A few minutes ago, I had a bit of a disaster with my setup. I had printed the brackets linked below to hold my spools of filament. Everything seemed fine until I heard an incredibly loud crash. Upon entering my office, I was greeted with broken brackets and everything on the floor (including the tv that was sitting underneath the shelves, unfortunately).
https://makerworld.com/models/168987
I’ve attached pictures, but it’s pretty obviously why the brackets failed. I think, what happened, was wall mounting the AMS Lite yesterday was causing vibrations that traveled to the brackets which eventually caused them to fail. My question is, would printing the brackets again in PETG this time likely work better? Part of me is hesitant to tempt fate by using the same brackets again, but I’m willing to give it a try if it’s likely the fact that I printed them in PLA that’s the issue.
Can you illustrate how those brackets work? I can’t quite tell. Making some assumptions here - you will want to print these laying flat so that the little hooks/pins are not dependent on layer adhesion.
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They attach to the Skadis pegboard system from IKEA. I’ve attached a photo of the bracket attached to the pegboard. They basically slide into the holes and then downward to lock them in place. The brackets are printed lying on their side.
Could you design so that they used two sets of holes (width-wise)?
I think most non-engineering filaments will be problematic supporting this kind of weight - the nylons could do it.
Check this chart…
I’m curious what ideas others might have?
They do use two sets of holes (width-wise). I’m attaching another photo that shows a better angle of this.
I see. May just be too much weight. PPA-CF could do it. $$$
PLA is not actually so bad mechanically. Depending on the loading condition.
PPA-CF is much better in bending but (according to the Bambu tables) it is pretty bad at Z impact strength. However, pretty much everything but PA6-CF is worse than PLA in z-Impact. In fact, PA6-CF is the only material outperforming PLA everywhere.
I made this graph a while ago from the Bambu figures to compare key filament performances against PLA. It may be helpful. 100% = PLA Basic values from Wählen Sie das richtige Filament – 3D-Filament Leitfaden für Bambu Lab Drucker.
After thinking about it, and looking at some stuff online, I think I’ve found a couple of things I did wrong that lead to the outcome I had. First, I think the brackets I printed just weren’t strong enough for the amount of filament I had on them. I used a 48" dowel, but I thought I would be ok since I printed a third bracket to support the middle. When looking at the broken pieces, however, I noticed that the whole print (including the hooks) only had a 15% infill. This meant the hooks were essentially hollow, which I imagine didn’t help things.
I also think the fact that I had clips that joined my four IKEA Skadis panels together didn’t help things since it essentially was transfering the vibrations from the AMS Lite up to the panels that held the shelves.
I found another bracket design that uses separate T-Clips to attach the bracket to the Skadis pegboard that I think I’m going to try next. That way, I can print the t-clips with something like 100% infill to insure they’re as robust as possible. I’m also going to cut my dowels down so they’re shorter (and therefore won’t hold as many rolls of filament).
Since I’m making new ones anyway, am I correct in thinking PETG would still be a better material choice than PLA?
Add chamfers and angles to the joint.
You have used cubes to slot into a flat surface, which makes sense on paper, but, it has inherent strength issues when the pressure is applied.
If you add 45º angles to each of the cube corners and when you have a 90º angle at the meeting points, try adding a rounded edge.
It will mean the connector sits a little proud of the joint, but, you will have designed strength into the bracket.
Let me know if you need a picture to help illustrate my point.
Before you consider swapping PLA to PETG, you must fix the inherent lack of strength in the design.
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You could also use a modifier to make a 99% infill in the hooks. Just right click on the bracket → Add modifier → Cube, then place and size and change the infill.
But saying that, it may be more effective to use a 999 wall count rather than infill. That way, you have solid part areas with their strongest properties in the wall direction.
And as mentioned by Malc, try to loose the sharp corners. If you print flat, you could even use fillets rather than chamfers.
PETG is unfortunately just PETG. In particular the HF is not so much stronger than PLA. The CF tends to perform a bit better.
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Infill is your problem…. But don’t increase it. Increase your walls until they fill the whole hook solid. Use Arachne wall generator to get a perfect fill. This is much stronger for your purpose than regular infil.
PETG is much tougher than PLA, but less stiff. They are inversely proportional to each other I. General. It will bend much more under stress, so it isn’t great for your purpose.
You want strength with stiffness. PLA with all-walls instead of infil will work. If not, you are in the realm of strong AND stiff filaments like PPA. Siraya Tech has a PPA that is less than half the cost of BBL brand, I use it - but it is still +$50 / kg
I greatly appreciate everyone’s feedback, but a lot of what’s being suggested is going way over my head. I’m relatively new to 3D printing (bought my first printer last month), and haven’t done much of any actual designing of my own.
Below are links to the two bracket designs I’m considering. The first one is the one I used previously that broke. The second is the one I was considering using next since the hooks that attach to the pegboard system are separate. Between those two, which would you recommend I use this time?
It sounds like either way, I will need to increase the number of walls instead of increasing the infill. Would someone be able to walk me through this process a bit more? I see where I can choose Arachne wall generator, but I’m not sure what other setting I need to change to actually increase the number of walls until it’s a solid part.
Finally, would using PETG be a significant disadvantage compared to PLA due to being less stiff? The only reason I ask is I’m actually running low on white PLA which was another reason I was planning on using PETG this time around. I could print in another color if it really will be a significant difference, but I was hoping to keep everything matching.
Thanks again for all the help. I really appreciate how quick everyone is to offer suggestions.
UPDATE:
Oops, forgot to actually attach the links…
https://makerworld.com/en/models/168987?from=search#profileId-363115
https://makerworld.com/en/models/467209?from=search#profileId-376253
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I am taking your design skills into account with this suggestion, it is not best practice, but, it will get you further without complicating things.
Tweak your design correctly by understanding how the Skadis panel socket is made.
You will notice it is just two cylinders with identical diameters separated by a fixed distance. You make this as the lug.
The panel has a thickness, your stand uses this as an offset.
My simple drawing…
- Lug (part pushed through the socket designed to fit the hole.
- Bar (identical in diameter to one of the cylinders) and the thickness of the panel.
Profile tweaks.
Increase wall loops of the model if you wish, ideally, you would do this on the lugs only, but, I am not sure you are ready to understand that yet.
Try 4.
Do not worry about arachne as it is not going to help.
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This video might provide some inspiration to improve the strength through optimized design and print orientation:
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I am not much of a designer, but I would go for the first one due to the miniscule size of the hooks on the second design. But @MalcTheOracle has much more experience and competence and may be able to give better advise.
As for how to do it:
- Right click the part, then add modifier, cube
- Use the sice, rotate and move commands to, well, size, rotate and move the modifier to encompass the area(s) you want to use different settings
- Then, looking at the individual objects, select the modifier and increase wall loops to 999
- There are also a few other settings I’d change globally. Such as the number of walls overall to 4+ and getting rid of crossing patterns.
=> That should then be much more sturdy
filament_holder_skadis_26mm(for_A1_mini).3mf (1,2 MB)
It may be more prone to curling though, so in particular with new PETG, make sure that your filament is bone dry.
PETG will be stronger. Also, 90 degree angles on the inside corners of the pegs are stress risers. Add fillets.
For something like this, I’d go with PCTG. But that doesn’t really matter, since I think the real problem is that the holes in Skadis boards are a bit too tight for a durable printed attachment if it needs to hold much weight.
I also have a couple of those boards (in black, so lucky I found them), and I solved this issue by leaving a space in my prints for a couple of the many different types of metal attachments you can get for Skadis. That way it’s 100% secure unless the entire pegboard rips out of the wall.
I would print it with mounting holes on the front of your brackets and then use metal bolts and locknuts… or nuts with lock washer to mount it to your pegboard.
I could redesign a stronger bracket for you if you don’t mind waiting. In my opinion, the hook design that you had printed isn’t designed in a way that would be strong. I have a Skadis with me and an idea on how to optimise the design, so I’ll be able to make the design when I’m free.
There is a high load on the bracket at the front due to the dowel taking all the weight. All that pressure will induce a rotation trying to pull the top rear pins out. Needs more pins at the top before you start considering filament changes. PLA is not recommended for long term load from what I’ve heard, can’t say for sure myself, never tried it. I agree with the suggestion of introducing metal screws or bolts. Consider, are you trying to make a strong shelf or a proof project for all plastic? There’s no law requiring 100% plastic.
