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geert_2

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Everything posted by geert_2

  1. 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...
  2. 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.
  3. 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.
  4. 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.
  5. Another option would be to just print everything, and then compare them to the design on the computer-screen and puzzle... :-) I would not do this for the main buildings for clients, but if it is for the surrounding decorative buildings ("filler buildings"), which often don't matter too much, this could be done.
  6. I once tried melting PLA together with this tool. It worked fairly straight forward: cut both filament ends in a 90° angle, put them in the guides, and keep them in place with two fingers. Heat a knife in a bunsen burner, and insert it in-between both ends. A soldering iron should also work. Slide the ends towards the knife or soldering iron, let them melt, remove knife/iron, and push molten ends together. Keep a while until cool. This goes easier than describing it. But then I had to cut off the inevitable flanges and smoothen these out with a cutter knife or Dremel-like tool. It worked well, but it takes so much time that it isn't worth the effort. But this technique could be usefull if you want a vase or toy with colors that change over and over, on a single nozzle printer. So, now I use these ends for atomic pulls, like kmanstudios and several other people here. If you have kids, you could soften these pieces, and make toys out of it, or wrist bands, etc.
  7. More than 50°C is too much for PLA, it will warp. It is best to stay below 45°C. While ethylene oxide may sterilise well, I am not sure if it is a good idea to use it. It is extremely explosive and requires very little ignition energy. It can explode in concentrations between 3% and 100%, contrary to most other gasses which only explode between 5% and 15% or so. The smallest spark is enough, e.g. from dropping a steel screwdriver. Almost all production plants in the world have suffered severe explosions. The plant I have worked in, also exploded a year after I left in 1986, and that shock was felt like an earthquake over 30km away, even though it was only one destillation column that had exploded. And even though the column was designed to "take off like a rocket", instead of exploding. According to witnesses it did take off indeed, but then still exploded at 500m high in the air... When in storage, ethylene oxide may spontanously decompose, or polymerise, both of which are very exothermic and often lead to explosion. Thermal runaway can occur from a bit above 50°C, if I remember well. Shaking it (e.g. during transport), or any contact with almost any other material may also lead to exothermic reactions and explosion, if in sufficient quantities. Usually, contact with other materials lowers the thresholds, making it more dangerous. Further it is chemically very agressive towards human tissue: it penetrates the skin deeply, without you noticing it. And then it starts burning and eating away the flesh, without any way to stop the reaction. Probably that is why they use it to sterilise? Spilling is not a problem if you spill a drop on your bare hand: it feels ice-cold and evaporates immediately, before it has time to penetrate. But if you wear gloves or clothes, it can not evaporate, and then it penetrates the skin. It goes through chemically resistant safety shoes, if you step in a puddle. We had several people severely wounded by these chemical burns. Know the risks before you start playing with this. If using ethylene oxide, all equipment should be equipped with good flame arresters, and be explosion-safe. And all bottles should have good safety valves, even small glass bottles. Maybe you could look into things like "isopropylalcohol + water" instead? They are less dangerous. I don't know anything about sterrad.
  8. Yes, I was going to say it looked too big indeed... :-) But in my model, the connection strands are not plates, but just sort of tiny "hairs": they are 0.5mm wide (=a bit more than nozzle-width), 0.2mm high (=2 layers of 0.1mm), and 1mm long (=the distance of the gap). Before you print the whole box, try the concept on a small test piece first, to find the best dimensions for your materials and printer. The concept is clearer in this pic, where only the outer supports are shown. For reference: the upside-down stairs and the table plates are all 1mm. For small models, these tiny strands provides enough strength, and they are easy to cut.
  9. Wow, if all that white is salt, then indeed you used way more than I usually do. I prefer a thin layer that is almost invisible: after applying the salt, usually my glass looks a bit "dusty" like a drinking glass that has been unused for a couple of years. For me, the first pic below (orange testmodel) has already too much salt; while the last one (with label "the salt method") has the optimal amount. Hardly visible when looking down vertically on it, and a bit misty when looking horizontally at it. But of course, it is best if you try different methods and choose what works best for you. Different materials, printers, and environments (temp, moisture) may all have an influence. For other materials than PLA, I recommend that you carefully watch the print, and don't leave it alone, until you know how well it sticks, or not. Or do a testprint like in the first pic, with inverted prisms: due to the very small bottom area to stick to the glass, and the very large overhangs creating huge warping forces, this is a good bonding test. Also, the overhangs tend to curl up, and the nozzle tends to bang brutally into these curled-up edges, making this a very hard test.
  10. Most silicones I have seen can withstand 200°C, and up to 260°C for a very short while. But molten nylon is likely to be too viscous at this temperature: more like thick sirup instead of water. You would have to inject it at very high pressures and speeds (which would deform or damage the silicone). It will also be very difficult to get entrapped air out. And indeed, it will cool quickly upon touching the mould walls, making it difficult to fill the mould. You would need liquids that chemically cure, like ahoeben said. But then still make sure they are not too exotherm, as this may damage the mould, or the epoxy/PU may catch fire. Also, saturate the silicone mould with silicone oil prior to casting. Otherwise the vapors of the epoxy will penetrate the mould and make it fail brittle and fail very soon, after a few castings. Silicone is water-tight, but not oiltight and not solvent-tight. Although I haven't used it, I read that PU exists in tough flexible versions similar to nylon (they use that to protect car undersides and trunks). Edit: there is a reason why plastic injection moulding machines require heavy metal moulds, and clamping forces up to some tonnes, depending on the model...
  11. If you design custom support structures, maybe you could add sort of dovetail things in it? (I hope this is the correct English word.) Like they used to do in old woodworking. See this: the bottom red symbolises the custom support, the middle white is the PVA, and the top red is the real model.
  12. geert_2

    Brains!

    How did you convert the MRI-data to something slicable (STL/OBJ)?
  13. You need to make sure you have no undercuts, and that all side walls have draft (=wider opening at the top). Otherwise the models get stuck. If in doubt, make the walls out of multiple parts, and provide strong flanges with holes to screw them together. Provide big openings for pouring in the liquid, and openings for venting air. Make sure no air can get trapped. Weight could also be a problem in big models: make the walls thick enough, and provide extra supports where required (like the beams on the sides of castles and cathedrals). And heat development: I don't know how hot concrete gets, but gypsum gets warm and could melt PLA moulds. For release agents, you will have to google. Not only do you need to find one that works well in combination with concrete, but it also should not inhibit the curing. Try on small test pieces first. Silicon oil might work.
  14. A bit off-topic: before printing 230 copies, have you tested if these 3D-models are fully functional and can withstand the desired loads, plus any brutal abuse (dropping, slamming into things)? If they want 230 pieces, it probably is for a functional test, not just for a visual demo...
  15. I modeled this test table in CAD in DesignSpark Mechanical (freeware, requires registration). Dimensions in this test model: - for reference: most plates are 1mm thick, text caps height is 3.5mm, text legs are 0.5mm wide - horizontal gap between supports and model: 1mm - tiny connection strands to keep support attached: 0.5mm wide (for nozzle of 0.4mm) x 0.2mm high (=2 layers of 0.1mm). These can easily be cut off, and cleaned. - inverse staircase in supports: steps of 1mm. This staircase reduces the overhangs curling up, but does not eliminate it. But in my tests these stairs worked better than a 45° overhang slope. - ribs on top of support: 0.5mm wide x 0.5mm high x 1mm horizontally separated. - vertical gap between ribs and underside of model: depends on model, usually 0.2 to 0.4mm. Try what works best for you. - supports extend sideways, bigger than the model: 0.5mm to 1mm. Making the support a bit bigger than the model improves the edges of the first layer of the model. Otherwise they sometimes sag and fall off the supports. I think this was the STL-file of the model: overhangtest11e.stl Also, for bigger models or difficult to reach areas: make very sure you implement enough features to insert pliers, hooks, knifes, and other tools to remove the supports. So you don't get stuck with unreachable and unremovable supports. This make take quite a lot of planning in complex models. Here too: the supports took way more time to model and test, than the table itself.
  16. Did you write "alignment-marks" on the pulleys with a marker? To see which one, if any, is slipping? Also check if your print head moves smoothly. If it would get stuck (e.g. no lubrication, dry bearings, or oil that got too sticky), it could cause the stepper motor to skip steps. I don't know if this could also happen if the steppers simply get too hot? Printing too fast could also cause skipped steps.
  17. Like tinkergnome said: also inspect the rods, bearings, rubber bands, nozzle, bowden tube, and rotating knob for wear, and the housing for scratches. My UM2s have 1000...1500 hours, and they still print fine. But you can see some wear on these parts. Depending on the material and temp printed, expect that the teflon coupler might also be worn (but this is hard to see, you would need to do a cold pull and inspect the outcome for deformations).
  18. Yes, I have also had a glass chip while cooling: I heard the normal little ticking sound of the model coming off gradually, and then suddenly I heard much louder snapping sounds... Forcing the model off while the plate is still hot, also seems a no-no to me. That would rather increase the risk, I think. Try a thicker layer of not too strong glue, that can absorb the expansion/shrinking. Personally, I use my "salt method" here too: wipe the glass with a tissue moistened with salt water, prior to every print. Let dry into a thin mist of salt stuck to the glass. For PLA this greatly increases bonding to a hot plate, and gives no bonding at all on a cold plate, which is very handy. For PET it does not seem to increase bonding, but rather slightly reduces it, but at least it also reduces bonding on a cold glass a little bit. I haven't had any chips since then. If you print without cooling fans, or with very little fan, it might work. With full fan, bonding might not be good enough and parts might warp. Try this on small test pieces first, and stay around to see what happens, so you can stop the print if it comes off.
  19. Yes, but this might be ugly, since the printer outlines every character. And for letters like E, N, H, etc, the problem is the same: here it may not be able to fill the openings. Some time ago I made character test sets with extruded text, recessed text, positive watermark text (=characters are solid, surrounded by voids, all below the surface of the model), negative watermark text (=characters are voids). Recessed text came out worst. For opaque materials usually I prefer raised text of 0.2mm high, leg width 0.5mm, caps height 3.5mm. For transparent materials I use watermark text (=just below surface) of 0.5mm to 1mm high, leg width 0.5mm, caps height 3.5mm. Some of the pictures below show this watermark text. For my 0.4mm nozzle I prefer text legs to be 0.5mm wide. When converting a curved shape to STL, it all become straight segment lines. If the width of the curved shape is exactly 0.40mm, then in STL it may variate between 0.39mm and 0.41mm. In which case the 0.39mm part might not print. So, I prefer to be safe and take 0.5mm as width in the design. See here for the character test set (STL-files and JPG-images): https://www.uantwerpen.be/nl/personeel/geert-keteleer/manuals/
  20. Up till now, all parts printed in transparent PET (brand: ICE, from Trideus in Belgium) and in NGEN (colorFabb) have survived well in my car, even in the hot summer of 2018. These can be printed quite easily, although NGEN is more difficult to glue with my cyanoacrylate glues. And indeed, parts in PLA warp, even in mild spring or autumn weather.
  21. For best quality of the text, I would print it on its back, thus the text facing up. But I would design custom supports, so that I would use far less material, and waste less time. Similar to this test with support bridges shown below, after an idea of user smartavionics if I remember well. I don't know if this feature is already integrated in newer versions of Cura? (I am using an older one.) If yes, try that first: it will probably give a much better undersurface. I have UM2 (non-plus) single nozzle printers, so I can print in one material only (this is PLA).
  22. If you suspect "not enough flow" is one of the causes, maybe you could try a (bigger) priming tower, or print a dummy block in PVA next to the real print, to keep more flow going through that print head? So it is always well purged? Try the idea on a small piece first, before doing a large job.
  23. I don't have a dual nozzle printer, so just guessing: When using dedicated support materials like breakaway or PVA, shouldn't the gap between support and model be zero? So that they are squeezed well together for a good bonding? Maybe you could try this on a couple of small test pieces?
  24. What about PET? This prints reasonably easy, although I don't know about compatibility with support material? Anyway, wasted PET bottles seem to survive very well in the ocean, without much degradation.
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