MK4 sometimes too fast, especially for the infill?  

RE: MK4 sometimes too fast, especially for the infill?

Usually this is because of the melt speed/extrusion speed of the filaments. Make sure to check if the filaments have a posted extrusion speed and dial the speed back in the slicer if you need to. PrusaSlicer sometimes does it automatically if you select the specific filament brand, but I've found that inconsistent (and extrusion speed can be inconsistent even within the same brand). You'll also notice that some filament brand themselves as "high speed" and melt more quickly so they'll perform well at higher speed printing, though I've found success with filament that wasn't labelled high speed. 

RE: MK4 sometimes too fast, especially for the infill?

Great point,  @cupajoe24. I have no data for my filament, but will try to tune that parameter first. 

RE:

This sounds like the problems that happens with grid infill.  The lines of infill cross over each other on the same layer, and the crossing point is in the same place on every layer, which causes a build up at the crossing points that gets bad enough to rattle the nozzle at IS speeds.  I find cubic infill to be the perfect alternative - although it still has crossing points, those crossing points have a different x,y coordinate on every layer, so there's no build up.  It's just as quick and strong as the default grid infill, but doesn't cause the same problems.

RE: MK4 sometimes too fast, especially for the infill?

The problem is even more pronounced when you print PETG. I usually don't even try PETG even more with IS. On the other hand, I just upgraded a Mk3S to a Mk 3.5—which means it prints with IS profiles all the time—, and with a 0.8mm nozzle it prints PETG flawlessly. Don't know why my Mk4's (0.4 nozzles) are less happy with PETG. 

And as Chris said, grid infill is just bad. 

RE: MK4 sometimes too fast, especially for the infill?

I checked the settings in a project that failed horribly (all PrusaSlicer default profiles):

• Max volumetric speed 15 mm³/s
• Grid infill

I'll try another infill type. Interestingly, Prusa even mentions that problem with Grid in their infill documenation. One wonders why that's the default at all - I recall that in my MK3S+ profiles I had Rectilinear instead (not particularly for this reason, but Grid always seemed somehow bad). I'll try with Gyroid for now as it specifically does not cross itself and seems to come out well with the modell I'm currently trying to print. Will see if that's good enough, or whether I need to reduce volumetric speed as well.

RE: MK4 sometimes too fast, especially for the infill?

I suspect grid is the fastest, so that's what Marketing demands as we all know these days kids seem to be more interested in speed than quality...

Gyroid is a great infill but with its twists and turns probably not optimal for IS. I ended up using adaptive cubic for most run-of-the-mill prints with IS, and gyroid for stuff I care about. 

RE:

I print primarily PETG, and almost exclusively with gyroid. Grid is a problem, and so haven't tested cubic yet because I believe gyroid is stronger and my prints benefit from that strength.  The only challenge I have with my MK4 and these settings is that on large first layers the tip can pick up some build up that continues to slowly grow during the subsequent base layers (on large solid based models, but once I reach infill layers of gyroid, the small build up tends to clean itself off in the infill.  Occasionally on a longer print of 5-8 hours, I'll need to pause the print, wipe the tip clean, and resume.  I use my printer for functional parts which usually means I've modeled them myself and only one or two copies are ever printed.  I have a VERY low failure rate on my prints, but I always check on them every 30-60 minutes to make sure all is well, and so far have not done any overnight/unattended prints.

*edited to add.   I also slow down the first layer speed to 30mm/sec, which helps with bed adhesion.

-J

RE: MK4 sometimes too fast, especially for the infill?

I'm forgot to include that the prints mentioned above are using IS, with PETG, and I get very good results.  I've used Polylite PETG, Hatchbox PETG, and now using VoxelPLA brand PETG, of which only the latter is technically rated for high speed.  

-J

RE: MK4 sometimes too fast, especially for the infill?

I have now finished my problematic print successfully. Avoiding grid and reducing volumetric speed to 10 mm3/s did not suffice, in the end I also reduced speed to 50% on the printer GUI just to get it done. With that it was flawless. 

Experiments will have to continue to find proper slicer settings...

Thanks all for chiming in!

RE:

I wonder if maybe your temps are indicating incorrectly.  You mentioned that the layer adhesion seems to be inadequate when printing infill at full speed using the default settings.  Have you tried "tuning" the hot end temperature up by increments during fast infill to see if this helps with your situation?  There have been rare reports of faulty hot end thermistors on here and if yours is reading off, it could be keeping the hotend from reaching the temps that are shown.  The vast majority of us are getting great results with the MK4's default speeds, so I suspect there is something else going on with your printer.  

-J

RE: MK4 sometimes too fast, especially for the infill?

I had similar issues setting up my profiles for the FLSUN V400.

It can reach insane speed of 350/400 but I learnt that the nozzle and the filament doesn't. 😑  Especially the PETG.

On the net there are tons of posting that say that PETG has a reliable volumetric flow rate of around 8-10 max. I know that today with fast printers you may reach 15-18 mm3/s, but in reality is a matter of what you mean for "reliable":

- start the same print several time and get it correct 60% of times, or do you want to get it correct 100% of times?

Now many people are putting the speed before the quality. I saw many prints that were defective in several areas, and I got the comment "yeah... I know it is a little defective... but it took 15 hours instead of 25!" 🙄 

I did not get many issues on the MK4 with PETG, but to avoid mess I also use Gyroid either on the MK4 either on the FLSUN, since it solves the issue of the PETG not well melted, sticking on the nozzle and dropping out of the straight trajectory of the grid line destroying the infill. With gyroid there is no risk.

However the secret is a good nozzle. I have a Volcano on the FLSUN, and for my MK3.5 I mounted a REVO 60W for high flow (immediately replaced with the 40W version, since the current FW does not support the 60W yet... 😡 ) to ensure a good filament melting.

Another dirty trick I used on the FLSUN was to slide raise the filament temperature over the limit, but ensuring it is always extruded at high speed, so that the over heath melts the filament very quickly ensuring a very high flow rate, but I need to put extreme attention, because a slow down of the extrusion speed can burn the filament in the nozzle and clog it.

I never used those things on the MK4 or MK3.5 since I am happy with the reliability of the current stock profiles.