Today, I’ll take and absolutely boring part and make it interesting - shelf brackets.
Using topology optimization with the free version of Autodesk Fusion360.
If you want to have a computer automatically come up with the best geometry for a part
that for example will support a given weight, yet use as little material as possible, there
are basically two different automated design processes that have become pretty popular
these days.
Both generate incredible looking shapes that you can sometimes hog out of a solid block
of aluminum with a five-axis CNC or ideally… 3D print them.
This right here was done with topology optimization, which is actually the more limited, but easier
version of the process.
You start with a shape, usually pretty blocky, these braces used to have all this material
filled in, to give the process some material to work with and then the topology optimization
runs a simulation based on the load you put in and it then gives you the option to remove
the material that contributes the least to strength and rigidity of the part.
So topology optimization, you start with something and then take away what’s not needed.
Generative design, on the other hand, work the exact opposite way - you start with only
the material that you absolutely need, like flanges and mounts, and then the software
adds all the connecting geometry by itself.
I think for 3D printing, Topology Optimization is by far the easier one to make use of - if
your input geometry is printable when it comes to size, overhangs, all that, usually the
output geometry will be printable, too, maybe not perfectly, but printable enough.
And, most importantly, topology optimization is actually included in the free Maker and
Startup license of Fusion360.
You can only run it on Autodesk’s “cloud” servers, unfortunately, which means my 16-core
CPU is bored to death while some server in Autodesk’s farm dedicates two cores and
what feels like the bottom spot in a queue to run my simulation.
But hey, at least they don’t charge free users cloud credits for it.
Generative design is only included in the paid version, and even then running a single
generative design costs you 25 cloud credits.
Which is 25 bucks.
And then, if you actually want to get that design off of Autodesk’s servers, it’s
another 100 cloud credits, so yes, another 100 bucks.
On top of you the subscription you’re already paying for.
So… we’re sticking with topology optimization for now.
Ok, my goal with these was to make them look cool, not necessarily to make them as strong
as possible.
I mean, sure, they should be able to hold up a few folders and all, but it would be
pretty easy to just design something with simpler geometry or, heck, even just throw
together a few sticks of hardwood.
Or buy the same thing ready-made for 3 bucks from Ikea.
I’m sure these are actually way stronger than anything that you would reasonably throw
at them.
But they aren’t unique.
Says the guy who literally lives in an Ikea catalogue.
I knew the rough shape that I wanted, it should have a bit of a swooping shape on the bottom,
two mounting holes out the back and it should fit flat on the bed of a MK3.
So that’s what I started with.
Taking that design to a topology optimized version is actually pretty simple in Fusion.
You head over to the Simulation workspace, select your original body, define where it
makes contact with “the outside world”, usually that’s just fixing the screw holes
in place, then you define where the part will see loads from that outside world, and if
you want to, you can also tell Fusion which parts it should definitely keep using these
green blocker shapes.
After that, all that’s left to do is to create the mesh and to run the simulation.
When that’s done, you get a model that, as I understand it, has all the bits removed
that, per volume, contribute less than half as much to rigidity and strength than what
the most important bits contribute.
You can then “promote” the results either into a new simulation for checking whether
the part is actually strong enough for what you’ve got planned for it or into the model
workspace, where you can edit and export the mesh.
So that’s what I did - many, many times.
I think if I was paying for cloud credits, this would have been well over 100 bucks just
in cloud costs.
So the original plan was to print these sideways to get maximum strength as that wouldn’t
be pulling the layers apart, but I pretty quickly realized that the parts just wouldn’t
be printable that way, at least not without a ton of supports and I didn’t want to go
down that route.
So I decided to try printing them with what was going to be the wall side against the
bed, which is quite possibly the worst orientation for strength.
So to verify that that was actually viable, I printed three of the designs that way and
tested them for strength.
You know, the classic way, actually mount them and break them.
And they actually turned out pretty darn strong.
So I was going for each brace being able to hold the weight of 10 fully loaded folders,
like analogue document folders, which was going to be around 30, 35 kilograms.
And looking at these 50% scale test prints, I was pretty confident they would hold up,
because:
The turquoise one was able to hold 24kg, loaded roughly at the center of gravity where actual
folders would sit, the orange one 23kg and the gold one over 30kg.
And these weren’t printed with, like super massive print settings or anything.
So I went on to design the actual braces that I would use at full scale.
First, they needed to fit vertically into the MK3’s print volume, which the older
ones did not at their original scale, I still wanted them to look cool, and I also wanted
to use a better, more accurate and more detailed simulation setup.
So, here’s what I did:
I increased the mesh detail by forcing Fusion360 to use smaller elements
I added a “sliding” constraint against the wall to let the simulation know it would
be able to brace the part against that; That adds that back plane, but also gets rid of
this cup shape near the bottom mount I switched the area load to an offset area
load biased towards the front of the brace since the shelf will extend past the front
edge of the brace Basically I get a bit more support towards
the front that way I realized I had to retain that restriction
of having that curve on the bottom, otherwise Fusion would find an even better option to
support the shelf that didn’t need the branches and fingers up top.
But also, it didn’t look nearly as cool.
I played with creating protected areas around the top mount where the earlier tests broke,
so that I’d get a bit more material there and make the brace stronger
I also smoothed the branches of the final result right within Fusion360, just for looks.
And because that slightly shrinks the branches, I used the criticality slider in the simulation
result view to retain a bit more material.
There’s one more thing I did to make absolutely sure that the braces would hold up, and that’s
using a modifier mesh in PrusaSlicer that increases infill around that top mount.
I also set the extrusion multiplier to 104% just to make sure everything would hold up.
Yes, that’s not going to make for perfect-looking prints, but hey, I’d rather see some ridges
than having 100 pounds of folders drop down on someone’s head.
For filament, I’m using PLA as that’s one of the consistently strongest materials
you can use, and I also needed a simple, low-warp material since, well, the braces are pretty
frickin’ big for a 3D print!
Originally I wanted to use the Tangerine Orange Metallic from Proto-Pasta, but I didn’t
have enough of it and shipping probably would have taken too long from overseas, but then
I saw Das Filament’s Multicolor transition spools, specifically the Galaxy type that
is this blue-pink-purple color and that actually fits the organic theme pretty well!
They were kind enough to ship out a few spools, and the very next day I could start printing.
Ok, time to test how strong this brace actually is.
Same setup, again loading it in the spot of the center of gravity and….
nothing.
Scale overloaded.
Well, I mean, that’s a good start.
That was probably at last 40kg, 90 pounds, so it’s definitely strong enough, but I
wonder…
Yeah, it holds my weight.
All 66 glorious kilograms of me.
So, yeah, definitely strong enough for holding some folders.
Time to print 3 more and to prep the shelves themselves, I grabbed some beech hardwood,
this is a fantastic local wood, I trimmed it down to 160 cm, gave it a good sanding,
chamfered the edges, and I thought I was just going to paint them all white, but after having
painted one side and all the edges, I actually really started liking the look of leaving
the top side natural.
So the top just got a simple clearcoat, and when I went to lightly sand the first coat
of white paint, and again, I just really started liking what I got, which was this worn vintage
look, and decided to stick with it, so one more round of clearcoat and the shelves were
done.
Now, for the braces, I wanted to highlight that combination of the clean, geometric starting
shape and the organic topology optimized branches and fingers, and my first thought was well,
obviously, dual extrusion and just have that outer shell printed in matte white, but this
is already a 26 hour print, with dual extrusion thrown in, it would probably have been more
like 40 hours, and of course, I’d never know whether the dual-extrusion setup would
actually be reliable for those 40 hours.
One hiccup and you’ve got to start over.
So, simpler solution, white paint for all the smooth surfaces.
And they’re done!
Let’s go mount them
on the wall.
So there we have it!
There are certainly easier ways to make shelf braces, but none of them look this cool.
Or actually teach you about topology optimization while you’re at it!
Here’s what I learned:
Topology optimization is an amazing tool that pretty easily gives you amazing-looking parts.
Whether they’re actually still strong after you’ve printed them is another question,
but if anything, you can use the results as a guide to what your design should look like.
Stefan has done a few great videos on that approach.
The look you get is super depended on your inputs, and most likely, the best looking
one is not the one you should actually be using.
One thing I realized is that Topology Optimization does not take the absolute load into account
- I could have told it that this shelf would need to hold 35kg or one gram and the results
would have been identical.
The idea is that you then still run a simulation to see whether or not the part actually holds
up, so Topology optimisation is just there to make sure that all the material you’re
using actually contributes to the part’s strength.
So I hope you also learned something from this process, if you create something cool
with Topology optimization, I’d love to see it, the best way is to tweet it at me
@toms3dp.
Make sure to be subscribed for more projects and printer reviews coming up, just this Monday
I got the Elegoo Mars, which is a super-cheap SLA printer, and i’ll unbox that this weekend,
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