I was browsing the net a few weeks ago and came across an engineering puzzle, the restricted nut, reasonably impressed with that but disappointed that it was actually a cheat rather than a puzzle, I started searching for potential engineering puzzles maybe even for my dad`s Christmas present - I like to make him something if I can (he is one of the only people who appreciate time spent engineering). I came across a smart little puzzle, it was an aluminium cylinder in which you had to remove the top...obviously something was restricting it. The website I found, the bloke had just made a recent post mentioning that he had cracked the puzzle after a few weeks of trying!! I emailed him and asked if he could tell me any more about the puzzle and he replied very willing to help me out. It took a while but I eventually got the concept in my head and started to draw up plans...
EDIT: I have since found the inventor of this puzzle is William Strijbos
http://www.puzzleworld.org/puzzleworld/toc.asp?t=_des/ws001.htm&m=des/ws000.htmSo, without further a do, here is the Cylinder Puzzle!
PUZZLE: The aim is to remove the lid. The lid lifts about 1mm and can be pushed down but clearly a spring is lifting it back up. There is a hole in the bottom of the cylinder, about 6mm and ball bearings can be heard rattling around inside at various times! If the lid is depressed more ball bearings can be heard rolling. When the lid is not depressed most ball bearings appear to be trapped and can no longer be heard.
SOLUTION: ---REMOVED ---
CAD PLANS
I`m totally new to CAD so this was my best effort! If there is anything wrong or bits are drawn incorrectly, I appologise. I really enjoyed building my parts from my own neat plans!!
SORRY PLANS REMOVED.
So I started with this 50mm bar of ally I`d had for a while!

Started turning it down to 40mm for the cylinder base piece:

I`m still not getting on with parting, so once it was down to about 42mm I took it over to the saw and hacked a piece off:

Turned it down to size, faced it up, drilled and then started to bore out the centre:

Put it on an arbour and started to clean and polish it up:

Also drilled the little 6mm window hole at the bottom. This really has no use other than to show the ball bearings from time to time.

OK ! Forgot to take a picture of the internal groove as I was getting a bit frustrated. I had to make a new tool which took some time and then after all that never took a photo! I`ve also drilled the semi-circle at the top directly into the groove.
REMOVED
Idea of size:

Then suddenly thought I better think of a spring so grabbed my box of springs and found this which was a perfect 23mm diameter and fit into the bore perfectly!

Started doing the top section - drilled to support it with the centre which isn`t in for some reason in this photo:

Opened out the centre bore:

Started to cut the groove in the core of the top:

The top section, still stuck on the huge bar! So part it off? Nope, back over to my hacksaw!

Then took the top section down to size and polished it up:

REMOVED
All the pieces plus 2 of the 4 ball bearings. To be honest, it works of course with just one but 4 makes it more difficult. I`ve only been putting 2 in for now! It still takes ME a few minutes to open it.
REMOVED
Top and bottom sections - spring lifts it to this height when you do get the satisfying pop when it opens!
IMG REMOVED
Just a little shot showing the ball bearings in the bottom window:

And here it is, locked and loaded! It is quite a challange getting it loaded. You just do it all in reverse of course and make sure you can`t see any bearings in the centre core, they all should be locked into the groove. The spring also serves in locking the balls up into the groove which means you actively have to be playing with the puzzle to have any chance and of course the lid must be depressed to align the grooves and allow the balls to rotate.

Finally, I`m going to give it one more polish and then take it to the engravers. I am going to give it my dad for Christmas and so I`ll have his initials with 2010 engraved. I`ll have one engraving on the top piece side aligned with the top groove and then one engraving on the bottom piece, 180 deg from the bottom hole. So the engravings will also have a bearing on the solution which should add a nice little addition. Pictures of that when it is done.
Well hope you enjoyed it. It works really well and it would be nice to see a few more made!! Literally took me a few hours although that isn`t including the time taken for the tool to make the internal bore. I`m going to order some smaller bearings and make a baby one out of brass. I think they are a real talking point. ... and if anyone could find the time to knock up the two parts in 3D CAD I`d appreciate it, just for completeness of the entire project!
All the best.
Chris