Print speed slow and appear to have regular extruder speeds
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@darnz What layer height are you using with that 1.2mm nozzle?
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@deckingman
Hi, 1st attempt was at 1mm
2,3rd and 4th attempt at 0.8mm -
@darnz
OK. Doing some very rough calculations, with that diameter nozzle and those sort of layer heights, I'd say that your extrusion rate is about 60% of the carriage speed. Now 11.4mm/sec for the carriage multiplied by my somewhat arbitrary figure of 60% shows that the extruder will be running at about 6.84 mm/sec. A quick look at you configuration file shows that you have the maximum extruder speed set to 400mm/min which funnily enough is 6.7mm/sec. Therefore it's fairly reasonable to come to the conclusion that your speed is being limited by the maximum that you have set for the extruder, so you need to set that much, much higher.The next problem you will face is that the speed you are able to print at will be limited by how fast you can melt the filament, but that's another matter altogether and has nothing to do with configuration settings. Having said that, it is probably the answer to your second question.
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Thank you for that!
Very helpful! And makes perfect sense!Have a super volcano on order as I suspect I will run into problems trying to keep up with the flow.
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@darnz Look at it this way. With a 0.4mm diameter nozzle and layer height of 0.3 mm, a 1mm long filament bead with have a volume of about 0.038mm^3. On the other hand, with your 1.2mm diameter nozzle and 1.0 mm layer height, the volume of a 1mm long filament bead would be about 1.13mm^3. That's almost 30 times greater. So you will be extruding about 30 times more filament than with a 0.4mm diameter nozzle and therefore the maximum carriage speed you could expect to use would be 1/30th of the equivalent speed using a 0.4mm diameter nozzle.
The super volcano will help, just as it would with a smaller nozzle.
Oh and you need masses of cooling air to cool the part. That kind of volume of molten filament takes a long time to cool (I know this from experience).
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So I Upped the max extruder speed and was able to achieve much greater speeds.
I did find that at just 30mm per sec, the extruder started to grind at the filament.
I don’t think that the standard heater cartridge and hot ended can deal with this kind of volume.
You mentioned making use of a smaller nozzle, I wondered if you had any advice for my current setup? Can I do anything to increase amount of flow
I did experiment with various temps, but again, at 30mm it starts to battle to keep up.For now I am going to fit a smaller 0.8mm nozzle.
I really just have the Aero on to see what this build can do.
I will soon be fitting a pellet extruder.
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@darnz Well as you have discovered, ultimately the print speed comes down to the volume flow rate of molten filament and that in turn is entirely dependent on the melt rate. If the extruder was grinding the filament at 30mm/sec then it's a reasonable bet that you started to get under extrusion caused by insufficient melting at about 25mm/sec. So assuming you used a width of 1.2mm and a layer height of 0.8mm then the volume flow rate is about (1.2 x 0.8 x 25mm/sec) = 24mm^3 / sec which is actually quite respectable for that type of hot end.
Now if you fit a 0.8 mm nozzle, the layer width becomes 0.8 and say for example that you used a layer of 0.6mm, then you carriage speed could be increased to (24/(0.8X0.6)) = 50mm/sec. But the print time will be more or less the same because you'll have more layers and each layer will be made up of more individual strings. Depending on the object geometry, it might actually take a bit longer because you'll have more non-print moves
Increasing the temperature should give a higher melt rate so should allow you to increase the print speed a bit (but not much). Beyond that, it's all about the laws of physics.
The melt rate is a function of temperature, surface area of filament that is in contact with the hot surface, and time. We can't do much about temperature without degrading the filament. Which means we have to concentrate on surface area and time. If you have a single melt chamber fed by a single extruder, for any given speed there is nothing you can do to increase the time that filament spends in the melt chamber, so the only thing you can do is increase the size (or more precisely the surface area) of the melt chamber. Which is essentially all that E3D do with their Volcano and variants thereof.
In my opinion, based on a lot of work that I have done, a better method is to use multiple melt chambers fed by individual extruders. Using something like a 3 colour Diamond mixing hot end, this give two things. Firstly, you triple the surface area of filament that is in contact with the hot surface because there are 3 melt chambers. Secondly, for any given flow rate from the nozzle, each individual filament moves at 1/3rd of that speed so you also triple the time that the filament is contact with the hot surface.
Using that technique, I have been able to print at 100mm/sec using a 0.9mm nozzle with 0.6mm layer height before under extrusion became apparent. That equates to a volume flow rate of about 54 mm^3/sec. You can read more on my blog here https://somei3deas.wordpress.com/2018/10/14/real-3d-printing-at-high-speeds-and-even-higher-melt-rates-with-a-large-nozzle/.
I have no idea how pellet extruders perform with regard to melt rate so would be very interested to know your findings.
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You can find the max flow rate for your hotend using a simple test and a formula. Then you can use those results in another formula to determine viable combinations of layer height, extrusion width, and print speed.
Max Flowrate = Max Input Feedrate * pi * (Filament Diameter/2)2
To find the Max Input Feedrate, assuming your extruder steps per mm is calibrated already and your heater PID tuned, you'll need to bring your hotend to the temp you'd normally wish to use for that material and start extruding some plastic. Start at 1mm/s and extrude 50mm, then increase it by 1mm/s and extrude 50mm again. Repeat this until you can see or hear the extruder start to skip steps. Back off the speed by 0.5mm/s until it stops clicking and try to extrude 100mm of filament at that speed. If it can keep up, you've found your max flow rate.So in my case, with a V6 hotend with 0.6 nozzle and 40w heater, I can extrude PLA at 6mm/s at 210c using filament measured at 1.71mm. Using the formula I get a max volumetric flow rate of ~13.8 mm^3/s. This is the volumetric limit of the hotend. This will be somewhat dependant on the material and temperature used, so feel free to try different temps and materials to see how they compare. I find that the ballpark is pretty inclusive of many filaments. To be on the safe side you can back off your max flow rate by 10% for a margin of safety.
I'm going to guess that you're not really successfully melting properly at the rate that @deckingman suggests above. 24mm^3/s for a V6 would be far beyond what you could really expect. I think the very wide nozzle is playing a part there because even though the plastic isn't fully melted, there is very little back pressure to cause it to skip. I would guess that your layer adhesions would be very poor. E3D suggests that you may be able to get a reliable melt rate of between 10-15mm^3/s based on temperature and material. My results fall in the middle of that range so it would seem to agree.
Using this result you can use the following formula to find your top speed based on the extrusion width and layer height you want.
Max Suggested Speed = Volumetric Limit / ( Layer Height * Extrusion Width)
So using that we can see a suggested print speed of 13mm/s, which is not exactly fast, but it's as fast as your hotend can reliable supply the volume of plastic requested. And as you can see, even though you could print at 54mm/s with the 0.6 nozzle, it's still limited by the melt rate, which is really the true speed of your printer. Using a volcano or super volcano greatly increases the volumetric limit and allows for large nozzles and faster print speeds.
I'm also very interested in seeing your results from the pellet extruder. From what I gather the flow rate can be quite high, but the system is very laggy.
If you want to play around with the excel spreadsheet I use to calculate all these things more easily if can be found here: https://www.dropbox.com/s/ihe3rl58z7sdyfu/calculators.xlsx?dl=1
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@phaedrux My calcs were very much "back of a cigarette packet" because I had to guess the layer height and the only clue I had about when under extrusion occurred was the Op's comment regarding the point where the extruder started to grind away at the filament. So the number I came up with was only useful in order to calculate what carriage speed might be possible with a smaller nozzle.
Your method would indeed give a better indication of the true melt rate.
For info, if you take a gander at the blog post I linked to, nozzle diameter does indeed play a significant part in all of this but in my tests, I had only had 0.5 and 0.9 to choose between. So it would be interesting to use your method with a much wider range of nozzle sizes to determine the exact relationship between nozzle size and volume flow rate. My gut feeling is that there will be a point at which further increases in nozzle diameter have no effect on volume flow rate. In my case, with my hot end, it could be greater it less than 0.9 mm. I have no way of knowing without buying a range of Diamond hot ends which would be really expensive. -
Many thanks, I will run these formulas today.
I think I will try them both on current 1.2mm nozzle as well as a 0.8mm
I really appreciate you detailed input and advice!
Thank you very much!
