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geert_2

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Everything posted by geert_2

  1. I have come across this terminology in manuals of power supplies, especially high-power units with separate sense-lines. If the ground-wire is too long or too thin, you can get a significant voltage drop across this line. Let's say the ground line has a resistance of 0.1ohm, and the current is 10A. Then you get a voltage of 1V across the ground-line. So the "ground" at the electronics board is 1V higher than at the supply. This was the definition of "ground level shifting". Hense the sense-lines in the power supply, which needed to be connected as close to the board as possible. The concept is also mentioned in manuals of analog to digital conversions, and precision measurements of National Instruments boards, but I don't remember if they used this terminology? But this effect can also happen within boards, if the wires are rather thin, or the currents are high. So, if there is a sensor that uses a common ground path with a power-eating source, then that ground level shifting could cause significant errors if the sensor works in the mV range. Power- and measurement-circuits need separate wiring, which should only connect at one point close to the supply (if using a common supply). I don't know the layout of the UM-boards, so I don't know if this effect plays a role here. But it is a theoretical possibility. And the difference in quality with bed on and bed off, seems to point in this direction, although there could still be other issues of course. And indeed, you can not measure this effect in a closed loop system by measuring the voltages in the system, since the regulation tries to adjust the situation to always read the same sensor-voltages. You need an independant temperature sensor with independant power supply (e.g. battery powered), parallel to the system under test. Basically a separate sensor or thermistor that you connect to the nozzle. Power supplies with separate sense lines were required in the age of mainframe computers, because they would draw enormous amounts of current, and the supplies were located quite far away from the electronics boards. Power wires could easily be 3m long, or more, so you would get a huge voltage drop across these lines. Anyone working on the wiring of such old mainframe computers, had to be aware of this concept. For example, the Aesthedes graphics computer shown below from the 1980's had two +5V 40A power supplies, one +12V 15A, and one -12V 2A, all loaded close to their maximum, so that is almost 80A on the 5V line. But when PCs came along, the importance of sense lines dropped, so I don't know if they are still used today (I haven't done much electronics the last years).
  2. Long ago there has been a discussion if the heated bed could be the cause? If it would draw so much power that the ground-level (zero volt) would shift up, and if the temperature sensor would use that same ground wiring, this could cause errors in the temperature the main board "sees". And then it would adjust incorrectly. But I don't remember exactly on what printer models this was (maybe UM2?), and what the conclusions or solutions were. Maybe you can find that again. It was several years ago. If you could print the same object on a cold bed, using glue, maybe you could rule this out? Then at least any ground-level shifting can't come from the bed. It could still come from the nozzle-heater, but that draws less power, so should have less effect. If this would be the cause, of course. Could be something entirely different also.
  3. Yes sure, anything according to that concept. As long as it separates your hands from the door handle, and it doesn't contaminate your pockets! This is why I wanted a cylindrical object, not an open flat one like most others, so the inside would not touch your pocket lining. My first idea was using left-over pieces of copper tubing, rain/drain-pipe, aquarium-tubing,... Copper tubing would have the advantage of being self-desinfecting: its oxide outer layer is poisonous and soon kills germs; it is sturdy, easy to machine, and can easily be further desinfected or autoclaved if required. Maybe copper-filled filament would also work, but then you lose the heat-resistance. Cutting plastic PVC-table cloth, rolling it up in a cylinder, and glueing or sewing together (whatever works on that plastic), also crossed my mind. So, if you have little ziplock bags, or other sleeves, that should be fine, provided it is handy enough. This below was the original idea, to be made from a piece of rain-pipe. And then it evolved into the "vase", since I don't have piping but I do have a 3D-printer:
  4. I designed a cover that separates care givers from contaminated door handles. The idea is that you carry this cover with you all the time, and slide it over a door handle to open the door without touching it. It protects you from contamination by dirty door handles, and vice-versa. You only touch the outside of this cover, and the door handles only touch the inside of this cover. There do exist lots of other means, but this one provides the best separation, as far as I have seen. And it can stand up vertically (it has to be printed this way), and can be re-used as a little vase, when the crisis is over. Obviously, every person should carry their own, and not share (that would defy the purpose). It can be desinfected and re-used. It fits straight door handles up to 21mm diameter. I designed it for use in our own labs and hospital, not only for the corona-stuff, but also for other chemical or biological contaminations during experiments or dissections. People tend to use gloves when doing experiments, and then they walk around opening doors with their dirty gloves, spreading more contamination than they would without gloves... This simple tool can help. Would you be interested in this too? If yes, I could upload the design files and STL-files. But I might require you to think about a couple of questions, before you are allowed to use it. (Click on the image to enlarge it.)
  5. She looks like sun-burnt now. :-) I was thinking, for simple models you could make an inverse as mould, and pour gypsum into it. Gypsum is a lot easier to sand than plastic, and its stone-like structure hides small defects and layer lines. Then you would have a solid heavy-weight gypsum girl. But that method won't work for this model, because she has way too much undercuts in the hair, and in her fine hands and arms: even with a complex multi-part mould, it wouldn't go. PS: I didn't do any "heat-acetoning" myself. I had considered it, but I didn't want to explode, so I dropped the idea. :-) But I have seen quite a few Youtube videos of it. However, I did both "acetoning" and "heat-treatment", but separately and on different models. For heat-treatment I tried annealing (60...80°C) in a lab-oven, to remove stresses and to increase temperature resistance. But this does not work well for me: the models did shrink in length and expanded in width and height, so they didn't fit anymore. It might work for art though, not sure. If you could get the stresses out from the printing and uneven cooling, it is less likely to split. The heating and cooling should be done *very slowly*, so everything has time to settle. If you don't have a computer-controlled oven, I think it is best to do this on a manually heated build-plate in the printer, and cover front and top with plastic. Or put a little box over the model. I also tried a heat gun to smooth, because this did work well on vacuum thermoformed models in the past (it was the officially recommended method). But this does *not at all* work on 3D-prints: it melts the outer layer (as desired), but it also heats up the entrapped air bubbles, so they explode and cause little craters on the surface. Making it much worse than before. Similar to printing wet nylon, but even more ugly. And it causes brown burnt spots. So I don' do heat-treatment anymore. For smoothing I tried dipping testmodels into acetone for some time, but this caused huge cracks, even diagonally through layers (not following the lines), and weakens the plastic and basically destroys it. So the only smoothing method that I use now and that works very well, is yours: brushing-on acetone. And then I wipe it with paper tissue to remove the whiteness, before it is completely dry. Then I can get off most of the white residu. Sometimes I do a second brush, but that doesn't seem to improve smoothness very much anymore.
  6. I think effects like this might also be caused by fluctuating temperature, because that changes viscosity and flow-rate (=less back-pressure when more liquid). And maybe also by a worn-out white teflon coupler? But I don't know a good means to reliably measure the temperature from the outside? A thin and heat-resistant sensor that you could move into the nozzle from above might be best? (Of course after removing filament, removing bowden tube, and cleaning the nozzle.) And then let the printer run, "printing" this same object. Thus it goes through the same moves, same temperatures, same heated bed, but only without filament?
  7. I would suggest: cut out a small part of this model with some text for testing purposes only, so you don't waste time and material doing the whole thing. Try printing at 25mm/s, cool (but without underextrusion), and in thin layers (0.08mm...0.12mm). See what that gives? 3D-printing is always searching for a balance between quality and speed, but often they don't go together. So you will have to chose your priorities... In my experience (with UM2) such text on the sides always comes out poor, due to ringing effects and widening in corners when slowing down. And you never get sharp corners anyway. Text on top of flat surfaces comes out *much* better. So if you could move the text to the flat horizontal plate halfway (if that doesn't get covered later on), this might be an option? Photos: Text on top of model: these characters are ca. 7mm high. Orange PLA. Left: smoothed with acetone. Center: heat-treated with hot air gun in attempt to smooth (this damaged the model, so don't do this). Right: untreated, as printed. Printed at defaults for PLA: 50mm/s, 210°C, flow 100%. Printing speed and layer thickness tests: Top row printed at 50mm/s, bottom row at 10mm/s. Nozzle 0.4mm. Material is transparent PET. Model is 20mm x 10mm x 10mm. Watermark text (hollows) is 3.5mm caps height. Layer-thickness from left to right: 0.4mm, 0.3mm, 0.2mm, 0.1mm, 0.06mm. So the only way to get good quality, is by printing slow and in thin layers. And then reduce temperature to prevent overheating, leaking, or decomposing of the material in the nozzle.
  8. I like the girl model. Have you ever tried painting such models in a gentle sort of "marble" technique? So it looks like stone or marble? I think that might work for this girl, and it might conceal layer lines and defects. I once knew an artiste who turned lightweight wooden crates into "heavyweight marble" bases for displaying sculptures. These bases were hard to distinguish from real marble. But I don't know how she did it, I only saw the results, not while applying it. Might be worth trying that? I also like the "old" look of the partially painted and sanded model. Maybe that would also be an option: paint multiple layers in slightly different shades of grey, and then sand off a couple of them? That too would help conceal printing-lines, in the way military camouflage hides the shape of vehicles or aircraft.
  9. I think it will be hard to find something that has the flexibility, chemical inertness, long life, temperature resistance, stickyness and grip of silicone. What you could do, is print a mould in PLA (or whatever), and pour your own silicone sleeves in it. Then you still need silicone of course, but at least you have the design flexibility you want, that off-the-shelf part can not give.
  10. I would suggest you embed the pictures in your message, instead of using external links. Then you are more likely to get answers. While writing your text, place the cursor in the desired spot, and drag and drop the picture from Windows Explorer into your message. I guess this should also work on a Mac or Linux. Due to the enormously increased phishing and hacking since the corona-crisis, people are less and less willing to click on links from unknown sources.
  11. For those who print in PLA: do not leave these masks in your car in the sun, or behind any window. Even not on mild spring days. Because it *will* deform due to the warmth, especially when under mechanical load: PLA starts getting soft from ca. 50...55°C, and that is reached in a car as soon as the sun comes out. Don't ask how I know. :-) For the same reason: Do not clean the masks with hot water or steam jets, and do not dry in hot air. Comfortable handwarm water is the maximum. Also explain this to the people who are going to use those masks, and leave a written note in the package. Most likely those people are not aware of this, and they are going to expect the plastic to be similar to Lego bricks (ABS) or or plastic bottles (PET), the plastics they are used to. Which it is not. Also make them aware that these masks do not protect against any bacteria or viruses. They only protect from direct spats (blood, spit, pus, acids,...) or from objects flying directly towards you (when drilling, sawing,...). Even though this seems totally obvious for us technicians and engineers, it doesn't occur to a lot of non-technical people. Every day I see people wearing mouth masks that are no better in filtering viruses than chicken wire or mosquito nets. Or sometimes they have a suitable mask (FFP2 or FFP3 without exhaust valve in Europe, which I think is similar to N95 or N100 in the USA?) but wear it only covering their mouth, and then they breath through their nose of course... While endlessly queueing to enter a shop yesterday, like in the heydays of communist DDR during the Cold War, I saw tens of people wearing masks, but not one wearing a correct mask in a correct way. Not even one. Seems like the virus and hysteria in the first place destroys their brains and common sense... However, for me, it seems it infected my tolerance for stupidity. :-)
  12. Hmm, synthetic plastic food and colorants. Can't be bad. :-)
  13. Another thing that might help, is when you keep sitting next to the printer. Then when it is reaching the top of the models, gently and gradually lower the flow-rate of the extrusion, via the Tune-menu on the printer (name might differ on your printer, depending on the model). Reduce flow-rate very gradually to 95% or 90%, try what works for you. Also, manually reduce temperature as it reaches the top; and here too: try what works for you. The shape will still not be good, but it will overextrude less. My test demos were printed with about standard settings, thus way too fast and too hot for these tiny cones. But they do show the effect very well. :-)
  14. These "insect antennas" come from the nozzle leaking while traveling through air. Upon arriving at the next wall, it deposits that leak as a drop on the side of the wall. Upon the next layer, the drop is deposited on top of the existing drop. And so on, causing a nice insect antenna. If you watch closely while printing, you can see the antennas growing with each nozzle pass. So you need to tune your settings for less leaking while traveling (print slow, cool, thin layers, enough retraction, travel fast through air), or for not traveling through air at all, if the model allows it. But I have never printed ABS (apart from one test cube), so I can't give more specific tips. Here a few pics: one closup, and the other showing the dimensions of the piece related to other parts and a ruler (in mm and cm). This is printed with a 0.4mm nozzle, in PLA, after I forgot to switch retraction on.
  15. My standard pic to show the effect of a dummy cooling tower (ruler is in mm and cm). In addition to what gr5 said, printing in thin layers, slow and as cool as possible also helps. Also, do not use 100% infill but rather 50% or less. But I could never totally get rid of the effect. At some point the hot nozzle just keeps sitting on top of the tiny model, preventing it from cooling down and solidifying. That is a limitation of this printing method.
  16. A few questions: Are there any soft leather, rubber or cloth straps as interface between the 3D-printed parts and skin, to increase comfort? So that the hard plastic does not continuously rub the skin, causing damage? I have worn safety helmets in the past, and they all had a hard outer shell for protection (obviously), a soft inner plastic frame for good fitting around the head and for shock-absorption, and then a thick, soft leather strap between that soft plastic frame and the skin. Otherwise it was not possible to wear the helmet for a prolonged amount of time, without getting wounded. How is that handled with these visors? (I have also wondered about this for the 3D-printed respirators, by the way: for a good fit without leaks, and for comfort and not getting wounded, they also need a soft liner. But I have never seen it mentioned?) Related: is the inside sanded or chemically smoothed to get rid of the most layer lines, for improved hygiene and comfort? Out of curiosity: what is the purpose of the lower strap? We usually don't see that on commercials masks? The design could also work as well for hobby use like gardening, working with a chain saw, or similar. It does not protect from dust or fumes, but it does protect against direct liquid spats and bits and pieces flying around.
  17. At big oil companies, but I don't think it is a good idea to go buying a vat of 160 liter... 🙂 And there are so many different specs for different purposes. I just use hydraulic oil because I had it for my hydraulic machine (and it is on-spec for that hydraulic machine, not necessarily for any other equipment). If I had to buy fresh oil, only for the printer, I would probably go for something close to the official Ultimaker specs: some light machine oil, like used for lubricating bike chains, fine equipment, tools, and similar. You can find that in car-accessories shops, or do-it-yourself hobby shops (at least here in Europe). No car engine oil (=way too thick), no ultrathin dislodging oil (could be corrosive and does not lubricate well), no real sewing machine oil from a textile shop (this is the one that turned into gum here), no brake fluid (this is no oil at all, but a different kind of high-temp liquid), no grease (too thick), no high-temp oil,... Note that I am not related to the Ultimaker-company, so my words are not the official company policy; it's just my personal experience as customer and printer-owner.
  18. I would suggest you add pictures to your post. Then you are more likely to get good answers. You can drag and drop JPG- or PNG-files directly from Windows Explorer into your post while editing. Set the cursor on the desired place, and then drag the picture into there. The reason is that the amount of phishing and hacking has increased a lot since the corona-crisis, so people are less and less willing to open unknown files from people they don't know very well. Without having seen your design (for that reason), my general experience with snap fit things is that it mostly depends on the material it is printed in. PLA works a couple of times, but then tends to break, while PET will keep working longer, provided that the design is good. But the layers may hinder smooth sliding, depending on the printing orientation. Not a snap lock, but it goes into the same direction. This carabiner in PET (green) keeps working well. In PLA (cream) it tends to crack after some time, and it tends to deform permanently.
  19. Indeed, I haven't seen this one. :-) Seems like I should bring my knowledge about tools up to date. The inserts I have seen on Youtube videos, but not tried myself yet. If you have used them, do they stick well, and does the molten plastic reflow around the ribs well? I have also seen a similar concept, in which the brass insert had to be screwed into the plastic hole, with a sort of self-tapping one-way screw on its outside, so this would get stuck and stay in there. But again, no personal experience.
  20. I tried tapping too with straight taps (I had never seen those spiraling ones, didn't know they existed), but indeed it didn't work well. Even not when tapping manually and reversing very often: 1/4 turn forward, 1/8 turn backwards. Chips would get stuck and the plastic would melt (even at very low speed, lots of cooling time and lubrication). Also, threads were very weak and got worn-out very soon (M3, M4, M5). So for most of my models, I now use standard nylon M4-screws instead, with a caged nylon nut that can not fall out. This goes a lot faster, and it works better: the thread (nylon nut) is much stronger than a 3D-printed and tapped one, and it can be replaced if required. Mostly variations on these concepts: 1. Fully caged nut; the backside of this opening is closed, it is only open on top. If the opening is tight enough, the nut will even be clamped. If slightly wider, it will wiggle, but not fall out (unless you totally remove the screw and hold it upside-down). 2. Another variation on the same concept: 3. Recessed hex opening for keeping the nut. This is a test model to try-out required tolerances for an M4 nut (ca. 7mm diameter between flats). 4. I haven't tried this yet, but someone (I forgot the name) suggested using "metrinch" cages for clamping the nuts. They seem to wear-out less than traditional hex holes, and allow tighter tolerances, since problems with 3D-printing are mostly around corners.
  21. Depending on the firmware-version the "Abort" on the UM2 can be plainly visible during printing, or in the "Tune" menu (I have both). In some UM2 there was an issue with driver chips overheating: then they would shut down for a few moments until cooled down, and then continue. Mostly with the Z-axis (up-down). I had this on one printer a few times in hot weather, when doing long print runs. I reduced maximum current a little bit, and since then it never happened again. I am not sure if this could happen to the X- or Y-axis too? But first try the other solutions, and only consider this as a last resort if the other things wouldn't help. Not only no oil, but wrong oil on the rods could cause issues too: I once had "thin oil" that soon dried into a sort of very sticky gum. So much so that I almost couldn't move the head anymore, it was almost glued to the rods. That caused skipping too. Then I cleaned the rods thoroughly with isopropyl alcohol. And now I use surplus hydraulic oil, as used in hydraulic test benches and machinery. I don't know if this is the best oil, probably not, but at least it lubricates well, has anti-corrosion additives included, and it never dries out. It works for me. I just regularly refresh the oil because of the dust that gets collected on the rods. When lubricating, do not pour oil on the rods, but rather add it to a tissue, and then wipe the rods with the tissue (without touching the belts). You do not want oil dripping all around in the printer: it would destroy bonding to the glass.
  22. I have tried these: - PLA, orange and white: bright colors, printed very nice and smooth, but stuck a little bit less to the glass than Ultimaker or colorFabb PLA when using my "salt method" (=wiping glass with tissue moistened with salt water). Seemed to be slightly less temperature resistant than other PLA. Otherwise no problems. Prints at standard speeds and temps. When burning pieces in a metal spoon on a bunsen-burner, it leaves very little black ash: just a little bit of dry, loose powder that can easily be wiped off. So, the same can be expected in the nozzle. - PET: prints okay, but doesn't like to do overhangs without cooling: when liquid it is more rubbery than PLA, so it does not make a nice string but rather snaps and folds back into a blob onto the nozzle. So it has trouble closing gaps. I don't know if this is brand-related or rather material-related, because I have no comparison. Could be just a general PET-characteristic. I use this PET for printing carabiner hooks (more flexible than PLA, and less creep), for printing watermark logos (transparent), and for stuff in the car (can withstand summers, contrary to PLA). Prints best slower and cooler than standard, I generally use 215...225°C and 25...35mm/s. When burning in a metal spoon, it leaves a thick glossy sort of varnish, that is hard to remove. So, when printing too hot, this might also occur in the nozzle, I guess. Again, not sure if this is a brand-characteristic, or PET-characteristic. Thus print cool. - ABS+: only printed one test-cube with it. Less strong than PET or PLA, way softer also. Warps a lot and smells bad, as you could expect from ABS. I can't compare with other brands, as I never printed any other ABS. But I would use PET or PLA instead. I think the PLA and PET are worth a try. I wouldn't use any ABS, unless really necessary. Models below are in ICE-PET: ,
  23. I think the extra width that you measure might come from ringing- and thickening-effects around corners? When slowing down to take a corner, the nozzle inside pressure does not immediately drop, it lags, so the nozzle extrudes a bit too much compared to the now slower speed. This makes corners thicker. Analog for ringing, sine-wave mechanical oscillations around corners. This could easily explain 0.2mm extra width. Also blobs and overextrusion could explain that, if they would be present. Also, "elephant feet", the sagging of the first layers, could make a model seem wider than it is, if you measure it. Another option would be that calibration is off. But as gr5 said, it really draws its strokes inside of the model-edge, not centered on the edge. It takes its nozzle-width into account. Similar to image-editing programs where you can stroke a selection with settings: stroke inside edge / centered on edge / outside of edge. Here it is inside.
  24. You can always disable all brim in Cura, and design your own in CAD, exactly how and where you want it. I often do this when I want some features to have brim, and others not, or if I need irregular brim.
  25. I would say: start by marking all pulleys, belts, etc. with a marker. And see if they move relatively to each other. Or otherwise, check if the driver-chips don't get too hot (e.g. cooling fan not working, vents blocked), so they do a temporary thermal shutdown, until temp drops again to a safe level. Check if the cables to the steppers are okay, no bad contacts? These are the first things that come to mind, but I don't know your printer, so there could be other issues.
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