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Everything posted by geert_2

  1. What happens when you sink most of the model into the build plate, so only the offending top parts are visible and printed?
  2. Slowing down will probably not be enough: if the nozzle stays too long in the neighbourhood of the already printed areas, the radiated heat will still prevent the part from cooling down. Since I often have small models, I tried all sorts of different solutions. For such small objects, now I always design and print a dummy model next to it. The dummy needs to have a sort of "inverse" or negative shape of the real model, so the total printing time per layer is equal: this is important for good quality. Sudden differences in layer printing time (and thus in cooling time) do show up as horizonta
  3. I once read about people drilling a small hole from an opposite side into the nozzle, or in an angle, so that the sensor could be pushed out from the back? I never had to remove a sensor yet, so I am not sure if this would work? Anyway, you would need to take great care that you don't drill through the filament feeding channel, nor come too close to it (could hurt heat distribution). Using dislodging oil, and very gently tapping (not hammering!) on stuck parts to make them loose, might also help: this is commonly done in old cars, to dislodge corroded screws. The very light tapping for some
  4. I have had that with PET and using dilluted wood glue as bonding. During cooling down I already heard weird cracking sounds. When I took off the model, it required very little force, but the glass was chipped. So it probably chipped already during the cooling cycle. Anyway, even with full cooling, I had absolutely no warping during printing. Now, if the model allows, I try to print PET without any bonding aid, and use less cooling (to prevent warping). Never had that sort of thing with PLA, using the "salt method" as bonding aid (=wipe the glass plate with a tissue moistened with salt wa
  5. In injection moulding, all manuals clearly state that you carefully have to dry the materials (usually ABS, nylon, PC,...) before starting to mould. Otherwise your models will be ruined. There is no reason why this should be different for 3D-printing with the same materials. But you really should try it: cut off 50cm of nylon filament, leave that out in the open air for a day, or let it sit in water for an hour, and then feed that manually into the nozzle after removing the bowden tube. And compare that with a dry piece of filament fed through. You will clearly see the steaming, and hear and
  6. If you are not allowed to operate the printer yourself (like in schools where students have to submit their designs to an operator), your best bet would be to kindly educate the operator. He may not be aware of bed leveling methods or bonding methods. Don't blame him or her, but offer help and give facts: that is easier accepted.
  7. If your cables are damages, maybe you could use some silicone as insulator? Normally, silicone is heat resistant up to 220°C ... 250°C; but there may also be high-temp versions. Or use shrink wrapping for cables (not sure if that is the correct English term): the sort of black tubing that you put around cables and then shrink with heat from a heat gun or soldering iron.
  8. Just out of curiosity: while printing with the old nozzle, did you closely watch what happened exactly, so why the hairs occured in your case? I am trying to understand, if an worn out nozzle would cause this, then why? Is it also the same filament as before?
  9. Depending on the amound of identical masks you need, another option might be to print one mask, glue that together, adapt it, and sand and post process as required for good surface quality and fit. And then make a silicone mould for casting additional masks in any material (except silicone). Or make a plaster mask, seal that, and use that for casting in silicone. Or use the 3D-printed model to vacuum thermoform additional masks, if you have a vacuum thermoforming machine at your school. Once you have a good mould, casting usually goes faster than printing for big parts. All these methods c
  10. I guess by "fluffy" you mean: sort of hairy, but not with thick strings, but rather very thin hairs? As far as I have seen on my printers, there are two main causes for strings and hairs: - Strings (=rather thick wires) come about when the nozzle leaks while traveling over a gap, and it leaves a string behind, or the leaking drop gets deposited on the side of the next object upon reaching that. - Hairs (=very thin) come about when there is a bit of overextrusion, or when molten material accumulates on the outside of the nozzle. And then, as the nozzle passes along the model, this molten
  11. You can find the full manual on the "salt method" here, with a lot of photos of the results and limitations: https://www.uantwerpen.be/nl/personeel/geert-keteleer/manuals I should update it, but meanwhile it is still useful.
  12. If you print 4 or 5 "skirt" lines around the object, this also allows you to verify and if necessary fine-tune the distance between nozzle and print bed (at least on UM2 printers, I don't know if this still applies to UM3).
  13. No I haven't. I only use cyanoacrylate glue, which works very well. If I have to pull parts off again, I often tear the PLA apart, not the glue. I did try "rotational friction welding": put a piece of filament in a Dremel tool, and then at high speed rotate that along the seam line, so they are melted together. This gives a very strong bond, it's all molten plastic. But it is also terribly ugly, and requires huge amounts of post-processing. If I would be printing art and statues, I would try two-component glue and add fine sand as a filler, to pour into the model to give it additional streng
  14. I also have this sometimes: the auto-logout function kicking in after one hour or so. The best thing to do is write the message in Notepad++, and then copy and paste it into the browser. But of course, I usually do not follow my own advice... It would be good if we could set the default auto-logout time in our preferences. I would probably set it to 4 hours. And then I would lose the next reply at 4:05h.
  15. Up till your question, I hadn't even heard about PMMA as 3D-printing filament, even though I have used lots of two-component PMMA materials (powder + liquid) and PMMA-based light-curing materials. So I googled it: indeed it does exist, and some people like it, but some complain it is very brittle (which is what I would expect, similar to two-component PMMA), and it shrinks too much, like ABS. Is there a reason you need PMMA, and can not use PET, polycarbonate, some high-temp polyester, or even PLA (but only for moulds not subjected to temperatures above room temp)?
  16. Or split the model in such a way that the seam lines sit in a natural indentation or other dimensional change of the model. Or create an indentation or decoration to hide it. So it becomes a "feature" rather than a defect. This may of course not always be possible.
  17. Moisture might indeed prevent sticking. I had that too in the beginning when the weather was warm and wet. Also, some cleaning aids (window cleaners or some alcohols) do contain soap or oils that prevent sticking. So, I would recommend to clean the glass with pure warm tap water only. You could use isopropylalcohol first (this should remove oils without leaving traces), but then clean again with warm water only. For printing PLA, I always wipe the glass with a tissue moistened with salt water: gently wipe and keep wiping until it dries. This should leave an almost invisible mist of salt st
  18. In the standard UM2 firmware you can also manually heat the build plate, via "Maintenance > Advanced". However, if you keep the temp high after print completion, then how are you going to get the models off? They do stick like glued, and you can lift the whole printer by pulling up a tiny model. While after cooling down they come off all by themself, without requiring any force. It may take you more time to get the models off a heated bed, than to wait until it is cooled and simply pick them off. You could speed up cooling by putting a fan in front of the printer, after completion. And
  19. More and more engineers in the USA and UK are switching to the metric system. Once you are used to it, it is sooooo much simpler and more logical than imperial units with their weird multiplying and conversion factors, and where some "units" have totally different dimensions, depending on where you are (such as gallons, if I remember well). It is just a question of time before everyone uses the metric system. So you can better be among the first than among the last. You will not regret it.
  20. Maybe you could leave the holes the size they are: they will probably come out slightly smaller anyway. And then drill. Just try. I would recommend drilling by hand, not with a machine: manually gives you much more feeling. A machine generates too much heat and may melt PLA or other low-temp plastics. Don't ask me how I know. I have bought a separate drill clamp (I don't know the correct name in English) to mount my drill into, so I can get a good grip on it. Edit: added photo of drill clamp for manually drilling.
  21. I don't have an UM3, so this is only a guess: from the photo there appears to be a way too big gap between support structure and bottom of the model. So the first layers of the model do sag. Also it looks like the support structure is not dense enough: not enough contact points between support and model for good support. I can't comment on the cause: a problem in the design? Or a problem with underextrusion of the support material? Or wrong settings?
  22. If material is leaking out of the nozzle while jumping over gaps (thus causing strings), then indeed you could have underextrusion in the area after this. The software has no knowledge of these leaks, it doesn't supply extra material to compensate. If you print slow, you might try a lower temp, so the material is less liquid: 10°C less or so? PS: don't leave a PLA printed model in your car in sunny weather, or don't leave it sitting in the sun on a concrete runway: it will warp. I don't know what effect warped wings would have on flight characteristics, but I don't think it will do any good.
  23. The bed temp should be around the glass transition temp of the material: that is the temperature where it begins to soften and get flexible (which is very long before it is melting). For most PLA this Tg is around 55°C, if I remember well. If you print PLA on bare glass, after wiping the glass with a tissue moistened with salt water, then the effects are as follows on my system: - no heated bed: model does not stick at all, extruded sausages curl up and come off immediately, - bed temp way too cold: printing starts fine, but model pops off suddenly during print, - bed temp a bit too co
  24. This is a late reply, but may still be useful. I am pretty sure it are micro-cracks indeed. When you manually bend a piece of translucent or transparant PLA, or when you straighten a bent piece (like a tight-wound piece near the end of a spool), then you clearly see white micro-cracks growing. Some colors show these cracks better than others. If you stop bending the filament and release it, the cracks stop growing. But if you keep it under stress, I guess they will keep growing until the material breaks or almost breaks. Near the end of spools, I always unwind a few meters of PLA, manually
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