Today I tried printing a own design switching quite frequently between PVA and PETG.
4 times, each resulting in a clogged nozzle which had be unclogged using hot pin.
I’m really new to the world of 3d printing.
So I would mainly like to know if this is a common problem or if I’m doing anything wrong + how to avoid in future.
Bambu Studio 1.9.3.50
P1S + AMS (latest firmware)
Layer height is 0.8 extra fine
Nozzle 0.4 Bambu PVA is only used for support interface Bambu PETG translucent is used for part itself + support base.
No changes to speeds or temp. profiles.
Only changes are support settings enabled, configuration of the support material used and support spacing zero for PVA.
Initially had a flushing multiplier of 0.5 and deactivated the prime tower (to reduce wasting material) - seemed to work for some PLA prints I did.
I already tried to recompute flushing volumes, using multiplier 1, re-enable the prime tower to use more support material.
Still got clogged nozzle.
The print seems to always clog the nozzle on layer 36 or 37 - 2nd or 3rd time switching from PVA to PETG.
I could observe that PVA is unloaded correctly - but when trying to load PETG and flush, nothing or nearly nothing leaves the nozzle and the extruder seems to slip as it can’t push the material in (if I interpret the sound correctly).
When I removed the hotend it was filled to the top with PVA and had to be unclogged by melting in a metal pin and then heating up the hotend and pulling.
Afterwards I always did at least 2 coldpulls using PETG and 250C to get rid of remaining dirt.
The first bit of the filament pushed out during the hot phase of the coldpull had a golden brown color.
I did see that PETG has higher max temperatur than PVA.
Is this a problem during flushing or should it simply work ?
I wonder if during switching the PVA is heated up to high or long.
Do I need to change the temp profile of the PETG to avoid such issues ?
Or is the small area of support material 3x7mm on that layer or the layer height a problem ?
Does it make sense to test using PLA instead of PETG ?
Just to see if this is a problem with the higher temp. of the “non support” material.
Any hints welcome
As said above - I mainly want to learn what I did wrong so I can avoid in future.
I did some further experiments without much success.
At least I could gain some more experience unclogging the nozzle
When using PLA and PVA (support interface) the part is printed without clogging the nozzle.
The PLA above some of the support interfaces looks ugly.
So I still need to fine tune PVA printing - but I don’t think this should cause troubles while flushing.
I noticed that the temperature when flushing the PVA when switching to PETG is 260C (max temp for PVA is 250). I tried slightly lowering that temp.
No success - nozzle was still clogged.
Does anyone has good experience using PETG with PVA as support interface ?
Could layer height of 0.8 be the problem ?
Could moisture in PVA cause clogging the nozzle ?
I unpacked it bit more than a week ago and also dried it in my oven - afterwards it was in AMS only.
Not sure how long you can use PVA without needing to dry again.
For now I’ll give up trying to use PVA as support for PETG.
I am also experiencing very similar issues as you using Bambu PVA and PETG.
To answer your question - “Could moisture in PVA cause clogging the nozzle ?” Yes.
But for me I know that is not the cause of the issue, as I made sure to dry it thoroughly and refilled my AMS with fresh desiccant.
I have not solved the issue totally yet, but I will say I’ve had better success with slowing down max volumetric flow of the PVA ≤ 1 mm³/s and tweaking some of the cooling parameters.
If anyone else has any insight to help us resolve the issue it would be greatly appreciated.
PVA is a very funny filament. It absorbs a lot of moisture and it gets sticky when it does that. In being sticky it will retract poorly and can easily lead to jams.
Before changing any settings I would advise to dry it thoroughly. You could be chasing windmills otherwise.
I did not try PVA in the Bambu but had a similar experience with BVOH.
The trick is in setting Min/Max temps for both filments into a common range. In other words, no Max temp in either material definitions shall be higher than the actual Max temp of the lower melting Material (PVA)!
Otherwise, the PVA will be overheated leading to both heat creep and burnt material residue.
Min/Max are, to my knowledge, only really used for filament change & loading. So if that is always in a safe temp range for both materials, it should be much improved.
Addendum: as @johnfcooley pointed out, water soluble filament is very prone to take up water. BVOH in the AMS did keep my dessiccant dry
I changed the PETG line to M109 S240 (down from 260) - but the PVA still gets somewhat brown/scorched
I also changed the PVA line to M109 S220 (up from 210) - the Bambu PETG basic was having problems being flushed - it made wierd noises pushing out the PETG (like starting to stick) around 215 but at around 213 the filament was all PVA - with 220, no more noises
I’m not sure how to completely eliminate brown/scorch. Gonna try a cold pull to get the brown completely gone and see if the brown I’m getting was just scorched left overs in the nozzle.
It sounds like you have room to play with a common max temp. Since the PETG seems to flush OK from 220 but you are getting burnt PVA when PETG is flushing it out at 240, I’d try setting both max temps to 230. And if that is still to high, you have the range between 220 and 230 to play with.
There is no reason to have sepparate Max temps as during a flush, both materials are present in the nozzle.
; FLUSH_START
; always use highest temperature to flush
M400
{if filament_type[next_extruder] == “PETG”}
{if filament_type[current_extruder] == “PVA”} ; added this line
M109 S240 ; added this line
{else} ; added this line - allows PETG to PETG color change to still use 260C
M109 S260
{endif} ; added this line
{elsif filament_type[next_extruder] == “PVA”}
{if filament_type[current_extruder] == “PETG”} ; added this line
M109 S220 ; added this line
{else} ; added this line- allows PVA to PLA color change to still use 210C
M109 S210
{endif} ; added this line
{else}
M109 S[nozzle_temperature_range_high]
{endif}
tested closely - the PVA did smoke/puff at 260 but not 240
tested and works with Bambu PETG Basic and new Bambu PETG-HF
Related to the scorching of the PVA, I ran out of Black PETG when testing and used white PETG. I discovered that the PVA was not scorching but was actually blending with the PETG. The support itself changed from the PVA smokey yellow (PVA only in test print) to a brown-black color (BLACK PETG) to a white tinted cloudy yellow (white PETG).
FYI when printing with the same test print and PLA black, the support was entirely the PVA color - no blending with PLA, only PETG.
The blended PVA/PETG supports did dissolve some but not completely like the PVA/PLA test print. If I have a print that I can’t get to the insides and scrape away the semi-dissolved PVA, I’d have to not use PETG.
Next task, I’ll look for ways to change the purge amounts to see if flushing additional black PETG can fix the problem. This will be a different thread/topic.
