So I've been using my latest greatest KISSlicer settings to make some parts.
In the following picture I printed the same part at different speeds. The left part was printed at 20 mm/sec, the right part at 30 mm/sec. All other variables were kept the same.
Both parts are starving for filament to some degree which is especially noticeable on their right edges; however why does the part on the left side of the pic look like it's starving for filament more than the part on the right side?
When I print at a slower speed for example 20 mm/sec vs 30 mm/sec does that also supply less power to the extruder?
No if anything the extruder should shave more torque available at lower speed, though at the speeds involved the differences would be minimal.
Could be that the filament is sticking to the inside of the Hotend more on the slower print, causing more back pressure. There is an effect with all metal hotends where plastic flows better above some minimum speed. Though that's not really an issue with hotends that use PTFE liners.
Hard to say exactly what is happening in the print, is it ABS or PLA?, how much retraction do you have set. Retraction can cause issues like the one you're seeing, and it's worth printing a few objects with retraction disabled, so you can rule it out as a cause.
I was surprised to find out that PLA printed better for me at 100 mm/sec than it did at 40 mm/sec. My theory is that the faster the extruder is turning, the less the impact of it starting and stopping in pulses. (Stepper makes a step, filament pressure increases, nozzle pressure increases. Stepper stops stepping, nozzle pressure decreases. So, the faster it turns, the less the difference in pressure.) I'm not sure if my theory is correct but it's the best I can come up with so far.
If you are printing ABS, you will not likely have problems with torque because it will go like a greased goose given enough heat. If you are printing PLA, pushing filament faster may help with avoiding heat soak that will eventually lead to jamming, simply because you are adding room-temperature mass to the equation at a higher rate. Heat does creep up that PTFE liner at some rate, so the greater amount of incoming filament per second will take up some of the heat from the liner. Even with hot ends that have cooling fins machined into the PEEK section, it still kind of sucks. PEEK is used because it transmits heat slowly, so using PEEK in a cooling solution that involves drawing heat out of a PTFE tube is already an uphill battle. (That's why so many people say the E3D all-metal hot end is the way to go for PLA.)
Temp can also be an issue. Some PLA likes to be printed at 180, other PLA doesn't get soft enough unless it's more like 195-205. AND, the same PLA that prints happily at 180 might need 200 in another hot end, simply because they have different thermal mass. There are actually three different varieties of PLA, and each has a different optimal temperature ranging from something like 170-220. If you're printing too hot, but not hot enough to jam, it may come out with an inconsistent sheen, so try playing with the temp. If you crank it up and it comes out with an odd reflectivity, dial down the temperature a little and see what happens. PLA is great stuff, but you have to be willing to deal with its learning curve. Once you deal with it for awhile it becomes easy, as long as you have the right hot end. If you don't have the right hot end, or your cooling isn't good enough, it can be a real bear.
