Thank you for your suggestion, but the picture I provided was a very simplified case. Many of the parts I design have extremely complex geometry, where the final dimensions are a compound result of many other dimensions. It would take a math wizard to predict how to apply that compensation at the early level so that it is correct after everything adds up together. I am certainly not that good, and even if I were, it would be even more work than using Move Face... That is why I want to apply this compensation at the very end of the part design, at the end of the feature tree.JPARKER wrote: ↑Fri Feb 24, 2023 3:47 pm I can see where the scale feature would make sense, but it is not manufacturing smart. So it just sees the whole body not the features when scaling.
My suggestion would be to utilize equations with a global variable for the thickness of the coating. Then you can add this to each dimension for a specific configuration. That would allow you to design in normal values, but then have a configuration that would represent the shrunk version automatically.
By trial and error... I know it is a bad way, I only mentioned it because I didn't want anyone else to go down that false road while trying to help.
I know, but like I said, with complex enough parts, simply adding that number to every dimension will not result in correct final offset, because of how different features interact together. It would require extremely complicated equations with lots of trigonometry to get it right. I believe that there are cases where even Move Face - Offset would not get the right result, but as far as I've tried, it seems correct so far.Frederick_Law wrote: ↑Fri Feb 24, 2023 4:49 pm Done correctly you can even have model of the coating.
Once you get into it, you'll see why it's not a simple scale.
Sometime not even a simple offset.
But that coat still has a non-negligible thickness, right? Or is it even thinner than my print tolerance? I would be very interested in exactly what material you used there. I tried several, and only epoxy seems to do the trick. But it is so annoying to work with. Would really appreciate the source for your car clear coat.Frederick_Law wrote: ↑Fri Feb 24, 2023 4:54 pm To make 3D print water proof, use a thin sealant/paint.
One that will get into tiny gaps on the part.
I even got it to work under pressure.
I spray it with car clear coat.
Very interesting idea. I will try this right away.
Thank you, that would work for simple parts, but again, when these dimensions add together, or are a result of non-analytical faces, it would be very difficult to get these dimensions right... I will try it nonetheless.josh wrote: ↑Fri Feb 24, 2023 5:09 pm I wrote a macro several years ago for tolerance analysis that creates configs of your part (leaving the default untouched) for MMC and LMC based on the tolerance applied to the dimensions. It does this by changing the dimension value to the tolereance limit, then analyzing if the part volume grew or shrank. So outside dims get smaller, holes get bigger. If you added a ±0.15 tolerance to every dimension in your part, then ran the macro, it would create a config for you where every dimension was 0.15 smaller. Of course, some of your dimensions may control two surfaces, in which case you may have to give a ±0.3 tolerance...
https://www.eng-tips.com/viewthread.cfm?qid=163937
It's thin and all you really need is fill up between layer. That's where the gaps are.But that coat still has a non-negligible thickness, right? Or is it even thinner than my print tolerance? I would be very interested in exactly what material you used there. I tried several, and only epoxy seems to do the trick. But it is so annoying to work with. Would really appreciate the source for your car clear coat.
Interesting. I seem to remember trying some clear coat a while ago. It worked fine for normal water pressure, but anything above 5 bar would leak through. I tried spray paint - that leaked through even at normal water pressure, perhaps I didn't apply enough coats... The epoxy I use sticks extremely well to PLA (after light sanding with 120/150 grit). I use Elan-tech EC 152/W 152 HR (https://www.polyplancomposites.fr/_dyna ... ing-95.pdf)Frederick_Law wrote: ↑Fri Feb 24, 2023 5:32 pm It's thin and all you really need is fill up between layer. That's where the gaps are.
You can fill up pretty thick there since it's a grove from the layer.
It just spray paint from Walmart or wherever you can buy automotive spray paint.
Paint design for plastic could stick better.
I tried UV epoxy, they just pile off PLA.
I tried this method now. Works really well, thank you! It is a bit annoying to set up, but after it is done, it requires no maintenance. Shame that features like Move/Copy Body, Shell and Combine cannot be saved as Library Features. I might end up writing a macro to create these features for me.
I am a bit wary of using thinner in this specific case, because as it evaporates, it might leave microscopic gaps in epoxy, which will ruin it's water-proofing properties. Instead, I usually heat up epoxy and the part a bit (to around 40-50°C), which makes it much thinner and easier to apply in thin coats. However, I find that since covering is done by hand (with a brush), the only way to truly ensure that there are no insufficiently covered areas, is to coat until the texture of the print is completely filled, turning the surface into a glass-like finish. That usually comes after 2 coats, but I add a 3rd one to be absolutely sure. It might seem extreme, but in my use case, I can't allow even a single drop of water to pass through these parts.RichGergely wrote: ↑Sat Feb 25, 2023 12:57 am Looks like a typical 2K coating (the type where you use airfed respirator to apply), can't you add (or more) thinner so the coating doesn't go on so thick. It should still harden, the excess thinner will just evaporate off. I often have thinned down epoxy primer with no issue, it just ends up not being high build which is what I'm after in those cases.
I would disagree. Scale and shrink are exactly the same. An example is that everyone who has ever talk about plastic part shrinkage for the given moulding method is totally wrong is scale and shrinkage are not the same thing. What we are actually talking about here is fundamentally surface offsets on the painted surfaces - no scale or shrinkage involved for the part as a whole.DanPihlaja wrote: ↑Mon Feb 27, 2023 11:43 am "Scale" is different than "shrink"
Scale uses a single point and reduces everything in the direction of that point. Which means that holes that are not on center will actually MOVE closer to the scale center after scaling (center line of hole will NOT remain in the same location)
While Shrink just essentially offsets surfaces away from MMC.
What you want is shrink for this and not scale.
Solidworks doesn't really have a shrink function.
You will have to almost do this manually.
I had a new thought, you may be able to create the surfaces you need with CAD/CAM software meant for creating electrodes for the EDM process. It would be in reverse to your outside surfaces = you would run it on the inside so the surfaces would be offset inwards.laukejas wrote: ↑Sat Feb 25, 2023 5:42 am I am a bit wary of using thinner in this specific case, because as it evaporates, it might leave microscopic gaps in epoxy, which will ruin it's water-proofing properties. Instead, I usually heat up epoxy and the part a bit (to around 40-50°C), which makes it much thinner and easier to apply in thin coats. However, I find that since covering is done by hand (with a brush), the only way to truly ensure that there are no insufficiently covered areas, is to coat until the texture of the print is completely filled, turning the surface into a glass-like finish. That usually comes after 2 coats, but I add a 3rd one to be absolutely sure. It might seem extreme, but in my use case, I can't allow even a single drop of water to pass through these parts.
I tried spray coatings, but my parts leaked through. Perhaps I didn't apply enough coats (I aimed for 5-6), or maybe I missed some spots. I found it very difficult to make sure that the spray particles can find their way into all small features of the part, while simultaneously avoiding pooling at sharp inner corners, small hollows, etc. This is an example of one of the more complicated parts that I am coating:
image.png
Maybe someone with better spray skills than mine could manage to coat such a part in smooth, even coat without any dry spots and no pooling, but I didn't manage, so I resorted to doing it with epoxy and a brush, which is labor-intensive, but very reliable.
DanPihlaja wrote: ↑Mon Feb 27, 2023 11:43 am "Scale" is different than "shrink"
Scale uses a single point and reduces everything in the direction of that point. Which means that holes that are not on center will actually MOVE closer to the scale center after scaling (center line of hole will NOT remain in the same location)
While Shrink just essentially offsets surfaces away from MMC.
What you want is shrink for this and not scale.
Solidworks doesn't really have a shrink function.
You will have to almost do this manually.
We might argue on what is the right term here, but I get what you both mean, that is why I included that example in my initial post, to show I understand the difference. And that I'm now looking for ways to do that surface offset automaticallyRichGergely wrote: ↑Mon Feb 27, 2023 3:04 pm I would disagree. Scale and shrink are exactly the same. An example is that everyone who has ever talk about plastic part shrinkage for the given moulding method is totally wrong is scale and shrinkage are not the same thing. What we are actually talking about here is fundamentally surface offsets on the painted surfaces - no scale or shrinkage involved for the part as a whole.
As for shrinkage, that is something I also compensate for, but I usually do that in slicer software rather than in SW. The usual shrinkage for PLA is very low - around 0.24%, but still significant if you aim for tight tolerances.I did try dipping, but with larger parts it becomes very uneconomical, as most of the epoxy is wasted. Also, after dipping it pools heavily in all small details, so excess has to be cleaned off with a brush anyway... So might was well just paint it with the brush in the first place. I usually apply epoxy quite generously, and the use brush to remove as much as possible, basically trying to get it all off - that is the only way I can ensure there will be no pooling. It takes more coats, but is safer.Frederick_Law wrote: ↑Mon Feb 27, 2023 12:16 pm You might want to drop it into a container of thinned epoxy/paint.
You need to fill gaps between layers and wall.
ie connection between extrusion.
You want epoxy/paint to sip and fill all gaps into the part.
How many walls did you print?
Try turn up the heat.
I didn't test with final product in the beginning.
I printed smaller caps.
Once I got that watertight with spray paint, I tested final product.
Can you elaborate on this? Do you mean do this in SW, or other software? Because like I said, my goal is to do this in SW, so that my workflow is as automated as possible... Adding even another piece of software would complicate things further. SW and slicer is already a lot, especially when I need to coordinate file versionsRichGergely wrote: ↑Mon Feb 27, 2023 3:24 pm I had a new thought, you may be able to create the surfaces you need with CAD/CAM software meant for creating electrodes for the EDM process. It would be in reverse to your outside surfaces = you would run it on the inside so the surfaces would be offset inwards.
Interesting. What pressure did you test your parts at?Frederick_Law wrote: ↑Mon Feb 27, 2023 5:56 pm I printed 3 wall, 20% infill. The part is a water spray nozzle. So most of it is just 3 walls.
Maybe you need resin printer.
The extra steps in coating could pay for one.
I am not exactly vacuum *bagging* the parts - I don't use a bag, I just cover the part with thin layer of epoxy, pour more epoxy in required cavities (usually this is done to permanently install hardware), and then place it in a vacuum bucket, making sure that no epoxy-covered surfaces touch anything. That is one of the reasons why I usually cannot cover the whole part with epoxy in one go, as I can't suspend it mid-air.
I had done several parts this way. It could be done with resin printing too I suppose, that would make sense to get a strong and waterproof part. But it is a lot of work.
Tried this as well. 3D printed molds are really hard to make well, since all the cavity surfaces must be smoothed out with sandpaper or filler, which throws off carefully designed dimensions. One tiny mistake, missed spot when sanding/waxing, and the mold won't separate. And the mold usually breaks during removal. Also, exothermic reaction of epoxy is very difficult to control when the part is enclosed in a mold - even placing it inside an ice bucket sometimes doesn't cool the core enough, and the resin boils, ruining everything. Even the slowest setting resin I tried is very prone to this. So again, it is probably doable for some parts, but really not well suited for rapid prototyping and many one-off parts.
Try different resin.
I tried this as well a long time ago (although I did it without infil). Again, there are 3 main issues: exothermic reaction, difficulty of getting air out even with vacuum, but the most important one is that the part is not fully waterproof, because water can still travel along the surface of the part in between these 3 walls. So for example if a part is a cap with some O-rings, the water will seep just under the surface, and pass through the O-ring from "underground", so to speak.Frederick_Law wrote: ↑Tue Feb 28, 2023 11:50 am Try different resin.
Another way to "seal" the part is: print 3 walls with Gyroid infill.
Drill 2 holes on "top" and fill with epoxy.
You can try put it in vaccum to pull some epoxy through the wall.
Dipping it in a pool would perhaps give you the "quality control" that you are not getting from doing it with a brush only, understandably it would cause more waste but if it fixes your issue you could then work around ways to save waste.laukejas wrote: ↑Mon Feb 27, 2023 4:42 pmI did try dipping, but with larger parts it becomes very uneconomical, as most of the epoxy is wasted. Also, after dipping it pools heavily in all small details, so excess has to be cleaned off with a brush anyway... So might was well just paint it with the brush in the first place. I usually apply epoxy quite generously, and the use brush to remove as much as possible, basically trying to get it all off - that is the only way I can ensure there will be no pooling. It takes more coats, but is safer.
Can you elaborate on the quality control part? You mean that dipping would ensure complete coverage? Thing is, like I said, I would still have to use brush to remove excess, and 1 layer is not enough (because after 1 dip, the brush will remove too much epoxy during excess removal - unfortunately it is impossible to control well enough so that it would remove excess, but still leave enough epoxy that would be equivalent to 3 regular coats). I seem to remember making an experiment many years ago that showed that a single coat, no matter how thorough, is never enough to fully waterproof the part, unless you put it on really thick (which, again, makes coating thickness uneven in different features of the part). So I would still have to make 3 dips to get required thickness with sufficient dimensional control.AlexLachance wrote: ↑Tue Feb 28, 2023 2:13 pm Dipping it in a pool would perhaps give you the "quality control" that you are not getting from doing it with a brush only, understandably it would cause more waste but if it fixes your issue you could then work around ways to save waste.
For example, that part I showed in screenshots before, is around 70mm in diameter. I usually mix 12g of epoxy for it, and end up using maybe 2g per coat, and the rest is thrown away - simply because I can't measure and mix a smaller amount accurately enough. Even so, 12g is just a small part of the cup. I can't imagine any way to make a dipping form that would use any less than 10 times that amount of epoxy, per single dip. The only way that could be economically sound is to mass-manufacture these parts... But I never do that. Correct me if you have an idea on how to save waste! I've never worked in that sort of thing so I have no knowledge of how it works, was just thinking off the top of my head. I was thinking that brushing off the excess would not cause the chance of it having an incomplete coverage.laukejas wrote: ↑Tue Feb 28, 2023 2:25 pm Can you elaborate on the quality control part? You mean that dipping would ensure complete coverage? Thing is, like I said, I would still have to use brush to remove excess, and 1 layer is not enough (because after 1 dip, the brush will remove too much epoxy during excess removal - unfortunately it is impossible to control well enough so that it would remove excess, but still leave enough epoxy that would be equivalent to 3 regular coats). I seem to remember making an experiment many years ago that showed that a single coat, no matter how thorough, is never enough to fully waterproof the part, unless you put it on really thick (which, again, makes coating thickness uneven in different features of the part). So I would still have to make 3 dips to get required thickness with sufficient dimensional control.
Not sure how I could work around to save waste
