This isn’t exactly a P1S question but that’s the printer I have…
This is a U bracket that fits on a plastic table, which has a desk lamp that sits in the hole on the left and swings around. The bracket that came with it won’t fit on the edge of the table which is plastic and oddly shaped.
I printed this in PLA with the 0.20 Strong profile and 0.4mm nozzle. It works OK, but cannot be tightened effectively. The bottom plate bends down way too easily.
My question is how best to make this stiffer. Obviously I can just make it thicker on the bottom and the left side (the 20mm and 10mm sections), but is there some magic in the four billion combinations of slicer settings that would be worth trying first?
One thing I did (and I can do more of) is design the bottom angled up a bit (it takes a 5mm up now that you can see relative to the red axis under it). I can do more, but it’s just so springy now…
I think the issue is more the plate itself than the corner, though it may be some of each. Are there infills that increase stiffness? There are hundreds of “what infill is strongest” but they seem to be related more about crush strength, which may not be the same as being flexible (or not).
Anyone have a good, authoritative document to read on such subjects. Youtube with its more than fair share of click-hunting idiots parroting each other is difficult to find good advice.
I think mainly just increasing the infill percentage would help with maybe a Gyroid or Cubic infill. You could also change the design so that you are squeezing a long rectangle against the bottom of the table instead of just the tip of the bolt. That may allow you to move the bolt closer to the corner which will reduce the bending.
Strong profile: 5 wall loops, 30% infill in gyro the whole model. Then use modifier to print the bottom bar, and the lower half of the vertical bar (the 20mm part) infill at 100%.
Move the tightening hole as close to the table edge as possible while still not losing the grip.
Use PLA-CF filament
Make the lower bar thicker and/or increase the width of the model (the height of the extrusion in your model)
I don’t see a way to make it significantly stronger. The problem is simple, even uber thick plastic stretched out over a span will always bend. Depending on how much force you need to resist, the only option is to go thicker and thicker.
On a different note, changing how the clamping force is distributed, you can increase the gripping force substantially, but the design will get bulkier. For example, this design (just for reference, I don’t think it fits your need), can take a lot of clamping force before the arm begins to flex. This is the type of mechanism that might be best to explore.
I’m using the strong profile, I’ll check those, but I can also set infill to 100% easily enough I think.
The tightning hole is about as close to the edge as I can get, though I’ll double check. There’s all sorts of edge plastic stuff there, plus some mechanism to fold the legs (this is just a cheap Costco plastic table).
I don’t have any PLA-CF, I did buy (but haven’t tried) a role of ASA-CF as I haven’t put in the hardened nozzle/gear. Does CF make it stiffer not just stronger?
Thicker bottom is clearly going to help the most in terms of physical shape changes, I’m just trying to learn how the print process can be changed to affect the resulting material characteristics better. So I’ll experiment with the infil as mentioned (since it takes 3-4 hours to print each trial and error is why I’m asking first).
@jetpad That’s the “Sparese infil” right/ There’s also an “Internal solid infil”. Right now it’s rectilinear for the latter and grid for the sparse. It looks easy to set to gyroid and also a modifier and set to 100%. Going to start a print (over 4 hours so … will be tomorrow before I cna respond.
That’s a fascinating design I’ll look up. But you are right, doesn’t fit here, this is a case of a side-mount light on a table whose side is all messed up so trying to reach past it. But I don’t need huge clamping force just enough to keep it from sliding around. Which actually gives me a different thought – maybe I just need some non-skid stuff (like on the bottom of toolbox drawers) under the top strip and the screw on the bottom, and/or a movable plate of a few inches long on top of the screw. It’s more grip than clamping force (I realize more clamp gives more grip, but there are also alternatives).
That’s an interesting thought. I can see it will reduce breaking but I guess material on a diagonal helps. I need to go do some measurements see what will fit. I can put a small radius there, but if I can find room for a large one it might make a real difference.
But the next trial is running for the next 4+ hours. I’ll see how that one goes. This is now more an educational exercise than anything else, the original actually works, just if I hit the top bar it slides (this is on a “lab” table where I solder and such stuff, so being a bit ugly is irrelevant).
Yes. I suggest using modifier becasue I thought you may not need the top bar to print at 100% infill. The lower bar, and don’t forget at least part of the vertical bar that connects to the lower bar should also be strengthened.
If this is for your own use and you don’t have plan to share it on MW, I would suggest doing the 100% infill and increaing the thickness to 15mm for the bottom bar at the same time so reduce the number of iterations needed.
Carbon fill makes the filament stiffer and stronger. But PLA is pretty strong and stiff as is. So unless you alreday have a roll of PLA-CF, probably no need to buy one just for this. Between 100% infill and increasing the thickness of the bar the springy problem can be solved.
Strengthen the design, introduce ridges to the shape, and you have essentially three rectangles joined together.
They all meet at right angles, curve them to increase strength and experience fewer tear forces.
Add some boolean cylinders into the surfaces, small diameter ones that you can add, say, five or more across the top and bottom rectangles on both the top and bottom surfaces. These bring the sort of benefits that corrugated iron sheets gain.
Maybe remove some material in the middle. Imagine taking a cylinder through the side walls of half the thickness, think Swiss cheese. This adds strength in the same way bridges gain strength from girders and trusses.
I played with an earlier iteration, and I suspect the top piece is also bending at the corner, giving a different angle to the side. So I decided to stop things and added 100% infill (apparently rectilinear is all that will do that?) to the whole thing. I also added a tiny fillet radius on the bottom (it is up against a square edge, so if I add much it just pushes a greater length which will be a tradeoff) and a bit larger at the top where I have more room.
This will work even without being stiffer, so I do not think I am going to redesign as suggested at least for this time. I’m also not exactly sure how I can do that design – it will hang out from the side of the table, and the mechanics will get in the way of the shaft from the light it supports requiring a lot greater depth (as viewed in this orientation) so both can fit.
Honestly the best design is drill a hole in this (cheap) table and screw through it instead of to it.
But as I said, this is more now about me learning how to make plastic extents stiffer. So thanks for all the feedback. 4+ hours to finding how it goes.
No, I don’t want to climb in to that mess, this is just for me. Though if more people shared fusion files maybe. I put all the effort into fusion and parameters, but it looks like most of the parameterized files there are OpenSCAD.
Maybe once I get better at it.
If increasing the infill to 100% works why would that make it inappropriate to share?
I actually took statics and dynamics in school (a millennium ago though), but never material science or real design so apologies for the simple questions…
Is the removal of material only to save it? Or are you suggesting that a swiss cheese approach is actually stronger than a solid? (I’m aware of things like rectangular tubing being almost as strong and much lighter than solid, but didn’t think it was stronger (though I guess it doesn’t have as much weight to self support)).
Same question with the cylinders, are you suggesting those as a way to add thickness without really adding thickness, or is there something more?
Maybe what I really need is a material science / design book. Might be time to visit a library. Or Amazon. But what it likely won’t have is the impact of the thread deposit directions and size and such. Or maybe there are some – FDM has been out a while.
Update later: I don’t mean the above to sound like I’m disagreeing, I am just asking; this is not a subject I know much about and trying to learn.
My answer was entirely focussed on strength and not material use or time to print.
The holes (Swiss cheese) add walls which aid in both compression and expansion when being stressed. It adds strength and lots of it when applied correctly.
It also forces infill to bind around the holes, adding more strength.
Adding cylinders that run the length of the top and bottom surfaces (think corrugated metal), which are cut out from those surfaces adds strength. You boolean them at the centre mark of the cylinder, half outside the surface, half inside.
You have likely seen this effect in cardboard boxes (the better ones have this as their internal walls, some biscuits (cookies) are packed with them as tubes surrounding the tasty goodness. If like me you have walked on corrugated metal, you understand the benefits.
Update
A quick and (very) dirty mockup of an extreme, but, basic example.
Thank you @MalcTheOracle very helpful. Turning in for the night. Still 3+ hours on this iteration, may try another tomorrow depending on what I’ve learned.
So… I’ve got stuff to do this morning but the reprint with new infill and some softening of the rectangular corners printed. To my un-calibrated fingers I do not sense a difference however there is a wrinkle in trying to tell.
The original was mounted over night (so maybe 16 hours total) stretched a bit. It is now permanently stretched, clearly it doesn’t behave in an elastic fashion (I guess it is, well, plastic).
Here is the original (left) and new (right). They would have been identical shape when printed, the new is 166g vs 111g so the infill added a lot of mass, but the original has been now distorted enough I am not sure there is a meaningful way I can measure its stiffness to compare. Not to mention I don’t have any good tools to do so. Maybe hang a known weight from each and compare change in opening size?
But it’s clear plastic in this design is not a good way to clamp, it’s stiffness is not only poor but really inelastic.
It does give me some indication of where the bend is – the back sides (old in background in this shot, new in front, bases precisely aligned) shows it has been bent on the back side and/or bottom corner. The actual arms sticking out, if I lay a straightedge along them, shows a very slight rounding on the old, but not nearly enough to account for the displacement – that’s coming from the “U” itself opening up.
That’s not to say that is where the flexibility is coming when I tighten, but that’s where the long term failure to maintain that shape is originating, which kind of makes sense given the leverage the long arms have. Which likely means modifications (e.g. as recent posts) to make the arms stiffer will just exacerbate the long term distortion in the “U” and it would need to be a lot larger/strong/different also.
Interesting exercise. Shows why when all you have is a hammer the answer is not that everything is a nail, but to get another tool.
This is why a few of us suggested the only real solution is a redesign.
Plastic isn’t the problem, how it is used is.
You have long thin bars with a screw adding pressure against straight 90° corners with all the grip at the edge of the desk and the force all the way at the other end.
In the picture supplied above with the c shaped clamp, there are many parts, making each one stronger as a result with the force being applied like your jaw does when biting.
The strength is in the parts, the grip is in the mechanics of it.
PLA is the wrong plastic for this. You need a plastic with a higher glass transition temp, stiffness and lower viscoelasticity. PEEK or PC or PA6-CF/GF or ABS-CF/GF. In that order.
Goes without saying, 100% infill. Wall count won’t matter.
Also, since the part will be under tension, you could “print in” some compressive force to compensate a bit. I exaggerated the idea so it’s clear in this picture. Make the open end a little narrower than the closed end.
Thank you. Yes, I am pretty space limited, and don’t have any of those filaments.
I had a weird thought and need to go experiment – I wonder if this table is thin enough magnets would work. I have some old HDD magnets lying around that are very strong.
But… this has been very educational. Which was the main point. If nothing else I think I’ll just drill a small hole in the top of the desk to lock them together.
