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Now that we have the correct amount of filament coming through the nozzle, it will be very useful to know the maximum extrusion rate that your extruder and hot end combo can provide. This will define one of the limits on how fast you can reliably print.

You can find the max flow rate for your hot end 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 Flow Rate = Max Input Feed rate * pi * (Filament Diameter/2)2

To find the Max Input Feed rate, bring your hot end 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.

On the Ender 3 Pro, using the PLA that came with the printer and heating up to 220c, I was able to extruder 50mm @ 6mm/s ok, but 50mm @ 7mm/s skipped. 100mm @ 6mm/s also skipped. 200mm @ 5mm/s worked fine, so 5mm/s will be the max feed rate.

Max Flow Rate = 5mm/s * 3.14 * (1.67mm/2)2 = 10.9 mm3/S2

So, for the sake of simplicity and to add a bit of safety factor, we will say that the stock Ender 3 Pro extruder and hot end combo can reliably extrude 10 cubic mm per second per second. At least for this PLA at this temperature. Every material will be slightly different, but this is a good starting point and should be more or less applicable.

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