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UMS5: print speed vs quality

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I have an UM S5, and I need to better understand the relationship between printhead movement velocity and print quality. Until yesterday, I always left the speed at the default value, which I think is 45 mm/s. Then, upon reading some posts here, I stepped up to 70 mm/s. The result was a horribly clogged AA0.4 print core, with an enormous blob of PLA encapsulating the nozzle and large parts of the print core! I managed to remove (most of) the debris with a combination of hot-air gun and dental surgical instruments.


Now I have reduced the speed to 30 mm/s, and the current print seems to be OK. However, I am not even sure that the printhead accident had anything to do with the increased speed (although it seems likely). Might community members please elaborate on speeds appropriate for various materials and nozzles, and offer some advice? Thanks in advance!

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When you print faster and/or use a thicker nozzle diameter, the AA 0.8 for example, then you also have to increase the print temperature to ensure, the needed amount of plastic can be melted quick enough for the higher extrusion. You probably don't need much more temperature, maybe 5° C for your case, so I am not sure if this caused really your clogged nozzle.


Maybe your nozzle was already a little bit clogged and the increased print speed was just the rest to cause the problem. It is also a good advise doing some hot/cold pulls from time to time and always when you change different materials (PETG, PLA, Nylon, ...)


You should also unify all the print speeds, which gives you a better result than different ones. When you set 70mm/sec, then only the infill I think will be printed with that speed. All other speeds are calculated from the base value you set. But with every change in print speed, you get a brief over or under extrusion which affects the print quality.


But also with default settings and 70mm/sec print speed you should be able to print. Maybe do now some hot/cold pulls to start with a clean nozzle and retry to 70mm/sec without unifying the speeds and just increase the temperature a little bit.

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Your print speed, nozzle width and layer height define the volume per sec of filament that needs to be extruded. As the volume increases you need to reduce the viscosity of the filament, which is done by raising the extruder temp. As the filament starts to become too viscous for a given volume you will start to get under-extrusion. As an adjunct, manual/hardware problems with the filament and feeder sub-system will lead to the same problem.

The reverse of all the above applies; if the viscosity is too low then that will lead to over extrusion.  

So whenever you change one of the three variables above you need to consider changing the extrusion temp. so that the viscosity matches the volume per sec. required to be extruded.

Now if you were to, say, change the print speed from 50mm/s to 60mm/s or the layer height from .250 to.260 it is extremely unlikely that you would need to worry about the extruder temp., unless you are already way off the optimum temp. and the small change pushes you over the edge. But if you were to double the print speed or double the layer height it is highly likely that you would want to increase the extruder temp.

Finally the filament being used has an impact and I am including here a PLA filament from the same manufacturer but in a different colour. For sure if the optimum setting on YOUR printer is say 4mm nozzle, .300 layer, 30mm/s at 190 temp. then just about all PLAs will go through OK with those settings. But that does not mean you are at the optimum settings, which is probably fine if you are at concept modelling stage but probably not if you are in final production.


If I buy a filament I have never used before I always test it to establish the optimum settings  for a range of print speeds and layer heights.


And may I endorse @Smithy comments on unifying all print speeds. The only time I would change that would be if I had something with a large surface area, > 50% of the print bed, maybe a plinth and it just did not make sense to print the infill so slow.

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