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Everything posted by geert_2

  1. To me this also looks like overextrusion, but it is difficult to see on the white. If you watch closely while printing, does the nozzle sort of "wade through the mud"? If yes, it's overextrusion. Probably you will also see accumulation on the nozzle, which then sags and gets deposited on various parts of the print, thus worsening the effect. Try printing a test plate of let's say 20mm x 20mm x 10mm, at 100% infill. And then play with the settings while printing: change flow rate, nozzle temperature, fan percent, printing speed, on the fly. Until you get it right? I usually print PET at 215...220°C, 30mm/s, no fan if the model allows it, 90°C bed temp. If I need fan for overhangs, then the temp has to be a bit higher, 220...225°C. My brand of PET has a tendency to overextrude when changing from printing long trajects to small details at high speeds: it seems the pressure in the nozzle can not change fast enough. The molten PET seems to be more rubbery than PLA, like chewing gum, and react slow. So normally on my UM2 the overextrusion happens on very short trajects only, not on long. It is when the printer has to frequently slow down to change direction. Then the built-up pressure in the nozzle can not immediately go down, resulting in temporary overextrusion. At least, that is how I understood it.
  2. For complicated designs, you can always design custom brims, custom supports and other custom structures in the CAD file itself. And then switch off the automatic brims and supports in Cura. Then you have full control. For example if you want brim on some areas, but not on others. Or if you want special supports with holes suitable for your pliers and tools, to make removal easier from the inside of complex models. It will take some trial and error (do this on tiny test plates or so), but once you have found a concept that works well for your application, you can re-use it quickly. For example in this tiny model (key chain), the orange and rose custom supports have some brim, and the green dummy tower also. The dummy tower is to provide extra cooling time, otherwise the top of the yellow model does not solidify well; it is too small. I don't want to risk a model being destroyed because a dummy tower or a support comes off, so they get brim. But the rest don't need any. Further, these supports need that extended shape, otherwise I can not grab them with pliers and wiggle them loose, and the space is too small to get in there with a knife. So I provide all this in the CAD file. For reference: text caps height is 3.5mm, and text legs are 0.5mm wide.
  3. Note that the pastel blue and green models shown above are not mine, but from neotko. But they look great indeed. My dimensions are in this pic below. The character sets (RSDOC-format) and testplates (STL) can be found here: https://www.uantwerpen.be/nl/personeel/geert-keteleer/manuals/
  4. In my very old Cura, it goes like this: Let's say these are the settings: - first layer = 0.3mm - layer height = 0.1mm - bottom thickness = 1.0mm Then it does: bottom = 1 x 0.3mm + 7 x 0.1mm = 1.0mm in total I would guess it is the same in Cura 3.6? You should be able to see this in layer preview, if you make a small test object?
  5. I always thought that this alternating was the desired behaviour? When the slicer encounters the first edge it turns the material on. At the second edge = material off. Third edge = on, fourth edge = off, etc...? Otherwise I think it has no way to know whether it has to fill a model or not, since the STL-file only consists of triangles, if I understood that well? Maybe software-engineers like smartavionics or ahoeben could shine a light on this? Anyway, I use this feature to make hollow text and watermarks inside a model. I design the watermark separately, outside of the model, and then I just move it inside the model. After export to STL it is automatically sliced correctly, thus Cura automatically hollows-out the text. Like here in this example, where I have copyright notices, a ruler, and some decorations as watermarks inside the model, a keychain. Or in the transparent testblock below. (For reference: text caps height = 3.5mm; text legs are 0.5mm.)
  6. Have you tried printing this in PLA? Then you know if it is related to the material, or to the model/slicing? Or else, design a couple of test pieces, with only the faulty parts, plus a dummy block to provide enough cooling time per layer. In some of those test pieces, model them as shown here, as separate models. In the other test pieces, do connect both edges of the openings with a thin plate to each other. So the printer does not have to stop printing, and does not retract, but can keep going. Then you would have this sequence: dummy block --- connection to the test piece --- test piece itself --- connection to the next test piece --- test piece itself --- connection back to the dummy block. So, no gaps, no retractions (theoretically and hopefully).
  7. Have you checked if the fans are running freely? Not (partially) stuck by sucked-up filament hairs and strings? Or no filament or other debris is covering the exit or inlet holes, or something mounted incorrectly, or something else along this line? What could help, is putting a desktop fan in front of the printer, at its lowest speed setting. This provides a huge amount of fresh air at low speed. But of course, this does not address the source of the problem. What also helps for overhangs, is printing in thicker layers, e.g. 0.3mm instead of 0.1mm. But that may not always be desirable for the rest of the model. Printing slow and cool also helps.
  8. Just a thought: is there no way to overrule that in the gcode files, or via gcode files? Or is it executed even before the gcode files are read?
  9. To me this looks like overextrusion, maybe due to the nozzle being a little bit too close to the bed? But this is not necessarily a bad thing, because then it is squeezed well into the bed, thus giving a good bonding, and probably a nice underside too? At least, that is what I get on my UM2 if the nozzle is a bit too close. (I don't know your printer.) Personally I wouldn't care too much, if this is only on the first layer(s), and does not show up through the whole print.
  10. Another thing that just comes to my mind: did you export it to STL as a solid, or as a bunch of separate surfaces? I don't know what the mathematical difference is, but in DesignSpark Mechanical there is such an option: "Connected Mesh" vs. "Simple Mesh". Maybe in FreeCAD too?
  11. I have read that PLA gets harder and more brittle due to changes in crystal structure. Over time it changes from rather amorphe to rather crystaline. This makes it harder but more brittle. Placing it in an oven for some time, could sometimes revert the crystal structure back to amorphe, to some degree. However, it could also have the opposite effect, speeding up the crystallisation... The same mechanism is said to be at work in plastics that you need to put in boiling water, after which you can mould them by hand for some time. When cooling, they stay mouldable for quite long, before the crystal structure changes back to crystalline and they get hard again. Often the color changes from clear to opaque white too. So you need to put it in cold water to solidify it faster. That is how the manual explained it. Then there is hydrolysis, where water-absorption breaks molecules. I think this is a bit similar to UV-light breaking molecules down and making plastics brittle? (Although I am not sure how this would apply to PVA, since this is basically glue? Or maybe it is a reversible process?) I am not a chemist; so this is just what I read on the internet and in manuals. Anyway, in my experience, 3D-printed PLA snap-fit lockings that worked very well when freshly printed, do break when using them after a year: they have become too hard and too brittle, and they don't bend anymore. In addition, I found that in PLA-filament under continuous stress, micro-cracks do develop. This happens for example when you straighten a tightly wound piece of filament, and you keep it straightened (fixed) by clamps. Under a microscope these cracks are clearly visible. So I would not be surprised if some of these mechanisms could also be at work in PVA? But which ones, and in which proportions? I would welcome the views of plastic-engineers from big plastic manufacturers (Bayer, BASF, DuPont, Eastman,...) on this. Photo: micro-cracks growing in stretched PLA filament. This is colorFabb natural 2.85mm, but I have also seen it in other PLA-filaments. Photo taken through a microscope. Maybe this also happens in PVA? Try cutting off a piece, stretch it under a microscope, and see if you can see any cracks growing? Then try again at different temperatures and moisture-levels?
  12. I haven't used FreeCAD for STL-export, so I can't comment on this specific issue. But in general my experience with complex shapes like this is that if you need to combine things (="union" function), make them *overlap* each other first. If the edges just touch each other, the software is more likely to have difficulties sorting out where the edges belong. Probably due to rounding errors? DesignSpark Mechanical usually gives an error-message that it can't do the combine, so it refuses, but it has never created invalid models. However, early versions of other commercial programs I tried, did sometimes create invalid models. And SketchUp nearly always creates invalid models, since it wasn't ment for 3D-printing anyway, but that is another topic... Did you make this screw by combining a rod and a spiral? If so, try again with a royal overlap?
  13. This could be an interesting method indeed for mould making. Did you try to smooth the PVA with water to remove layer lines and artifacts? And if so, did that work well?
  14. Yes, this is also a good idea, provided that the material can be glued well (PLA, ABS). Not for nylon or PP, or PE. In that case I would design alignment features into the model, so that both parts can easily be mated up. For example by cutting it along this blue line. Add a ~0.2mm tolerance gap (this depends on printer accuracy, material flow, temp,..., so you may have to experiment).
  15. I do a way more gentle pull than the traditional brutal cold pullings. Maybe this could help? - Manuall put print head in a front corner - Heat up nozzle (with bowden tube removed) - Push through some filament - Dial temp down to zero - Stop pushing filament, do a slight "manual retraction" of a few mm - Let cool down until nozzle is at room temp (25°C or less), so that the inner core of the filament also cools down well - If you have oil-free compressed air from a compressor, you can blow onto the nozzle to cool faster (but never use "air" from spray cans: this is often very explosive gas, and you don't want that on a hot nozzle) - When cold, gently try to rotate and wiggle the filament - Heat the nozzle to 70°C (for PLA, other materials need other temps) - While it is heating up, gently keep wiggling and rotating the filament until it comes out - Repeat as required. This method requires almost no force, but in my experience cleans as well as the original brutal cold pullings. The deeper cooling cycle to room temp is to totally solidify the inner core of filament. So, when heating up again, only the outside is molten, but the inner core stays strong and solid. The gentle pulling prevents damage to the nozzle, displacement of the coupler, and bending of the rods. It should also prevent breaking the filament. More info and pictures here (scroll down a bit): https://www.uantwerpen.be/nl/personeel/geert-keteleer/manuals/
  16. Or resonance due to a particular model geometry? Or due to the nozzle banging into curled-up overhangs, or into a half-detached print, or so? Were the models still stuck to the glass? Or had they come off (maybe you can see if they came off before the jump, by analysing any spaghetti)? If you can get it to work again, try the same model again, but now stay around? Anyway, it seems like a good idea to glue or screw an edge to the tables. Or maybe put rubber antislip/antivibration feet or mats under it?
  17. Maybe you could design it in the CAD file, like I often do for custom supports in hard-to-access areas? Then you can give it all the features you want. Question: how do you remove such a thick brim? Isn't that too hard to cut with a knife?
  18. geert_2

    Food safe

    The biggest problem will be the layer lines and the little pockets of entrapped air. These will make the chocolate mechanically stuck, thus hard to remove. And they make the mould difficult to clean, and thus promote bacterial growth. So, if I had to do this for myself, I would select a material that can be post-processed very well, and that can be smoothed very well. And it should be temperature resistant up to at least 80°C. Probably I would try ABS, even though that gives of chemical fumes while printing. But when cold, it should be chemically stable. Lots of kitchen stuff are in ABS, like egg-cups, citrus presses. And ABS can be smoothed very well with acetone, into a really glossy finish without layer lines or openings at all. PLA won't be heat-resistant enough and is more difficult to smooth. Alternate solution: print the negative of the mould (thus make a mould of the mould), carefully smooth and post-process that, and then make a silicone mould to pour the chocolate into. Silicone is chemically inert, food-safe, heat-resistant, very flexible (easy to remove the chocolate), non-stick.
  19. For people who do not have a mechanical engineering background, technical specifications such as hardness, tensile modulus, impact strength, etc..., are very hard to read. These numbers have no meaning because they don't relate to real-world materials for non-engineers. So, it would be good if all manufacturers could add a description *in plain language* of how the material feels, and how strong and flexible it is. This can best be done by comparing it to very well known standard materials like PLA, ABS (Lego bricks), PET (Coca-Cola plastic drink bottles), LDPE (lids of food boxes), PP (fridge boxes), car tires, rubber bands, human flesh, etc... A dummy example: Material ABC-123: - feels a bit waxy, similar to PP (polypropylene, fridge boxes) - glossy look, similar to PET (Coca Cola plastic drink bottles) - impact strength similar to ABS (Lego bricks, Playmobil) - flexibility similar to PP - good layer bonding similar to PLA and PET - low warping similar to PLA - mechanical post-processing: similar to ABS - glueing: cyano-acrylate, hotgun, most plastic glues - chemical post-processing: dissolved by strong solvents (e.g. acetone, thinners) - can easily be painted - chemical stability: can withstand mild acids and bases, is dissolved by solvents - heat resistance similar to ABS, starts to deform from 110°C, melts around 150°C, really liquid at 200°C - printing recommendations: nozzle 180...200°C, bed 80°C, speed 40mm/s, travel speed 120mm/s, fan 50%, layer height 0.1mm, good bonding to glass bed with product XYZ-456. - [then a couple of pictures of the filament, and of printed models, in an office environment] All this could go in the general description, so that we can estimate at a glance if the material might be suitable for us, without having to open all attachments with detailed specs. The pictures should be taken in an office environment, surrounded by common office stuff, so we can easier compare it to the real world. (Studio-lighting, althoug beautiful, often does deform the appearance and it makes it difficult to really interprete the pictures.) Could you consider this?
  20. A minimum layer time may not be enough: if the object is very small, the nozzle may keep sitting on top of the object, and radiate heat, so it can not cool down and solidify. Setting the nozzle outside of the print is also not good, because then it leaks, causing defects on the outer walls. And this interrupts the flow, causing different material temperatures and viscosities, which also shows up. The flow also has to be as constant as possible. So that is why printing a dummy block next to the real model is usefull. Further, in my experience it is best to keep the printing area per layer constant for small objects. Sudden changes from a large surface to a small one, also show up. So, for small objects that need more cooling time, I often make the dummy block less or more into the inverse of the real model. Then the total printing time per layer is constant, and while the nozzle is printing the dummy, the real model can cool. I recommend adding a flange to the base of the dummy, to make sure it sticks well and is not knocked over. This first pic shows the effect of not enough cooling (dimensions mm and cm). The pictures below show dummy blocks: the theoretical concept, and a real example.
  21. In DesignSpark Mechanical there are settings for STL-quality: coarse, medium, fine, custom. Coarse gives the same as you show here. Fine is okay for 99% of prints. With "custom" even better results can be got, but then the amount of triangles and thus the file size of the STL go out of the roof. Search for a setting like "STL export options" or something similar.
  22. Do you mean the ribs on top of the supports? I usually design them on a 0.5mm grid, so they are usually 0.5mm wide (a bit wider than my 0.4mm nozzle), and 1.0mm separated from each other. But this is not critical, and occasionally they may differ in my designs. The vertical gap between the support-ribs and the bottom of the real model usually is 0.2mm to 0.3mm. The idea is to get the supports as close as possible to the real model for best accuracy, but without fusing them. So, dimensions may depend on the material you use, printing temp and speed, amound of fan (more fan = more cooling = less fusing). I would suggest that you make several small test pieces with slightly different dimensions, and then select the one that works best for your situation. It may require some trial and error...
  23. Yes, this is a good point to consider. My prints usually require 1m to 3m of filament. So I rarely have more than 1.5m left over. But if you have half a spool, but just not enough for the next large print, then indeed it makes sense.
  24. This is probably because the bonding is not so good? Can you see it wrinkle already while printing these layers? I have noticed that in PLA from the ICE-brand the outer edge also curled up a little bit, although otherwise it printed very well. So there seems to be quite a difference in bonding from PLA brand to brand. For Ultimaker and colorFabb PLA bonding was better for me.
  25. In my tests I wiped off the white residu with a paper tissue a few minutes after the acetone was dry, but the PLA still flexible. But I have to be very carefull how I handle the model, otherwise my fingernails get imprinted in it. If I pick it up too soon, when just dry, then my fingerprints also get into it. So, this is a great way to immortalise your fingerprints in PLA. :-) There is a spot where the model is hard enough to handle but not too hard, where wiping off works best for me. But I have 100% filled models, so the inside stays hard. I am not sure how it would work with your hollow models with thin walls. It is the left model in this pic. The middle one was heat-gun treated (which doesn't work: trapped bubbles expand due to the heat and explode into craters), and the right one was untouched, if I remember well. For reference: the plates are 10mm wide, and text caps height is ca. 5mm. This is colorFabb Dutch Orange, but it also works with red and yellow.
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