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geert_2

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Posts posted by geert_2


  1. Would it be an option to hollow-out the model in CAD, instead of in Cura?

     

    Let's say we have a solid cube. Then, in DesignSpark Mechanical you can delete one face, and set a wall thickness for the remaining walls (so it is printable). This turns the object from a solid cube into a hollow cup.

     

    I don't know if your software has such an option?

     

    Also, make sure you have enough contact-area to ensure a good bonding to the glass. This may depend on the bonding method. For my "salt method", a single wall is good for low flat objects, but it is likely to come off for high objects, or objects with overhangs. I don't know for glue-methods, as I haven't used glue in years.

     

    This is what I mean: (my statues are not as artistic as yours.  :-)

     

    image.thumb.png.52118344408625aaf352ae6a2016a160.png

     

     


  2.  

    In PLA-based filament it is known that microcracks can grow if the filament is bent or stretched (thus kept under a load) for a longer period of time. So, don't let material sit still in the feeding-traject after the print is finished, but unload the spool immediately.

     

    Some materials also get brittle due to changes in crystal structure, becoming more crystaline (often reversible), and due to moisture absorption and damage (not reversible as far as I know). Both happen in PLA.

     

    Keeping it dry obviously helps against hydrolysis. But I am not sure what the best solution is for "un-crystalisation"? Melting should help, but then you lose your filament. Heating up to the point just before deformation might change its molecule structure in both ways: making it soft again, or rather making it harder (encouraging crystal growth), similar to post-curing and annealing. I don't know which one wins. And your warm room might speed-up these effects?

     

    I don't know your material, so I have no idea if it is affected by these phenomena.

     

    Try what the effect is of heat on a few short pieces of this filament.

     

    Keep in mind that when heating it too much above its glass transition temperature, it will shrink in length, but get thicker (e.g. from 2.85mm to 3.10mm), and then it may no longer fit in the bowden tube or nozzle. You could also try unwinding it manually, and manually straightening it a bit, after which you release it again (to stop crack growth), so the bending radius is not as tight as before. Then it will get stressed less in the feeder. It may take trial and error.

     

    It could also be a bad batch or spool, or a filament that is very brittle by nature, especially if it is a filled filament.

     

    Pictures:
    Microcracks in PLA/PHA filament after straightening it, and then releasing it again, so the stress is off. If the bending stress would be kept on, these cracks would keep growing until the filament would break.

    DSCN5649.thumb.JPG.6bbdd1ca1552266ce1b66269de7edea5.JPG

     

    DSCN5654.thumb.JPG.8d711ff4f62ff3d1d91eaee3b0ffa713.JPG

     

    • Like 1

  3. I was referring to the squishing of the filament indeed. I have two older UM2 printers with manual bed-adjustment, and I adjust it closer, so it is squished more. I prefer a nice glossy bottom, even if that causes a little bit of "elephant feet" sometimes. Not only does that stick better, but it makes watermark text in transparent materials (=inside the model, close to the bottom) easier to read.

     

    In Cura, I usually set the first layer to 0.2mm. This too helps in giving a flatter bottom than 0.3mm, and gives better bonding.

     

    I have no experience with UM3 or newer, so I can't say much about their procedures and their auto-leveling. I think you can switch it off, but I don't know if there is an in-between such as "auto-level to my prefered height"?

     

    • Like 1

  4. Belts are replaceble, and the procedure should be somewhere on the Ultimaker-site. If you are a bit handy, you can do it yourself. Your local dealer should be able to provide the belts. Or you can have him/her do it.

     

    While you are at it, I would take the time to have a look at the feeder too: is that clean and in good condition?

     

    Also clean the metal rods near the belts, and lubricate them with a thin oil that does not dry out.

     

    And also clean the nozzle with cold pulls or "atomic pulls". See the official method on the Ultimaker-site, or use my gentle method here (I am no Ultimaker-staff, just a user):

    https://www.uantwerpen.be/nl/personeel/geert-keteleer/manuals/

     

    And check if the white teflon coupler above the nozzle is still okay, not deformed, not burned.

     


  5. Just randomly printing Lego pieces doesn't seem like a good idea to me, since: (1) they won't fit, as a 3D-printer doesn't have the required accuracy (microns), and so the pieces would be useless; and (2) you will soon run into copyright claims and huge damage claims, as these are protected models.

     

    What you could do however, is go to a local school, and say that you have unused printing capacity.

     

    And then let the kids design things themself, so they learn how to do it and they get enthousiastic, and then print those models. Also learn them the possibilities and limitations of this sort of 3D-printing. This would give them a lot of fun and satisfaction, and understanding.

     

    Kids are very fast in learning new technologies, even (what we consider) complex software as 3D-design.

     

    If you explain and show how the printer works, they will understand.

     

    • Like 1

  6. Most materials should be reasonably airtight if printed *slow*, in *thin layers*, and with good flowrate. So you get good layerbonding, and absolutely no underextrusion (important). A little bit of overextrusion could also help, but might create blobs. Do not use separate support materials (PVA) that dissolve: if they made strings in a print, these will dissolve and become holes.

     

    But all models will have tiny "canals" and pores where bacteria can grip and grow. It's just that the water or air won't blow through.

     

    For shell thickness, I would use at least 2 lines (=0.8mm for a 0.4mm nozzle), maybe 3.

     

    Don't pressurise 3D-prints: they might explode at a much lower pressure than injection moulded models.

     

    For huge models (1m), I would rather apply a coating, I think? Maybe even reinforce them with glass fiber mats, and then apply epoxy resin? Do tests if a 3D-print can handle the required loads and temperatures (PLA softens and warps in the sun).

     


  7. If you look at the bottom, did it lift from the glass? Thus making a dent in the bottom?

     

    If yes, it could be caused by dirty, greasy spots on the glass? Clean with isopropyl alcohol, and then a few times with pure hand-warm tap water only. (No soaps.)

     

    A thinner bottom layer gives better bonding for me: 0.2mm is much better than 0.3mm. I guess because the material is squeezed more into the glass, and it has less room to escape sideways?

     

    Then use a bonding-method for better adhesion. Some people use the glue-stick, some use dilluted wood glue, hairspray, 3D-LAC,... Find a method that works well for you, and that you like.

     

    For PLA, I prefer my "salt method": wipe the glass with a tissue moistened with salt water. Gently keep wiping while it dries into a thin, almost invisible mist of salt. For PLA this increases bonding while hot, but gives absolutely no bonding when cold: models come off by themself. Then re-apply before the next print.

     

    This works very well for my typical low, flat, long models. But it is not recommended for thin vertical models like lantern poles, or for high models with overhangs. Overhangs tend to curl up, and then the nozzle bangs into them. So these models might get knocked off, as the salt can not absorb shocks. Glue is better in absorbing shocks I guess.

     

    For the full text, see here: (it is old, and I should probably update it, but it is still usefull)

    https://www.uantwerpen.be/nl/personeel/geert-keteleer/manuals/

     

    Bottom layer of part printed with the salt method: glossy, but with tiny pits from the salt. The second pic shows the mesh of a fan reflected in this bottom (I could not get bottom and reflection both in-focus, so they are separate pics).

    underside_mirror.thumb.jpg.d9e8c12251778b0a33338a0eac202c6f.jpg

     

    Typical view of the glass:

    saltmethod3.jpg.b36952a07208ed06aea2e5142716121c.jpg

     

    Inverted prisms are the edge of what can be printed: some warp but can be completed. Some come off and produce spaghetti. The tiny bottom area and huge overhangs and warping forces are a hard test. Try such a model with all your bonding-methods while evaluating them.

    DSCN5814.thumb.JPG.579cd13d93beed9cc55ec4cb5ab6c366.JPG

     

    Bottom with pits from the salt:

    DSCN4938.thumb.JPG.90124a14e04953b171581afa5e8f9e9a.JPG

     

    • Thanks 1

  8. 15 hours ago, sjstein said:

    ...

    I'm using the nylon itself now as its own support material. It prints much better, but removing that nylon is a chore.

     

    I haven't printed with nylon yet, so I can't comment on material-specific things.

     

    But if you are not happy with the default supports, you could design custom supports in CAD, and switch off support in Cura. In this way you can provide features to make removal easier: holes and gaps where you can insert knifes, hooks, pliers; or tree-like structures to save material and provide additional gaps for access; sideways support for higher models to prevent wobbling; extended supports with extra brim for or tiny features; free-hanging supports to not damage the plate below it; etc...

     

    Below a couple of methods I used during the past years.

     

    The pink and orange supports (center left) are extended, so I can grab them with pliers and wiggle them out. This model is way too small to insert a knife between support and model. Ribs on top allow tigher gaps, without the model and support fusing too much.

    support_ideas1.thumb.jpg.01b652b9b15851890834b65181100d91.jpg

     

    Free hanging supports prevent the area below from damage, and can be cut away easily.

    overhangtest11c2.thumb.jpg.a46d23123127b77f81082a2efa4daa80.jpg

     

    Idem. They also reduce material-use. The bridge plates are 1mm thick. The tiny support-connection strands are 0.5mm wide, 0.2mm high, and 1mm long if I remember well, and can easily be cut.

    overhangtest11e.thumb.jpg.1f92bf0e3eb064e1d9edbdf9edd16b3c.jpg

     

    This is a small keychain, where the blue fork has to slide into the yellow slider. The orange and pink supports got an extra brim, due to their tiny ground-area (only a few mm^2). Without brim they might get knocked off, since the overhangs tend to curl up, and then the nozzle bangs into them brutally (the pink and orange supports do not rest on the yellow slider, they float). For reference: watermark text capitals height is 3.5mm.

    ostrcp_key_v20_zoom.thumb.jpg.c85991865979ff09557a37d9ca6ad20f.jpg

     

     


  9. 12 minutes ago, SandervG said:

    ...

    Also make sure your build plate is clean before you start (no dust and no grease).

    ...

     

    And no soap: that prevents bonding as well.

     

    Clean with whatever means you need, then with isopropyl alcohol, and then a couple of times with pure hand-warm tap water only. Rub and wipe dry with paper tissue, without touching the glass with your hands.

     

    Also kinks in the filament which prevent the filament from passing through the feeder, or the filament stuck under other windings on the spool which prevent it from unwinding, can cause underextrusion.

     

    I had the last one recently. So, never let the loose end go, never let it hang around, and never let it get under other windings.

     


  10. The best is: make a few test models that have all typical features of your models. And then print them with various settings, to see the difference. Make them small enough so they don't waste endless amounts of time and material, but not too small, so the models still gets enough cooling (=without the hot nozzle sitting constant on top of the same place).

     

    Further: print slower and cooler than standard. This will give better corners. How slow and how cool depends on the model and material, and layer-thickness, so you have to try. For PLA, try something like 25...30mm/s and 200°C, and adjust from there. Unless this would go too slow and take too much time.

     

    Try all layer thicknesses and see which works best for your models. But 0.3mm goes 5x faster than 0.06mm. So, printing at 25mm/s and 0.06mm layers is 10x slower than 50mm/s and 0.3mm layers. Hence the need for relatively small test models.

     

    Personally, concerning colors, I would choose nice warm light-grey colors: stone, sand, rock, and similar natural colors, instead of white. White easily gets dirty. Or use the real colors the building will get, if available. (I never understood why architectural models are so often white?)

     


  11. I kind of like the worn-out look of the first lady. Looks a bit like a corroded ancient statue that is in restoration, after being discovered in an old castle. Maybe you could keep it this way? Just fill and sand the splits, but no painting?

     


  12. That overhang is very impressive, indeed.

     

    And what is the effect of this setting on the "curling up" tendency of steep overhangs? Where the edges bend upwards instead of sagging, causing the nozzle to bang hard into them, and causing vibrations and ugglyness too? And in extreme cases knocking the model off the bed?

     

    See these tests.

     

    DSCN5679b.jpg.369ab32c7990bf99558d198e2ecf8321.jpg

     

    DSCN5686b.jpg.a9820bddeaf6d37b7dd30feb5f4de786.jpg

     

    DSCN5814.thumb.JPG.579cd13d93beed9cc55ec4cb5ab6c366.JPG

     

     

     


  13. 11 hours ago, kfsone said:

    ...
    Lastly, I tried making the models not actually overlap and separated them by .1, .5, 1.0 and 1.1x layer height, all to no avail.
    ...

     

     

    I was about to suggest this. 🙂

     

    If they are totally separate, with a gap, and support is switched off, I see no reason at all why the base plate would be influenced by the X-character? Weird...

     

    1. Have you tried printing them in one material, with only one nozzle? But with tiny gaps everywhere (even 0.01mm should do)? Just to see how it is sliced?

     

    2. Have you tried putting both models into one STL-file? (Your models above are in separate files.)

     

    At 100% infill, on my single-nozzle UM2, the model below is sliced correctly in my older Cura. I quickly created it in DesignSpark Mechanical, and exported it as one STL-file. There is a tiny gap of 0.1mm between X and base. Base is 20mm x 20mm x 2mm. At less-than-100% infill, the area below the X is hollowed out according to the fill-percentage, but without outlines.

     

    x_on_base1.thumb.jpg.b343fbc713e09075c861300b3cdf6fae.jpg

     

    STL-file: x_on_base1.stl

     


  14. Also, when calculating the STL-triangles in MATLAB, make sure the coordinates of begin- and end-points of shared triangle-vectors are exactly the same, down to the last digit behind the decimal point. If these X-, Y- and Z-coordinates would be rounded off in your calculations, even to 20 digits behind the decimal point, it might create gaps in the STL-file, and then it would no longer be watertight.

     

    Let's say you have 3 triangles A, B, and C that share one corner. If this corner is (x, y, z): for triangle A=(10.00001, 20.00001, 30.00001), and for B=(10.00002, 20.00002, 30.00002), and for C=(9.99999, 19.99999, 29.99999), then this model would not be watertight, and would get messed up in slicers and CAD-editors, even though the gap of 0.00001 is not visible on-screen.

     

    (I think this is  the problem that SketchUp has with 3D-printing too: it was originally designed for visual models only, like in computer games, but not for watertight printable models. Models look solid on-screen, but when you zoom in 10000x, you start seeing gaps.)

     

    Maybe you can add calculations to make sure that points that are very close together, do snap onto each other? Similar to the "snap" function in Powerpoint, Inkscape, and most 3D-CAD programs. Make this snap-radius adjustable, e.g.: "if points are less than 0.001mm apart, then snap them onto each other", but then in a math formula. So the three shared corner of triangles A, B and C in the example above, should all snap to (10.000, 20.000, 30.000).

     


  15. As far as I know, STL-files have no dimension units (mm, inch, meters,...). But if I remember well from older posts, Cura *assumes* that the dimensions are in mm? Is that correct? If so, maybe you can set that in MATLAB to render or export the model to a size of maybe 20...50mm? And then definitely run it through an STL-analysis and repair, just to be sure.

     


  16. 5 hours ago, P3D said:

    If I understood the original post correctly, it is also about waiving the build height restriction for the last part.

     

    Yes, that is how I also understood it. That is what I meant by "moving the parts around on the glass": place the lowest model the furthest away from the home-position, and the highest the closest-by. And then hope that Cura is clever enough to print the furthest and lowest parts first, and then the nearby high parts. For low objects (<20mm) this seems to work in my older Cura version for my UM2-printers: at least it starts from the furthest away models. But this does not work for high models (100mm or so): then it prints them all at once. I have no idea about newer Cura versions and printers.

     


  17. My old Cura version can display this model, although it appears extremely small, maybe 1mm^3. So I have to scale it up 20...50x to make it printable. However, this older Cura-version can not slice it: then it hangs up. Maybe there is something wrong with the STL-file?

     

    Maybe try saving it with different parameters? Or run it through an STL-analysis and repair program? But I have no experience with these, as I never needed them for myself.

     


  18. For dimensioning threads, I think you could reuse the guidelines for plastic injection moulding. These threads generally use shallower angles than typical metal threads (M20, etc...), wider teeth, rounded corners, to improve the molten plastic flow, increase strength, and reduce stress-concentrations in corners under load. Indeed very similar to what you have done.

     

    If you use a standard thread, you can screw existing caps on it (e.g. recovered from PET bottles).

     

    Search for "injection moulding guidlines pdf", or: "part design guidelines for injection moulding pdf", "lanxess part and mold design guide", "injection moulded threads" (and then go to "show images"), and similar, but without the quotation marks. Most plastic manufacturers do have excellent guides on injection moulding.

     

    • Thanks 1

  19. 15 hours ago, kfsone said:

    Here's a trimmed down version of the two models.

    X-Base.stl 684 B · 0 downloads X-Fore.stl 127.52 kB · 0 downloads

     

    This is indeed what I would expect to work, at least if you have 100% infill. If less than 100% infill, say 20%, then I could imagine that the slicer would generate a heavier structure below the letters, to support them.

     

    I guess this will have to be answered by the developers, or people with a dual-nozzle machine and a better understanding of the slicing-internals.

     


  20. If the model is opaque, and the letters are raised, then maybe you could make the whole baseplate in one solid model/color? And only switch to the letters once you are above the baseplate? Thus without digging into the baseplate, rather like icing on top of a cake?

     

    If it has to be transparent, or if the letters are recessed into the baseplate, then of course this method would not work.

     

    (Note: I don't have dual-nozzle printers, so no experience, and just guessing.)

     


  21. Can't you move them around on the build plate, and in that way influence the printing order?

     

    In older Cura versions you could print multiple models apart, as long as they would not collide with the print head and rods. So you couldn't put very much parts on the bed.

     

    I haven't tried this in newer versions.

     

    But especially for very small parts, printing model per model separately, instead of all together, might not always be a good idea: then the model does not get enough cooling, since the hot nozzle is constantly on top of it, radiating heat, and adding hot filament. So it has no time to cool and solidify. This is why I often print a dummy "cooling tower" next to my small models, so the nozzle moves away printing someting else, and the model has time to cool. (Just moving the nozzle away without printing is also not good, this interrupts the flow, and changes melt-temperature and viscosity, which shows up in the print. Flow and temp need to remain as constant as possible, especially for small models, in my experience.)

     

    The effect of heat on small models. The dummy towers minimise the effect, but do not eliminate it. (Printed at 0.1mm layers, 100% infill, don't remember temp and speed, ruler is in mm and cm.)

     

    DSCN5603b.thumb.jpg.83c20560cfab90d56590243bc6015f12.jpg

     


  22. Thanks for the photos.

     

    It might be fillers in the black that decompose due to the acetone? Or due to UV-light, or age, moisture, or whatever else? Or the fillers that reduce layer bonding, and thus make it more prone to splitting?

     

    Also, I think manufacturer should mention in their specs for each filament: "Can be acetone-smoothed" or "Can be whatever-smoothed", and then the recommended product, time, method (brushing, wiping, dipping, vapour, whatever), and amount (thin, thick).

     

    I have just smoothed a handle (using your brush-on method), yellow PLA, and now I am going to put it in the lab-oven to see what happens. First at 60°C for half a day, and then we'll see.

     


  23. 2 hours ago, Smithy said:

    ...

    Just one hint for the Glowfill that you are not disappointed, it will not be visible very long, maybe 20 minutes or so. So for the most use cases it is useless for me.

     

    I have colorFabb glowfill, and indeed, it does not glow for very long. It is very bright for a *very short* time, and then quickly fades. Usefull brightness as a sign is a few minutes, maybe 5 at best. And then it is still barely visible, but unreadable, in pitch black darkness for indeed maybe 20 min. Just a blurred pale green shade. Useless as emergency exit sign, or as night-light in a room.

     

    In the old days they had radio-active glow-in-the-dark paints, used on clocks. These did glow *very* bright all night, for +10 years. This was really fascinating, and very usefull. But these paints are forbidden now, even though their radio-activity level was less than the normal background radio-activity in nature. Rocks, (natural) gypsum and river-water are radio-active too. Uranium, thorium, and radio-active argon are natural elements found in the earth crust. And much of the heat in the inner earth comes from natural radio-active decay of these elements. So the whole globe is a nuclear powerplant, sort of, and even a "melt-down".  :-)

     


  24. I believe the effect you see is overextrusion, due to the printer slowing down at the corners or ends, but the nozzle pressure is still up and takes some time to dissipate by leaking away. This gets more visible when printing lots of small segments.

     

    Printing slower and cooler helps, but does not eliminate the effect. But for me it is no problem.

     

    I haven't tried features like "coasting" (if I remember the name correctly, stopping to extrude just before a corner, so that pressure has time to drop). Maybe this might help? But if you overdo it, it might cause gaps at the start of the next segment. So try just a little bit.

     

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