Thursday, January 5, 2017

Designing Homemade Cardboard Boxes in 3D CAD

I'm currently selling my old phone on eBay and I needed a sturdy box for shipping.  I could buy one, but why waste money on a box when I can get my hands on cardboard for free.  It was also important to make the package as small as possible to keep my postage fees low.  So the obvious choice was to make my own.

When I was young I used to make cardboard boxes for everything (That's right I was just as exciting then as I am now).  They were simplistic and held together with staples, but never anything too complicated.  So I thought that this would be a good opportunity to up my game and emulate how the professionals do it.

I don't know the name of the box I'm trying to make, but I'm certain you've seen one before.  Quarter circle shaped flaps on the lid slide into the sides, locking everything together.  Let's work backwards  and start with some photos of the final product.

Cardboard Box
Final Box
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Cardboard Box
Quarter Circle Flaps
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Cardboard Box
Side Slots
I'm quite happy with the result, but a few bits were cut off during assembly to make things fit.  I assume that this was due to the inaccurate way I transferred the pattern to the cardboard.  Tacking it onto the cardboard and scoring it with my wood marking knife was rough but worked..  My end goal was the template below that was transferred onto scrap cardboard and cut out to make the box.

Template
2D Cardboard Box Template
To generate the template I used Fusion 360 from Autodesk.  Before starting, four parameters were specified, the thickness of the cardboard, the height, width, and depth of the box.  By using these parameters for dimensions, the design can be altered later.

The process is simple but frustrating.  Make 3D components for each part of the box and then define how they join together.  They don't have to be the right size, as long as they are close you can change them later.  Defining the joins is the hard part due to the software being uncooperative.  Once you have a 3D version of the template you can generate a 2D version to print.

3D Cardboard Box Template
The first thing you will need to think about is how to model bending cardboard.  To me, a good approximation was to assume that the midpoint of the material acts as a pivot point.  In the image below you can see the bend between the back (red) and top (yellow) of the box.  This means that when laid out flat they will meet in a butt joint and be easy to mark out.  You can then move forward by defining all joints between components using this assumption.  Your mileage may vary, but this seems to have worked for me.

Pivot Point Of The Faces
Now for the "fun" part.  Using the CAD package, assemble the box as you would in the real world by bending each joint one by one.  As you do this, make sure parts don't interfere with each other.  You may have to resize some.

Assemble a Box
Fold Up The Sides
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Assemble a Box
Fold In The Internal Base Flaps
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Assemble a Box
Fold Up The Side Flaps
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Assemble a Box
Fold The Side Flaps Into the Box
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Assemble a Box
Fold the Inner Side Flaps Into The Box Leaving Slots
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Assemble a Box
Fold The Top Down
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Assemble a Box
Fold In The Ears On The Sides
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Assemble a Box
Insert The Ears Into The Slots

I think the results are pretty good.  If the cardboard I was using was flatter and I had transferred, cut, and bent the pattern with more care I think the results would be even better.  It would be great to get a pen plotter to draw the outline.  I kind of joke about going overboard and spending too much time on this but it was a conscious decision.  I got some more practice in 3D CAD and because the model is parametric it can be easily reused for other purposes.  At least the box from my computer case is being put to good use.

There was meant to be a nifty little animation of how assemble the box to go with this post but the motion study feature of Fusion 360 is a dumpster fire.  Que sera sera.

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