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geert_2

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Posts posted by geert_2

  1. On 3/31/2021 at 3:37 PM, gr5 said:

    ...

    You can also use PLA as breakaway if you are printing nGen.  This is my favorite combination.  It works so incredibly well and the quality of the result is fantastic.

    ...

     

    This method is new to me, but it could obviously have great potential.

     

    How well does NGEN bond to the PLA, and how well is it removable? And the other way round, PLA to NGEN?

     

    Does this also work for PET, CPE, etc.?

     

  2. Most bottles for chemical products are made from PE, both HDPE and LDPE, or PP, so these have a reasonable chemical resistance. For use on the ground, maybe this could be an option, if they meet your strength-requirements?

     

    However, for use in airplanes, I doubt if they meet the temperature range? Especially PP might become very brittle when well below freezing temperatures. Also, they degrade quite fast in strong UV-light, so not very suitable for outside applications, especially not at 30000ft. Impact-resistance of PP is lower than PE, this could also be a factor.

     

    I have no experience with printing them, so I don't know about layer-bonding, warping, settings, etc.

     

    Maybe another option might be to design and 3D-print a mould, and then cast a suitable material in it? Maybe PU-rubber, or hard PU (whatever you need)? Probably not silicone rubber: silicone is water-tight because it repels it. And it is chemically quite resistant. But it is for sure *not* oil-tight, and not solvent-tight. I found out after a full cup of liquid parafine leaked through it overnight... After cooling down, the whole silicone cup was impregnated with parafine too, opaque white instead of transparent yellowish. That is why it is a good idea to thoroughly impregnate silicone moulds with silicon oil, prior to casting solvent-like composites: this saturates the mould with silicon oil, and reduces the amount of solvents that can seep in and destroy that mould by curing in the silicone itself.

     

    I often make PLA moulds for casting silicone models. Or silicone moulds, around a PLA- or plasticine model, to cast PMMA epoxies.

     

    If you would go the moulding way, make sure to follow classic design and moulding rules: no undercuts, drafts, pouring openings, venting openings, etc... Print the mould very fine, and then smooth it by sanding or chemical smoothing (dichloromethane). If well done, you can make multiple casts from one mould.

     

  3. As gr5 said, design the supports in CAD. I almost always do this too, to have full control. I design features into them so that I can get in with scalpels, hooks, pliers, etc...., to easily remove the supports.

     

    Often, I also let them begin from the model, so they don't go all the way down, and don't damage underlying areas. Thus "free hanging supports", sort of.

     

    Here a few of my classic examples and ideas. Do test the concepts on a *small test model* that has your typical problem areas, before doing it on a large model that takes days to print.

     

    support_ideas1.thumb.jpg.01b652b9b15851890834b65181100d91.jpg

     

    overhangtest11c2.thumb.jpg.a46d23123127b77f81082a2efa4daa80.jpg

     

    overhangtest11e.thumb.jpg.1f92bf0e3eb064e1d9edbdf9edd16b3c.jpg

     

    These free hanging supports are easy to remove and create very little damage to the side walls, and none to the lower areas:

    DSCN5727b.jpg.8aeeef6796d24bf7adbbdaa5eb24f52a.jpg

     

    Idea for a spring:

    spring1b.thumb.jpg.c1de384602569626c7a4fb80a292b74a.jpg

     

    Here the supports (red and orange) have extra custom brim, to prevent them from being knocked over, due to their overhangs.

    ostrcp_key_v20_zoom.thumb.jpg.c85991865979ff09557a37d9ca6ad20f.jpg

     

    clamp1.thumb.jpg.376227acc930e40f6de8d3919b3f0a7f.jpg

     

    anemometer1b.thumb.jpg.c006a1ccc8e1465c2c9a18fe6d91bf0f.jpg

     

    More free hanging supports below. These are small models, the supports in total being ca. 5mm wide.

    supporttest12b.thumb.png.504e11c4d360abd18960d889c271f2a4.png

     

    supporttest12c.thumb.png.a4bbb089d43486b97df974e68e645196.png

     

    supporttest12d.thumb.png.928a8b2050f412c67de15eea58791d75.png

     

     

    • Like 1
  4. Annealing does not just shrink the model by 5%: it shrinks it in X- and Y-size, but it gets thicker in Z-size, and it severely warps due to the relaxation of built-in stresses. Better use filament that can handle the required temperatures from the beginning. And even then, the result is only a poor less than 10°C better temp-resistance for PLA: still not usable in a car, it will still deform in a mild spring sun.

     

    I tried annealing in different ways: by putting a fridge box on top of the model, and keep the build-plate hot (60...70°C for PLA). And in my well-controlled lab-oven.

     

    annealing_box.thumb.jpg.793349f158ebb7f96e73a2c883e9c791.jpg

     

    An untreated, and a "too well" treated model (a bit too high temp): this one got much shorter, but much thicker. And it obviously warped severely...

    warped1.thumb.jpg.c796132c0f7622f90d967d7645ae0c9c.jpg

     

    Some filaments warp in both directions: first upwards, then after a day in the opposite direction downwards. Very weird, I have no explanation for this, and very unpredictable. Thus unusable for accurate parts.

    annealed_warped2.thumb.jpg.8c23207ac1458cd42eb4dc6cfa87670c.jpg

     

     

  5. The cause is filament leaking from the nozzle while traveling through the air, due to the pressure in the nozzle not immediately dropping to zero. Especially with flexible, compressible filament. This leaking causes a sort of "insect antennas": the drop on the nozzle is deposited on the edge of the next wall the nozzle encounters. And then on the next layer, it is deposited on the previous drop, and so on, creating these antennas. However, you have a peculiar form of it.

     

    Rubbery materials (when molten) like PET also have this tendency.

     

    Maybe print still slower, cooler and in thinner layers? So there is very little pressure build-up  in the nozzle and bowden tube? And the filament leaks less due to being cooler? Printers with bowden tube are more prone to this obviously than direct drive printers, due to their long feeding traject under pressure.

     

    A close-up of these "insect antennas":

    microscope5.thumb.png.0a792ceff97c232fc3c2e9ac90f6de48.png

     

    For comparison: ruler next to the item with antennas is in mm and cm.

    microscope10.thumb.png.f19ba929a276abe9c32cc4b0c807b4c9.png

    • Like 1
  6. Something I just thought about: depending on the job, and if you would only need 2 color bands, maybe it might also be possible to do the coloring trick after printing? Then you can adjust the height of the color bands by dipping it deeper into the water? I think with pre-colored spools the outcome is always going to be a bit unpredictable, and variations in surface area are going to cause variations in color band height.

     

    @kmanstudios: I have no experience with food colors myself, but a friend uses them a lot for cupcakes. But they are not left long enough to fade...   :-)

     

    What about textile colors? They can easily be found in supermarkets here, and should be reasonably stable I think. They work well for cotton and bamboo, but I don't know if they work for synthetic stuff like nylon? I don't even know if they are pigment particles or inks?

     

  7. 18 hours ago, kmanstudios said:

    You can make your own with nylon filament.

     

    Follow from there. I know it is not gloss, but you can always put on your own gloss. This way you can create your own colour schemes.

     

    I was going to say this, but you were first.   :-)

     

    These models came out very well. On Youtube I have also seen videos on which colors/pigments to use, and the whole coloring procedure. If I remember well, some people used food-colors.

     

  8. Forgot to say: due to the dissolving-effect of the solvent, the outer layer of the parts gets soft for a while. So that will leave fingerprints, and it may warp the whole part if it is thin. Also, if you print with little infill, it may evaporate the solvent inwards into the hollows, where it keeps working. I found that a mould I printed with 25% infill and of which I smoothed the inside (=where the cast comes), began to warp slightly after one month. I think that might be a result of the dichloromethane-solvent, because it never happened in similar unsmoothed parts in the same conditions (=room temp, average moisture).

     

  9. It might also be a good idea to search on internet for demo-videos. Then you get an idea of how smooth the extruded sausage is, and if it fits your application. Most models that I saw gave a quite irregular extrusion, or maybe seemed irregular due to our hands moving irregularly? It would work very well for creating trees in miniature railroad landscapes, but not for smooth geometric objects.

     

  10. At least for prototyping, I would begin with classic materials like PET or even PLA. But do some smoothing on their surface to reduce layer lines, so dirt and bateria have less grip. These do withstand desinfecting alcohol.

     

    For smoothing, have a look at the thread I did some time ago, with lots of pictures of the result. Search for: PLA and PET smoothing with dichloromethane.

     

    Chloroforme should also work, but I haven't tried that (too much hassle, requires special permissions here). Be aware that after smoothing, the parts will breath-out that chemical for several hours, so you need to give them time to dry completely.

     

    • Thanks 1
  11. I just read this now. An option might be to print it in nylon, but a bit too small, and then using a vice press it on the brass element with brute force? So it will seal well and won't fall off? Nylon may be able to handle this brute force.

     

  12. There are people on the forum here who use PLA or dedicated mould-making materials to print a model, and then encapsulate that in sand (or whatever special mould-material), then burn the plastic model out, and cast metal into the cavity. I have seen videos of it, but I don't know the exact methods and materials. There are jewelmakers who do this with silver and gold, and also general hobbyists who do it with aluminum. Maybe you can find tutorials on Youtube?

     

  13. Catia, isn't that from the Dassault company? If yes, I think it might use the same engine as DesignSpark Mechanical (but then at full power, not feature-limited like the freeware DSM)?

     

    I rarely have this sort of problems in DesignSpark Mechanical. But what occasionally happens is that things do not want to merge (or round, chamfer, cut, extend, whatever,...) if the edges do *exactly* fall together. If they overlap 0.01mm or so, this is not a problem. It is the "just touching" that is the problem. I have also seen this in other software, and in computer games as well: then you get flickering or zebra-patterns when both surfaces "fight" to be displayed.

     

    Most of the time all those math operations just work fine in DSM, but if not, a solution is: make a small gap if you do not want (automatic/undesired) merging, or make a small overlap if you do want merging.

     

    In DesignSpark Mechanical, you can give each object a different color. If they do merge during editing, on purpose or by accident, you will notice it because they all get the same color suddenly. This is a visual check, sort of. You can also see in the model tree if it is one object, or lots of objects.

     

  14. Also, printing in thinner layers normally gives a smoother surface. But twice as thin takes twice the time to print...

     

    These blocks are in PET, printed at 0.10mm and 0.06mm.

    DSCN6022.thumb.JPG.a72e3faf1f92cb1f2b61ed08edd6a101.JPG

     

    The green model on the top right is in PET too. It's hard to see here, but the surface is quite smooth, letting a hollow watermark text shine through. Note that this model is small, see the ruler in mm and cm below. The red object shows 50% underextrusion (was part of an underextrusion test).

    microscope10.thumb.png.f19ba929a276abe9c32cc4b0c807b4c9.png

     

  15. An STL-file describes a 3D-model in triangular surfaces. But a 3D-printer can not print triangles, it can only print single extruded lines. So the model has to be cut into thin slices first, and these slices then have to be cut into toolpaths, trajects that the nozzle can follow while extruding. This cutting into slices and toolpaths is done with a slicer-program like Cura. It outputs a gcode toolpath file ("somefilename.gcode"). This gcode-file is the file you need to put on the SD-card to print. So you need Cura.

     

    You usually have 3 file formats of each design:

    - the model in its native 3D-fileformat of your CAD-program (SKP-file for SketchUp, I think),

    - the model exported as STL-file, needed for slicing,

    - the toolpath GCODE-file made by the slicer, which can then be printed,

    - and I also add a JPG-picture of each model, so I can easily recognise the design in my Windows Explorer, without having to open all CAD-files

     

    But as said above, SketchUp is going to be an endless source of troubles, because it produces incorrect STL-files that can not print (at least not without lots of repairs). So you would better use another 3D-editor. DesignSpark Mechanical is free (requires registration) from RS-components, is easy to learn, and there are lots of good tutorials on Youtube. That might be a good alternative, but there are lots of others too.

     

  16. Yes, just do tests on tiny items, so you know from which point on the dummies become necessary. This takes only a few minutes due to their small size, but it can later save a big model. After some time you know and you can add the dummies from the beginning in the design.

     

    Below is a real application: the dummy is the green cube at the top right. Its bottom is hollow, its top is filled from the height onwards where the large flat areas in the blue object ends, and only the tiny high yellow part remains. Without dummy cube, the top of the yellow part would seriously deform. For reference: text caps height is 3.5mm, text legs are 0.5mm, thus all is quite small.

     

    ostrcp_key_v20_zoom.thumb.jpg.c85991865979ff09557a37d9ca6ad20f.jpg

     

  17. I am going to do some wild guessing: could this be a result of high pressure in the nozzle, after printing infill at high speed and temp, and then suddenly slowing down to the outer layer. Thus the built-up pressure and temperature has to leak away, sort of? Or a result of a move through the air, where it temporary stops extruding, with the same effect? Or both together?

     

    If the first, then setting all speeds and temps equal should minimise this effect. If the second, printing slower and cooler should minimise it (but printing cooler of course might reduce layer bonding).

     

    But as said, this is guessing.

     

  18. On 3/9/2021 at 11:27 PM, gr5 said:

    Maybe he can melt away the mold?

     

    Yes, but then it's a single use mould. Not the best option if you need a lot of casts. It sort of defeats the idea of moulding and casting.

     

    A good alternative to a fully 3D-printed mould, could be a silicone mould in a hard 3D-printed shell. It goes a bit like this:

     

    - Print the real model in PLA or whatever.

    - Design in CAD a shell that is sitting at some distance from this real model, maybe 5mm to 10mm (depending on the size of the model: bigger models need a bigger distance). This can be a very simple shell: two parts, with clamping flanges, alignment keys, stable baseplate, and big opening on top. Make sure to minimise details and undercuts in the shell.

    - Mount the real model in the shell, and verify there is some distance around the model. Bolt or glue the model to the shell. Removable glue like "rubber cement" might be a good choice. If not fixed, the model will go swimming around.

    - Carefully seal all seams, they must be absolutely watertight, or the silicone will leak away.

    - Pour silicone into the shell, around the model. Preferably transparent silicone, so you can see the model through it. Let cure (often overnight, depending on the silicone).

    - Remove the shell. This should be very easy if well designed, due to the simplicity of the mould and the flexibility of the silicone.

    - Now using a scalpel or very sharp knife, cut the silicone in half, or in multiple parts as required by the model, so the model comes out. While cutting, make zig-zag movements, so you get natural alignment keys in the silicone. It looks ugly, but it works very well. Cut along natural seam lines of the model.

    - Treat the mould with plenty of silicone release spray before casting, so it really soaks in.

     

    In this way, you get a reusable silicone mould, easy to clean, easy to demould, suitable for many many casts.

     

    There are lots of excellent tutorials on Youtube, search for: moulding and casting

     

    Pics:

     

    3D-printed shell. Model (teeth) was mounted with plasticine. Alignment of both mould-halves is by M4-screws, also used for clamping the mould. Note the lots of draft in the mould, required for easy demoulding from the shell. Also note the zig-zag pattern in the silicone halves.

    mould_teeth.thumb.jpg.ec2a28f7073bd489bc0bc181629e9f9d.jpg

     

    Old-school mould, with hard shell of two-component epoxies. Note the zig-zag in the silicone, for alignment. Also note the bottom plate for positioning it upright stably, and the big pouring opening on top, and the alignment keys.

    mould_tool1.thumb.jpg.611df49da6138e1b740b71f1e52ef171.jpg

     

    Side-view. The flanges of the shell are for clamping the mould and for the alignment keys. This was made manually, long before 3D-printing. But you can use the same concept.

    mould_tool2.thumb.jpg.f1bc453ab331a0a3e9cbb1fc3185b9c7.jpg

    This is fast-curing silicone: advantage is that no sealing of the mould is required: it cures before it leaks away. Disadvantage is that bubbles can not be evacuated: it cures too fast...

     

    For casting solvent-like stuff like polymethylmetacrylates (PMMA) or PU, lots of silicone release spray are required. Otherwise the solvent penetrates the mould and makes its life much shorter. Silicone is watertight, but not oil, parafine and solvent-tight: these seep into it, and would cure in there, thus hardening and destroying the mould. So, saturating the silicone with silicone oil prior to casting helps a lot.

     

    • Like 1
  19. If I had to do this, I would probably do the mould-making in CAD: subtract the model from a solid block. And then cut the block to pieces along natural seam lines, so the cast can be demoulded. Next add flanges to clamp mould parts together, add alignment features ("keys"), add a stable baseplate so it does not fall over or slide away when pouring heavy plaster in it, add air venting holes if required, add pouring holes if required, add features to lift the whole mould, add features to insert a screw-driver in-between mould-parts to wiggle them apart later on so you can open the mould, etc... Requires lots of work, and lots of thinking, but it gives you way more control and understanding.

     

    Making a mould is not that difficult. But afterwards opening it, and getting the cast out undamaged is...  :-)

     

    • Like 1
  20. Not NGEN, but for other similar products (PET): I have to print them very slow, in very thin layers, and around the lower edge of their temp-range, in order to get them reasonably transparent. After printing, sand and polish to remove layer lines.

     

    It is the entrapped air in-between the sausages that causes the whiteness, due to reflections and diffractions. Like sugar crystals look white, although they are transparent.

     

    If sitting in the nozzle for too long, due to the slow printing speed and thin layers, PET starts to decompose and discolor brownish. So, lower temp to minimise this effect.

     

    Make a simple test block like this below, and print it with various settings.

     

    Top row: speed 50mm/s, bottom row 10mm/s.

     

    Layer thickness from left to right (out of a standard 0.4mm nozzle), both rows: 0.40mm, 0.30mm, 0.20mm, 0.10mm, 0.06mm.

     

    DSCN6014.thumb.JPG.6048c647bd1b456f5146ffa114b83051.JPG

     

    DSCN6016.thumb.JPG.34c84f7029de80f9e26ea5e3e778fe0a.JPG

     

    At 0.06mm and 10mm/s: left as printed, and right after sanding and polishing a bit.

    DSCN6032.thumb.JPG.956086cf9ab2ee915b21b6eaba774967.JPG

     

    The model: 20mm x 10mm x 10mm, with floating watermark halfway (text caps height 3.5mm, legs 0.5mm, thickness 1mm):

    block_geert_1b.thumb.jpg.7fad8a5326c68526dcc30ccb58666dd9.jpg

     

    Printed in 0.40mm layers:

    DSCN6025.thumb.JPG.ffc1547d179f793f396731beba704792.JPG

     

     

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