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This project means extra funny work for the more daring of you readers ;-) indeed it's only a 3d model, and it has to be built.
I'm not very familiar with 3D printing, so I'm not sure about tolerance between moving parts. Anyway there is a fast explanation of my design and how to model it in 3DS Max. It's not a full modeling tutorial, because it would have been too long and complicated, but I'll show you the main phases and I'll attach the 3ds complete model in next step so you can see it in your 3D favorite software.

Step 1: Some Sketches

I'm sorry about the bad condition of my sketches, but I had trashed them before thinking to post them in the instructable ;-)
I also made a big mistake in modeling, which I could have avoided if I had looked better at my drawings (yes I know that you're thinking there is not much information in them!).
The project consists in a flat safe-box with a combination lock. It's very flat, about 8 mm thick, and it's arranged with two inner compartments. You can keep inside a lot of folded banknotes or a ring, a necklace, anything fits in a 4 mm drawer.

Step 2: The Working Principle

The working principle of this safe is very simple. It consists in four disks inserted in the cover with a groove engraved in each disk,  these grooves keep eight nail heads attached to the rib on the bottom container. These nail heads are released when the disks are in certain position, so that cover and container can mutually slide and release each other.

Step 3: The Locking System

To build a better locking all around the sides of the cover, I decided to make it slide in the nails seats, so to unlock all the fastening on the sides.
In this way there are two movements to open the cover after setting the right combination of the disks:

  1. slide the cover on the front end, it will be blocked if one or more disks are not in the right position
  2. lift the cover to reveal the two compartments
There is a video at the end of the instructable, in which the two actions are well showed.

Step 4: The Disks

To make the rings the best way is to draw a shape of one ring section, then duplicate it four times, leaving a little space between them, and make them following a circle (with the loft function).
I closed the central disk since I didn't need the hole.
You notice that with this disposal of the side teeth of the rings, if you pull up the grooves, the "pyramid" will dismantle, but if I had bended the disks in the right direction, the teeth should have kept the pyramid joined. This was my big mistake and I'll fix teeth direction in last part of modeling.

Step 5: The Nail Grooves

Here you see as I built some shapes to enlarge the grooves in the positions corresponding to the unlocking rotation. Since I decided to paint (or attach) the letters on the finished product, you can "drill" these holes wherever you want around the circles. However the most appropriate way is to make them aligned, so to attack them handy over the rib between compartments.

Step 6: Releasing Mechanism

When you have the mold ready you can copy it on every groove and subtract them from the disks. Each disk will have two holes, opposite in diameter, one external and the other inside the groove. 

Step 7: Tolerances

The mold has to be a little larger than the nail head, so to let ot comes out with no restriction. You see in pictures the tolerance I left between parts, both for horizontal and vertical movements. These tolerances could be a bit shorter, depending by the precision of the 3D printer.

Step 8: Attach Nails

When all the nails are in position inside the holes you can translate them into the locked position, reveal the box and merge them with the central rib.

Step 9: Side Fastening System

To make a stronger locking system I decided to add ten grooves on the sides, where little cylinders could slide with the cover movement. These side spines would also keep the cover straight when sliding.
I decided to make an hole for the pivot, so to distinguish better a side of the box, and also to let you substitute it with a metal screw in case it breaks.

Step 10: Removing the Interferences

Now you can unhide all the model parts and try to make them move. You'll notice some interferences between box and cover, so we have to smooth the long edge near the pivot.

Step 11: Types

As types you can use letters or numbers, or also any symbol. On the external disk I decided to put all the alphabet, and I chose some letters for the inner disks, so to compose many words. Look the final movie to discover the secret word made for this ible.
If you engrave the letters in the model, it will be more pretty, but you can't change the word. On the other hand, if you only add a gap where to glue an adhesive, you can change it when you wish.

Step 12: The Notches

Add one or two little notches to mark the right alignment of the secret word letters. If you add two of them it will add some confusion to an occasional user, but you can remember which is the right side.

Step 13: Assembling Helper

With a wedge and the boolean function of the program cut the side plates to make an easier entrance for the pivot. The slide will let the pivot to enter in his place with a little flexing of the plastic when the cover is opened, and will be a sturdy join when the cover is closed. The pivot will stay in place also with box opened, if no flexing is applied to the piece.

Step 14: Smoothing the Edges

Let's refine the look of the box smoothing some external edges and corners, as you see in wireframe views.

Step 15: Types Texture

To draw the texture for the disks you can save the top view of the model and keep it as reference to know the disks position. I didn't put a lot of effort in placing the text so it resulted crooked and some types exits from the area, but since they could be decals, this mistake gives reality to my rendering. You can use the same image as bump, mine is a little blurred, anyway you don't notice it in images.

Step 16: Suggested Improvements

I've made a movie of the working gear:

 

Writing this instructable some improvements came to my mind, and you can add them to your own project:
 
  1. add some vertical dents between disks so to mark the single steps in rotation and have the possibility to align the types better and faster
  2. add some horizontal dents between disks so the could stay joined also with box opened
  3. the nails stems are a bit thin, it's better enlarge them and the corresponding grooves
  4. make a dent between bottom box and cover on the two sides without fastenings, so that when the cover is closed the dent keeps the two pieces joined
  5. model a flat layer with 3d types engraved, which could be glued to the disk, so to decide the secret word
There are infinite improvements, you only have to find them ;-) In that case let us know!
what materials do you use to make it
This is a very interesting concept Andrea. I think I might even try it on my printer. As I see it, some degree of accuracy can be attained by making the printer resolution fine (on one of mine that's 0.1mm). I think the 'nail heads' are going to be too fragile to print (or survive prolonged use), so my inclination is to let them print, but then remove them and use the locations to drill a small pilot hole and insert real nails epoxied down. OR...I would print it, do a test fit and then disassemble the whole thing and make a mould out of at least the bottom half and cast it in soft aluminum (such as might be derived from a bunch of fizzy drink cans). Hmmmmmm.....
Good, let me know if it works! You're right about the nails, they're very thin...
do yr research on that. could be any where from 50 bucks or more but do yr research tho
umm 1 problem is thst u need to put yr idea in either copy write or a public common license b4 some tries to patent yr idea. an u lose wat ever profits u might might make!!
and how much that costs?
seems like you'd be able to crack the code by applying pressure and feeling for the pins to enter their slots.
Not at all, since it works as many other simple locks: <u>all the slots</u> should be aligned to let the pins moving, which are all the same piece together with the cover ;-)
if all the holes and all the pins were perfectly aligned that would be true, but nothing is perfect. your blueprint may be perfect, but designs don't translate into real life without flaws. that's why there are things like quality control and the lemon law.
Actually alignment between pins and holes don't affect vulnerability of the lock. The essential detail to make a similar functional lock is the absence of reciprocal play between disks and the good alignment between nails axis and grooves tracks. That will make 6 pins keeping the other 2 pins (in this case) on a trace, also if they are near the holes. That's the same principle of the almost totality of traditional locks, the more the pins (ad disks) are, the safer the lock is. <br>Of course a 3D printed gadget can't be perfect (and is not due to any quality control) but I'm sure that it could be a good challenge, you can always smash it since it's made by plastic ;-)
didn't your english teacher ever warn you about excessive wordiness?<br>nothing you just said actually contradicts my point. <br>yes, more pins would obviously make it more difficult to defeat the mechanism.
You need to take this to a patent attorney. This would be a good kickstarter project
Do you think that? I'll research about that.
A pretty interesting design Andrea, if I don't build this, at least I can draw inspiration from it!
Excellent work. Protect it. One idea for an improvement, if someone else hasn't suggested it, is to use four different symbols around the edges where the single alignment indicator is. So, instead of the notch, you might have N, E, S, W for compass points, or simple shapes. Only you know which of the four you used to make the password. <br> <br>I see it as novel on a small scale, but a larger-scale safe, maybe three feet across, with bearings in the codex wheels, and deeper, of course, flush mounted to a wall. You could have ten wheels or more to make the password all the harder. Wheels that big you could add numbers and symbols, as well. <br> <br>As for the 'construction notch,' you can lose it by making the base in two parts, and a jig. Assemble and join them together using whatever method would apply (screws, glue, weld, epoxy, etc.)
Awesome!!!
Great idea! If someone actually creates this, please, PLEASE post the results!
WOW!! Love the concept, if you ever make a few I will be waiting!! :P
all right, italian tradition is to never donate a wallet empty... which bank-note do you want inside? <br>;-)
Haha, any!
One big improvement I could see being made is if you could figure out a way to build this without having the thing with the nailheads in the middle. If I put a dollar in there, the nail heads would have to punch through it in order to close it. Perhaps you could make it so that the ridge thing folds out, or (even better) stays on the lid somehow when it is opened.
You have to fold the banknotes in order to put them in one half (I've taken measurements referring to a 50&euro; note), in the other half you can keep coins or something else... maybe there is a better design, but it would be a completely different project ;-)
amazing, would like to have... your on to something with this idea.. Reminds me of these small puzzle boxes I use to buy but this actually has a useful application
Yes I also love those puzzle boxes!
OOH this is a really neat idea! So very clever! I want to see this in action. nice work, I'm assuming you are entering the contest, I will be voting for ya. :)
Actually, althought the contest gave me the idea, I didn't entered it because I didn't use 123D but 3DSMax... thanks anyway! :-)
Well darn, it's still really cool! :)
clever! So are the first two photos just a rendered model? It looks real!
Yeap! Nothing real yet :-)

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Bio: I'm an Italian freelance structural engineer, graphic designer and photographer. I'm also investigating electronics, robotics and science in general. I enjoy hacking and ... More »
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