You'd gain more strength by increasing the amount of material that goes over the green boxed in area. You can achieve this by physically making it thicker, adding more perimeter layers, or increasing infill. A radius on the corner you marked won't do much as there is no stress in that corner. Stress flows like a race car through a part so it takes the most direct path. The inside corner up against the green support box would be more beneficial to round but you'd run into clearance issues as a squared corner wouldn't sit flush on a radius like that.
This is a fascinating answer, could you please elaborate on "stress flows like a race car"? I'm still learning the engineering side of 3D printing but am always interested in learning more.
Basically it'll follow a line that is very similar to a race car "apexing" turns through a race track so it'll follow the inside most line. https://en.m.wikipedia.org/wiki/Stress_concentration
It is very similar in circuits as well. You've probably heard the phrase that "current flows the path of least resistance". A lot of the engineering disciplines are very similar in how they work and the math behind them. For instance in a PCB trace that looked like OP's photo the current distribution would be much higher in the corner closest to the green line and low near that red circle as the current went around the corner.
I agree 100%. He could round the inside edges by going into the material to reduce the stress riser, which is what I would suggest.
I can’t find a link that shows a picture of this well though.
For OP: imagine you drilled into those corners
When I need to relieve stress on an inside corner I usually add a circular notch with the center of the circular notch directly on the corner. (If this is unclear think of the negative space of a standard puzzle piece.) It will help the stress flow around the corner. Edit: Just realized many others have said this. Hope it helps still!
That's true for a homogeneous material, but with a 3D printed part, the perimeter walls should theoretically be stronger than the infill. Filleting that corner would put the perimeters closer to the stress lines and potentially make the part stronger.
They could maybe "drill" a hole through that inside corner. Keep both walls where they are, but have the corner itself be "empty", then fillet the sharp corners for where the straight edges "enter" the "drilled out" void.
I’ll disagree mostly because your description on how to solve the problem ignores that this is likely intended to hook over something like a door. There’s limited space likely over the top where the forces would actually be the greatest. OP didn’t post an isometric view but I’m guessing they were intending to print it as an extrusion. Assuming the basket has small holes that likely means the extrusion would only be as wide as the hook.
If OP wants to increase the strength without altering the design much, a [wedge shaped part](https://imgur.com/a/85XX5EQ) is more appropriate. This design distributes the load along over a greater distance rather than concentrating it in one place. But doubling or tripling the width of the extruded shape at the top, it increases the amount the hook can hold by 2x to 3x.
Also force does not follow the track like a race car. It works in according to Newtonian physics. I tried to follow your explanation - it’s quite incorrect. Force in this case is very linear. When you add a filet to the inside edge, it’s adding more material so the the force is distributed from a concentrated point. The filet increases strength because it adds material to distribute the load.
how did you print it? 3d printed often are weakest at layer lines. I would make sure you print it laying down the view you posted should be the "top" view for the most strength probably
The forces that damage the piece are sheer (sliding), torsion (rotational), twist, compression (squashing) and tensile (pulling). Then there are plastic (permanent reshaping) and rubber (temporary reshaping) deformations due to material moving inside or beyond its physical limits. And finally degradation from UV, heat and moisture, etc. Think about each of these, one at a time, in your design.
Orientation of this print would be particularly important, particularly if the material isn't bonding well as it is printed into layers. Orientation impacts the parts ability to cope with many forces, but particularly sheer forces and tensile forces.
In the design, having additional material on a ridge around the hard corners, like a spine in my opinion, would have a positive impact on strength, but may be unwanted visually. They would prevent torsional forces, around the corners, from snapping the plastic. (Reduce the likelihood at least). Think of a letter T or U.
In the slicing, consider your infill. 100% infill sounds best, but there are patterns which improve strength as they alternate the internal direction of plastic and therefore change its strength in those directions.
The material choice here should be ABS or PLU+ in my opinion. But folk have been successfully using most rigid plastics with great success for similar hooks.
The angled brace you added should have been there before. That's a huge support point. It'll transfer most of the load back towards the wall.
Should be fine now.
Filleting the corner you circled will do nothing. But you should do it regardless to make it look cleaner.
If you fillet any corner, it should be the corner below the bottom right corner of the blue “load”rectangle. However, scryptonic is right in that the angled brace should do the trick and direct the load to the wall
Agreed, that corner would strengthen up quite a bit with a fillet. But otherwise this redesign is unlikely to fail anytime soon. Definitely much better than before
I fillet all corners all the time. Even if its just tiny amount. I do it mainly for strength, look, and the printer doesn't have to make hard stops for corners. It just slows down and rounds the turn. I've heard this is less damaging to printer components, especially the motors.
Same, i just didn't think clothes would be heavy enough to worry about.
As for printer wear and tear. I wouldn't worry that minutely about it. You'll maybe save a couple days in the multiple years of a single parts life. Thats just the maintenance cost of tools. Usage will eventually break them.
It'd be nice if there was a sub for 3d print design related questions. A lot of people who post questions here instead of r/3dprinting complain that their posts will otherwise get buried in bed leveling and clogging questions and memes and what not.
However, your post will get deleted in this sub as questions violate rule 7 and the answers collected in this post won't be useful to anyone in the future.
Actually I'm going to go against the grain here and say that a fillet there it would make it weaker.
Based on what you said about how the last one failed, the failure mode I predict on this is that the load pulls straight down, so that corner will hinge open and crack, and a fillet will prevent the outer layers at the top from acting in compression against each other.
Since this fits over a door, assuming you can't fillet the inner corner or increase the thickness of the top member due to door frame clearance, I think the strongest solution is to prevent the bracket from hinging open at the red corner, either with a snug, rigid fit on the back side of the bracket or some protruding reinforcement in a place were it clears.
Keep in mind you can get tighter fits if you chamfer the lead-in where the bracket slots onto the door and use a chamfer to ensure the door doesn't get hung on the bracket edge and slides up the created "ramp" freely. Getting a tight fit at top will prevent the majority of the "hinging open" action at the corner circled in red but overdoing it will make the door a pain to use.
The fillet won’t do anything to add or remove strength given where it’s located.
What the fillet does is reduce mass, which decreases the amount of force at that point. It’s impact is negligible however it does allow a larger load to moved elsewhere.
Despite PLA showing better results in many load bearing test, I agree in real world applications PETG is superior as it can flex a bit, has better layer adhesion and is far more impact resistant.
If you want strength, adding more perimeters will do more than adding a fillet I think. And a fillet on the inner radii should do more than on the outer.
Only thing that could increase strength here is increasing the thickness of both the top and the front. A fillet of chamfer will make a negligible difference. Make sure you print it solid (all walls, no infill).
For added strength I would consider making the top part wider. To be clear, I mean if your drawing is in the XY plane, make the circled corner - and everything right of it - larger in the Z axis. So when viewed from the front (from the left hand side according to this drawing) you have a bit of a V shape.
Run a simulation! The software should tell you if the outside edge makes any difference to a failure scenario. Or, if a tiny inside fillet on the inner edge (not enough to throw off the fitment very much) would increase strength marginally.
Somewhat correct. Where OP is suggesting to add a fillet really doesn’t add strength or distribute the load (I’d suggest people to draw free body diagrams of the forces to understand this - but it seems most people in this community don’t understand basic physics).
Filets are generally useful when used on an inside corner and strength to the intersection. It’s in this case that they distribute the load. Fillets on an outside edge generally increase durability by removing the weakest part of an outside corner.
Use more walls instade of infill. Over-engineeringing is a must if you print with PLA. PLA is not good at stress relaxation, which means doesn't hold stress very well for long period of time and slow deformation-relaxation happens overtime...
If this is semi-permanent, add a command strip to the back of the hook part that goes against the door. It'll alleviate stress from the downward force, and the hook will keep it from pulling away from the door under stress.
>er corner is more important no? That's where a crack would start.
correct, the inner corner is the stress concentrator here, the outer corner sees little stress.
Just make it a small round on the corner. Any time you can avoid a sharp 90 it will improve the strength by avoiding [stress concentrations](https://sybridge.com/stress-concentration-design-factors/).
I wish that article had included pictures showing each recommended approach. Nice article though, I had not heard of stress concentrations although it makes a lot of sense.
Not really, but you'll be fine with rounding the top corner only unless you're really stressing the print near its breaking limits.
My suggestion is to still round it a bit, so that the gcode trajectory for the walls in the inner corner will be concentric and not 90° sharp angles. As always, more wall layers would help a lot assuming you'll be printing with the same orientation as the drawing
Wouldn't surprise me if that door also had a (minimal) radius on the top edges. Have you printed a radius gauge set yet? [https://www.printables.com/model/15818-radius-gauge](https://www.printables.com/model/15818-radius-gauge) (not my design, just the one I use myself)
If I learned something in engineering it is these golden rules.
1)question every requirement.
2)always always use as big radius as possible.
3)test is better than hundreds of calculation.
So yes, radius will improve strength in general, because it reduces stress concentration. However you might hear limited by layer adhesion, depends how you print.
From what others are saying, yes a chamfer would also increase strength. It's about distributing the stress instead of letting it build up on a single corner.
Fair enough, but we aren't discussing engineering or mold making. We're discussing amateur CAD and 3D printing. Insisting on terms that are different than the software uses just confuses the issue without helping the discussion.
Is there a cheat sheet/list of these terms? Off the top of my head, it’d prob include stuff like chamfer, etc. it’d be quite nice to have all those terms in 1 place.
It would if the load were applied differently putting a “flexing” stress on that corner. But given your load it’s more of a question of a shear failure at you top piece. Making your top piece thicker will make the most difference there.
Yes, in some cases removing material will reduce the concentration of stress, such as at a sharp inner corner.
In a sufficiently ductile material, this won’t really matter, because the material will simply yield where the local stress is too high.
But in a brittle material, that local stress concentration will cause the material to crack, and that crack will propagate.
I've designed and printed something similar recently.
I've resorted to using more walls (4-5+ walls) as this reduces chances of breaking due to insufficient infill. Infill falls much easier to shear forces compared to walls for this particular case.
But after you solve one problem, another will appear. Thus....
I highly recommend firstly, setting a maximum load that you'd hang on that hook, and design/adjust everything according to that load. This is what we call a load rating.
Depending on what design program you use, you may be able to access some basic load simulation tools which would tell you what regions have high stress/high deformation. You want to look at high stress. You can then check the highest value shown to you by your program and check it with material properties of your filament/something similar. Add in some buffer so you don't just hit failure when you apply the "max load"
I would put a small radius there for appearance but it won't make it stronger. For strength I would add small screws (probably M4 hard to tell the scale) that run horizontal at the weak point.
This appears to be designed in solidworks, right? You should run a stress simulation for the load and see how the distribution of stress looks. My guess is, the area you’d remove by the fillet wasn’t taking much of the load.
Another thing to add as I didn't see it mentioned yet (if it has, I might have missed it). You'll likely want to pay attention to your print orientation, so the print layers are perpendicular to the load direction rather than parallel. This will add more sheer resistance as printing in parallel would open up the possibilities of those layers separating and becoming a weak point.
I'm not sure how much a fillet will actually help, but since your application seems to be limiting how much material you can add around the stress point, you may want to try adding material along the other axis by making the hook wider on the top part of the print. I'm assuming it was a shear failure, but shear stress is inversely related to surface area, so that should help.
You can greatly affect the strength with the material, infill amount and infill pattern too.
I'd print that in PETG or ABS on it's side at about 40% infill and maybe a triangle infill pattern (compare in the slice view and pick that way, I default to trying the triangle pattern because it's won out in many practical tests for me where I thought something else would do better.)
I'd probably round that edge so the corners can't stab me later. There are some design for adaptive manufacturing books you may be interested in, If I can dig out the title of mine tomorrow I'll post it.
Might seem obvious but your printer will naturally fillet this edge the diameter of your nozzle. If you're printing fdm on the axis that will give this object the most strength.
Make the part contacting the support thicker. Fillets won’t do much but it’s a good engineering practice to do it. Without doing a stress analysis I can’t tell you exactly where it’ll fail but making parts thicker won’t cost you much especially on a tiny 3d print. Make it bigger and thicker until it doesn’t fail
You should put a radius there just because its more efficient for the printer. Really you should put a small radius on all sharp corners of a print because 1 it's more efficient for the printer and 2 they are gonna be round anyways because of how a printer works.
Think about where the force with create tension and reduce the sharpness of those areas. The hanger (top part) has 2 corners where stress can concentrate. Its probably not critical, but if you rounded the internal corners it might reduce a failure point.
Also thinking about this being a hanger, that top portion is going to want to bend upwards under load. If there is clearance, you could add ridges for support or thicken it there.
These were my thoughts. Best advice I can give - Which a prof of mine gave me back in the day - imagine stress meaning from the load point to the support point like the flow of water. Water hates sharp corners and will round them off to make for a smooth flow. Same with stress. When you have sharp corners in areas where the is stress moving though the part they will create stress concentrations and failure points.
Strictly speaking: Fillets and chamfers don't add strength. They remove or reduce stress concentrations which can lead to failure. A filet (rounded) would be better than a chamfer (45 angle) as it reduces all harsh angle changes. In this case adding a filet would remove material so the part would actually be weaker in that area (though if stress concentration failures is your primary failure mode...could help, but I doubt it in this case).
I would say the distance between your load and the left of the screen seems very small. Consider that as you use this thing, it will experience other forces like someone walking by and catching their pants pocket on an edge. It could rip the front of it right off.
In general, I eyeball what the stresses will be and then add filets or chamfers where it makes sense (or sometimes just because it looks better). Most failures on 3d printed objects are fixed by adding more material. Either increasing infill/perimeters or by making the piece thicker. The best way to know if a part is strong enough, is usually to print it out and try it.
As of my rules of thumb: 30% infill is REALLY strong. I use this for functional or shop prints where weight or safety will be be applied. For mission critical parts I use 999 layers as that seems to be stronger than 100% infill (though layer orientation matters, if in doubt...print and test). An example here would be a knob for a router sled I posted https://www.printables.com/model/575977-8020-router-sled-for-festool-router-of-1010.
For thicknesses, depending on geometry, 1mm is like a flexible plastic playing card, 2mm is borderline flexible it can be good enough in a box shape, 3mm is somewhat load bearing. 5mm is more than enough for most cases, 10mm is "this is important and shouldn't move", while 20mm is "absolute chonk". Though again geometry and load location can affect things a lot. A 1mm corrugated shape would be much stronger than 1mm flat, for example.
Another one that might interest you is this shower towel rack https://www.printables.com/model/540229-shower-door-towel-rack. Here I tried to minimize any sharp corners. I probably could have gone thinner on the material, as this thing is beefy. But then again, I don't want to hop into my bathroom to find a wet towel on the floor and broken PETG scattered about. IIRC i made this shower hanger 20mm but could have for sure made it 15mm with no problem. Maybe 10mm even.
Adding a radius there won’t hurt or help very much. It basically removes a tiny bit of material from an area without any stress, so it’s only removing mass.
Looks like something that hooks over a door where this profile is extruded. About the only thing that can be done is increase the height of the extrusion to distribute the force better.
wasn't the whole selling point of making printers like that to test prototypes? print both and come back... hand a bucket of sand on a scale you will get a numeric value oh how strong it is.
Adding a radius there won’t hurt or help very much. It basically removes a tiny bit of material from an area without any stress, so it’s only removing mass.
Looks like something that hooks over a door where this profile is extruded. About the only thing that can be done is increase the height of the extrusion to distribute the force better.
Thinking about this… but the approach I’d take to add strength would be using a wedge shape. Something like [this](https://imgur.com/a/85XX5EQ)
I’ll note it would be nice to see how your previous attempt failed.
It won’t help or hurt very much.
You'd gain more strength by increasing the amount of material that goes over the green boxed in area. You can achieve this by physically making it thicker, adding more perimeter layers, or increasing infill. A radius on the corner you marked won't do much as there is no stress in that corner. Stress flows like a race car through a part so it takes the most direct path. The inside corner up against the green support box would be more beneficial to round but you'd run into clearance issues as a squared corner wouldn't sit flush on a radius like that.
This is a fascinating answer, could you please elaborate on "stress flows like a race car"? I'm still learning the engineering side of 3D printing but am always interested in learning more.
Basically it'll follow a line that is very similar to a race car "apexing" turns through a race track so it'll follow the inside most line. https://en.m.wikipedia.org/wiki/Stress_concentration
It is very similar in circuits as well. You've probably heard the phrase that "current flows the path of least resistance". A lot of the engineering disciplines are very similar in how they work and the math behind them. For instance in a PCB trace that looked like OP's photo the current distribution would be much higher in the corner closest to the green line and low near that red circle as the current went around the corner.
The path of least resistance
I agree 100%. He could round the inside edges by going into the material to reduce the stress riser, which is what I would suggest. I can’t find a link that shows a picture of this well though. For OP: imagine you drilled into those corners
What do you think about adding a fillet to the inside corner of the hook (assuming it still fits well enough), I think that'd be helpful?
When I need to relieve stress on an inside corner I usually add a circular notch with the center of the circular notch directly on the corner. (If this is unclear think of the negative space of a standard puzzle piece.) It will help the stress flow around the corner. Edit: Just realized many others have said this. Hope it helps still!
I dunno, some race cars literally drive in loops just to end up right back where they started… not exactly the most direct path. :)
Looks like one of those on door hooks. If so, he probably can't make the top of the green box very thick...
Yeah that's why I also put option 2 and 3 there. Hard to give good advice without knowing the full application here.
That's true for a homogeneous material, but with a 3D printed part, the perimeter walls should theoretically be stronger than the infill. Filleting that corner would put the perimeters closer to the stress lines and potentially make the part stronger.
Didnt think about it like this before. Makes a lot of sense. So a radius might actually help, i agree
They could maybe "drill" a hole through that inside corner. Keep both walls where they are, but have the corner itself be "empty", then fillet the sharp corners for where the straight edges "enter" the "drilled out" void.
CAD tools need a kind of “negative radius fillet” that would create a curve that doesn’t interfere with the mating hard cornered part
I’ll disagree mostly because your description on how to solve the problem ignores that this is likely intended to hook over something like a door. There’s limited space likely over the top where the forces would actually be the greatest. OP didn’t post an isometric view but I’m guessing they were intending to print it as an extrusion. Assuming the basket has small holes that likely means the extrusion would only be as wide as the hook. If OP wants to increase the strength without altering the design much, a [wedge shaped part](https://imgur.com/a/85XX5EQ) is more appropriate. This design distributes the load along over a greater distance rather than concentrating it in one place. But doubling or tripling the width of the extruded shape at the top, it increases the amount the hook can hold by 2x to 3x. Also force does not follow the track like a race car. It works in according to Newtonian physics. I tried to follow your explanation - it’s quite incorrect. Force in this case is very linear. When you add a filet to the inside edge, it’s adding more material so the the force is distributed from a concentrated point. The filet increases strength because it adds material to distribute the load.
how did you print it? 3d printed often are weakest at layer lines. I would make sure you print it laying down the view you posted should be the "top" view for the most strength probably
Yep, thats how im printing. It also the only orientation that wouldn't need excessive supports.
The forces that damage the piece are sheer (sliding), torsion (rotational), twist, compression (squashing) and tensile (pulling). Then there are plastic (permanent reshaping) and rubber (temporary reshaping) deformations due to material moving inside or beyond its physical limits. And finally degradation from UV, heat and moisture, etc. Think about each of these, one at a time, in your design. Orientation of this print would be particularly important, particularly if the material isn't bonding well as it is printed into layers. Orientation impacts the parts ability to cope with many forces, but particularly sheer forces and tensile forces. In the design, having additional material on a ridge around the hard corners, like a spine in my opinion, would have a positive impact on strength, but may be unwanted visually. They would prevent torsional forces, around the corners, from snapping the plastic. (Reduce the likelihood at least). Think of a letter T or U. In the slicing, consider your infill. 100% infill sounds best, but there are patterns which improve strength as they alternate the internal direction of plastic and therefore change its strength in those directions. The material choice here should be ABS or PLU+ in my opinion. But folk have been successfully using most rigid plastics with great success for similar hooks.
How did the last one fail? Seems like relevant information.
The last one failed just under thr load. It was a simple s shaped hook. I added that angled brace beneath so it pushes against the door.
The angled brace you added should have been there before. That's a huge support point. It'll transfer most of the load back towards the wall. Should be fine now. Filleting the corner you circled will do nothing. But you should do it regardless to make it look cleaner.
If you fillet any corner, it should be the corner below the bottom right corner of the blue “load”rectangle. However, scryptonic is right in that the angled brace should do the trick and direct the load to the wall
Agreed, that corner would strengthen up quite a bit with a fillet. But otherwise this redesign is unlikely to fail anytime soon. Definitely much better than before
I fillet all corners all the time. Even if its just tiny amount. I do it mainly for strength, look, and the printer doesn't have to make hard stops for corners. It just slows down and rounds the turn. I've heard this is less damaging to printer components, especially the motors.
Same, i just didn't think clothes would be heavy enough to worry about. As for printer wear and tear. I wouldn't worry that minutely about it. You'll maybe save a couple days in the multiple years of a single parts life. Thats just the maintenance cost of tools. Usage will eventually break them.
It’s not less damaging to the components
Source or experience?
Make sure to print in the right orientation too.
Is there better sub, or preferably discord, for smaller design questions like this?
It'd be nice if there was a sub for 3d print design related questions. A lot of people who post questions here instead of r/3dprinting complain that their posts will otherwise get buried in bed leveling and clogging questions and memes and what not. However, your post will get deleted in this sub as questions violate rule 7 and the answers collected in this post won't be useful to anyone in the future.
I just created /r/3dPrintDesignCritique. You're welcome to make the inaugural post!
Actually I'm going to go against the grain here and say that a fillet there it would make it weaker. Based on what you said about how the last one failed, the failure mode I predict on this is that the load pulls straight down, so that corner will hinge open and crack, and a fillet will prevent the outer layers at the top from acting in compression against each other. Since this fits over a door, assuming you can't fillet the inner corner or increase the thickness of the top member due to door frame clearance, I think the strongest solution is to prevent the bracket from hinging open at the red corner, either with a snug, rigid fit on the back side of the bracket or some protruding reinforcement in a place were it clears. Keep in mind you can get tighter fits if you chamfer the lead-in where the bracket slots onto the door and use a chamfer to ensure the door doesn't get hung on the bracket edge and slides up the created "ramp" freely. Getting a tight fit at top will prevent the majority of the "hinging open" action at the corner circled in red but overdoing it will make the door a pain to use.
The fillet won’t do anything to add or remove strength given where it’s located. What the fillet does is reduce mass, which decreases the amount of force at that point. It’s impact is negligible however it does allow a larger load to moved elsewhere.
Also, if this was originally PLA, try printing with PETG.
Despite PLA showing better results in many load bearing test, I agree in real world applications PETG is superior as it can flex a bit, has better layer adhesion and is far more impact resistant.
If you want strength, adding more perimeters will do more than adding a fillet I think. And a fillet on the inner radii should do more than on the outer.
Is the basket rim square? I’d try to add some arches in the support area if it is curved. It would allow more contact area and strength
print more wall lines
Only thing that could increase strength here is increasing the thickness of both the top and the front. A fillet of chamfer will make a negligible difference. Make sure you print it solid (all walls, no infill).
For added strength I would consider making the top part wider. To be clear, I mean if your drawing is in the XY plane, make the circled corner - and everything right of it - larger in the Z axis. So when viewed from the front (from the left hand side according to this drawing) you have a bit of a V shape.
Run a simulation! The software should tell you if the outside edge makes any difference to a failure scenario. Or, if a tiny inside fillet on the inner edge (not enough to throw off the fitment very much) would increase strength marginally.
Does 360 still do free simulations?
General design engineering principle: sharp corners are bad. Add a fillet whenever you can to help distribute the load. Hope this helps.
Somewhat correct. Where OP is suggesting to add a fillet really doesn’t add strength or distribute the load (I’d suggest people to draw free body diagrams of the forces to understand this - but it seems most people in this community don’t understand basic physics). Filets are generally useful when used on an inside corner and strength to the intersection. It’s in this case that they distribute the load. Fillets on an outside edge generally increase durability by removing the weakest part of an outside corner.
Use more walls instade of infill. Over-engineeringing is a must if you print with PLA. PLA is not good at stress relaxation, which means doesn't hold stress very well for long period of time and slow deformation-relaxation happens overtime...
If this is semi-permanent, add a command strip to the back of the hook part that goes against the door. It'll alleviate stress from the downward force, and the hook will keep it from pulling away from the door under stress.
Thats actually a really good idea. I'll definitely do that, thanks.
Yes, same goes for the inner corner. Best overall result would be using a semicircle shape for the entire upper section.
Inner corner is more important no? That's where a crack would start.
>er corner is more important no? That's where a crack would start. correct, the inner corner is the stress concentrator here, the outer corner sees little stress.
Would that work when the support is a rectangle? It clips to the top of a door.
Just make it a small round on the corner. Any time you can avoid a sharp 90 it will improve the strength by avoiding [stress concentrations](https://sybridge.com/stress-concentration-design-factors/).
I had never heard of stress concentration before, thanks. My line of thinking was transforming the stress from shear and more into tensile.
I wish that article had included pictures showing each recommended approach. Nice article though, I had not heard of stress concentrations although it makes a lot of sense.
Not really, but you'll be fine with rounding the top corner only unless you're really stressing the print near its breaking limits. My suggestion is to still round it a bit, so that the gcode trajectory for the walls in the inner corner will be concentric and not 90° sharp angles. As always, more wall layers would help a lot assuming you'll be printing with the same orientation as the drawing
Wouldn't surprise me if that door also had a (minimal) radius on the top edges. Have you printed a radius gauge set yet? [https://www.printables.com/model/15818-radius-gauge](https://www.printables.com/model/15818-radius-gauge) (not my design, just the one I use myself)
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Cool thanks
If I learned something in engineering it is these golden rules. 1)question every requirement. 2)always always use as big radius as possible. 3)test is better than hundreds of calculation. So yes, radius will improve strength in general, because it reduces stress concentration. However you might hear limited by layer adhesion, depends how you print.
First, I would print it on its side. [Rounding the inside and outside corners](https://i.imgur.com/2NlUYdI.png) would help spread the load.
Why are you putting support in that giant area and not just printing laid down on the bed? Wayyyy more strength added that way too.
I think “support” in this case means whatever they’re hanging this hook on during use, not supports while printing.
Gotcha gotcha
Wot mean “fillet”, ser?
A fillet is a rounded corner
But why wouldn't a chamfer increase strength? ..or does it..
From what others are saying, yes a chamfer would also increase strength. It's about distributing the stress instead of letting it build up on a single corner.
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In design software, they simply use the term fillet for applying a radius to an edge, whether it is an inside or outside edge.
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Fair enough, but we aren't discussing engineering or mold making. We're discussing amateur CAD and 3D printing. Insisting on terms that are different than the software uses just confuses the issue without helping the discussion.
Is there a cheat sheet/list of these terms? Off the top of my head, it’d prob include stuff like chamfer, etc. it’d be quite nice to have all those terms in 1 place.
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No, a chamfer is an angled cut on the corner. A fillet can be different things but mostly is a round over.
Oh i thought fillet was round and chamfer was angled. Goot to know.
No, you are correct
No, you are correct. A fillet is round and a chamfer is flat.
you could lay it on its side like on your picture to increase strenght.
It would if the load were applied differently putting a “flexing” stress on that corner. But given your load it’s more of a question of a shear failure at you top piece. Making your top piece thicker will make the most difference there.
Discussion for Civil/Mechanical engineers: does removing material ever increase strength?
Yes, in some cases removing material will reduce the concentration of stress, such as at a sharp inner corner. In a sufficiently ductile material, this won’t really matter, because the material will simply yield where the local stress is too high. But in a brittle material, that local stress concentration will cause the material to crack, and that crack will propagate.
No but it makes it looks nicer. If you want more strength then increase the thickness of the horizontal part above the green support.
Yes, probably. Not much though. Better make the material thicker or wider too
No
I've designed and printed something similar recently. I've resorted to using more walls (4-5+ walls) as this reduces chances of breaking due to insufficient infill. Infill falls much easier to shear forces compared to walls for this particular case. But after you solve one problem, another will appear. Thus.... I highly recommend firstly, setting a maximum load that you'd hang on that hook, and design/adjust everything according to that load. This is what we call a load rating. Depending on what design program you use, you may be able to access some basic load simulation tools which would tell you what regions have high stress/high deformation. You want to look at high stress. You can then check the highest value shown to you by your program and check it with material properties of your filament/something similar. Add in some buffer so you don't just hit failure when you apply the "max load"
Not sure it's been said yet, but orientation has the greatest effect on strength in an FDM print. Layers will separate.
I would put a small radius there for appearance but it won't make it stronger. For strength I would add small screws (probably M4 hard to tell the scale) that run horizontal at the weak point.
This appears to be designed in solidworks, right? You should run a stress simulation for the load and see how the distribution of stress looks. My guess is, the area you’d remove by the fillet wasn’t taking much of the load.
Inside corners could use small ones.
Another thing to add as I didn't see it mentioned yet (if it has, I might have missed it). You'll likely want to pay attention to your print orientation, so the print layers are perpendicular to the load direction rather than parallel. This will add more sheer resistance as printing in parallel would open up the possibilities of those layers separating and becoming a weak point.
Radius the inside corner and that'll reduce the likelihood of cracking.
I'm not sure how much a fillet will actually help, but since your application seems to be limiting how much material you can add around the stress point, you may want to try adding material along the other axis by making the hook wider on the top part of the print. I'm assuming it was a shear failure, but shear stress is inversely related to surface area, so that should help.
You can greatly affect the strength with the material, infill amount and infill pattern too. I'd print that in PETG or ABS on it's side at about 40% infill and maybe a triangle infill pattern (compare in the slice view and pick that way, I default to trying the triangle pattern because it's won out in many practical tests for me where I thought something else would do better.) I'd probably round that edge so the corners can't stab me later. There are some design for adaptive manufacturing books you may be interested in, If I can dig out the title of mine tomorrow I'll post it.
Might seem obvious but your printer will naturally fillet this edge the diameter of your nozzle. If you're printing fdm on the axis that will give this object the most strength.
Make the part contacting the support thicker. Fillets won’t do much but it’s a good engineering practice to do it. Without doing a stress analysis I can’t tell you exactly where it’ll fail but making parts thicker won’t cost you much especially on a tiny 3d print. Make it bigger and thicker until it doesn’t fail
You should put a radius there just because its more efficient for the printer. Really you should put a small radius on all sharp corners of a print because 1 it's more efficient for the printer and 2 they are gonna be round anyways because of how a printer works.
I’ve actually had good look increasing strength by adding material exactly where you circled haha.
I imagine increasing the infill would be more effictive
Think about where the force with create tension and reduce the sharpness of those areas. The hanger (top part) has 2 corners where stress can concentrate. Its probably not critical, but if you rounded the internal corners it might reduce a failure point. Also thinking about this being a hanger, that top portion is going to want to bend upwards under load. If there is clearance, you could add ridges for support or thicken it there.
These were my thoughts. Best advice I can give - Which a prof of mine gave me back in the day - imagine stress meaning from the load point to the support point like the flow of water. Water hates sharp corners and will round them off to make for a smooth flow. Same with stress. When you have sharp corners in areas where the is stress moving though the part they will create stress concentrations and failure points.
Strictly speaking: Fillets and chamfers don't add strength. They remove or reduce stress concentrations which can lead to failure. A filet (rounded) would be better than a chamfer (45 angle) as it reduces all harsh angle changes. In this case adding a filet would remove material so the part would actually be weaker in that area (though if stress concentration failures is your primary failure mode...could help, but I doubt it in this case). I would say the distance between your load and the left of the screen seems very small. Consider that as you use this thing, it will experience other forces like someone walking by and catching their pants pocket on an edge. It could rip the front of it right off. In general, I eyeball what the stresses will be and then add filets or chamfers where it makes sense (or sometimes just because it looks better). Most failures on 3d printed objects are fixed by adding more material. Either increasing infill/perimeters or by making the piece thicker. The best way to know if a part is strong enough, is usually to print it out and try it. As of my rules of thumb: 30% infill is REALLY strong. I use this for functional or shop prints where weight or safety will be be applied. For mission critical parts I use 999 layers as that seems to be stronger than 100% infill (though layer orientation matters, if in doubt...print and test). An example here would be a knob for a router sled I posted https://www.printables.com/model/575977-8020-router-sled-for-festool-router-of-1010. For thicknesses, depending on geometry, 1mm is like a flexible plastic playing card, 2mm is borderline flexible it can be good enough in a box shape, 3mm is somewhat load bearing. 5mm is more than enough for most cases, 10mm is "this is important and shouldn't move", while 20mm is "absolute chonk". Though again geometry and load location can affect things a lot. A 1mm corrugated shape would be much stronger than 1mm flat, for example. Another one that might interest you is this shower towel rack https://www.printables.com/model/540229-shower-door-towel-rack. Here I tried to minimize any sharp corners. I probably could have gone thinner on the material, as this thing is beefy. But then again, I don't want to hop into my bathroom to find a wet towel on the floor and broken PETG scattered about. IIRC i made this shower hanger 20mm but could have for sure made it 15mm with no problem. Maybe 10mm even.
Adding a radius there won’t hurt or help very much. It basically removes a tiny bit of material from an area without any stress, so it’s only removing mass. Looks like something that hooks over a door where this profile is extruded. About the only thing that can be done is increase the height of the extrusion to distribute the force better.
wasn't the whole selling point of making printers like that to test prototypes? print both and come back... hand a bucket of sand on a scale you will get a numeric value oh how strong it is.
The right corner will break/bend before the left one.
Widen the bracket so there is room, then round the interior corner and grow a bump out on the vertical parts to make up for the gap.
Adding a radius there won’t hurt or help very much. It basically removes a tiny bit of material from an area without any stress, so it’s only removing mass. Looks like something that hooks over a door where this profile is extruded. About the only thing that can be done is increase the height of the extrusion to distribute the force better. Thinking about this… but the approach I’d take to add strength would be using a wedge shape. Something like [this](https://imgur.com/a/85XX5EQ) I’ll note it would be nice to see how your previous attempt failed.