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RyMoeller

Francis Barker Mk III Compass

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I'm dropping this in the Chat About Anything Here topic as the subject pertains not to a timepiece but a rather a different instrument- a prismatic compass.

I've been told an important part of any watchmaker's kit is a compass which can be used to determine if a mechanical watch is under the influence of magnetism.  As the theory goes, place the compass next to the watch and if it's magnetized the compass will point to the watch instead of magnetic north.  Perhaps this little bit of kit would have saved me some work in the past although I've been in the habit of demagnetizing watches before checking them out for sometime.

Back to the story:  my wife gifted me a nice liquid dampened lensatic compass several years back when we were still dating.  She's well aware of my fascination with any instrument under glass and even tossed in a how-to booklet for orienting.  Unfortunately between moves the compass disappeared.

On the hunt for a replacement I began searching for a Francis Barker Mk III or M73 compass since they are considered the best in the business and I had long pined for one.  Fortune favored me as I discovered a 1943 model, produced under license by the Canadian Kodak Company, in Greece (and in poor repair).  The price was right so I made the purchase straight away and anxiously awaited my prize.

This particular compass was produced Commonwealth soldiers during the war.  The term Prismatic comes from the technology used to deliver a bearing to the user- a small prism built into the compass magnifies the reading on the compass rose which is visible as the user peers through the sight.  The compass is also liquid dampened with kerosene; the liquid softens the movement of the card as it settles on a bearing.

Luckily for me the poor condition of the compass assured it's delivery.  You see, these compasses were painted heavily with luminous paint containing Radium 226.  The Radium isotope is still highly radioactive today and there are many stories online of customers purchasing these antique compasses only to have them confiscated at the US border and destroyed when the Radium sets off alarms.  The kerosene within my compass had long ago leaked out taking much of the Radium with it and rendering the compass relatively inert.

My plan is to completely restore the compass to the original specifications while replacing the Radium paint with either Tritium capsules or Superluminova.  Thus far I've only completed disassembly which you can see below.  I'll update this thread as work progresses hopefully from start to finish.

Here is the compass as received.  The bowl containing the kerosene dampening fluid is empty now and water has entered at sometime resulting in oxidation and clouding of the crystal.

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Step one was to remove the rotating bezel which then gave me access to the eight screws sealing the bowl.  The crusty white paint is either just that or Tritium or Promethium luminous paint as it gives of very little radiation.  Originally it would have been Radium based luminous paint.  Two small screws on the exterior of the compass secured the bowl to the housing.

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With the bowl opened and the card out you can see a bit of radiation is still present.  The compass card would have been painted with Radium 226 inside the small lozenge pointing north. Also the card, which is cut from mother of pearl, is tranluscent; lying beneath the card inside the bowl is a small tray which also would have been painted with Radium 226.  The copious amount of luminous paint would have guaranteed usability of the instrument during the dead of night.

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Various issues were uncovered during disassembly- the first being the oxidation of the magnetic needle.  A lot of rusty debris was left in the bowl which came from the needle affixed to the bottom of the card.  Water had entered the bowl at sometime oxidizing the only iron based component in the entire assembly.  The needle must be magnetized in order for the compass to work properly so the rust may be a big problem.  Furthermore, the water was clearly contaminated with Radium 226 as the needle is now highly radioactive.  in the end I may need to replace the entire compass card.  :mellow:

Here is a view of the debris accumulated inside the bowl.

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Which came from the mother of pearl compass card.  You can see the printing of the compass rose is still quite crisp.  In the center is a clear sapphire bearing (much like those found in mechanical watches).

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The underside of the compass card is a right mess though and since the rust is impregnated with Radium I'm not I can chance cleaning it.

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Secondary issues discovered included some not so nifty repairs from the past.  The crystal within the lid for example was not a great fit and needed some help in the form of epoxy and an ill fitting gasket.

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Many screws had damaged heads too.  This is the filler plug which has been manhandled in the past and sealed with a bit of epoxy.

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The gasket for the bowl was also a poor fit which is probably why the dampening fluid was missing.  I've begun research to determine the proper material for a replacement- it will need to stand up to prolonged exposure to kerosene so natural rubber will not do.

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This job requires many of the same skills used in watch repair as the parts are small and made of soft metal (brass).  With disassembly complete I'll move onto cleaning and have already begun researching replacement parts.  When the job is done I'm aiming for a vintage compass which looks about as good as new and functions the same way.  It's a lot of work just to check the magnetism of a watch movement but in my opinion restoring the tools is as much fun as restoring the watches.  :)

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Today I set about removing the old paint down to the bare metal.  The compass housing will be repainted black as it was originally, but since there was so much paint missing to begin with I thought a full strip down made the most sense.

Here's the compass housing following stripping today.  It's made of brass but appears to have been silver plated before paint was applied.

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This is the top of the bowl which houses the compass card.  The ring was not painted originally but was plated with silver.  Much of the plating came off during cleaning and will need to be replaced.  The crystal has been cleaned but the staining remained.  I'll need to polish it with some glass polish to remove the stains.

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I should have some more pics soon!

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I suspect the plating is nickel and not silver.
Fascinating narrative. Thank you
Cheers, Neil


Sent from my iPhone using Tapatalk

Could be.  It doesn't polish to a shine and isn't very "sticky" as a rub with the pegwood will take it off the brass.  I was starting to think it might actually be lead.

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The "rubber" seal is a substance called Viton and you can get O rings in various sizes and is impervious to fuels like petrol, kerosene etc

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Ah thanks for the info Bill!  I wasn't sure what the material was so I ordered a Fluorosilicone o-ring since it's supposed to be unaffected by kerosene.  We'll see how it goes but if it's an improper fit then I'll find a proper Viton replacement.

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Update on the compass project-

After stripping the case clear of paint I found that I forgot to strip the brass ring containing the top crystal, so the crystal was pushed out with the press and the ring stripped of paint.  For whatever reason this particular part was not plated prior to painting but was simply black paint on brass.

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All the parts where then primed and painted with black lacquer.  I tried to match the original look by selecting a semi-gloss but kind of wish I'd gone for a simple flat black.  Regardless, I'm sure it will look fine in the end.  I'll allow the lacquer to cure for a few days before repainting the markings on the exterior of the case in white.

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Setting the parts aside to let the lacquer cure, I returned to the compass bowl which had troubled me as the filler plug was secured quite well.  A good soak in thinner and a proper sized screwdriver eventually freed the plug from the bowl.  The fiber gasket was soaked with varnish as well and needed to be coaxed carefully from filling hole- I'll need to find a replacement that is just the right size.  Below you can see the gasket still tightly glued in the hole.

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Lastly I turned my attention to the crystals.  The crystal for the bowl was badly stained but this cleaned up with a bit of Dialux compound the rotary tool.  Sadly the lubber line had become a bit faint during cleaning.  The same happened with the degree markings on the rotatable crystal.  Since the degree markings and lubber line are etched into the crystal, I simply needed to fill the etchings with a bit of black enamel.  When the enamel dries, some thinner and pegwood will be used to remove the excess from outside the etchings.

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The crystal for the case lid was chipped and didn't survive being pushed out of the ring so a replacement was ordered yesterday. I also ordered a couple tritium tubes to replace the luminous radium paint.  

More to come soon. ^_^

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Ah thanks for the info Bill!  I wasn't sure what the material was so I ordered a Fluorosilicone o-ring since it's supposed to be unaffected by kerosene.  We'll see how it goes but if it's an improper fit then I'll find a proper Viton replacement.

Fluorisilicone will be fine too. Both are used in aircraft fuel systems and will last a long time. Fluorosilicone benefits from a lower glass transition temperature and so will seal down to much lower temperatures than viton. Back in the day I suspect that a Nitrile seal would have been used, but they will have a much shorter life... but don't get me on this subject or we'll be here all night!

 

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Latest update:

I returned to the project yesterday and began the lettering.  This entails painting the degree markers which run around the outside of the compass housing and the manufacturer's data on the underside.  The work takes a steady hand. Fortunately the markings are stamped into the brass housing making the job a bit easier than freehand lettering.

I started with the bottom of the compass housing and am thrilled with the result.  It actually looks a bit better than the original lettering.

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Tonight I'll continue on with the degree markings.

I've finished repainting the markings on the rotating crystal and moved to lacquering the bezel which is polished brass. The bezel was cleaned with a scotch bright removing the last of the original lacquer, the coin edge was cleaned with a wire brush, and the entire assembly polished with the rotary tool.  I covered the crystal with a bit of painter's tape which will make clean-up that much easier.

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I had the bowl lid and the eight screws which secure it to the bowl replated in silver.  This step was important to bring back the original look- the degree markers which are printed on the rotating crystal will hover just above the bowl lid.  In order for these numbers to be clearly legible the lid was originally plated either nickel, cadmium, or silver.

Unable to source a replacement compass card and needle, I had to bite the bullet and clean them.  This was a nerve wracking experience that I wouldn't suggest anyone else attempt without the utmost caution.  Here a ounce of prevention is worth more than a pound of cure.

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The next step will be to install the tritium lights (still waiting on their arrival) before sealing the bowl and refilling it.  I'm getting anxious to see the project done!

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Thanks for this thread it is a thoroughly enjoyable read and a credit to your skill, lovely piece and well done.
Cheers,
Vic

Thanks for the support!

Well I received my alternate light sources in the post the other day and set about applying luminous paint and tritium tubes where needed. The compass was originally painted with radium in five different locations.  Radium paint glows all the time without need of recharging under UV light. Tritium does the same but it's not quite as bright as radium paint and since it is also radioactive tritium is now kept in small glass tubes.

I installed the tritium tubes under the compass card and on the large crystal which is set in the bezel. The luminous paint was applied to the compass card, and the marker on the bowl lid. I was on the fence about whether or not to use tritium throughout but felt the tubes would be too distracting and opted to hide them where possible. Below you can see the four tubes which were installed in the tray beneath the compass card.  Originally the tray would have been painted with copious amounts of radium paint.

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The luminous paint used is a Europium based paint from a company called United Nuclear.  I've not used it before but opted for their product since you can get a course grain base powder which emits a brighter light. Below you can see the compass card with the north marker now painted with Europium.

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In a test run, I filled the compass bowl with purified kerosene and secured the crystal and lid with all eight screws.  These have to be torqued in much the same way you would torque the bolts of a cylinder head. Satisfied that the flourosilicone gasket was doing it's job, I reopened the lid and installed the compass card before topping off the kerosene. The large bubble was dealt with after rescuing the bowl lid.

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The compass was filled to the brim using the filler hole on the side of the bowl. This turned out to be quite a job because even though I had a syringe for filling the bowl, kerosene doesn't play nice with rubber and the piston in the syringe was made of rubber.  Whenever the kerosene mades contact with the rubber it would expand and seize up. I went through three syringes before getting nimble enough to ensure the kerosene never contacted the piston head.

With the bowl filled completely I tightened down the filler cap and sent the bowl on end. Here it will stay for a few days to allow any air bubbles to appear and also ensure the gasket continues to hold.

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