Mandatory (according to me) disclaimer:
Just because you can print at 250mm/s does not mean you should.
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It requires specialty high speed filament (AFAIK only available in PLA). Most spools of filament will have a recommended printing speed either printed somewhere on the side of the spool or come with an information booklet (depends on the brand).
- For regular PLA it's usually around 60mm/s.
- Loss of quality is not the biggest potential problem: if the filament just can't keep up with the print head it won't adhere properly and you'll get a failed print. Either stuff will go down where it's not supposed to or it just won't stick at all and you'll end up with a nice trail of spaghetti coming out of your nozzle.
Even sticking to a reasonable top speed, just because your printer can accelerate at 2000mm/s² does not mean you should.
- Too fast (especially on the first layer) and you'll definitely have problems with adhesion.
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Since filament doesn't dry and set instantly, I've experienced times where my Ender-3 V3 SE (maximum acceleration: 4000mm/s²) will drag a part it's just printed when it starts a travel move and subsequent layers will follow that so your print will be warped.
- I've found this problem especially prevalent with supports, so much that I wrote my own post-processor that significantly reduces the acceleration while printing support and on a travel move immediately before or after the support to avoid the last bit getting pulled.
- In addition to that, I've lowered all the max values anyway. Slow print > bad print > failed print.
Settings for if you really insist on being a speed demon:
- Print speed. Duh. Set it high. By default Cura prints infill at that speed at everything else at half that so set the print speed to your printer's maximum speed and then set the speed for every feature type (not just infill) to the printer's maximum speed.
- Acceleration control. Also duh. Make sure everywhere (other than the max Z or E acceleration rates) that it's the highest your printer can handle.
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Jerk. This controls how much the printer can instantly change speed at a corner. In an ideal world, a printer could slow down as it reaches a corner, stop on the corner, then start moving off in the next direction. In the real world, you can't do that because it'd leave a blob at the corner. Jerk is how much the print head is allowed to instantly change speed at a corner:
- Lower limit = better quality (until you reach the aforementioned point where it starts leaving blobs).
- Higher limit = often instead of making a corner, the filament will just take the fastest route it can to try and keep up with the print head and will end up cutting corners a lot.
- With a high jerk value you also run the risk of the build plate moving so violently that it can vibrate the whole machine and cause the plate to move a step or two out of alignment with the motors. This can cause layer shift, where higher layers are printed not exactly directly above the previous layer because it's out of alignment.
Admittedly, have I ever tried printing a Benchy at 250mm/s with 4000mm/s² acceleration on my E3V3SE with regular PLA just to see how 😞 it turns out? No. But I've failed enough prints in enough other ways to have some reasonably good expectations of what would happen.
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GregValiant 1,411
Go to the Cura MarketPlace and load the "Printer Settings" plugin. After restarting Cura you will have a new category below the Experimental category.
Within the printer settings are "Max Accel", "Max Feedrates" and some others. Cura has to rely on those numbers because there is no communication between the app and the printer. Those numbers in Cura must match what the printer has in it's default settings. You can use an app like Pronterface to send M503 to the printer and read the response. It would look something like this which is the response for my Ender 3 Pro.
If the settings in Cura don't match what the actual printer settings are then the estimated time can vary by a lot.
You can enter a number like Accel 2000 into Cura and it may be a legal setting value but when the gcode gets to the printer and the printer has the Max Accel at 500 then that print would be a lot slower. It's a garbage-in-garbage-out sort of thing.
Another problem can come up with "Minimum Layer Time" and "Minimum Speed" which are both in the Cooling settings.
If your print speed is 200 but the model is small (like a Benchy) then Cura will slow down the speed (to the Minimum when necessary) to allow the layer to cool before the nozzle comes back around again. If you try to drop the Minimum Layer time to something like 1/2 second, and your layer cooling system isn't up to the task, you will end up with a pile of poop. I see that the "F" values in Layer 7 of that gcode are 7200mm/minute which translates to 120mm/sec. The speeds for the funnel are also 120mm/sec which points to the Acceleration setting being the slowdown.
There is a new post-processor "Display Info on LCD" which has a fudge factor for the print time. Some Creality printers won't except the M117 line but if yours does then the time remaining will be displayed on the LCD. If you find that your prints are consistently 10% faster than the Cura estimate then you could adjust the displayed time by 10%.
I wrote that post so I've been using it for a while and over time I've found that a fudge factor of 97% works for me. That's a difference between the Cura guestimate and the actual print time of only 3%. Close enough for government work.
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