De-Bubbling a Compass

There are a couple of things wrong with this compass. First of all, there's the huge and obvious bubble. Second of all, the not-so-obvious misalignment of the index line. Each affect the instrument's accuracy. We will fix both of these problems in this Instructable.

Here's what we need:

• Prying Tool
• Drill
• 1/16 drill bit
• Clamp
• Kerosene
• Syringe (3ml)
• Needle (I used a 23 gauge)
• Rubbing Alcohol
• Paper Towels
• 2 Part Epoxy
• Sandpaper
• Hot glue gun

Items used for other modifications:

• Craft foam
• Exacto knife

Although there will be differences in the disassembly and reassembly of this compass when compared with other kinds, the basic operation of taking a bubble out should be the same for most compasses. Do take note that some compasses purposefully have a bubble in them to facilitate leveling the compass. In this case, leave it alone, or only take out any excess air, leaving enough for the bullseye.

I found this compass in my grandfather's archaeology tool box. He always tried to do things as economically as possible. He would make his own tools when he could and when he couldn't, he'd get things on the cheap. This fits in the "On the Cheap" category..

There are no brand marks on the compass; it just says "Lensatic Compass," "Liquid-filled," with, "JAPAN" on the back. This was probably bought at a time when Japanese products were not very well made. I really have no idea how old the compass is but it is quite worn and glow-in-the dark features don't hold the glow very long. My grandfather probably used this in marking out his dig site grids and documenting various aspects of the area.

Some would say it's not worth the time to fix something like this up. It wasn't manufactured with the highest degree of craftsmanship in mind. But as worn out as this compass is, it holds a lot of Mojo for me. It is both relic and talisman. It can still function in it's original purpose, (although not as well with the bubble) and holds an air of the past. It's something I like to carry around and fiddle with. It feels good in the hand. If I can improve upon it and make it more usable, then all the better. In my free time I am an assistant scoutmaster, and I like to show the boys the old fashioned ways of doing things. This tool is right up my alley.

There are a few steps that we have to take to totally dismantle the compass. First we have to pry off the cover. This is technically called the "floating dial" and the ridged metal band is the "bezel". Use the prying tool of your choice to gently raise up the edge of the bezel and remove it with your hands.

This compass has a small cardboard band around the outside of the compass body, so we'll have to take that out too. I used a pin to pull up one edge and the rest came out easily.

Finally, we need to remove the base from the housing. It's glued to the bottom, but luckily they didn't use much to secure it. With some gentle pressure it should come up fairly easily--just be very careful and try not to crack the base or bend the housing. I found that a pushing motion, rather than a prying one, worked well. The old glue was pretty brittle and eventually gave way without much effort. A little sandpaper will clean up the remainder.

I put the compass body in a rubber gripped trigger clamp and then put that clamp into my bench vise. Using the smallest drill bit available, slowly drill into the side of the compass body. Be careful not to plunge the bit into the cavity of the compass thereby damaging the compass card (the plastic disc with all the writing on it) and/or the needle inside. I could see a divot that was originally used to fill the compass. I'm going to go into the same spot.

Once that's done you'll have to drill a second hole about 5 to 10 degrees to the side of that one. This will make getting the air out much easier.

Contrary to what the picture shows, this step is easier to accomplish if you remove the compass from the clamp. Even the slight pressure of the clamp deforms the compass plastic a little. When you release the clamp, the plastic relaxes and pulls in a little air. I ended up setting the compass upright with an old T-shirt packed around it for support.

Position your base so that one of the holes is perpendicular to the ground and your bubble is centered underneath it. Fill your syringe with kerosene, put the needle on, and place it in the second hole which is off-centered from the first hole. Slowly inject the kerosene and watch as the air escapes out the top hole. You may need to give it a flick or thump to make sure that any smaller bubbles combine and enter into the top hole.

Slowly remove the syringe while continuing to inject the kerosene. You don't want any air entering to fill the void that the exiting needle creates.

Take an alcohol prep pad, or rubbing alcohol on a rag or paper towel, and gently clean off any excess kerosene on the outside of the compass. Don't press hard or squeeze the compass as you will expel kerosene that you want to leave in.

Now we need to seal the holes. Mix a little of your two part epoxy and smear it over the holes. Make sure not to force it too far into the hole. You want some to go in there, but not so much that it protrudes past the interior surface and interferes with the rotation of the needle. Let it set up a couple of hours. Add a little more. Build up several layers of glue and leave overnight. After it's cured properly, knock down any rough edges with some sandpaper.

I could have left this as it was, but I didn't like this plain cardboard liner. I decided to upgrade to some foam craft board that was lying around. It seems like this would make a better shock absorber if the compass was dropped and is more water resistant than the cardboard.

Simply trace the cardboard onto the craft foam and cut out with an exacto knife or scissors. When placed back into the housing it should fit just below the recessed area for the bezel.

Make sure that the rear sight and the sighting wire are lined up accurately before putting the compass back in the housing. Mine were a little off, so I've bent the rear sight over just slightly so that they are lined up again.

Test fit everything! Line up your compass base so that the index line is exactly within your rear sighting slot. Put a mark at the top of the case where this lies. This will make it easier to align once the gluing starts.

The fit was so snug with the new foam ring, I chose not to do this, but you may. Put a dab of hot glue onto the bottom of the housing and press the compass body down into it making absolutely sure that the black index line lines up with your mark and that the compass base is down far enough so that everything closes completely.

Now is a good time to clean the glass of the floating dial. Pop it back on.

Finished! Now go out and use your refurbished compass. There are plenty of instructions for use on the internet. See if there is a compass course or orienteering group in your community and practice your compass skills. If you don't have a course in your area, find a field and use the instructions in the above picture. All you need are two markers, 100 feet apart. Good luck!

Compass manual (PDF)

http://www.us.orienteering.org/clubs

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