geert_2
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Posts posted by geert_2
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When you are new into 3D-printing, I would suggest that you print a small testmodel, that does not cost much time and material, at various settings:
- temperature: start from recommended setting, then also print it in steps of 5°C lower and higher, until it gets deformed (underextrusion when cold, or way too liquid when hot). But do not go too hot, so the material does not decompose and gets brown or gets stuck in the nozzle.
- speed: idem, start from recommended, then change in steps of 10mm/s up and down. See the effect on accuracy and under-/over-extrusion.
- try various layer heights: thin layers give smoother surfaces, but thick layers give better overhangs (on my printers).
- design a model with various angles of overhangs, and see how they print.
- design a model with tiny holes, and see how they shrink and print.
- try the various options and settings, and see what effect they have.
- try various bonding methods.
- try changing speed and temp on the fly, if your printer allows it: then you can quickly see the effect.
So, design a small test model with some holes, some 90° angles (to examine effects like overshooting and ringing at corners), some smooth radiusses, various overhangs, bridges, etc.
When printing fast, increase temp a bit, since the nozzle has to melt more plastic in the same time. When printing slow, decrease temp, so the material does not decompose due to sitting too long in the nozzle. Generally, printing at the cooler and slower edges of the range, improves the results. But it takes more time...
Keep watching the printer closely: how it extrudes, how it moves, how it pulls along the extruded sausage, what defects if any, how the nozzle leaks, how it creates strings, etc... Just watching this will give a lot of understanding.
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Moisture in the air might also play a role: when printing PLA on bare glass, it sticks way better in very dry air, like in freezing weather, than in very moist air, like in rainy summer weather. Not sure if this effect also works when using glue...
Also double check, or tripple or quadrupple check, if nothing else has changed in your setup? Such as different calibration, different temperatures or speeds of the first layer, different filament (or even a different color or batch),...?
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I would be very carefull with pressurised 3D-prints. Layer-adhesion is far lower than in parts from solid casts. They might burst open.
If I had to do it, I would use very thick walls, solid infill, print slow, and switch off the cooling fan for best layer adhesion. Or probably I would print one original, carefully post-process and smooth it, and then make a silicone mould from it and cast some suitable tough UV-resistant epoxy or PU in that mould?
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Wow, from photo it is impossible to tell the difference between this one and a real one. Beautiful.
How did you do the handle: printed in one piece with supports, or in two pieces glued together?
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The inside of the teflon gets really burnt and worn-out: it severely deforms over time. So the material gets stuck in it when doing retractions.
You can see the deformations when doing a cold pull.
The orange cone at the bottom is what a good teflon coupler looks like on the inside (the other cones were pulled-out too soon, before the material was solid). It mirrors the inside of the coupler and of the nozzle.
The white cone at the bottom shows a thick ring, just inside the teflon coupler (where the teflon coupler was before pulling the filament out). That thick ring is where the teflon coupler is damaged inside. So during a retraction while printing, the hot melt is pulled upwards into the teflon, cools down, solidifies, and then gets stuck and can't move forward easily. It is due to the pressure of the hot melt against the side-wall, when pushing forward again after a retraction, that the teflon coupler is slowly damaged due to the heat and pressure. So, less heat and less retractions, mean less damage. If I understood everything well, that is...
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Could it be that: or you forgot to enable retraction, and/or you are printing too small items way too hot, so they have no time to cool?
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Isn't there something like "enable combing" or so, to make the nozzle stay inside the material? (But I don't have that Cura version.)
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It looks like underextrusion to me, but I don't know why only there, so no real help...
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On 11/15/2021 at 11:25 AM, TimonR said:
Hi @gr5,
In principle all condensation polymers (polyesters like PLA, PETG, CPE = branched PETG, CPE+ = PCTG, and polyamides/nylons) have this issue. These polymers are 'coupled' by connecting monomers, which releases water. The opposite (decoupling / hydrolysis) happens when you have moisture and high temperature.
See here a very nice explanation on viscosity decrease at higher temperatures (hydrolysis) of polyamides: http://extrusionist.com/presentations/prejudices about polyamide.html (from slide 20 onwards).
Now, it basically depends on the moisture uptake of these polymers how 'bad' the situation will be.
CPE is a branched PETG, and has therefore a slightly higher viscosity to start with (which means that it needs a bit higher temperature to print).
CPE+ is a PCTG , which has higher stability to degradation than PET(G) (cannot find a nice public reference to explain that now unfortunately). Also, PCTG likely absorbs less moisture than PETG, which means that there is less moisture (at similar conditions) in the material during printing.
So to sum up: the combination of moisture uptake, printing temperature and bond-type basically determine how much hydrolysis = stringing you get. Ideally you want to reduce each effect as much as possible (by drying your material before printing and selecting slightly lower printing temperatures if possible).
From my personal experience (not backed by data): PETG is most sensitive to stringing, then CPE and finally CPE+.
Hope this clarifies something!Thanks for the explanation. Such deeper understanding is what is often lacking in manufacturer's manuals and tips on 3D-printing.
And in my view, personal experience is also "data". The first people to discover or to do something new, are collecting data by experience. So I think personal experience is equally valid, if not more, than citing references from others.
When molten, PET (or variations of it) stay way more rubbery and elastic than molten PLA. PLA gets a sort of yoghurt-like consistency, while PET is more like chewing gum: it strings more, but at the same time is more difficult to bridge gaps, because the strings tend to snap and fold back onto themself. Like a rubber band or chewing gum string that snaps.
Also, there are different sorts of strings:
- insect antennas: the nozzle leaks while traveling through air, and deposits that drop onto the next object it encounters. The next traveling move, it deposits its drop onto the previous drop, etc, causing the insect antenna. These are in your pictures too.
- big strings from the nozzle taking off from an object.
- thin hairs when material accumulates on the outside of the nozzle, and this gradually sags and sticks to other parts, pulling very thin hairs
Printing near the cooler edge of the temp-range, and slower, reduces these effects for me, but does not eliminate them. Because then the pressure in the nozzle is lower and the material is less liquid, so it leaks less.
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There have been posts in this forum how to do it, but it is very risky: you can easily break things. Maybe you can find these posts? I have never done it myself.
There is also a section on hot pulls and cold pulls, somewhere on the site, but i guess you already tried these? Sometimes warming the nozzle up and manually pushing the filament through is possible, if not totally blocked. Or sometimes you can get in from below with a thin needle to remove blockings, like a grain of sand. But I don't have much experience with blocked nozzles, I never had one. Just once a partial blockage (=reduced flow) by a piece of debris: I could push this upwards with a needle, then extrude some fresh filament, and then do enough atomic pulls to get all dirt out.
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And what about bying standard gears with the correct teeth and diameters, although too wide, and grinding them down? Before we had 3D-printers, a lot of prototyping was done by making a mould, casting composites, and then with a Dremel tool or similar manually post-processing them. Seems like that might work here too?
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I think they are snap-in parts? So maybe they came out of their slots and are now hanging loose, wiggling around?
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What you can always try to see if there is a mechanical obstruction: switch the printer off, and then manually rotate the Z-screw to see if the bed comes up, and feel if there is anything blocking rotation. If that works fine, gently try pulling the bed upwards manually by hooking your fingertips under the bed, but only at the back near the guiding rods, not in front. Normally you can pull up the bed in this way. This should let you differentiate whether it is a mechanical issue, e.g.: dirt in the Z-screw. Or whether it is an electrical or electronic problem, e.g.: steppermotor or drivers, or a Z-stop switch that is defective so the printer can't find it and keeps pushing the bed down to try to reach it, to know where the Z-zero position is. The printer does not know where the bed is when switched on, so it first has to move the bed down to activate the Z-stop switch to find the zero-position. Only then it can move the bed upwards safely by counting steps up, and not crash into the nozzles. My guess is that it is this Z-switch that does not give proper contact, or that came loose and dislocated. But as said, this is a guess...
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So I did a quick 5 minutes concept model: start with a square, rotate it 45° into a diamond, add a flange at the bottom to make in printable (you can make holes in that flange to mount the tube if desired), round the corners, and extrude into a tube. And that is it, basically. This might not work if it has to fit into an existing installation, but it might for a new one.
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For things like this I would recommend settings optimised for mechanical strength, if it needs to survive real use.
I guess this would require supports to prevent sagging of the overhanging areas. But removing supports from the inside of tubing might be difficult.
Does it have to be a round shape? If not, a teardrop shaped tube, or diamond shaped, might print much better: it would be cleaner, stronger, and better watertight. Look at the cross section of the model in the center below, and imagine the whole tube having this rounded diamond shape (disregard the other models, this is an old picture from something else):
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I have never printed gears, so no experience with that aspect. It is an interesting test, and I am curious about the long term results.
I did print quite a few clamps in PET and PLA. My PLA-clamps suffered from creep deformation, thus slow deformation when under continuous load, so they would soon lose their clamping force and start sliding around. Under higher loads, continuous or intermittent, microcracks did form. In my car all PLA items would soon deform due to heat, even in a very mild spring- or autumn sun.
So I would guess the gears might work for light use in a railway bus (or how do you call such things, not a regular tram, but a sort of diesel bus with manual gearbox, driving on train tracks?). But if you are going to pull heavy freight trains, or if the gears are close to the warm motor, I would doubt they would survive for very long.
My PET clamps would also snap suddenly when overloaded, but they are more flexible and can handle deformations better, with less permanent creep deformation. But the load they can withstand is not that strong.
A few pics:
Microcracks in PLA filament that was kept under continuous load (bending) for some time:
Idem, seen through a microscope:
Cracks and permanent deformation in carabiner hooks in PLA (left, cream), but not in PET (right, green):
The PET carabiners do also snap after some time, suddenly and without warning, without slow creep deformation, nor cracks. This is the cross-section of the fracture surface:
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I don't know the concentration, and it is not critical, although best below the point of saturation when storing it in the fridge. I just pour some salt in a bottle of water and shake it. A bottle such as the glass bottles used for mayonaise or so works well. After wiping, it just has to leave a thin mist of salt on the glass, almost invisible, that works best. Too much salt reduces bonding again, thus no thick crust.
When you do testing, be sure to stay with the printer and watch what happens.
The salt method is the only bonding method I have used in years for PLA and PET, and it never failed for long, flat, low models. However, narrow tall models like lantern poles and similar tend to be knocked over, and a brim or custom brim is needed. In this case using glue might be able to absorb the shocks better of the nozzle moving around and hitting the objects, especially when overhangs do curl up. Small single-wall hollow objects occasionally tend to peel off too, if the bed is a little bit too warm, for example a hollow cube of 10mm x 10mm x 10mm. If solid at 100% infill, it sticks like rock.
The biggest advantage of the salt method for me is (for PLA and PET): good bonding on warm glass, no bonding on a cold glass bed. So the models stick well while printing, but come off by themself after cooling down. I never need to take the glass out of the printer.
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These are "insect antennas": the nozzle is leaking a bit when traveling through air. Upon reaching the next object, that drop is deposited on the side of the model. The next layer, the drop is deposited on the previous drop, sticking out a bit more. And so on, causing these nice insect antennas.
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Something else that just occured to me: if you want to print each gear in multiple parts and then glue them together, you might consider making the mating shapes square instead of round. That will prevent them from slipping. I remember that one of my HO-model trains had a slipping gear on the motor axis, when I was a kid. The gear was all metal back then, but a way too soft metal. I had to hammer the inner opening of the gear out of shape to make it clamp again with a tight fit.
I am still wondering if 3D-printed gears can withstand real use, since even real metal or injection moulded gears would wear out?
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For PLA it is especially when the weather and air are very moist that the salt method gives much better results than printing on bare glass. A few weeks ago there was a post in which I gave a lot more info about the salt method, plus a lot photos, but unfortunately I don't remember the title or the context. But maybe you can still find it back?
For ABS the salt method did *not* work: the prints warped and came off. This was based on only a couple of small test prints, since I normally never print with ABS. But that was 6 years ago, so I don't know if ABS for 3D-printing has evolved since then.
If you would do any tests on any materials, or on various brands, feel free to report the results, good or bad. The experience is always welcome. Even for PLA there is difference between brands, and between colors in one brand, some sticking better than others.
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To make PLA stick better to the build plate, I use my "salt method": wiping the glass with a tissue that is moistened with salt water. This leaves a thin mist of salt stuck to the glass. For PLA, this greatly increases bonding when hot, but there is no bonding at all after cooling down.
For PET, the "salt method" does *not* improve bonding, on the contrary, it slightly reduces bonding. But it does also reduce sticking to the glass after cooling down very much, so PET parts come off easily, instead of chipping the glass when printing on bare glass.
I have no idea what it would do on breakaway? But since that is a blend of PLA and TPU (I think?), it might have some effect? Maybe try a small testprint in a corner of the bed on a side that you don't use too often? Be sure to stay with the printer and closely watch what happens.
This salt method is for glass beds, I never tried it on any other surface.
See the (very old and unupdated) manual here:
https://www.uantwerpen.be/nl/personeel/geert-keteleer/manuals/
A couple of pictures of the salt method in use:
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Yes, I could imagine that insufficient cooling causes issues. Try printing a dummy block next to the models, to move away the nozzle for some time and allow the gears to cool down. The goal is to keep the flow through the nozzle very constant, so the temperature and viscosity of the melt is also very constant. Thus do not "park" the head aside somewhere, but let it keep printing dummy blocks instead.
A hot nozzle that stays on top of a tiny print, will keep radiating heat and prevent the model from cooling and solidifying.
To make sure that the bed is at the correct height, and there are no Z-movement irregularities: if you print a test cube, does that have perfectly straight sides and corners, or do they also show some sort of beveling distortion, or elephant feet?
Picture: dummy blocks to improve the cones: this reduces heat deformation (insufficient cooling) but does not fully eliminate it:
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I don't know Fusion 360, but just as a general remark: couldn't it be that there is some fixed or stuck part in the F360 template, that is always loaded when you start a new design? For example if the template would contain a border, or a patch with your name and logo, as in technical drawings? Even if it is only a piece of unprintable text, or a surface instead of solid 3D-part, it might end up in the STL or 3mf-file, and throw off the alignment calculations in Cura? Something like that? Just guessing...
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When you delete a couple of files by accident, and you discover it *immediately* afterwards, you can usually get them back with undelete-software. If you manually deleted the files, maybe they are still in the garbage bin, and you can recover them from there. But if you uninstalled or updated things with the official (un)installer, the files usually aren't in the bin. So you need that undelete-software to find them and restore them. This is not convenient to recover hundreds of files or complete installations, but it works reasonbly well for a couple of individual files. However, if the files have been deleted some time ago, and you did other work on that computer such as editing designs, or you installed new programs, then the old files may have been overwritten and be unrecoverable.
If the files would sit on a server instead of your home-computer, maybe that server has shadow-copy software running in the background, with which you can recover deleted files up to several months ago. But that is not likely on a home computer. You might need to contact the administrator of the servers for the procedure to find the files.
Better is of course to make a regular backup of your files, including programs and settings. Then you can get the missing or damaged files from there.
3d print looks like spaghetti wrapped around a wire frame
in Improve your 3D prints
Posted
Normally, too thin sausages are caused by underextrusion, which can have a ton of reasons: printing too fast, too cold, nozzle partially clogged, too much resistance in feeding traject, teflon coupler worn out, drive wheel worn out or dirty, filament stuck, filament near end of roll causing too much unwinding resistance,... And probably a lot that I forget. There is an extensive list somewhere on this forum, but I don't know the title, so you might need to search a bit.
But in your case, due to the weird shape of the straight lines, I am wondering if it couldn't be a defect in the model, in the STL-file? Are these straight lines supposed to be there? Maybe show a picture of the model itself in CAD, and of the preview in Cura, and compare all of them.