BIG blobs on purge towers

[dbrandwood 0]

Most people seem to have issues with towers toppling over. hat's not my issue. I'm printing a piece and it has a band of a different colour mid-way up and another near the top. My problem is when this colour change occurs it's leaving big blobs of filament from the band colour on the edge of the tower, each layer in a slightly different position around the edge of the tower so eventually there's a few rings of these blobs. What seems to be happening is when the band colour comes in, the hotend pauses over the the edge of the tower, after purging the filament, the tip oozes and a blob forms, the hotend then goes on to do the new layer, the blob then cools. My problem then becomes that at some point during this repeating process the hot end catches on one of these blobs which protrude above the current layer height of the tower with such force that it either moves the magnetic bed plate of it skips a tooth on the drive belt then from that point on I have a step the alignment of print (see picture) and the print is ruined. sometimes it dislodges so much it's printing in mid air for part of the print and then the old birds nest appears. It never blobs on the primary colour, only the secondary colour. I've tried different filaments, same issue, The first couple of times it happened I had the filaments at different temperatures (only 5 degrees) and I thought the temperature change was what was causing the pause. So I matched the temperatures of both filaments but I still get the pause, the resulting oozing and the inevitable blobs which in turns results in the bed shift. My towers are solid, they don't fall over but they're still causing me a great deal of grief and many a ruined print. I tried swapping to Prusaslicer, the towers are far superior but I just can't seem to dial in the print settings to get as good a print finish as I can in Cura. I a perfect world I'd have Cura but with Prusaslicer's towers, Alas not an option, can some please tell me where I'm going wrong with Cura.

[Slashee_the_Cow 272]

It would really help if you could share your Cura project file (.3mf, in Cura get it ready to print then go to File > Save Project). At least knowing what printer you have would help 🙂

 

I'm not sure if you're using the term "purge tower" correctly 😕 A purge tower is what a multi-extruder printer prints in a corner usually to get the new extruder ready when before it starts printing with it. It's completely there for function and doesn't matter if it looks like crap.

 

I'd be very surprised if your nozzle was able to grab or push the model with such force as to move the print bed (unless the magnetic force from the bed is so weak it couldn't even hold a paperclip). Skipping a step or two on the motor when it hits a blob is something which might be possible if you don't have your belt tensioned correctly.

 

You might also want to check your setting for Travel > Retraction Extra Prime Amount: if it's retracted the filament, that makes it push a bit more than was retracted out to make sure there's enough pressure in the nozzle that it can start extruding as soon as soon as it's supposed to, but it can also result in overextrusion. I've never needed it, but it really depends on the printer (and you're more likely to need a little bit if you've got a Bowden extruder just because of how long it takes the filament to react to changes).

Also if Travel > Retract at Layer Change is on, it'll be doing that every layer, and if it's overextruding a bit that effect can sort of build up.

 

Without a project file or anything to go on it's really hard to try and make informed suggestions.

[PizzaTijd 12]

Pictures or a video wouldn't hurt either. As slashee said, prime/purge towers are meant to look sloppy. Whenever I use it it's usually completely covered in oozed blobs of breakaway - which then don't end up on my proper print.

 

Where it gets weird is that the blobs interfere with your print head enough to the point where it's pulling the plate with it. Prime towers are generally pretty thin in diameter and should just fall over if you apply any real sideways force on them - the amount of adhesion you would need to your build plate would be pretty impressive (ofc this is with my specific printer setup, which is an S5 with a heated glass build plate)

Edited April 25 by PizzaTijd

[Slashee_the_Cow 272]

38 minutes ago, PizzaTijd said:

Where it gets weird is that the blobs interfere with your print head enough to the point where it's pulling the plate with it. Prime towers are generally pretty thin in diameter and should just fall over if you apply any real sideways force on them - the amount of adhesion you would need to your build plate would be pretty impressive (ofc this is with my specific printer setup, which is an S5 with a heated glass build plate)

I'm guessing a much less expensive printer than an S5, with a magnetic PEI/PC plate like my Ender-3 V3 SE.

 

It would still be pretty damn impressive to be able to pull one of those plates off though (unless your magnets are exceptionally weak).

Edited April 25 by Slashee_the_Cow

[dbrandwood 0]

Hi guys, Firstly, apologies for my "purge tower" description but you obviously understood what I meant, I'll just decribe it as tower from now on. Thanks for the responses. Whatever is giving it's not the bedplate. I have two Geeetech A10M's (you're right, cheap compare to a S5 but trying to find a decent dual colour printer sub £500 isn't easy, one is a standard stick-one sheet that comes with the unit, the other is  a magnetic bed with a PEI plate, on only one occasion did the  PEI plate move, practically ripped the plate off the magnet. I'm not joking about the tower not budging, it's rock solid. Especially on the stick on bed plate. I don't know what Geeetech use but my prints (and tower) are so well adhered I have to use a craft knife blade to get them off the bed (before your ask, no my Z offset isn't too low, even after the bed has cooled back to ambient temperature). I used to have issues with the towers knocking over but I increased the size to about 35 diameter and put a brim on them and haven't had much of a problem with that since. As for retraction I've turned it off, a peculiarity of the A10M is if your filament is retracted, the other side fills the gap and just causes jams as the two are so close to the nozzle.

 

I know exactly what you mean about getting blobs, I had a CR-X until it died and this used to leave a length of filament on the tower about a millimeter in diameter and about 5mm long on every swap, almost looked like a sonic the hedgehog but these are definite round blobs about 6-7mm spherical diameter. I've no video but I have attached a 3mf file if it helps First attempt failed but would let me delete it so tried again so there may be two attached).

GA_R3_14th Silver Dock Base.3mf Dock Base Apr24.3mf

Edited April 26 by Slashee_the_Cow
Removed second link to file

[Slashee_the_Cow 272]

The parts of your model aren't quite lined up:

It could be getting caught when it attempts to print juuuuuust slightly further around than the main section.

 

Also at the top, there's a small gap between the ring and the area surrounding it:

It's because the ring is "rounder" (has more segments in its circle) than the model around it.

The same applies to your coloured sections:

Hard to see (so I added a highlight) but there's also some sections where the difference is enough that there's actually a gap between the two:

 

There's absolutely no way I can say with any certainty that's what your problem is. But it definitely doesn't help. If it's trying to extrude slightly out of position relative to what's already there it could get a, especially if it's priming itself as it gets there.

 

(Mod tip: you should probably edit your first post to change the title to something like "big blobs at colour change" or something like that)

[dbrandwood 0]

Thank you for your analysis of the model and I it may not be perfect but the misalignments are microns and in Inventor the two models are aligned  to more than 4 decimal places (in millimetres at that) via planes so maybe that's a Cura issue too, the alignment when merged in the program but we digress and I can live with the miniscule misalignment as it certainly isn't the problem. As I'm the one who's been seeing this happen I know full well it's not the model causing issues. If I sit around and melt the blobs away while it creates them with a flame and flatten each one,  the model prints beautify and the misalignments you've noted aren't visible without a magnifying glass. When I say the blobs are the issue, you (well, I actually) know it, they go with a hell of thump, the whole machine judders and it's ALWAYS when it set's off on the return to the print job. If I get chance I'll see if I can catch it on video this weekend. I know it sounds like I'm exaggerating but believe I'm not. Also it's definitely an issue related to Cura towers, it NEVER happens when it's coded in Prusaslicer, their rectangular towers give me no grief what so ever, however, as I've previous said for whatever reason I just can't seem to get Prusaslicer to dial in the quality of print I can get in Cura hence why I want to do them in Cura and not Prusaslicer. What would be perfect is Cura doing a tower like Prusaslicer as it never pauses over the tower and thus does ooze whacking great snot ball over the tower, but that's not going to happen any time soon lol.  Maybe if Cura had this pause over the entre opening in the tower then wiped on it's way outward would be the answer. I'm simply looking a resolution I didn't have with the CR-X but only applies to these damned A10M's. I'm not blaming Cura, If I'm doing something wrong I'd just like to learn how to correct it

[Slashee_the_Cow 272]

Any chance you could post the exact gcode file you're trying to print? There might be something that explains how the printer is doing it (even if not why).

[dbrandwood 0]

Hope it helps. be nice if you could figure out the issue, it's doing my head in lol

GA_12th Dock Base.gcode

[Slashee_the_Cow 272]

The discrepancy between the two models is enough to see in the gcode preview (orthographic view):

Which would possibly explain something if it started or ended sections of that colour at the ends... but it doesn't.

 

I can't help but notice you're printing the second colour a little cooler than the main one. With PLA that shouldn't cause any problems like warping. Although your materials show it's glowing PLA - I have no experience with that (and how it behaves), although in your photo it looks like it's a ballooning out a bit. Have you tried printing with just some regular PLA as the second colour to see how that behaves? If that works you may need to dial in the material settings on the glow PLA.

 

And remember: small scale testing is your friend: if you use the move tool to turn off Drop Down Model and then move a lot of it through down through the build plate, you can get to the sections you're having problems with a lot quicker (and with less wasted filament):

[dbrandwood 0]

While I do appreciate the constructive criticism/help on the model issues, it's not really those that are the issue here, it's the bloody great globules of molten filament I need rid off on the towers and with all due respect there's been no comment on that other than the disbelief they hold up when being hit by the nozzle. I was more hoping someone could help me resolve these. The code I loaded up does have a temp difference, it was originally like this as from temp towers the two differences where the best settings for each filament but then, I had my blobs issue. I manually changed all M104's to the same temperature in the hope it would stop the pausing over the tower at filament changes but it didn't. I still have the pause, it still oozes excess material in the same spot. What I'd really like is for it to ooze in the empty centre of the tower and wipe on it's way out and that is what this post is about really rather than trying to fine tune my model.

[Slashee_the_Cow 272]

13 hours ago, dbrandwood said:

While I do appreciate the constructive criticism/help on the model issues, it's not really those that are the issue here, it's the bloody great globules of molten filament I need rid off on the towers and with all due respect there's been no comment on that other than the disbelief they hold up when being hit by the nozzle. I was more hoping someone could help me resolve these. The code I loaded up does have a temp difference, it was originally like this as from temp towers the two differences where the best settings for each filament but then, I had my blobs issue. I manually changed all M104's to the same temperature in the hope it would stop the pausing over the tower at filament changes but it didn't. I still have the pause, it still oozes excess material in the same spot. What I'd really like is for it to ooze in the empty centre of the tower and wipe on it's way out and that is what this post is about really rather than trying to fine tune my model.

My suggestion of a test using regular PLA as both filaments stands, regardless of the quality of the model.