So, I've gone nuts, and installed a 0.9 degree stepper on my extruder. I'm running Marlin 22.214.171.124 on the Predator, and had previously calibrated the extruder to 410 steps per mm. So I upped that to 820 to compensate for the new motor. I had to swap two wires, and the results are well worth the effort, even without fine tuning or calibration. No ghosting, no salmon skin, no blobs, no stringing.
Tomorrow, I'm going whole hog and replacing the axis steppers with 0.9 degree units, and replacing the drive pulleys with genuine Gates 16 tooth units, the belts with genuine Gates 2GT3, and the idlers with genuine Gates 20 tooth units (to replace the stock smooth idlers). I've also got an E3D V6 hotend, which will take a bit of machining to install. But steppers, belts, and pulleys first. Just placing the new Gates belt in the new Gates pulleys feels distinctly more "precise" by hand, so I'm looking forward to the results.
I'm also going to install Sorbothane 40 OO pads under the feet to help in killing mechanical crosstalk between the x,y, and z motions. With these mods, the machine is down to 5 micron resolution.
I obtained all of the parts (motors, pulleys, belts, hot end) from E3D-Online, and they all arrived 3 days after I placed the order. At least for the extruder motor, I didn't have to do anything other than re-set the steps per millimeter, and shorten three screws on the extruder because I'm direct drive (no bowden).
I'll follow up after the axis motor, pulley, and belt transplant.
There will be major improvements in the next release of Marlin, particularly in heater control. The difference is astounding, and ADC errors that have plagued Marlin for years have finally been fixed. No. Really. Even better is a completely new heater control paradigm called MPC (Model Prediction Control), which makes PID obsolete, IMHO.
At least on my Predator, the factory part cooling blowers are 24 volt, 0.2 amp Boosfan JD4010M, and they truly suck. They barely move air.
I replaced them with Delta BFB0412HHA-A units, wired in series to just one FAN0 connector. These are 12 volt, 0.08 amp units, and are physically a drop in replacement. I use two in series electrically so that each drops 12 volts, and the pair can run off of the same 24 volt FAN0 connector with the same PWM.
Although it is not considered "best practice" to wire BLDC motors in series, these are locked rotor protected, so that unless one blower fails shorted phase to phase (very unlikely), their low current draw and high impedance will prevent catastrophic results.
Why do this? The original units would barely start at 75% PWM, and barely move air at 100%. The new units actually start moving at about 5%, run smoothly and reliably at 10%, and will lift the printer off the bench at 100%. Just kidding, but the airflow is astounding, and actually having real air speed control over a large range is a huge benefit. And no monkeying with PWM settings in Marlin, either.
Plus, the new Delta blowers have dual ball bearings, so they should last for years. I don't know what the old blowers had for bearings, nor do I care, since they barely worked anyway. I may dissect one to find out.
The Delta blowers are commonly available from many sources, starting at about $7 each. I got mine in 2 days from Mouser for $14 each.
I use the Bakak duct from here on Thingiverse, and highly recommend it. The factory original duct basically just blew on the nozzle with the anemic air flow from the factory blowers, and I got rid of it long ago.
EDIT: I opened one of the old Boosfan JD4010M. It doesn't really have ANY bearings, per se. Just a plastic shaft rotating directly in a hole in the plastic housing. It's a miracle that these things spin at all.
I was hoping that Marlin would leap to 2.1, but no. Anyway, the latest full release works well on the stock Predator, and you can even use the MarlinUI, rather than the ClassicUI. MarlinUI is a full color touch screen interface. Temperature control seems more stable, as it should, since they finally realized that the Trigorilla Pro uses 12 bit, rather than 10 bit ADC's (thanks to me). In my opinion, it's still not good enough for platinum RTD sensors, but I'm working on that.
Motion control (steppers) seems to have been tightened up a bit, although I have no proof of that, other than M48 reports more realistic and repeatably believable values.
If you do use MarlinUI in configuration.h, you will have to "de-comment" Mesh_Edit_GFX_Overlay in configuration.h to get it to compile. Under ClassicUI, it compiles fine, and seems to work well. Bug report submitted.
I have a large STL that will go right to the extents of the build plate.
Everything lays down perfect and sticks well for 85-90% from center out, but that last outer bit close to the edge never gets close enough to stick down.
I have leveled and the probe hits all the points, is there anything else I can do?
The printer is really set up well and dialed in, I really want to use it for this STL