Hi Robert - Thanks for your help. Retraction is enabled and I have the following settings in the Expert menu:
Minimum travel: 1.5
Enable combing: Ticked
Minimal extrusion before retracting: 0.02
z hop when retracting: 0.0
I can see the little blue lines going up after slicing.
You may also check if you have melted material on the outside of the nozzle. Check also below the cover of the print head.
Check also that the Bowden tube is secure at both ends.
On my brand new UM2, 4.5mm (the default) wasn't enough. It needed more like 5.5 or 6mm. 5.5mm was enough for me. After I secured the bowden better (a month or two later) I was able to reduce that to 4.5mm. Try increasing your retraction a bit.
Also for some filaments I have to lower the temp to 190C to eliminate stringing but that may mean printing even slower. Although usually 210C is plenty cool enough. Also make sure your travel speed is fast - 150mm/sec minimum - try 250mm/sec. This helps break the thread/string. Moving at 250mm/sec is not a problem for pretty much any 3d printer out there - it's the acceleration where the UM is so impressive.
Thank you all for your help.
Things are getting worse as I don't seem to be able to print at 210°C anymore. Nothing comes out despite numerous atomic cleanups and ensuring that the outside of the head is clean.
Is it possible that these problems are caused by some debris is stuck in the Nozzle? If so, what should I do if the Atomic method doesn't help?
I have a ultrasonic bath at home. Is it worth a try, and if so, is there a tutorial somewhere that shows how to dismantle the Nozzle?
Cheers
Things are getting worse as I don't seem to be able to print at 210°C anymore
This is a common problem on the UM2. I suggest you go over to this thread and print this test piece at 230C which will test out your thermostat, extruder path, feeder, bowden, filament, everything at once. It is *critical* you test at 230C even if your problems are at 210C.
http://umforum.ultimaker.com/index.php?/topic/4586-can-your-um2-printer-achieve-10mm3s-test-it-here/
No, it's unlikely to be related to nozzle problems. You've got too much filament coming out, rather than not enough. You need to make sure it's really retracting; that the plastic you have laid down has space to fit, and time to cool; keep the head pressure as low as possible (i.e., print thin layers and/or slowly) and make the moves as quickly as possible.
1) Make sure retraction is actually happening. Do you hear the double chirp of the retractions, and if you hold the filament lightly between your fingers can you feel it moving out and back in, each time? I'd turn off 'enable combing', and set the minimum extrusion amount to zero, to make sure retraction really happens.
2) On the printer, set retraction to 5.5mm at 35mm/s.
3) Set the travel speed as high as possible - you should be able to do at least 250mm/s. This will reduce the time spent moving, and so the time for oozing.
4) It looks like the columns are printing solely out of concentric passes, due to the thick shell? Try reducing the flow a little bit so that there's no chance of excess plastic building up in a limited space. If it does, it will get on the outside of the nozzle.
5) Make sure all your fans are running properly, and be sure to set a minimum layer time of at least 7 seconds or more, so that the plastic has time to cool.
Re-reading the thread that gr5 pointed me to, I un-thightened the four screws at the top of the head and ran the cylinder test. It looks alright, but I'm not sure that I understand why I've got holes at around 5mm3/s and not after?
As the cylinder looked quite good, I re-launched the print that was causing me troubles to see if the untightening of the screws solved the problem. I'll let you know how it goes.
@illuminarti: Thanks so much for taking the time to highlight all these points. I'll retry the print with the heavy stringing using your suggestions once the current print is done (probably tomorrow).
The problem at 5mm³/s was probably just a random skip due to something about the filament... maybe it got caught up on the spool, or had a slight irregularity in it or something. The fact that it recovered ok, and compelted the test shows that there's nothing to worry about.
I don't understand about loosening screws. Did I say to loosen screws? The 4 thumbscrews should be tight. The bowden itself can be locked down better if you want but isn't mandatory. I think I suggested a longer retraction distance (more than 4.5mm - maybe 6mm is right for you).
Several people mentioned loosening the four thumbscrews in the thread which you kindly provided above. This really worked for me in terms of solving my second issue (being unable to print at 210 and hence not being able to implement your suggestion of lowering temperature). In fact I'm about 12hours into a fairly long print at 210 and it hasn't failed yet.
The stringing issue is still there and I will be implementing your and illumination other recommendations over the weekend.
Thanks again!
The thumbscrews need to be snug, but not overtight. Depending on what position the Bowden and collet are in before you tighten the screws, you can end up putting too much stress on the end of the Bowden and causing more problems that way.
Also, I've seen a printer where the thumbscrews were tightened so much during assembly that the linear bearings in the head deformed and started making some very weird noises as the head moved.
I've made several more tests and stringing is getting better (although it still there), but I now have a new issue. The layers don't seem to be aligned anymore the final result looks "wobbly" (see pictures).
All the settings are the same as in my first post, except:
Something is slipping on one axis. Most probably it's a pulley which got loose.
@Dim3nsioneer: Thanks for your help. I had a quick look but couldn't find anything loose and the belts seem to quite tight. Would you have any advice as to how best to check if a pulley is loose on an UM2?
Just from a very outside view (as I do not have an UM2), you may try to make a mark with a pen on each pulley and an according mark on the rod, print something and check if the marks still correspond after the print has been shifted (just abort the print).
Good idea. Many thanks!
I need to go but will try that tonight and revert back once it's done.
The higher speeds moves are causing skipped steps, it looks like. It might be a physical slipping of a pulley... most likely on the short belts. Or perhaps some extra frictions somewhere, such as a belt or pulley rubbing on the frame, or not sitting quite straight in the pulley.
Power the printer off, and try moving the head by hand - pushing on both sliding blocks on an axis at the same time is best. Feel for any resistance; both axes should be equally easy to move. Have you lubricated the printer lately? A few drops of sewing machine oil on the axes and cross rods may help.
You might only need to tighten all the pulleys. Tighten the heck out of them. The hex screw should twist a bit. There are 5 per axis on the UM2 (6 on the UM Original). The most important 2 are the one on the motor and the other one on the short belt.
Technically there are 5 on one axis, 6 on the other, on an Ultimaker². At the top, the y short belt goes around a double-sided pulley with a single screw in it, that also functions as one of the 4 long belt pulleys. The x short belt has its own pulleys, separate from the 4 for the long belts.
@illuminarti and gr5: Apologies for not having replied sooner as I was travelling. I really appreciate your help and will lubricate the axles and tighten the pulleys tonight. I'll keep you posted.
Thanks again!
I've lubricated the axles and made sure to tighten the pulleys. It looks like it's done the trick as print quality is back to "woah"!
Many, many thanks for all your help and advice.
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IRobertI 521
I didn't see a mention of retraction being enabled or not, that would be the first thing to check. It's a checkbox under the "Basic" tab in full settings mode. Also check the expert settings for retraction and see that "Minimum travel" hasn't been set to something weird.
After slicing the object, switch to layer view and look for little blue lines going straight up from the print, these indicate retractions.
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