I’ve had several questions asking what my design process was for creating the 3D models I print. Stuart and I agreed that it would be a good topic, but until now I really didn’t have a good example project that was fresh in my mind. Then I was notified about an Instagram post by @jeremy.joseph:
The video post shows where he used wooden cleats to make a Milwaukee Packout hanging system. I was asked by another person if it was possible to 3D print something similar.
A small caveat before I start: as with many things, this is the type of skill that takes practice and experience to develop and hone, and I am in no way a master. There are probably easier and better ways to do things, but that doesn’t stop me from trying nor should it stop you.
In the past I’ve hesitated to design a tool box hanger, because I wasn’t sure that a 3D printed part would be strong enough to withstand the amount of force a loaded Milwaukee Packout toolbox or organizer could put on a hanging cleat. I didn’t think fused thermoplastic would stand a chance, but when I saw the Packout cleats made from thin wood, I realized that maybe I could have been wrong.
I didn’t make a formal list at the time, but as I set about designing the part I kept these criteria in mind.
The part should:
- Be as strong as possible
- Maximize contact with the slot in the bottom of a Packout box
- Require minimal material and print time
- Be easy to print with no supports
The “strong as possible” criterion is pretty self explanatory – it just means that I needed to make sure the areas that would come under stress were as thick as possible. I needed to maximize contact with the slot in the bottom to spread the force over a wider area, because the wider the area the force is spread over, the less likely there would be a point of failure under normal use.
It’s always a good idea to minimize the amount of material used, as the less material used, the lower the part will cost to make. Also, using less material can – but not always – reduce print time. Not having to print and remove supports also reduces the amount of material used, and the amount of time required to make the object.
I primarily use two different programs to design models: openSCAD and Fusion360.
openSCAD is basically a programming language, where you create designs by coding different shapes and then combining and manipulating them. The power of this program is that you can create a model that is easily to manipulate by just changing a few variables. Models written using this code can be modified by users on Thingiverse.com to create customized versions of your item.
OpenSCAD is completely open source, with no cost, and you are completely free to commercialize your designs any way you want. It works on Mac, Linux, and Windows computers, and doesn’t require a huge amount of processing power to run — except when you actually preview or render the model.
Fusion360, on the other hand, is more like a conventional CAD program. The basis for Fusion360 models are sketches, which are similar to the 2D CAD drawings you are probably used to seeing. Once you have your basic two-dimensional sketch, you can extrude the model into three dimensions, manipulate it, and even add more sketches to define the profile of the model from different angles.
Fusion360 runs on Mac or Windows computers and requires a 64 bit processor. It is not completely free to use in all situations, but there is a free startup license for companies under a certain income limit, or hobbyists. This means that if you want to make money off your models, you are somewhat limited unless you purchase a license.
Why do I use openSCAD sometimes and Fusion360 other times? I tend to use openSCAD for simpler models that I want people to be able to customize. It’s also much harder, but not impossible to create fillets, concave surfaces, and chamfers in openSCAD. When I need to design something more complex, that’s when I will use Fusion360.
In this case, there’s really no reason to customize the parts, and I also planned on making use of fillets to make the cases slide onto the cleats easier, and so I used Fusion360.
To hold and retain the Packout cases, there are two separate parts: the latch catch, and the cleat. The latch catch isn’t always necessary and isn’t the critical component — that is if I couldn’t make a usable cleat, the latch would be irrelevant, so I concentrated on the cleat first.
My first revision was based on the wooden cleats that @jeremy.joseph made. After modeling the simple cleat, I found it didn’t fully engage the slots in the bottom of the Packout case. It turns out that he actually mislabeled one of the dimensions, but by that time I had already started measuring to refine the part.
After printing my first version of the cleat, one thing I noticed when I looked at the Packout cases was that the front and back slots weren’t flat, they had this ridge that was preventing my cleat from fully engaging the slot. I didn’t want to make the cleat thinner because then it would just rest on that ridge, and a thinner part would also be more prone to failure.
My second revision incorporated the notches to avoid the ridges in the case slots, and I also reduced the size of the overhanging tabs to remove material. When I slid the cleat into the bottom of the Packout case, the cleats still weren’t fully engaging the slot. I noticed that the end of the slots were sloped, so I filed away the front of the tabs to make them engage even further.
For the third version of the cleat, I further removed material by rounding the back part, and I incorporated an angle into the front part of the cleat.
At that point, I was ready to actually try mounting the Packout cleats to see how well they worked. For this, I switched filament types, from PLA to a stronger type: PET-G — it’s basically the same material that water bottles are made from. I also decided that I would add a slope to the outside of the tabs to assist in aligning the Packout case.
When I actually mounted two of these cleats to a board and tried sliding a Packout case onto them, I still had problems getting the case to align with the cleats. At this point I decided to redesign the cleats to make aligning the Packout boxes easier.
I cut off the back half of the cleat because it wasn’t serving any purpose, and extended the front to catch in the valley between the slots. This made it much easier to align the Packout case, as it meant I needed to be close, but not exact. As I pulled the case forward onto the cleats, they would snap into perfect alignment.
In my last revision I just tweaked the height. You can see in the above photo that the base of the Packout wasn’t resting on the board, so I just lowered the total height.
To mount the cleats, I inserted them into the bottom of a Packout case and covered them with carpet tape (double sided sticky tape), aligned them on the board exactly how I wanted, pressed down hard to get the tape to stick, and removed the case. Then I screwed the cleats in place.
Latch Catch Revisions
With the cleats finished, I started work on the latch catch. I needed to modify @jeremy.joseph’s design, because I couldn’t figure out how to correctly model a countersunk screw head on a ramp. It seems like an easy thing to do, but for some reason I couldn’t get the bore and the countersink to align just right.
Instead, I started out with a flat spot on the top of the catch to screw it in. I also added tapered sides ending in wings to direct the latch into the right position.
After printing the first design, I found that the latch didn’t behave like I thought it should. The ramp and flat spot ended up being too long, it interfered with the cleats catching the bottom of the box correctly. To fix this I made a steeper ramp, but this made it more difficult to push the box over the catch.
In my final design, I widened the entire catch and placed the screw holes on the sides. This allowed me to decrease the length of the ramp while still having a slope shallow enough for the box to easily slide over.
The black latch catch is actually the same version as the orange catch. I purchased some black PET-G to give the end product a bit more professional finish.
After 6 cleat versions and 3 latch catch versions, I had a working system. Above is a demo of how the Packout cleats work. I’m only showing a half-width box, but it should also work with a full-width box just the same.
I’m still not convinced that these cleats would be strong enough to hold a fully loaded Packout case in place inside a moving van, but I think they should hold up to light use in a garage or workshop if you don’t overload the cases or try to mount one of the large boxes.
I’m thinking about modifying the design, so that I can cut the cleats out of aluminum on a mill, but that’s another project.
I’ve uploaded the STL files to Thingiverse.com (see link below) and I’ve included the Fusion 360 archive files if you want to see how they were drawn.
Download Files (via Thingiverse)
Warning: This is a 3D-printed part, and as such it is NOT suited for high strength or heavy load applications.
Hopefully I’ve been able to give you some insight into how I design parts for 3D printing. Not every project requires the same process, but in general I find that an iterative process where I focus on only a few parameters at a time works best for me.
I find that making a crude model first allows me to see how the part will interact with the real world and helps me solve problems early in the design, before making major changes would be painful.
Still, you shouldn’t be afraid to redesign a part or throw away a design completely. While it might seem like a waste, the insights you gain from your previous iterations give you valuable knowledge about the problem you are trying to solve.