18 minutes ago, gr5 said:I don't think your part needs support. You might want to just skip the pva. I'll read your whole post later but also know that Nylon is very tricky to print. Once you know all the tricks it is easy. But until then it's frustrating.
Thanks gr5 for the reply. The model has internal horizontal structures, which I assume they need support. I can definitely try to print it without (once the hardware issues are fixed, that is). Do you think the Cura parameters are OK?
7 hours ago, Xen said:The model has internal horizontal structures,
okay then you are probably right that it needs support.
Okay so I finally read your post. I'm sorry you hit so many issues so early on. I will probably miss something so ask again if I miss something.
1) Nylon soft - this is the easiest to fix - just bake it. I haven't tested UM Nylon for when it slumps but I suspect it's fine up to 100C. PUt a small piece on the heated bed at 100C and put a towel on it, come back 20 minutes later when it's at temp and make sure if you squish the nylon it doesn't permanently get distorted. If it's fine then repeat with your printed part to dry it out. The nylon I've been using lately can handle 100C no problem. If UM nylon can't then try again at 90C. Anyway after baking it you part should be much harder - closer to the flexibility of the raw filament.
2) tower falling over. This is easy to fix. Basically put it in the rear center - not the right rear corner. The glass that comes with UM3 is quite flat but the worst spot will almost always be the rear 2 corners. The more you squish the tower on the bottom layer the better it will stick. Also I think you can make it a bit bigger - I think there is a setting now in cura - if so - increase the base by another 50% bigger to make it stick better. The reason the rear center is good is because it's near one of the 3 leveling screws which tend to be leveled most accurately. Also maybe consider turning that screw 1/3 turn CCW to squish the filament even more into the glass.
Also it's good to put a thin layer of pva on the glass. You can use some of that water that was soaking with pva in it or you can just spread a little glue stick and then spread it around with a wet paper tissue - you want an invisibly thin layer of pva spread evenly.
You might want to just skip the tower. It is supposed to help if one nozzle is leaking - I've found the temperatures are getting so good now with the profiles that the idle nozzle tends not to leak. I like towers but I sometimes create my own supports near the tower so it's less likely to fall over.
3) nylon ground and failed - well that really sucks. That doesn't happen very often. To me anyway. One reason is I do not print the infill at double the speed as the shell. Maybe that's one reason. If you have lots of retractions such that there is > 10 retractions on the same spot of nylon that might grind it enough to cause a failure. Dust can get in the head. not particularly likely but it can happen. If it's something in the nozzle you will have lots of problems until you do a cold pull (cold pulls are done from the menu). If your internal structure is like voronoi - for example if you have 50 little islands on one given slice inside that tube then that is the most likely situation. I need to see your internal structure to have an idea.
Try turning on layer view and check the box that shows moves (blue lines) and see if there are many dozens of these blue lines on a given layer. If so I can give you the fix. There's two parameters to mess with.
I really don't know why it stopped extruding nylon. Also check for a filament tangle. Inexperienced users aren't careful and one loop of filament gets under another and this tangle propagates forever until you remove the filament and fix the last 2 meters on the spool and then carefully re-insert the filament into the printer.
4) KEEP NYLON DRY! It gets water in it too easily and if you are printing and you hear hissing/popping/snapping sounds then you need to dry it on your heated bed for something like 4 hours. Keep it in a sealed bag when not in use with desiccant to keep it from going bad. I even print it out of the bag with a narrow hole but that's not normally necessary. I don't think you can dry it with desiccant alone - but you can keep it from absorbing.
5) I strongly recommend you cover the front and top of your printer when printing high temp materials like ABS or Nylon. And keep the fan low - 3% is good. Front can be covered with any clear plastic. Top with a box - it doesn't have to cover everything - I use the box that comes with reams of paper inside. It's the perfect size and has room at the back for the bowdens to go in. It's not completely closed but good enough to get the air up to 35C which is perfect.
5) Materials - well did you try PLA? What are you trying to do? Do you need something that is really tough and flexible because that's nylon.
6) I don't know so much about nylon - I think nylon is better - but with PLA anyway you need the PVA to have a continuous path down to the glass. There is this feature "horizontal expansion" for support. It defaults to 3mm. This hopefully allows you to have PVA all the way down. Because PVA does not stick on top of PLA very well at all. But in your cylinder if you have internal shelves then maybe there is no way for the PVA to reach all the way down. So this would be a tricky print. If it's possible to print the cylinder sideways but not need any support inside the tube then maybe you could do that and use "support touching buildplate" versus "everywhere" and get better results. maybe. I'd like to see the internal structure of that cylinder.
1
I've printed about a dozen parts with Nylon, half of them with PVA, so I have a bit of experience, although I never troubles like you.
First, yes, UM Nylon left for too long in water, especially warm water, will have a tendency to warp, depending on the shape of the print and the inner structure, of course. I had that happen with a piece that had a large flat base, the base warped some. It wasn't much of a problem for my customer though, since he screwed it on top of a metal plate, and the Nylon got flat again once screwed. According to UM, their Nylon can go up to 80°C, then problems arises.
Then, I confirm some of what @gr5 said: Keep Nylon dry (dryboxes during printing are a must), same with PVA, put the prime tower away from the corner (I put it on the right side, mid-way between the corners) and make it thicker (there's an option in CURA for this, I put mine at 3mm or 4mm thickness to ensure they have a base large enough not to fall).
I've never used glue with Nylon, it sticks well enough on it's own, though YMMV.
Could you post the stl file of your cylinder so we can take a look and see if, maybe tehre's a problem with the file or when it slices?
As was mentioned, it's best to avoid too many retractions with PVA, although your design seems simple enough to not provoke that kind of behavior.
I see you're printing using the USB. This may also be the cause for problems. Did you try printing directly from your computer, by connecting it to your printer? I seem to recall reading that some people had troubles due to the USB stick. I've never used it personally, so I can't help, but you should be able to find the threads on this forum that discuss potential sisues with USB printing.
USB printing through a cable is not officially supported on UM2. UM3 can't do it at all. Printing from the USB flash is fine. That's the only way I print with the UM3.
4 hours ago, Brulti said:I put mine at 3mm or 4mm thickness
I think you mean 3cm or 4cm?
Thanks gr5 and Brulti. The printer is currently being serviced, which is weird given that we had it for less than a week! I will try your suggestions when we get it back. Note that we also bought the advanced printing kit and always use the front cover when printing.
I think the design I was trying to print is quite complicated. It has many little islands at each cross section and thus many retractions, as gr5 suggests. Viewing this in Cura is really challenging, because it freezes all the time in layer mode. That's not my PC's problem, as any other programs I use at the same time work fine while Cura is crashing. Any suggestions for other slicing software?
Indeed, after a few days the print actually returned to its expected shape. I guess the water has dried out. I will now keep it in lukewarm water for a few hours, remove as much melted PVA as manually possible, leave it to dry, and then back in water. How can you keep nylon and PVA dry while printing? We tried PLA for our very first printing, which was the Ultibot design in the supplied USB stick. So, you would assume that it was sliced with proper settings by experts and would work fine. But, nothing came out of the nozzle! So we just skipped it and used nylon instead.
I attached the stl file of a part of the design. This is for research purposes, hence the small part and why I removed some of the pictures in the first post! The small inner cylinders are ~10cm in height, but are all connected in the middle of the design for structural support.
Thanks again.
Edited by XenI took a look at the part, but did not actually try printing it. I think if you can change the way your thread runs out into the root diameter and eliminate the very thin section (probably not practical in a real world part anyway) and turn the part so that the inner cylinders are on the build plate as support, you can probably build this part with no support at all with 50% infill. Sometimes you need to design the part with the printing process in mind from the outset, while not compromising the design intent.
Just a thought
On 31/03/2018 at 9:55 PM, gr5 said:USB printing through a cable is not officially supported on UM2. UM3 can't do it at all. Printing from the USB flash is fine. That's the only way I print with the UM3.
I think you mean 3cm or 4cm?
Erf, yeah, sorry. 
And I didn't mean print via a USB cable, but via the network cable that hooks on the back. I have my printer linked to the local network via the network cable and a router, so I can send prints from my desktop directly. Way easier, in my opinion, and better control: if I see something gone wrong via the camera, I can stop the print through CURA. Useful when computer and printer are not in the same room.
@Xen The only way to keep filament dry while printing is by using what is called a drybox. You can find some on shops, or make your own. There are designs for that available on Thingiverse, including one that is very nice done by Ultiarjan, a member of this board. Basically, it's a plastic box with a hole to push the filament through, a holder for the spool and room to put something that absorb humidity. It's a must, and I'd even say that it is mandatory for long prints requiring PVA, because PVA is a magnet for air moisture. You'll be able to make a couple prints ok, then it will go to hell.
I've taken a look at your part in CURA, had no problem opening it in layer mode. It slows a bit when you slice it on Extra Fine 0.06mm, but otherwise it's ok. However, I'm a bit concerned about what CURA shows me when I look at it in Line type: why is there so much shells all over the place? Especially right in the middle of the top screwing part (sorry, I'm French, I don't know the word for the top part that screws onto something). It feels to me that there was a problem in the export to stl, or maybe even in the way the piece was build.
CURA shows so many tiny islands of shells, little red circles in line type view, that I'm not surprised it had problems printing it. The Nylon probably ended up ground up in the feeder with so many retractions happening in some of the layers. I'll take a closer look at it in Blender later, need to get out for a bit. But, in my opinion, there's definitely a problem with the way the file was done.
Ok, I've run your file in CURA again and in Blender, using the 3D printign add-on to check if the part was suitable for 3d printing. It isn't. According to the checks done by the add-on, your part is not manifold, which means that it isn't considered as one solid object all over, and it has a lot of intersecting faces, which can easily confuse CURA or any slicer, because it's like two objects at the same coordinates and they don't know how to interpret it.
Here's a couple pictures: the first one is what CURA shows in layer view - Line type, which is already showing problems.
All the red lines I pointed at with black arrows are shell, ie walls, in places where there should not be any wall, or doing shapes it shouldn't be. The small squares of wall around the hole in the object shouldn't be there. But each of them means retraction as the printhead moves from one to the other, thus grounding your filament so much even a rabbit would be impressed! 
Now, a picture from Blender:
You can see on the side the result of the check done by the 3D printing add-on. All the highlighted bits are intersecting faces. I do not know what software you used to model the part, but it screwed somewhere. You didn't used Sketchup, did you? Because Sketchup is notoriously awful at exporting objects in STL and rarely, if ever produces stl files that can be used for 3D printing.
That being said, if you want, I'd be happy to try and redo your part in Blender. The design seems simple enough, I'd just need you to send me the sizes of the various elements so I can redo them properly. Then you can test it again.
And, as a last note, it is advised to service the printer when you first receive it: it's not uncommon to have axis misaligned and such due to rough handling during transport. When I got mine, one axis was off the support and they were slightly misaligned, thus making the print skip and print the second layer 5 millimeters away from the first one.
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gr5 2,167
I don't think your part needs support. You might want to just skip the pva. I'll read your whole post later but also know that Nylon is very tricky to print. Once you know all the tricks it is easy. But until then it's frustrating.
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