This puzzle you can either 3D print or make using some M16 & M8 Brass nuts and bolts.
The origional idea for this puzzle is based on a puzzle from "homemade puzzles" http://homepage.ntlworld.com/bruce.viney/Bolt%20P...
3D files are available at Thingiverse or GrabCad
How it works
The aim is to get the washer off the bolt. The idea is the magnet is glued into the top section of the main bolt with epoxy. Which will hold the steel rod in place when the assembly is together. To open the puzzle you need to slam the base on a hard surface dislodging the rod and allowing you to remove the other parts of the puzzle so you can remove the washer.
Step 1: What you will need
Step 2: The main bolt & nut
Start by drilling through the M16 bolt and nut in one go. This way you hole and the threads will be lined up perfectly.
Now that the hole is drilled you can unscrew the nut.
Step 3: Drill the cross piece
Even though it is difficult you still want to center punch on the threaded area of bolt.
If you don't the hole will be off centre and the steel rod will not slide freely through it.
Step 4: Magnet and Rod
2. The metal rod should also be flush with or recessed into its position. The rod should move freely in the hole, if it does not I would suggest getting a slightly smaller rod rather than drilling the hole bigger because you will also need to drill the hole on the cross piece larger as well. (I tried making the hole larger and I ended up snapping the cross piece while I was drilling it)
Step 5: Fine Tuning and Finishing
I found that I had to tapper the ends of the steel rod slightly because having the ends flat the magnet held on to tight and no matter how hard I hit the bolt on a hard surface the steel rod would not come free. If I had of assembled the puzzle completely I may never have been able to get it apart.
As you can see from my pictures the holes are not all in the centre this came from not using a centre punch and caused me a lot of trouble getting all the holes to line up correctly, I ended up having to do a bit of filing and re-shaping to get it to function correctly.
I am planning on making another one of these hopefully this time without making the same mistakes. A friend of mine also suggested an improvement that I might try. Which is to drill my holes straight through the top of the bolt and not cut it. Then put the steel rod in and braze the hole in the top and file it flat. I may try doing this but I don't have any brazing gear at the moment.