Spring-Loaded Iris Gift Box

This spring-loaded gift box closes using an irising mechanism. Perfect for giving gift cards, candy, or other 3D prints to your loved ones around the holidays. I used this model this year to make giving gift cards a bit more fun. 

Though I did not intend it to be, this is apparently a puzzle box. Many of the people I gave it to took a few minutes to get it open, lol. Mostly they all tried to spin the whole top and blocked the iris leaves in the process instead of pushing only on the hemispheres.

I am a mechanical engineering doctoral researcher working in robotics. l like details and well-written instructions so prepare yourself for WALL OF TEXT!

Safety

While the mechanism looks menacing, it is quite safe. You can put your finger in it and release the spring and you won't feel hardly anything. This is one reason why iris mechanisms are generally relegated to low-force applications like camera shutters or to the realm of sci-fi. In reality, they are generally space inefficient, have low closing-force output, are difficult to seal in any way, and are just too unnecessarily complicated for most applications. But hey, they look really cool!

Models

1. Tiny box: This is the smallest I could make this mechanism. It is more for testing and as a showpiece than a useful gift box.
   1. Internal Diameter: 65 mm
   2. Internal Height: 10 mm
2. Vertical Card Box: This box holds a normal-sized gift card vertically. It easily holds most gift cards (Approx. 85x54 mm).
   1. Internal Diameter: 75 mm
   2. Internal Height:  95mm
3. Horizontal Card Box: This box holds a normal-sized gift card horizontally. I have included it for those that want a larger box or that want to lay their gift cards sideways.
   1. Internal Diameter: 115 mm
   2. Internal Height:  70 mm

For Those Trying to Remix from the Fusion 360 File

I have included the Fusion 360 model for this file to encourage you all to make improvements. It is parametric with many user parameters that can be changed to achieve a different box. BE WARNED! The drawing that calculates the path of the driving pin is extremely complicated. Fusion does not allow for the direct implementation of mathematical equations so I had to discretize that relationship to every 5°. This means that the sketch is really complicated. Every time I change the internal diameter, Fusion poops its pants and creates a neutron star of intersecting bodies. If you go back through all the broken sketches and mess with them (try to move points that it says aren't constrained, but actually are; edit dimensions dependent on functions; etc.) Fusion suddenly figures out that everything is ok and generates the model correctly. The “Compute All” button sadly does not do this, though you would think it would. Large changes in diameter may not be fixable. I recommend making repeated small changes, stopping to fix the sketches as they break; particularly sketch 21. Here is a video that shows that process.

You will probably need to up the spring thickness and space between coils (I generally make these the same number) as you go to larger boxes. A mainsprings force per degree turned is inversely proportional to its diameter.

Printing

I have included the gcodes for my prints. Thanks to Prusa's amazing viewer, you can see exactly how I printed them. Also, for those that didn't know, opening the gcode as a text file allows you to see all the super useful additional information that Prusa appends to the machine code. It has everything from millimeters of filament required to what filament I printed it in.

These models were all printed on an Original Prusa i3 MK3S+. The tolerances are tight, so I recommend printing with 0.2 mm layer height at maximum. The only supports you should need are at the tip of each iris (assuming you print the irises upside down like I did to get the nice printer bed look on the top of your box).

Assembly

As previously mentioned, the tolerances for this mechanism are tight. You may find it necessary to sand the bottom of the leaves and the top of the lower ring to ensure smooth actuation.

I recommend tensioning it one peg past the first possible counterclockwise peg from rest. The first one is about 15 degrees rotated counterclockwise. It will work (it is the one shown in the video), but is a bit under powered. In later assemblies, I set mine a full peg past that, which would be 87 degrees counterclockwise from rest.

Future Improvements

Here is a list of planned future improvements. This section will change over time as improvements are implemented.

1. Use of non-printed parts: My original goal was for this model to be fully 3D printed. While that challenge is always fun, Iris mechanisms have high tolerances and easily bind in the presence of too much friction. As such, there are some useful non-printed additions I would like to make.
   1. Use of ball bearings for the inner wall and maybe also for leaf travel. This will make the mechanism much smoother and more robust.
   2. Use screws or pins for holding the iris leaves. There is a minimum diameter for the pins holding the iris leaves below which they tend to snap. Using metal of some kind would allow for a smaller inner wall and an overall more compact design.
2. Bow. I'm not sure what this will look like yet, but I would like to have an optional bow for the box. I was thinking it might screw on where the iris leaves meet and hold them together, but figuring out how the print that screws on top of the ribbon without using supports (I like how the top ribbon looks when it is directly printed on a textured bed) was too much to implement before the competition ended (assuming I didn't lock myself in a room, shun my family, and devote myself entirely to this project, lol).
3. Make the lower ribbons come up just a bit higher. They can't collide with the leaves and I would prefer people not have to sand to make them work well, but it would look aesthetically better if they came up just a bit more.

Please leave any improvements you think of in the comments, or, obviously, you can make them yourself. I'll be keeping an eye on the makes and remixes to see what you all come up with.

Note on Types of Iris Mechanisms

Some of you who know cameras or iris mechanisms may have noticed that this does not function like others. I have yet to find a paper on the nomenclature of iris mechanisms also referred to as iris diaphragms. There is the kind I use, a kind with overlapping thin leaves like on a camera shutter, and a kind similar to the one that I use that involves triangular leaves that slip past one another and maintain a circular opening at all times rather than splitting. For those going on to design their own, I would note these things.

1. Iris mechanisms like the one I used
   1. Generally the most space efficient, as they do not require that the area the leaves go is part of the mechanism. As part of this, you can make your opening very close to the size of the box in sits on.
   2. Do not maintain a circular opening as the mechanism is actuated
2. Camera shutter-like mechanisms
   1. Made of thin overlapping arching leaves that must deform somewhat. This means that, while they can be space efficient in the horizontal plane, the stacking of the leaves means that you cannot make them very thick or you will have horrible vertical space inefficiency.
   2. Maintain a circular opening when actuated
3. Sliding triangle iris mechanisms
   1. These are the most space inefficient, as the paths that drive the iris leaves must go all the way along the actuated stroke length of the iris. This means that the outermost part of your mechanism must be about twice the diameter of the opening that your leaves create when actuated
   2. Maintains a polygonal opening when actuated

Acknowledgments

This model draws inspiration from designs like 3D Printy's Twist Lock Presents for the ribbon and mainspring (https://www.printables.com/model/89174-twist-lock-present) and counterspatula's Iris Door Box v3 on Thingiverse (https://www.thingiverse.com/thing:140048). It was modeled from the ground up, however, and now bears only a superficial resemblance to those models.  The iris mechanism in particular is completely changed in how it is driven, the iris leaf shape, and the calculations involved in determining the driving pin's path. No stl, other solid model, or dimension from a solid model from these or any other source was used in the making of this model.

I'm not sure whether this is a remix or not. The mechanism is completely different. Only the spring style and general gift box idea are the same, but I was definatley inspired by 3D Printy's boxes and love all his work!