MakerGear Forum

I'm going to try to change the print speed on one of my prints from 80mm to 160mm, I'm' trying to cut down the print time and want to see how it turns out at double speed. Would running at that speed need me to compensate by increasing the nozzle temperature. I'm assuming since its going twice as fast there's the possibility the filament may not melt fast enough at the current temperature and eventually clog?

Figured I'd ask you guys before I screw something up.

jdacal wrote:compensate by increasing the nozzle temperature

That'll overcook the filament when it's printing at less than maximum speed, which will be most of the time. Probably a Bad Idea, given how much fuss people around here make over setting Exactly The Right Temperature. [grin]

Thermal conductivity limits how fast you can ram filament through the extruder: the heater must melt the plastic and bring it to the proper temperature as it passes through (more or less) 10 mm of hot zone. The volume of plastic depends on both the cross-sectional area of the thread deposited by the nozzle and the XY printing speed across the platform.

Run the numbers: depositing a 0.4 x 0.2 mm thread at 80 mm/s requires melting 6.4 mm³ of plastic per second, which is 2.8 mm/s of filament going into the top of the hot end. If the hot zone is 10 mm long, the plastic must go from room temperature to 200-ish °C in 3 s. Increasing the XY speed to 160 mm/s means feeding filament at 5.6 mm/s and passing through the hot zone in maybe 1.5 s.

In round numbers, the heater must deliver twice the power to the plastic in order to melt it. That won't double the heater duty cycle, though, because nearly all the heat goes to the surroundings, but you'll certainly notice the little blinking red LED on the RAMBo will be ON more than it's OFF.

Bottom line: don't adjust the temperature, double the XY speed, fire that devil up, and see what happens. If the hot end can't melt the filament fast enough, the drive gear will carve a divot and tell you everything you need to know...

Thanks Ed! ... look for the mushroom cloud to the south.

The V3a running overvolted on a 0.66mm nozzle could keep up with anything you threw at it.

I link this video occasionally, this is 0.5mm layers (assumed 0.7mm width) at 100mm/sec print speeds. I'm running a 12v V3a at 19v, print temperature of 210C. Parts were ... ugly. I don't know what kind of PLA this was -- it felt almost waxy compared to normal stuff. It's my favorite plastic I've ever used, shame I only had 1lb of it.

https://www.youtube.com/watch?v=BGJska4xnyw


edit: if I did my math right that's 35mm^3/s, which seems pretty high ... but then again, that drive gear is hauling ass.

Hey Ed your numbers were right on the money it stripped at 160mm speed in about 10 minutes. Tried it at 120mm and seemed to run ok, but needs tweaking. Running back at 80mm until I get time to mess around with the settings. I am using low-end filament for this print, might have held on better with the higher priced stuff (as far as the stripping), but the cheaper stuff is needed for this one.

jdacal wrote:it stripped at 160mm speed in about 10 minutes

The divot tells all!

I'd expect the hot end temperature display to decrease slowly during that adventure, but, because it measures the temperature of the metal parts, rather than the melting plastic inside, it can't show you what you really want to know. Running the plastic faster increases the temperature difference and makes the readout less useful.

Your original idea of increasing the temperature would compensate for that difference, but only under those exact conditions of high speed output. When the plastic flow rate decreases (first layer, perimeters, layer changes, whatever), the temperature difference also decreases and the hot end overcooks the (slowly moving) plastic.

Keep an eye on the heater duty cycle: that gives a direct measure of the power draw, showing how much additional power goes into the fast-moving plastic to maintain the same hot end temperature.

If you can find a temperature high enough to make the fast flow work and low enough to not scorch the plastic at rest, while maintaining the layer bonding you need, you'll be good to go!

Sorry to be such a buzzkill... [grin]