Just got my MkIII Compass back from Trademark London

[Claven2]

Well I just finished building a slavage G150 Stanley (current issue version of the British MOD MkIII Liquid Prismatic compass). I "acquired" two written off G150s from a forum member (you know who you are - thanks!) that were deemed "unrepairable". While that is true when each compass was examined individually, with some effort the two were cannibalized to make one decent and representative example of a current MOD compass.

One compass has a duff prism assembly, the latch spring screw holes were stripped in the lower casing, the lid was missing a glass retainer and screw, the lower casing had some denting and assorted other damage, the liquid seal had leaked and about 1cc of fluid had come out leaving a bubble in the glass, the index mark was missing from the tritium index marker and a screw was sheared off in the lanyard loop.

The second compass had a lid with the opening tab busted off and the sighting glass missing. The hinge pin was worn out and the movable indexing glass had a broken tritium tube. Several of the screws were missing, including the screws that hold the prism assembly on (it was in a baggie loose) and the retained plate for the prism was broken. The bowl had a bigger bubble in it than the first compass and the back side of the bowl at the membrane had a sizeable dent in it which warped the bowl casing enough that it did not slide easily in and out of the casing. The index mark for the tritium index marker was present but crooked. The spring assembly that retains the lid was missing but the screws were present in the same baggy as the prism assembly. Luckily the lower casing, although the paint was worn, was in serviceable condition with no stripped holes and it even retained the original friction ring on the base.

The taper pin that holds the lids on these compasses only comes out one way, so you have to be careful which way you pound on it. It's also easy to break a hinge wing, so you have to be careful. I used a short starter punch with the compass casing (bowl removed) rested on a piece of natural rubber and a jeweller's hammer to get the pins started out and a small arbor press to remove it the rest of the way. I put the good lid on the good base and re-pressed in the pin with the least wear.

I scavenged all the parts off the rejected lower casing and was able to build up the good lower casing into a complete unit - luckily one of the two prism assemblies was good. I also pulled the index marker off the garbage bowl assembly and cyano-acrylate glued it to the good bowl assembly's tritium index marker.

The fluid in both bowls was good and clear, so on the better of the two bowls, I removed the filling screw and carefully cleaned off the sealant. The fibre gasket looked reasonable. I then opened the second bowl and drew out some isopropyl alcohol with a syringe and checked that it was clear, I then used this to top up the first bowl. I let it set for 6 hours for any bubbles to come out and then gave it a tiny amount more fluid and re-installed the sealing screw, tightening it down as much as I dared without shearing the screw off to try and make the fibre gasket effective. Finally, I set it on end with the screw facing up and poured polyeurethane varnish over the screw head (liberally) so that the whole counter-sink was full of varnish. I let it cure 30 hours until hard before handling it. This should add enough seal to compensate for any leak-by at the fibre gasket. Only time will tell if the top glass gasket is still good or not, but I suspect it is or more fluid would have been missing and I could detect no sign of a leak.

The compass was then re-assembled and checked for magnetic north against my known accurate Kodak MkIII. Interestingly, you need to keep these compasses a good 10m apart from each other or their needles tend to point toward one another a bit. I hadn't thought they would be that sensitive, but they are.

Here's the mass of "duff parts" that were left over:



Some small pieces are still good like screws and such, but generally this is junk.

Now here's the rebuilt compass casing. The upper is repainted matte from a prior refurb in UK service and the lower casing retains the original semi-gloss paint from the Stanley factory. Oh well, it's franken-compassdom is painfully obvious, but at least it works. I've seen a lot of these both here in Canada and in UK service and like many military accountable items, refurbs are common and this is not the first time I have seen a compass obviously patched together from two broken ones



Here's the good bowl all ready to go. I can spot at least three different colors of screws. Some look like Francis Barker MkIII screws, others look like M73 screws and a couple look like black-oxide Stanley screws. This is the bowl out of the compass that had been through a refurb in the UK. I guess at that time, this bowl was reassembled from the parts of two or three other compasses.



Membrane is in good shape.



And here's the filling screw after the varnish has cured:



The lead solder and file marks you see on the side of the bowl is from manufacture when the lower tritium light and card mount bridge was soldered into the bowl casing.

And voila! Assembled and ready for more service:

[Peter Laidler]

That's what I call perseverance!

[Cruisey]

Hey Cruisey - have you made any more progress with that one? Any pics?

I had finished it Claven, but hadn't reassembled it as yet, as other projects had taken my attention.

So tonight, after seeing your post, i thought, great, i'll put it all back together & take some long overdue pics & post them.....

It seems though, my attention to detail was lacking on the day I sealed the bezel back in place ...... the compass wouldn't seat back in the body properly ........& then I noticed the cutout for the screw that clamps the moveable ring I have sealed it up 180 degrees out of whack

Looks like I have another project

On the plus side though, It cleaned up well, & I learned something

[mike1967]

Nice Aussie there I think it might need a comprehensive rebuild though as there appear to be putty substituted for the bowl gasket - that never holds up for very long, sadly.

I have this exact model and mine also shows the same putty ? In nice condition but also has a bubble inside.

[Peter Laidler]

On the subject of depressurising or evacuating the damping liquid in the bowl, my friend (another Instrument Technician....) mentioned that they'd made a temporary vacuum tank to degas a much needed survey instrument. They used a sealable tin with an outlet tube to which they'd connected the vacuum line from a kitchen freezer bag vacuum sealer. Sounds like a brilliant idea to me. HE nor I don't know what vacuum level it depressed to but once the hose was clamped, it certainly retained a degree of depression (sorry, it's getting complicated now.......) for a couple of hours when they clamped the vacuum hose. Sufficient to degas the liquid damping medium and seal the survey meter again. So far as he knows, it's still in use on the tank ranges as we speak........................ I suppose if you were hard pressed, you could create a fairly good vacuum by drawing air out with your mouth and lips!

Anyway, just a thought if anyone wanted to set up a degassing production line for the compass bowls

[Devils Own]

Hello Everybody

I am about to ship one out as part of my summer clearance scheme. I know next to nothing about compasses. The one I have has the protection bars on the outer case. It is a MILS compass and on the back it has H.B. & S MILS MkI. I am about to sell this and would like to describe it accurately. Any comments would be appreciated. Mainly, what kind of date would this item be?

Thanks for any info.

Steve

[Claven2]

pictures would help.

[Peter Laidler]

If it's marked in Mils, then it's post 67/70 ish

[Devils Own]

OK, thanks. I'll get some pics.

[Claven2]

Could it actually be "F. B. & S." MKI MILS? That would make more sense and place the compass as either a Francis Barker M73 compass (purpose built in MILS) or an older MkIII refitted to M73 specification, also made by Francis Barker.

With all these items, condition has a huge effect on value, as does serviceability. Pics will be needed for a good approximation.