So recently i have discovered my 3D printer (velleman K8200) has a serious problem with printing overhangs with PLA which causes them to curl up and catches on the nozzle to mis-align the print and distorts it. I have done a lot of research but to come up with solutions i’ve already tried including improving how it cools the print to slowing down print speed but to come with the same result. Using a test model for overhangs ranging from 45 degrees to 15 degrees overhang and currently it is barely doing well up to 40 degrees.
I am running out of ideas fast to resolve these issues that just ruins a print with the nozzle catching and mis-aligning the prints so if there are other solutions other than cooling or slower print speeds feel free to respond.
How did you improve cooling?
Looks pretty melty. Try dropping your nozzle temperature, maybe to 180-195C for PLA. Try disabling your heated bed. Maybe try dropping your extrusion/flow multiplier a bit, too; it’s hard to tell from the photos, but you might be overextruding.
You could play with different layer heights and see if you get different results. For slight angles, a smaller layer height might reduce any single layer’s overhang. For extreme overhangs, a bit thicker layer might freeze in midair better instead of tearing.
You need WAY more airflow.
Thinner layers do overhangs better. There’s less material sticking out over the edge.
It’s not just way too melty looking, it’s also overextruding like hell.
I agree with those who are saying “more cooling” or “more airflow”
@Tim_Visible It is already at good temperatures at 190C with a fan blowing on it and it also does suffer with under extrusion, it is at the mininum i could go before the prints started to have ‘waviness’ in the infill and causes them to curl up just like the overhangs. It could be how slic3r turns on the fan automatically since it seems it can’t detect overhangs that well to turn it on at max.
And to better explain what happened in the photos is the print has been massively mis-aligned with the nozzle as the result of it jamming against the curls. The strings at the overhang site was printing in mid-air after the nozzle mis-aligned it to about 15mm.
Oh, so just the stock fan on the machine? Bring in the big guns. As a test, put a big desk fan or window fan next to the printer and have it blow over the bed during the print, starting after the first layer. See if that helps.
Desk fan is my standard setup because I never got around to mounting a part cooling fan. One day.
@Tim_Visible The problem i can see with this is that the heated bed will cool down too quickly and the printer actually stops as a failsafe until the heat bed recovers, plus the fans that i have are way too big for my desk as it’s ment to chill a room.
What does your part cooling fan and extruder setup look like? From images I see on the web of this system is it really just a unducted fan hanging off to the side? As others have mentioned I’d focus my attention there.
However, there could be several things going on at once here with the cooling efficiency of your part cooling fan, the layer thickness, and the speed of the print.
Your material temperature is in a normal range for PLA but a bit towards the low side. In this case a slightly higher temperature (+5 to 10 C) might help as it will reduce the curl coming out of the nozzle and produce a flatter strand.
In general the thinner the layers (less material mass to dissipate the heat) and the shorter the dwell time of the head on the overhang (print speed between 40 - 60) with as fast as possible part cooling, the better.
I can not emphasize enough the importance of really good part cooling. I have a high efficiency duct I designed my printers that directs air right at the nozzle tip (you do not want it blowing across the heater block) parallel to the top of the model removing the heat away from the model quickly. It allows me to generate 5 mm horizontal overhangs in mid air and is flat by the third or fourth layer printing 0.1 mm thickness. I can do 15 mm spans with less than .1 mm of sag. My longest span to date was around 95 mm with less than 0.3 mm of sag and flat by the third layer. Here is an example of the part cooling fan duct I use. http://www.thingiverse.com/thing:1454709
Bed temperature should not come into play with PLA if you are spanning more than 1mm above it. Bed temperature is typically a factor or getting the first layer to stick and then keeping the part stuck to the bed without curling and without cracking or popping off the bed.
Here are my set up parameters:
Use calibrated filament to compensate for physical dimensions as well as its thermal properties.
PLA at 195 - 210 C
Print speed 45 mm/s
0.2mm first layer thickness and 0.1 for all others.
Bed at 60 C minimum for the first layer. This is the minimum glass temperature for PLA and helps it stick to the bed.
Part cooling fan comes on 33% for the second layer.
By a total height of .5 mm (Layer 4) the fan is on full speed and the bed drops to 45C.
This drops the bed and first layer temp below the glass temperature “setting” the PLA so it will not curl up at the edges as upper layers cool more but keeping it warm enough that it does not release from the bed.
I use this simple bridge test as a benchmark.
Provides feedback on span distances and worse case horizontal mid-air overhangs. I can also check what the infill is doing and monitor ringing on the vertical sides with one of them being non-parallel to the print axis.
I can tell you right now that there is no possible way in hell that this machine is ‘almost underextruding’. You have piling on the solid infill. You have piling practically everywhere on this print.
You are using a heated printbed right? Don’t use it for PLA. The heat rising up from your printbed is causing this. The temperature below your overhang is higher than above… Adding lots of ventilation helps, but switching of your heated printbed solves it. You don’t need a heated printbed for PLA if your ambient tempereature is somewhere in the 20-30°C region.
Agreed, set your heated bed temp to 0. You shouldn’t need it for PLA, and the extra heat it’s radiating into the part is working against you.
I’ve had some PLAs be able to print on unheated glass, and others wouldn’t. So don’t take the advice of “turn off your print bed” to be 100% accurate. It’s worth a try though. Another option is to turn off the heated bed after the first layer is finished.
@ThantiK . True. Had the same issue which is why I use a gluestick for those types of PLA when I print designs with steep early layer overhangs. Only heating up the bed for the first layer didn’t work for me. I insulated the bottom of my printbed, so it heats up faster but retains it’s heat for a longer time. As a result it is still too hot for the first few overhanging layers and the curling still occurs. @Raymond_Tang , if you want to validate this empirically, but you experience first layer adhesion issues, use blue painters tape or a gluestick to work around this.
Xxxmov