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geert_2

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  1. geert_2

    line width

    This option exists in older Cura-versions, with the "minimum layer time" and "cool head lift" options. I don't know if it still exists in new versions? I tried this, but it did not work very well for me. The problem is that if the nozzle is simply moved away while waiting, the filament gets hotter and more liquid in the nozzle. So it starts leaking more, and the more liquid plastic flows differently upon starting the next layer. Further, the added heat during this waiting period, also has to be removed in the cooling cycle, so it does not really help very much. Any differences in layer printing time, or in molten filament temperature, show up as horizontal lines and deformations on very small objects. In my experience, you need a very constand flow rate, constant temperature, and thus constant layer area, for best results. But the nozzle needs to be away from the object long enough, so it has time to cool down. So, we need to print multiple models at the same time, or print a "dummy cooling tower" next to the real model. Ideally, this dummy should have the opposite layer-area as the real model, so the total area per layer is constant for the whole model. This is especially true for very small models, with 100% infill, and thus a lot of stored heat which has to be removed. When models get bigger, this is no longer required, as each layer gets enough cooling time anyway. See these pictures I made a few months ago:
  2. geert_2

    line width

    Originally, I also thought so. But I got inconsistent results when measuring these extruded strands: they could be anywhere between 0.40 and 0.60mm. So, something was off, but I didn't know what. Later I saw a Youtube-video of "nozzle-developers" (I don't remember from which company), and they said this very common assumption was not true. When the plastic comes out of the nozzle, it is still molten. Molten strands of plastic usually have a strong tendency to contract. This is because during extrusion their very long molecule chains are stretched. These chains are then under a very high stress. When that stress falls away (=as it exits the extruder), the molecules tend to relax to their previous shape. So the strand gets shorter and wider. At least, as long as the plastic is still molten. This effect is similar to when you heat most plastics in a flame or with a hot air gun. Especially for thin rods that have been extruded or injection-moulded under high pressure. The width of the rod expands, but the length contracts. I haven't discoverd this, I am just echoing their findings. :-) After watching that video, I tried this on my UM2 printers. I manually fed material through a very hot nozzle (with bowden tube removed). When pushing hard, I could get sausages of up to 0.8mm to 1.0mm, out of this 0.4mm nozzle. When extruding manually at very low temperatures, barely above melting temperature, and at very low speeds/pressures, the expansion is far less, and I usually got to ca. 0.45mm. So you can not use the extruded sausage-diameter as an accurate reference of the nozzle diameter, only as a crude estimation. A better way to measure the inner diameter might be to use copper wire strands, clean the tip (often deformed after cutting it), and then try which ones fit into the nozzle. And then measure the width of these strands with calipers. I have grinded down a soft steel injection needle, and use that. I made it for the purpose of cleaning, but I also used it for measuring. The needle tip of 0.39mm could easily get into the nozzle opening, but a bit further where the needle was still its original 0.41mm, it could not get into the nozzle anymore. So, given the +-0.01mm accuracy of my calipers, and my imperfect sanding of the needle, nozzle opening was quite accurate. Today, a couple of years further, the same needle easily goes up into the nozzle all the way, and it still has some play at 0.41mm, so the nozzle has worn out a bit. If you mathematically want to calculate volume, when feeding electronically via the feeder, you also have to account for the partial slipping of the feeder wheel. The feeder bites into the filament and deforms it. At low speeds and low pressures, these are nice square indents. But at higher speeds and pressures (=more mechanical resistance), the feeder has to push much harder, and instead of squares, these indents become stretched, long diamonds. You can see this deformation under a microscope. So, the effective amount of fed-through material is less than calculated, due to this "partial slipping". To compensate, you need a higher flow-rate. Due to the huge amount of other variables involved, I wouldn't know how to accurately predict or calculate all this. So I use the good old and proven, "trial and error", and use that experience as stable starting point. Any method that gives good results, is a valid method. :-) What I often do for new materials (but you could also do it for new nozzles), is remove the bowden tube and manually feed some material through the nozzle. Then I adjust temperature on the fly, and watch and feel how it melts and flows. This gives me some feeling for the material (or nozzle). Then I print a couple of test pieces, starting from the default values, and on the fly I adjust speed, temp, flowrate up and down, to get an idea of the edges up till where it still works fine, and where it starts to go wrong.
  3. You could do this kind of tests on small test pieces, of only a few mm high. In these tests, provide as much different features as realistic for your typical models: different line-widths, different holes, different extensions (poles), overhangs, curves and roundings, bridges,... If you use bolts and nuts, also model the required hex-recessions into these tests. Idem for dovetail- or snap-fit mechanisms, etc...
  4. In my experience: - If bed temp is too low: the model is very stiff, and the model-edges generally do not lift much, but the whole model may suddenly pop-off the glass, due to insufficient bonding. - If bed temp is too high: the bottom of the model stays too soft, so the edges may lift due to shrinkage forces acting upon the higher layers, and the whole model may gradually peel off the glass. - Walls too thin: walls are pulled inwards (similar to the effect you see), and the models tends to lift at the edges and gradually come off the glass. It is like a cardboard box that you fold inwards. - Not enough infill: walls may be unstable and sag if printed rather hot, and if the bed is rather hot. - Models with high infill (70...100%) rarely deform, althoug they may lift edges if the bed is too hot. - Very small models need an extra "dummy cooling block" next to them, so the print head is moved away for some time, so this small part gets time to cool and solidify. I needed to find a balance where the bed temp is high enough to make the model bond well, but not so high that it deforms, sags, or peels off. The optimal bed temperatures differ from material to material: for PLA it is 60°C, for PET it is 90°C in my system. But this could be different for your printer and materials of course. Thin-walled objects with sharp corners and no infill, need a brim. This could be the standard brim, or a custom designed brim in CAD, depending on the model (sometimes only one little area needs a brim). Otherwise I get the effect you see. Models with high infill, generally need no brim for me. I am not sure that these are the effects you see in your models, but it could be. Have a look at this: the dummy cube (green, top-right) needs a brim because it is hollow at the bottom. Otherwise the walls tend to bend inwards and it tends to come off the glass. The supports (pink and orange) also need a brim because they are very small, only a few millimeters, and they have long overhangs which tend to curl up, making the nozzle bang into these curls and knock the part off. The rest prints perfectly fine without brim. All have 100% infill (except the hollow text and ruler, and the dummy cube). For reference: text caps-heigt = 3.5mm, and its legs are 0.5mm. The green dummy block is to provide enough cooling time for the top-section of the yellow part, otherwise these top layers do not solidify. This prints well in both PET and PLA.
  5. This looks like severe underextrusion, which could be caused by a lot of factors: too low temperature, partially clogged nozzle, worn-out teflon couplers, incorrectly mounted bowden tube, dirty feeder, slipping feeder due to wrong tension, too high speed, wrong filament diameter or setting, too much friction in the whole feeding traject, spool wound too tight (often when almost empty), material decomposing in the nozzle, way too moist, and so on. Somewhere on this forum there is a good list of causes (but I don't remember the name exactly), or google for underextrusion causes on the internet. I made tests some time ago, and yours looks like an extrusion-rate of maybe 50%? (Pictures are a bit out of focus due to taken on a dark winterday, but you get the idea).
  6. The cones can not solidify because the hot nozzle (200°C) is continuously on top of it, and it keeps radiating heat, so the model can't get below 50°C. The "dummy cooling tower" allows the nozzle to be busy for some time, far away from the object, so then it has time to cool down. This greatly reduces this overheating deformation, but it does not totally eliminate it. In very small objects you might still run into it. This is another picture showing the effect: they are 20mm high. The ones printed standing (left, printed in different temperatures and speeds) are deformed due to insufficient cooling. The ones printed laying on their back (right) with several together, are okay. Try various approaches, and various temps and speeds, with and without "dummy cooling tower", so you see the difference.
  7. Even if you could get it to print, you are likely to run into cooling issues, like this below. Unless you would print multiple parts next to each other, or with a dummy cooling tower next to it (=the square blocks in this picture). An option might be to make the walls 0.5mm thick, so they print well on a 0.4mm nozzle, even after converting to STL. And then manually drill out the hole with a separate drill chuck. But it won't have much strenght. I don't have a 0.25mm nozzle, so I can't comment on that. Maybe you might want to search for a totally different solution too, if the purpose allows that. Or go for SLA if it doesn't need any strength (these light-curing resins might become very brittle and might deform under loads).
  8. In my experience, normal PLA gets *much* harder and stiffer after a year, which is a disadvantage if parts need to flex a little bit (like the carabiners above). While PET keeps its original flexibility. How does tough PLA behave in this aspect in the long term, in your experience?
  9. I recommend that you experiment with various concepts on small test models, to see what works for your application. In this spool holder for my UM2 printers, I use several different mechanisms: - Two snap-fits for the main holder (cyan part), where it fits into the printer, just like the original. This snap-fit has long travel-ways, and the openings in the printer have a lot of dimensional tolerance, so it is not likely to break. - The pins (red) are clamped and kept in place by other parts. - The rotating head and bearing are mounted on the main house with a big inox M8 bolt and self-locking nut (mediumblue and darkblue). - Both halves of the bearing-housing (yellow and spring-green) and the bearing itself (purple) are secured with nylon M4 bolts and nuts. - The bearing (purple) is a standard 608 bearing (as in skater wheels). My designs often are a compromise between ease of printing, ease of assembly, functionality (it has to work), and strength and stability. For printing, I want a big flat bottom plate sitting on the glass, and an orientation that does not require too much overhangs and bridges (as I have single-nozzle printers). If supports are needed, they should be in an area that does not damage the model (like in the main cyan housing: supports are required and would be on the inside, and it would be printed with the wide opening down). The anti-unwind clamp shown below also uses two M4 nylon nuts and bolts to clamp things, and it can very easily be printed on its back. One bolt clamps the filament, the other clamps the whole thing on the rim of the spool. By itself, the red models snap-fits and freely slides around the rim of this spool.
  10. If you are on Windows, I would suggest you try DesignSpark Mechanical for editing: this is also free (just requires registration) and is much easier and more stable than FreeCAD. There are a lot of good tutorials on Youtube. Have a look at them and see if you like its concept. Or try any of the free online-programs (I have no experience with them). Then for mounting, in my experience: For multiple-part objects, I often mount them with nylon screws and nuts. Provide the holes and hex-indents for the nut and screw in the model, so they sit recessed and are easy to assemble and disassemble. Press-fitting parts requires a lot of testing to get it right, and PLA (and lots of other 3D-printing materials) tend to creep under mechanical loads, so they deform over time. So the fitting may become loose. Snap-lockings work well for PET. For PLA they work when inserting, but after a year the PLA gets harder, and then the snap-locks break apart when you try to unlock them. 3D-printing screws and threads is hard, and tapping them is even harder, especially in PLA: this melts almost immediately. Glueing with cyanoacrylate works pretty well for PLA. Depending on the circumstances, this can be a good option. One of many possibilities of a clamping bolt and nut (this one has to slide and be adjustable):
  11. When giving lessons or presentations in front of a public, or when doing electronic exams, or research projects or production runs, you definitely don't want automatic updates interfering. Stability and predictability are key. So, for me only manual updates, no automatic, even not optional via settings. Very often the default is "yes", and if you forget to reset this after a manual update, next time you're in trouble. I remember the Firefox 29(?) disaster, the Windows 7 to 10 auto-update disaster, Adobe- and Windows-updates in the middle of lessons, updates in the middle of exams of our students (even though updates were switched off), and so on. The only auto-updates that are funny, are those that fail on billboards in the street, creating a new form of street-art. I also dislike software that splatters its program files, settings and temporary files in hundreds of different inaccessible directories all over the harddisk. In Windows typically: the register, program files, program files (x86), appdata, application data, userdata, local settings, my documents, temp, and tons of subdirectories of these. This is creepy and disgusting. Just have a look at where your browser and office-programs put all their files. So I prefer manual installations from a zip-file: unzip and manually copy to the desired directory. And manual test-runs from standalone versions (sort of portable) where the settings are stored in the same directory as the program. I think all programs should be self-contained, independent units (directories), that you can carry around from one system to another, or move from one directory to another, without any negative side-effects, without losing settings, or without influencing other programs or older versions.
  12. If you purge more, for example by printing ten lines of skirt, doesn't it come through? Or if you manually purge a bit of material before the print? Or is that blob sitting in the way and somehow blocking the movement of the filament?
  13. I usually use "Fine", which suits 99.5% of my models. Only for big balls or smooth curves this gives a bit of visible segments. If this is a problem, I would take "Custom" and select lower values. In DesignSpark Mechanical, after exporting to STL, you can import that STL again, see the segments, and compare it to your original model. And so finetune your export-settings before beginning the slicing and printing.
  14. Bubbles are caused by gasses, could be water, could be others. Ethylcellulose, does that contain alcohol, or chemically bonded alcohol, ether, or something similar? If so, could it be that the alcohol/ether evaporates, or the compound is broken down into its basic substances (alcohol + cellulose, or whatever the composition is)? That might explain both the bubbles and the poor extrusion / clogging. Maybe you could heat a bit of filament to the same temperature with a soldering iron, or on the outside of the nozzle (not inside, so you don't clog it), and see if and how it decomposes and degrades? Or google for how this material breaks down and burns? PS: what is the purpose of printing in this material?
  15. Yes, the last two ones remind me of the time we lived in Jurassic Park. :-) They could as well be real fossilized dino skulls in a swamp.
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