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FalmouthLouis

Problem with long tall prints

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As I've printed using UM2s, a UM3 and, most recently, a UM3E I've noticed that, as prints rise in height, the nozzle(s) seem to start catching on the print surface, in that I can hear a sort of thumping noise as the print head does rapid movements across the print, and tall thin structures can sometimes be knocked off balance.

 

Most recently, I've done an 80 hour print on the UM3E of a copy of a sculpture involving a lot of support material. (I used Breakaway and have separately commented on how well that has performed).

 

The overall print ended up 15 cm high, but the prime tower was knocked over at around the 9 cm level. This happened overnight, so I didn't pick up any advance notice of anthing going wrong. This led to a mess where the machine tried printing over where the tower should have been. I slowed things down and monitored more closely so managed to get a completed print, but, once again, I sensed that the nozzles seemed to be hitting the top of the print - which meant that I throttled right back to 50% print speed.

 

So, a couple of questions. Might the volume of a print slightly increase during the course of a long print,thus leading to an upward creep of the relative printing surface?

 

Is there any reason why the mechanics of shifting the print bed downwards should deteriorate over tall prints?

 

What can one do when a prime tower gets knocked over during the course of a tall print? How much would the quality of my print have suffered if I had printed without a prime tower? I'm tempted by the idea that one could have a mechanical replacement ready to put in place if the prime tower fails. I see something which could be carefully calibrated upwards until the print heads start putting a firm print down again. That may sound excessive, but printing for 30-40 hours with the machine printing birds nests where the prime tower should be is not fun.

 

 

Rook 01.jpg

Rook 02.jpg

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I'm finding prime tower failures come from:

 

Over cooling - fan on tower.

Print temps too low, increase standby temp

Make tower much bigger

Manually add in a shield to catch ooze from failed tower.

After days of failed tests, I'm using ooze shield instead.

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Latest version of CURA has circular prime towers, much less likely to topple. Also, it is best to move the prime towers away from the default position in the corners and put it in the middle of any sides. I put it middle-right, other put it middle-back, but don't keep it in the corners due to the deformation of the glass in the UM3/E. And make the tower a bit thicker: you can manually set the thickness of the tower, instead of letting cura calculate it on it's own, thicker tower will be more stable.

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Brulti: I'm using the latest version of CURA, so was dealing with a circular prime tower, and had it in the middle of the right hand side.

 

I take your point about toughening the tower up.

 

I still have this worry that, after a certain height, it sounds as if the nozzles start brushing against the print surface, suggesting that the print has expanded slightly. I'm fairly careful about printing with brims, so I don't think we would be talking about warping on the plate.

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I've printed some tall and big things, and I don't remember hearing the sound your describe at any point.

 

As far as I know, if cooling is done properly, there shouldn't be any expansion of the material during a long print.

 

Did you print with PLA? Did you have a front door or an enclosure?

 

The only reason I can see that the movements of the bed could deteriorate is if there's something blocking the way on the big screw, like a bit of filament stuck there after a print, or a lack of grease that makes it stick.

 

Not much you can do if the prime tower gets knocked over except stand there and catch the filament being extruded to prevent a bird nest and ruining your print.

 

Also, prime towers aren't mandatory when printing with UM materials. Their settings are quite good now, and there's little to no leakage when doing dual printing. I've yet to test breakaway, but I recently did a dual print with PLA of different color without a tower and there was no mix between both colors, no tiny bit of one color leaking while the other color is being printed. That being said, it also depends on the material: I wouldn't try a dual print with TPU without a tower, given how leaky TPU is.

 

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My tower failures all step from poor layer adhesion on the PVA/PLA interface on the tower. I'll get a bunch of good layers, then a section of bad layers (~7-20 mm up) Then later eventually the tower will get stretched.

8 hours ago, FalmouthLouis said:

I still have this worry that, after a certain height, it sounds as if the nozzles start brushing against the print surface, suggesting that the print has expanded slightly.

 

There is a chance the two nozzles aren't leveled right, one is dragging? Not sure which printer  you are using.

Most of the time I get rubbing like that, it is due to a small amount of part warping - fine edges can curl a little.

More fan can help with this.

 

7 hours ago, Brulti said:

Not much you can do if the prime tower gets knocked over except stand there and catch the filament being extruded to prevent a bird nest and ruining your print.

 

I drew a simple "arch" to form a manual ooze shield, it works for failed towers though I would prefer towers which don't fail.

VDIsy0fdgAbmOjrSmpS-LrVz8bsen_UTHH2gWUBe

 

EZsvH1qqJ-T11EURcsT93VpyJa6B9zIXzQ4QlX_B

 

 

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Brulti: This dragging noise is something I've had using both UM2s and UM3s. I work with an open front, which might be a factor.

 

I take your point about perhaps not needing a priming tower at all. My experience of an 80 hour print involving PLA and Breakaway left me feeling that I would trust Breakaway to behave itself. I've done a separate report on my experiences on this print, which you can find elsewhere on this site. Just search on "Breakaway"

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I'm pretty interested in the whole thing because breakaway is just not an option for me, my real prints have cavities which are not accessible.

 

Then again, my problems are less with stringing and more with poor layer adhesion from the printer choosing to print at temperatures other than entered into the settings.

=============

Oh, the temperature settings I'm having problems with were accessible, but hidden. I may well be doing a lot better than I was.

Edited by AbeFM

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@FalmouthLouis I saw your report on Breakaway, and I find it very interesting that it worked so nicely with a complicated form like your bird, while UM advertises this for long flat surfaces and advises to use PVA for things like your bird. I have yet to try breakaway, but I already have a positive view on this new support material.

 

As for working with an open front, past experiences have taught me than it is way better to keep the front open when printing PLA, especially for long prints like yours. I've lost countless prints until someone here on the forums suggested to leave the front door open to ensure better cooling, and it improved my prints tremendously.

 

 

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