dgsharp

I just wanted to echo this. For a long time I had a worn isolator and I spent a lot of time looking at the wrong things. ABS was the only thing I could print. When I finally realized it and got a new isolator, it was a whole new machine.

A more stable Z stage that doesn't bounce around so much. The current one is cantilevered out way too far, reducing print quality and compromising bed leveling. Auto bed leveling. Much less necessary with a beefier bed but still very handy. Feeder that doesn't jam so much. I designed the Hive76 Milled Bolt, a pinch-wheel with very positive grip. Once there was a filament jam with one of the printers with the filament spool hanging from the ceiling and the machine climbed right off the table. I'm sure there are lots of approaches that will result in a less finicky feeder than the UM2. All metal hot end? I think it's clear that Teflon makes for fairly disposable isolators. Dual material. I don't care about color, I can paint it if I wanted that, I need real support material so I can print functional parts. I love my UM2, but there's lots of room for improvement! -Dave

I did one or two test prints at 20um early on and they turned out ugly, fuzzy, etc. I didn't think it was worth trying to improve it because trying to get that sort of resolution out of this type of machine is basically a waste of time: it takes forever and just isn't worth it for anything I've seen.

As 3DMaker4U suggests, it all depends, especially based on the mechanical properties you need. That being said... In my experience typically PLA is capable of capturing finer details. It also prints with a more glossy finish, whereas ABS prints with more of a matte finish that can sort of blur fine details out a bit. The glossiness of PLA can also bring out more subtle flaws and artifacts though, like 'ringing' from acceleration.

I found the same thing with NinjaFlex (I had to move the knurled pinchwheel onto the shaft further). Even with the snap-on part of Robert's feeder the filament still squishes through sometimes, so I have to watch the first 2 layers or so. If it fails I check things over, maybe add a touch of oil to the bowden (not very frequently), just check everything over. Cut off that section of filament if it gets really permanently kinked up at the feeder. Maybe pull the bowden out of the hotend and do a cold pull with PLA to clean out anything that might be getting held up in there. Usually I have to do this sort of thing a couple of times before it starts printing, and then it's printing fine as long as it's running (12 hours or more), but when I go to start up another print, I might have to do the whole thing again. Kind of a drag. I haven't totally figured out the tension on the Robert's feeder, I will sometimes try loosening or tightening it some and eventually it starts printing. I'm not super happy with the feeder though. I often use 30 mm/s, 0.15mm layer height, 20-50% infill, 2 shells, 225C head / 50C bed, and 120-140% extrusion. I wish there were fewer knobs to tweak!

Dirkels, one that frequently bugs me is that if I have a model that takes a long time to slice, and then I decide to switch the settings for Support Type or Platform Adhesion, I am forced to wait until the slicing is done before Cura will allow me to change settings. If I try and change these settings before it's done slicing, the dropdown combo box will not stay visible long enough for me to do anything. That gets pretty old. I often have to resort to something like scaling the object down to be very tiny (so it slices quickly), changing the settings, and then scaling back up. -Dave

ALL RIGHT!!! Ok, I am tentatively saying this is solved. I installed a new bowden tube, new heater block and nozzle (the old ones had totally seized up solid and broke while trying to disassemble it to clean it), and straightened out the filament. I was able to print one of Illuminarti's cylinders completely. I had my finger dragging slightly on the end of the knurled wheel so that I would immediately feel any pops of under-extrusion, and there wasn't a single one. Beautiful! Now if I can just get it to stay that way! Thanks once again Illuminarti! -Dave

I see. I've been using the latest firmware, and 20mm sounds about like what it's doing. Until I replaced my teflon piece today, 20mm retraction would be a "huge amount" and result in an immediate jam if allowed to cool that way. Now I realize that my teflon part was almost certainly the culprit of that particular symptom, allowing the large bump to form internally which then can't be effectively drawn back through the bowden or pushed through the extruder. The material I'm printing is silver PLA, slightly under-sized and in the past it has printed very well for me. I am down past the halfway mark on my spool so it does have a bit of a tighter radius than it did to begin with. I did have a nasty issue with some black filament a while back and had to straighten it out, which helped some, but I think I had a couple of other issues going on as well. It doesn't take a lot of force to push the filament in or out of my bowden tube, I did that a few times this morning during the teardown and it's often how I load material. I will try straightening the filament on the next print. I'm currently about 10 hours in, and there was a little bit of under-extrusion several hours into it in one area, nothing like before but still an issue. After this print I'll try swapping out the bowden, straightening the filament, and cobbling together some way of more easily feeding off the spool. Thanks once again for all your input.

Another status update: about 2-3 hours into my print I started getting really nasty under-extrusion again (speed 50mm/s, height 0.1mm, temp 230C). I slowed it down to 50% (25 mm/s) and let it run for several layers and the under-extrusion didn't stop (feeder stepper kept skipping steps). I did notice that it seemed to lose steps around one particular area that had several retractions, so I lowered my retraction speed from 35 to 25 and distance from 5.5 to 4.5. I then bumped the speed up to 75% (37.5mm/s) and let it go a few layers, and it still seemed good. I had to abort the print so I figured that was a good opportunity to try Illuminarti's cylinder test. The feeder skipped 4 different times during the bottom 3mm/s band. Looks like it's back to the drawing board. So let's see what's left... I can tear it down again, take the nozzle off and thoroughly clean it out with acetone (ugh, I HATE taking the nozzle off). Replace the bowden tube. Anything else? I'm running out of ideas. I probably ought to print out something to help make pulling filament take less force, though the under-extrusion was still happening despite me manually providing excess filament. Can we get Cura changed so that when you hit "Abort" it doesn't retract the filament a huge amount and then forget to ever re-feed it? Every time I need to abort a print (which is frequently these days) I have to either manually "Move Material" afterwards to undo what it did, or (what I often do as it is much faster) I just power the machine off mid-print and lower the build plate manually. -Dave

Finally an update: I've received my replacement teflon part, and now that I have the two side-by-side I can see just how bad my teflon part had become. I'm attaching a picture showing them both holding a short section of identical silver PLA: Despite the poor quality of my picture, and beyond just the obvious blackened tip of the old part, there is a very striking difference in how closely the parts fit around the filament. The new part actually holds onto the filament slightly here, due only to the slight bow in the filament. The old part is extremely loose, with lots of clearance between it and the filament (it's even more obvious in person). I think this greatly enlarged insulated cavity may be where my filament had been piling up, jamming my hot-end. At my last hackerspace they had an old Stratasys machine they were trying to salvage, but the equivalent part (called the inlet buffer) was made out of polyimide and one of them was broken. It was ridiculously expensive stuff (McMaster has 1/2" round stock for $54.51 per linear inch!) but we were able to find some small blocks of it on eBay for cheap and I was able to make a few copies using my lathe and CNC mill (which of course I no longer have..). The polyimide was harder and more brittle than teflon but it machined pretty well. Teflon was kicked around as an alternative but it was deemed that the temperature ratings weren't high enough, at least for the Stratasys (IIRC their head temp was more like 270 or 275C?). Wikipedia is saying that the pyrolysis of teflon is detectable at 200C, suggesting that eventually all of our teflon parts will probably need to be replaced. Given this it seems like investigating alternative materials would be a good idea. Currently I'm printing with the new teflon part at 50mm/s and 0.1mm layer thickness. I think I may have heard a few occasional pops of under-extrusion but I wasn't paying close enough attention to say for sure that they weren't just the bed dropping for the next layer (they're very different sounds but sometimes if I'm not paying attention I can't swear whether I heard one or the other). I forgot to do Illuminarti's cylinder test before starting a long print, silly me. This is definitely an improvement over before though, as I had it down to about 20mm/s and it was STILL under-extruding badly at 0.1mm layer height. I'll post an update if I have any issues or notice anything interesting. I do wonder what I must have been doing to abuse this part so badly compared to others. All I can think of is using ABS and nylon. -Dave

Thanks again for all the thoughts and PM. I took off the heated build plate and poked around and saw no signs of blackened wires or loose connections anywhere. It did look like at least one of the screws holding the black rubber piece that attaches the cable to the build plate was loose though. My current theory is that because that was a bit loose it allowed the solder joints on the back of the build plate to cycle and wiggle just enough that one of the solder joints failed. I opened it all up and the surface-mount connector came off, quite possibly due to my handling. One of the solder joints looked different than the others (more shiny and a darker brown color) which may or may not be important. I soldered the connector back down and reassembled and it seems to be working again. I removed the Bowden tube from the hot end and did my best to make sure it was seated firmly against the teflon (with thumb screws already tightened). I then performed the "HAS-CAP" procedure a couple of times and got a very similar "shoulder" / bump on the filament. I trimmed it and put it back together and used Move Material to do the same thing with the Bowden tube bottomed firmly before adding the clip, and the results seem the same as before. It's almost as though my teflon piece is too short now or something. I am almost tempted to apply a series of light but recognizable scratches to the end of my Bowden tube and inside the teflon part, so I can look directly on the filament after I pull it out, and the culprit will be the piece that made its imprint on the filament. I'm supposed to have a replacement Bowden and teflon piece coming so hopefully in a few days I can get it fixed either way. Anyway, fun for another night.

Thanks for your thoughts, I will investigate them all as soon as I get a chance. As for the heated bed, it gives no error, it just never prints, or the advanced option to heat up the build platform isn't able to affect the temperature. No wires seem to be loose but I need to fully tear it apart to get a better look at things. My Bowden tube doesn't move at all, but I will be careful to try the directions you linked me to. Thanks again, will report back when I can.

Well I put everything back together and left a print running at 210C. I came back after 9 hours or so (24h print) and halfway through one of the parts had popped off the build platform and it was printing air spaghetti. But spaghetti is better than caramelized PLA. I went to try re-printing it using the new raft option and.... my heated bed never got hot. (Presumably the heated bed died mid-print, causing one of the parts to let go of the glass.) So it seems like I have another issue in addition. Will update as I get a chance to uncover things. I haven't noticed any loose or discolored wires anywhere yet, but need to tear things apart more to look closer. http://www.sadtrombone.com/ (I went to that web page and the ad was for an Ultimaker2. How it mocks me!) -Dave

I've been having more under-extrusion problems (UM2). The highest I've ever gotten on Illuminarti's cylinder test since trying it the first time was about 7, and I tried the other day and it was popping multiple times per loop, utter failure. Lately there has been some kind of gap somewhere causing filament to pile up, so that when I go to change material or when I do the "HAS-CAP" hot-end cleanout procedure it leaves a big nasty bump. I tore down the hot-end (except the extruder) and it's puzzling. I do the "HAS-CAP" procedure and I can see daylight through the nice round hole, but it's giving a ton of resistance, even at 230C. I forced some PLA through with it all taken apart and was able to see it push the teflon piece up in the air, filling the new void below the teflon part with a puddle of PLA resembling the shoulder on the PLA ends in the picture. So it seems to me like what I'm getting is a combination of unusually high pressure in the hot end, and a teflon piece that is moving up under that pressure, causing further problems. I have a very strange lip/groove on the inside of my teflon part (which I've seen in one or two pictures on here before, attaching pic), and they're sending me a new one, but I'm not convinced that's my only problem. This filament is slightly under-sized, and has printed very well for me in the past. Is it possible that the pressure is so high in my hot end just because it's coated in a layer of built-up burned-on PLA / ABS / nylon residue that is acting as a thermal insulator? And if so, is it expected that the teflon piece would push upwards and create a void underneath it, or should it be held in place more firmly somehow? I've got clips on the bowden tube and there is no play at all there, but I've been careful not to tighten the knurled thumscrews on top too tightly as I've read about here.. I'm sure people will say that printing multiple materials should be avoided, and maybe that's true.. Thanks for any suggestions! I'm dying here. I just tore it down again and put it back together, dropping the temperature back to 210C from my usual 230C to maybe prevent it from burning in there. Layer height is 0.1mm, speed is about 30mm/s, but at least it hasn't seized up yet this time. That's one thing about ABS, even when my best PLA is barely able to extrude at all, the ABS just comes pouring out.. -Dave

It could be something in the model itself. I've gotten wonky print files from people before and it turns out that the surface normals are goofy or there are unintentional internal faces and such. If you can get it into Blender or a similar program and really poke around to make sure everything is as you suspect, you may find your issue there. Usually when I have a strange disagreement like this between what I expect to print and what Cura produces, it comes down to the model. Might be worth checking if the settings don't fix it. If you'd like to upload the file, I'm sure someone here would be glad to poke around at it to help you out.