brittle, to the point where I feared if I inserted a watch, it would snap into pieces.
I came across a thread in http://www.thegsresources.com which discussed various methods of returning some flexibility to old rubber. I chose a method that involved using oil of wintergreen mixed (33% oil) with water and heated to 65C. In theory, old rubber may contain plasticizers which evaporate over time. The hot water softens the rubber and allows the Wintergreen oil to penetrate and to some degree, replace the plasticizers in the rubber. Other reasons rubber deteriorates are due to oxidation and the breakdown of antioxidants and antiozonant stablizers in the original formulation. Wintergreen can’t restore this type of decomposition. (post 67, themess http://www.thegsresources.com/_forum/showthread.php?169370-Wintergreen-oil-for-revitalising-rubber-parts/page7)
The Wintergreen was purchased (special order) from London Drugs, a common drug store found in Western Canada for about $7.00 per 100 ml, enough to do the job. A spacer was used to keep the rubber off the base of the pot and the solution stirred to maintain an even temp and mixing of the oil and water. The holder was flipped a few times too and it was noticed that not only was some raw rubber was coming into solution but the surface of the holder was sticky to the touch. I only continued the process for about 30 minutes although the literature suggested several hours may be required. The surface swells during this process as that area is of course more exposed to the oil. After half an hour, I felt the rubber was pliable enough. I rinsed and lightly dried the holder, reinstalled it back on the panel and slipped in the watch with minimal difficulty where I left it to dry completely. Mission accomplished; from a visual perspective.
I haven’t tried to remove the watch – it’s an unnecessary risk at this point but the rubber now feels somewhat pliable. I wouldn’t be surprised to find that the fine detail in the embossed lettering has been degraded or maybe even lost but out of sight, out of mind. It appears that the cracks in the rubber initially visible, have been greatly reduced and the small ones even eliminated.
If I was to do this again for this specific item, I think I would soak the rubber in hot water for some period first, then add the wintergreen and at a lower concentration, maybe only 20%. A stir bar in a hot water bath would help to mix the insoluble oil and maintain even water temp.
A friendly reminder. Oil of Wintergreen, methyl salicylate, while it smells pleasant enough and relieves the old arthritis, is toxic (LD50 ~1gm/kg, oral). Do this outside where the area is well ventilated.
Has anyone else tried different methods to restore old rubber watch holders?
Regards,
Wayne Logus, Alberta, Canada
By: zorgon - 15th May 2016 at 02:38
Hi Fleet16b:
In response to “I have an actual mould that was used for making these stop watch holders”.
Wow! What a desirable item to have; a great find. Could you post a few pictures? Particularly of the (reverse) impression of the lettering. I think I have see a few different examples of the raised format so perhaps they were made under contract by a few companies?
Maybe, rather than you finding a replacement formula, you should try to find a company that makes traditional real rubber items and have them do a limited run with your mold (put me down for one too). I believe someone in Britain did this a few decades ago in both black and white versions and those particular high quality replicas were still selling for a hundred to 150 quid or so (or a gazillion Canadian Dollars) recently. I guess it depends on how authentic one wishes to be. Certainly silicon and the modern urethane’s would do the trick, look great and last much longer but they’re just not, … “real”.
Ya, 3D printing. I guess I have to get with the program. It’s hard for an old phart.
Thanks,
Wayne
By: QldSpitty - 6th May 2016 at 12:26
ABS plastic 3D printed holder for my Sopwith Camel panel.I could use the 3D model to do both halves of a female mould for casting..Another substitute is ordinary black silastic mixed with Corn Starch.
[ATTACH=CONFIG]245743[/ATTACH]
By: hindenburg - 5th May 2016 at 18:27
Bought a lovely condition one and did my own mold from it…yet to find the correct composition rubber to do a pour yet…the same as the c-type earphone holders material wise…any suggestions?
By: Fleet16b - 5th May 2016 at 13:01
Thanks , I will have to see if I can find a supplier here in Canada
An old buy I know had the mould and gave it to me
I think originally the rubber holders would have appeared smooth , not pebbly and pitted like the ones pictured .
The mould has smooth surfaces
EDIT NOTE ******
I have found a supplier for product here in Canada . https://www.smooth-on.com/distributor-regions/canada/
When I have time , I will have to try it out.
By: powerandpassion - 5th May 2016 at 12:40
Polyurethane
Guys
I have an actual mould
If someone could identify a good product that is two part , thin enough to pour into the mould and is flexible like rubber once it cures , then I can make
hundreds of these holders.
Polyurethane is a two part elastomer that comes in a wide range of formulations providing a wide range of results. The bushes you might see used in aftermarket car suspension systems are cast polyurethane as is foam cavity filler used to insulate around plumbing entries through walls. The Germans developed polyurethane during the war as a rubber substitute. (I think they were actually trying to make a coffee substitute but the cup kept bouncing off the floor):)
There are many suppliers of polyurethane. Open up the phone directory and they will be there. Take an original holder in or ask them to recommend a black polyurethane formulation of a similar hardness or durometer to natural vulcanised rubber. You will need some release agent to stop the polyurethane sticking to the tooling. Some polyurethanes will set without heat, generating an exothermic heat during the chemical reaction. Some set with external heat.
I will take a few watch holders! How did you end up with this tooling ? Any more tooling ?
By: Fleet16b - 5th May 2016 at 11:43
Guys
I have an actual mould that was used for making these stop watch holders
The problem is finding a product that can be poured into them .I used one product but it cured to a hard plastic with no flex
If someone could identify a good product that is two part , thin enough to pour into the mould and is flexible like rubber once it cures , then I can make
hundreds of these holders.
By: windhover - 5th May 2016 at 08:28
Spade grip Dunlop covering can be replicated with black Milliput epoxy putty. It just takes a long time to get the wrinkle finish looking correct.
By: powerandpassion - 5th May 2016 at 08:11
Another substitute for rubber is Sugru.
QldSpitty, love it and luv u, even though you are from Qld and love Spitfires! I think I will sugru my face, create a bit of a mantlepiece bust out of cast plaster, share some of the goodness with future generations ! I do enjoy new products like this.
So now you can CAD up a rubber part, 3D print a male and female mold, and sugru out a finished part.
Now I wonder if black sugru will sort out spade grip material….
By: Versuch - 5th May 2016 at 08:01
QldSpitty, thats interesting stuff.
Cees, its a RAAF Beaufort NAv ,Bomb Aimers panel located in the nose.
Thanx Wayne for getting this rolling..
Regards Mike
By: QldSpitty - 5th May 2016 at 06:38
I 3d printed mine for my Camel panel..Another substitute for rubber is Sugru.Would be great for Lord mounts and BFP isolation rubbers
https://sugru.com/buy?gclid=CNqO3vSbwswCFU4IvAodzE0FaQ
By: powerandpassion - 5th May 2016 at 05:42
Interesting info. Always wondered about how to restore and stabilise old tyres, for display.
British rubber came from Malaya up till 1941, after that I understand South American rubber kept the show on the road. I always wonder where the Germans got their rubber, unless via Vichy France and Indochina. Still you had to ship it, using neutral shipping, but how would a submarine know? The history and struggle of Allied merchant marine is known, but I wonder about the Axis merchant marine.
Lack of access to raw rubber meant the use of more recycled rubber crumb. In grappling with the modern problem of vulcanised tyre recycling, a great body of scientific literature exists on the topic from WW2. But this was more for applications like tank wheel lining or solid rubber tyres for artillery pieces. I doubt whether raw rubber watch holders were used after 1941, as much as the old fob watch was replaced by the wrist watch. The old rubber watch holders would be made from high quality rubber. I understand that aircraft tyres would require high quality rubber : there was a great movement towards standardisation of tyre sizes to make use of rubber more efficient. I understand the development of polyurethanes and nylons was the key way Germany dealt with the rubber tyre question. Dealing with the chemistry of early polyurethanes would be very challenging.
I understand that in any vulcanised natural rubber presentation some material would remain unvulcanised : that a solvent may ‘swell’ some part of a formulation to create some pliability. Rubber science is quite established and accessible, even though most rubber product manufacturing has shifted to China. A good ,practical understanding of rubber chemistry might be got from the local retreader, and they might have some insight into compounds that affect rubber.
By: FarlamAirframes - 4th May 2016 at 17:40
Wayne I was impressed by your thermal process to get the oil back in. The wintergreen should at least make it smell better.
I hope it keeps supple for many years.
By: zorgon - 4th May 2016 at 16:11
Hi All:
Thanks for the interesting and educational link Brian. Not surprisingly, it is complicated chemistry but interesting to read that Castor oil might be the preferred compound in restoring some of the initial properties of the old rubber. Retaining tensile strength, shape and providing a lasting rejuvenation are all of course critical considerations.
It would be great if there is still anyone left who worked at the plant near to where Air Ministry lives who remembers anything about the initial manufacturing process or compounds that went into rubber manufacture during the war; it’s probably buried in a book somewhere. I believe latex purity wasn’t foremost on their minds, as would be expected, during wartime manufacturing. It’s amazing any of these watch holders have survived actually. I recall seeing one rubber holder on eBay a few years ago, in the original box, that looked almost in mint shape and it sold for over $200 as I recall.
Peter, I’ve seen your Halifax instrument panel and it is wonderful, detailed and accurate creation, congratulations on that project.
Thanks to all for the feedback and images,
Wayne
By: FarlamAirframes - 4th May 2016 at 09:58
It is many years since I last compounded natural rubber on a two roll mill and added plastcisers.
This article discusses the effect of various oils on Natural rubber and which affected the hardness ( Shore A) of the resultant rubber.
Castor oil seems to have had a beneficial effect.
By: CeBro - 4th May 2016 at 09:08
What’s that panel from?
Cees
By: Versuch - 4th May 2016 at 08:08
Wayne thats a very interesting idea, I tried to restore my rubber mount having it sit in extra virgin olive oil over Summer 2014, came out a little less brittle, Just checked it again on the panel, its like a rock!!
Maybe I should try a pasta sauce…
Kind Regards Mike
By: CeBro - 4th May 2016 at 07:09
Me too. Must be a Halifax thing.
Cees
By: Peter - 4th May 2016 at 00:14
I picked one of those up from Ebay from my halifax project.
By: Arabella-Cox - 3rd May 2016 at 21:02
An interesting technique, let’s watch this space…
I can honestly say that in all my years of collecting, I’ve never yet managed to get my hands on a 6A/269. That said, how odd that the majority were probably churned out by a now defunct rubber firm about a mile away from my home!
If your renovation doesn’t last, I’m sure you know that replicas are available. With a hefty price tag I would expect.
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May 3, 2016 at 6:04 pm