My girlfriend and I have recently started geocaching and we both really enjoy it. We've seen/been to some neat places that we otherwise would have just passed on the road or would have never visited unless we were hunting one of these things down.
We have also been stumped by more than a few of the more difficult ones known as "nano" caches. these things are nothing but a tiny canister with a magnet and only enough space inside to hold a rolled up piece of paper to log your visit, and people get really clever when they hide them. So I decided to try my hand at making one of these evil little things.....only more evil!

Step 1: Materials

This is a pretty cheap project to make, all you need are some hardware bits you may have lying about and some simple tools. the most expensive material needed was the nano cache itself, cost about $10 at my local R.E.I.

Materials:

-A bench vise
-A pneumatic cutoff wheel (and air compressor of course, or a hacksaw)
-Some J.B. Weld
-A 1/2" diameter by 2 1/2" hex bolt ( I chose 2 1/2" to give me some material to play with)
-A 1/2" Nut that fits on the bolt
-Two 5/16" internal diameter washers (these are the exact diameter of the nano cache)
-One 1/2" internal diameter washer (This will fit around the hex bolt)
-A small rare earth magnet (I scavenged this off one of my girlfriend's old name badges from her job)
-A metal file
-Toothpicks & something to mix the J.B. weld in

Step 2: Clamp It, Cut It, Grind It

Secure your bench vise to your work surface. Screw the bolt onto the nut and thread it down close to the head of the bolt, this will give you a more stable surface to put in the vise.

Next cut a piece of the end of the bolt.
I decided that 1 1/4" was long enough to make the geocache look passable, in the end i want this to look like a bolt that penetrates something metal. I filed down the treads a little where I want to make the cut.

After the end piece is cut off you want to make the cut end as flat and even as possible. To hold it still while being filed I screwed it part way into the nut and screwed the rest of the bolt in the other side, after hand tightening it was secure enough to put back into the vise and begin filing.

Once the end is flat and even file down the threads a little where it reaches the edge. I didn't want to have any sharp edges on the thread. I tried to make it look as symmetrical to the other end of the piece as possible.

Step 3: Grind Down the Existing Cache

Now you want to flatten the top of the nano cache with the file to make it suitable for attachment to the smaller piece of bolt.

Unscrew the larger half of the hex bolt from the nut and place the nano cache in the nut with the smaller end of bolt you just filed and secure it in the vise. The magnet in the bottom of the cache should help keep it from moving. Now file down the top til it is flat and the new surface is even with the edge where the dome ended.

Once this step is completed you can J.B. Weld the top of the cache to the flattened end of the bolt you just filed down. To keep everything stable I put the cache inside the nut with one of the 5/16" washers at the bottom. Mix equal parts of the J.B. Weld together and apply a small amount to the filed end of the cut bolt. Be careful not to accidentally glue everything to the nut!
I affixed it to an altoids tin and left it on a shelf to dry.

While this dries you can go to work on the head of the bolt.

Step 4: Off With Its Head!

Now You want to cut off the head of the Hex bolt.

First I measured the thickness of the 1/2" washer and the thickness of the magnet. The washer being about 1/8" thick and the magnet about 3/32". To make things easy I put the washer on the bolt and marked it roughly with a sharpie to know where to cut. Affix it in your vise and grind away CAREFULLY. You want to try & make your cut as square as you can.

Once the head is cut free you want to put the washer back on to see how much more metal needs removing. You only need to grind off enough to make the magnet flush with the washer. To expedite this I put it back in the vise and carefully ground a little away with my cutoff wheel.

After another dry fitting with the washer and the magnet only a small amount of metal needed filed away to make the surface of the bolt even and the magnet flush with the washer. Again, try & make it as flat as you can.

Now you want to J.B. Weld the magnet to the head of the bolt. This can be tricky because the magnet will attract the metal in the J.B. Weld causing it to "crawl" so only use enough to get the job done. It doesn't take a lot.

Spread a thin layer of J.B. Weld onto the bolt and do your best to place the magnet dead center on the first try. Using a clean tooth pick clean away any excess J.B. Weld that might "crawl" onto the top of the magnet. Place high on a shelf to dry.

Step 5: Finishing Welds

After all parts up to this step have dried it is time to weld the rest.

Take both 5/16" washers and J.B. Weld them together, try not to have it ooze out the edges. Then take the 1/2" nut and put enough J.B. Weld inside it to only go about 1/4 to 1/3 of the way into the nut & make sure the threads have enough J.B. Weld to fill them in. be careful not to use too much or you might not be able to screw the geocache together/apart when its done. Apply some J.B. Weld around the outside opening of the nut as well.

Take the assembled geocache with the welded bolt end and carefully push it through THE END OF THE NUT WITHOUT THE J.B. WELD! This can be a bit messy so take your time. If you are worried you might accidentally weld the top of the geocache to the bottom half then unscrew the top and push the bottom half through the nut with a dowel, you can then clean out any excess J.B. Weld with a damp Q-tip.

After the geocache is through add more J.B. Weld to the bottom of the nut if needed and place the washers on the end of the geocache. Wipe away any excess J.B. Weld with a wet paper towel and affix the whole assembly magnet side down on something magnetic (like an altoids tin) to dry. You can also use a clean tooth pick to clear away any oozing J.B. Weld from where the nut mates with the washers.

Now to finish the head of the bolt.

With the magnet welded in place it will be easier to weld the washer to the head. Put a small bead of J.B. Weld around the inside circumference of the 1/2" washer, try to only put it on the flat side and not the inside edge. Remember the magnet will attract it.

Secure the head of the hex bolt in the vise with the magnet facing up. Hold the washer securely with both hands (J.B. Weld facing down of course) and carefully place the washer onto the head of the bolt, you don't want the magnet to grab the washer it will be messy. Place somewhere to dry.

Step 6: Final Shots and Placement

Now that everything is dry and securely welded make sure you can unscrew the threaded bolt end from the rest of the nut assembly. If you were careful you shouldn't have to worry too much.

Place the log inside, re attach the top of the geocache and find something outside that has a lot of nuts and bolts holding it together (like a water pipe assembly in a park or a metal gate).
Separate the two halves of the geocache and arrange them as if it were actually a bolt penetrating something metal.

Log the coordinates on a geocaching website and watch as the "didn't find it" responses grow and grow.

Behold the EVIL!