Getting good prints with a e3d volcano hot end can be very tricky. But I've figured out a couple of base rules to follow that can help with printing. For my example, we'll be using a 0.8mm nozzle/width.
Step right or step off
First thing first, this guide is totally useless if you haven't properly calibrated your extruder steps. I explain how to easily do that in a previous post. Go a head and read how to calibrate your e-steps guide. After that, you can check that you are extruding the proper width. Once that's done, continue below.
It's all about the size
First thing to know don't try to print layer heights larger then 80% of the nozzle width. It's a general rule to follow for any nozzle type not just even a volcano. For our example of 0.8mm width 0.6mm layer height would be your max.
Printing speed is dictated by layer height
If you want to print fast, (ie.: 60mm/sec), you want to use a smaller layer height in comparison to the width of the nozzle. The height should not exceed more then 50% of the width of the nozzle. For this example, you can print at .4mm layer height with the 0.8mm nozzle and get a reasonable looking print with speeds of 60mm/sec. If you go faster make sure to set a smaller layer height. Your millage will vary, but seems to hold true on my system and of course the type of filament you print will also have an effect.
Go large, go slow
When printing at 80% height of the nozzle width you want to print slow around 30mm/sec. What I have personally found is printing at layer heights of .5 and .6mm at anything faster then 30mm/sec, would not get good layer adhesion and would stretch out and begin a ball of spaghetti. There just isn't enough time to squash down the filament to the previous layer.
Heating and cooling
Lastly, sometimes it might help to either reduce the temperature you normally melt filament or increase it if you are going fast. This is something that is totally dependent on your printer. But be aware to make sure you use active cooling, since the filament retains more heat due to the thicker lines it lays down, overhangs can be an issue. Good active cooling can help with this, even on filament such as ABS etc...
Throw everything out the window when messing with flow rate
Just when you thought things were clear, there is one exception to all of this. The flow rate better known as, the extrusion multiplier. Can be used to help print quicker at larger layer heights. So lets take the example of printing at 0.6mm layer height. For my printer, in order to get a decent print I have to run it at 25mm/sec speed. At 0.86 extrusion multiplier, I get a perfect .96 diameter line when printing. But at .6mm layer height I can't print any faster then 25mm/sec. If I increase that multiplier to 1.5 I can print at higher then 25mm/sec, but I lose a bit dimensional accuracy. The reason for this, is that you are pushing out much more plastic then before. There is a simple formula to figure out how much more plastic you are pushing out:
Print speed * extrusion width * your layer height = flow rate mm^3/s
My example would net: 25 * .86 * .6 = 12.9mm^3/s.
So what can we do with this number? I'm not really sure to be honest, other then you have some sort way to keep track of things numerically.
I think it's easier to just write down and track at what speeds you can print with and play with the extrusion multiplier to increase speeds on larger layer heights. No need to work with a formula. For example I have the following saved and I refer back to it when I need to print things:
0.32mm layer height
best quality, printing speed at 35mm/s
good quality, printing speed at 40 and 45mm/s
ok; sloppy infill quality, printing speed at 65mm/s
sloppy infill quality, printing speed at 75mm/s
Just use a calibration cube with an infill of 20% and run a bunch of tests at different speeds and layer heights. Keep a log of how things print out. And you have a handy chart to follow.
Retraction and stringing
One thing you will start to notice is a ton of stringing, especially if you use PLA. So far I've been using a retraction distance of 4mm and an Extra Restart Distance of -0.4mm. The last part completely removes blobs and zits caused from the retraction starting points. This is something you will need to experiment with and can change with different filament.
I'll make sure to add on more info as I discover more. Good luck and I hope this can help another 3D printing soul.
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