Newbie 3D printer here, working with my 15YO son so both of us can get experience with 3D printing. I’m a Hardware/Software Engineer so I’m comfortable with technical topics, just new to 3D printing. We have a brand new Lulzbot Mini (wanted to spend our time actually printing rather than assembling someone’s kit). My son needs it for his various hobbies, and I need it for some work-related plastic models.
We are using Cura, as shipped on the USB stick with the printer.
We purchased some MakerGeeks PLA because PLA is supposedly a good starter material. We also purchased some Taulman 618 nylon for the work models I need. We’ve tried both so far and are seeing some odd behavior. We have tried multiple off-the-shelf prints as a starting point and they’re all exhibiting some/all of the following, so I don’t think it’s a problem with the print file.
The printer is doing its cleaning cycle, measuring the print bed, etc. so its basic operation seems OK. When leveling, the left front measurement seems to involve more force than the other three, but I see what appears to be an offset correction in the on-screen text so I presume it really is off-level a bit and Cura is adjusting for it.
We did print the Rocktopus with the enclosed short section of HIPS. There were a few imperfections (a “hair” coming off the top of its head at the end, a few bubble-like places here and there) but overall it’s fine. It doesn’t look as perfect as the example Octopus that was included with the printer.
On all prints, even the Rocktopus, it appears like the head makes 1-2 passes around the first layer(s) without extruding any material at all. It literally appears that the printer is wasting time. On the Rocktopus, the result was that the “ring” around the actual part wasn’t fully completed… there was a gap where I suspect the printer thought there was material, but wasn’t. I’m concerned that it believes it’s laying down the first 1-2 layers when it really isn’t. Yes, we carefully installed the filament and did the multiple “10” test to insure we had a good feed going. This also happens on the 2nd, 3rd, etc. prints without changing the filament spool, so even if it was a misfeed on the first one that should not be possible on subsequent prints.
With the PLA, it appears that the nozzle is dragging through the previous layers. This results in a “trough” like layer, with high sides and a low center, as the nozzle melts through the previous layer and displaces that layer’s material to the sides.
I can imagine these two behaviors might be related. If the Z axis is “off”, then it might not extrude at first and then believe the table is lower than it really is, causing the nozzle to drag through the previous layer(s).
We’ve looked through the settings and can’t find anything that appears to control or adjust this sort of behavior. (As a side note, we also looked for something that allows the first layer to have a separate temperature, something suggested in other forum posts, and can’t find such an option in Cura.)
Any advice will be greatly appreciated. Thank you!
Further research, using a 3mmx20mmx20mm “short cube” test model. We’ve dried the spool of nylon in a 160-170F oven for six hours since my earlier post, just to make certain moisture isn’t a problem.
Since it feels like overextrusion (i.e. too much material is being laid down), I tried backing off the percentage from its default of 100% to (at first) 95%. That didn’t make any noticeable difference. So I figured go WAY down, just to prove that things are changing, and dropped it to 70%. And that did, indeed, clean things up a lot. It’s now slightly UNDERextruding (I can see some gaps in solid surfaces) but at least the nozzle is not dragging through each layer. Each layer is now clean, and the next layer sits on top of it properly.
I also played with nozzle temperatures a bit, and discovered something very odd. When I specified 240C, the print started when the nozzle was reported to be 230C and stayed right at 230C for the entire print. I then dropped it to 230C, and sure enough - printing started when Cura reported the nozzle was 220C and kept it there the entire time. For some reason, whatever value I specify, the nozzle is held exactly 10C lower. Is there some sort of “offset” build into things here that I haven’t seen in the documentation?
Retraction doesn’t seem to be working. I specified 3mm (what Taulman recommends for 618 nylon) but I’m still getting threads across the object when the nozzle makes a large movement to the other side. Do I need to also use some Z hop? Seems like retraction ought to keep the stray threads down with or without Z hop.
Looking forward to any advice, or suggested experiments to run… thanks!
This morning my son bumped the percentage from 70% to 80%. The resulting print was more “filled in”, but some of the smaller details were sort of smooshed out. I am now splitting the difference and trying 75%. I also bumped the retraction amount from 3mm to 4mm since most nylon manufacturers seem to recommend a greater retraction amount.
Sure would be nice if anyone else could chime in here with their own experiences on the flow percentages, printing with nylon, etc.
I have had most of the problems you’ve mentioned. Z axis height was a big one for me. If the nozzle is pushing the corner down, it is not detecting the leveling washer properly. Be sure your nozzle is clean - same goes for the washers. It also sounds like you need to update the printer firmware. If the nozzle is pushing down the bed corner it should go through a re-wipe process. If it fails the bed leveling process a few times the print aborts.
To update the firmware, download the latest version of Cura Lulzbot Edition from here: https://www.lulzbot.com/cura. Once downloaded, make sure you are in quickprint mode (Expert>Switch to quick print), then click Machine>Install default firmware. This will update it to the latest firmware and will apply the new bed leveling procedure.
Next, do a test print and let it lay down only the first layer. Stop the print and measure the layer thickness. In Cura switch to Expert mode by clicking Expert>Switch to full settings. It will ask if you want to copy the quickprint settings, click Yes. Click the advanced tab and check the Initial layer thickness. That will give you how thick the first layer should be. Hopefully it matches your printed layer thickness. If it doesn’t, click Machine>Machine settings and look for the Z-Offset field. Take the difference between your measured layer and the expected layer and enter it there. If your printed layer is too thin, add a positive value. If it is too thick, a negative value. This will help zero in your Z axis. Keep printing and checking until you get close. My layer height is within ±.05mm generally. Going through the above procedure helped me quite a bit.
The printer not extruding filament for the ring around the print (called the skirt) is common. The skirt is there to prime the nozzle for printing. As long as it is extruding by the end of the skirt, you should be fine. I have actually set my printer to do more than 1 line on occasion just to make sure it is fully primed.
I have started printing with nylon and have not made any adjustments to flow or filament diameter. I have adjusted retraction to help with oozing. All of my adjustments have been to temperature, cooling and layer height. Your issues with nozzle temperature is a bit concerning. It should be reporting accurately. That may be part of the problem as well. I am not aware of any temperature offset, but I know my Cura temperature and my Mini temperature match. If the temperatures aren’t quite right that can cause all sorts of issues.
Hopefully that gives you a place to start troubleshooting. I know how frustrating it can be when it is just one failed printer after another. Eventually you get things dialed in and then you switch filaments and have to start over
Yep, I discovered that really, REALLY cleaning the nozzle eliminates the excessive force on the first corner of bed leveling (really, bed measurement). It’s obvious that it’s looking for electrical continuity, and anything residual on the nozzle will interfere with that. I now carefully wipe the nozzle with a paper towel just before starting each print and cancel/reclean/restart if I see that excessive force. What’s surprising is that it came from the factory “dirty” enough to cause this problem… I’d have expected a brand-new nozzle (other than the test Octopus print) to be clean.
It also sounds like you need to update the printer firmware.
Going to do that this morning.
Next, do a test print and let it lay down only the first layer… This will help zero in your Z axis. Keep printing and checking until you get close. My layer height is within ±.05mm generally. Going through the above procedure helped me quite a bit.[/quote]
Thanks for those instructions, I will follow them and see what I find.
Eventually you get things dialed in and then you switch filaments and have to start over >
That’s what I told my son last night! “We’re going to have to go through this process for each type of filament.” Yay.
Excellent response, thank you so much, back soon with what we find!
Regards over extruding. First off are you measuring your filament and putting the value into cura? This is VERY important to getting a nice print, it doesn’t take it being far off to cause issues.
Second, e-steps calibration is also highly advisable. It’s easy and only takes a couple of minutes, once it’s done it’s done. Search the forum, there’s a lot of info and debate about it on here.
Third regards retraction, I think you misunderstand its function. It doesn’t suck the filament back up the nozzle, it relieves pressure to prevent more being forced out. The plastic sat melted in the nozzle will still be there and will still ooze out making your threads. This is combated in S3D with the coast and wipe functions. I haven’t updated cura for a long time so I don’t know if these are now included but they weren’t on the older version I have.
Yep, with professional dial calipers. Multiple measurements in multiple places, averaged, and entered. This Taulman 618 nylon is pretty consistent, right at 2.85mm with variation well under one percent.
Second, e-steps calibration is also highly advisable. It’s easy and only takes a couple of minutes, once it’s done it’s done. Search the forum, there’s a lot of info and debate about it on here.
Haven’t heard about that, will research.
Third regards retraction, I think you misunderstand its function. It doesn’t suck the filament back up the nozzle, it relieves pressure to prevent more being forced out.
No, I get that. Once it’s melted it’s not going to be pulled out. But retraction does relieve pressure as you say, which means you’re “only” fighting gravity at that point with respect to “drooling”.
