dkightley wrote:Holding that thought.....looking at the physics of exactly what is happening inside the nozzle, we have a pool of liquid plastic being forced through a hole at a fairly high speed. With a bigger nozzle....and demanding a greater amount of plastic...then the amount of plastic being "shifted" is higher. Stopping the flow of plastic cannot be achieved instantly.....so to get the flow to pause at the right time, then the moving force needs to be withdrawn sooner. Comments on the thread indicate that this "advanced stopping" of the flow has been turned off (or not used). I would prefer this to be tweaked, not turned off!
I have tried both coasting and wiping (multi-process to test what effect it had on the defects), neither helped. In fact, coasting caused a gap to appear, and wiping didn't do anything.
dkightley wrote:Now with a larger nozzle, there is a larger mass of plastic being extruded for each layer. With PLA, the sooner the plastic is solidified the better....and with a greater volume of plastic to cool, then more cooling is required. In the factory file, the cooling fan speed is set at 60% from layer 2. I think you actually need 160%...which is not achievable, so 100% will have to do....and for the print speed to be slowed down slightly to give time for the excess heat to be removed...solidifying the plastic before it can get distorted or moved by further printing.
The reason I turned down the fan - it was causing the temperature of the tip to drop. I have been contemplating designing a different fan shroud so it blows less on the tip, and more on the part. I upgraded my plus (at home) to the 50mm blower fan and printrbot's 50mm shroud design, and had to do the same thing (turn down speed).
dkightley wrote:My final thought is that you're seeing ....and I agree quite rightly.....a visible effect of the z axis movement at the end of the layer. Again, looking at your factory file settings,, you have this end of layer point on the outer perimeter....in exactly the place you don't want it. I would use the "outside-in" perimeter order, rather than "inside-out". This will move the left-up-right movement to where it can't be seen....and you then only have to work on tidying up a left-right-left move!
I will give that a try again - I had tried switching perimeter order with the test cubes. This becomes a challenge with extreme fillets on the bottom layer of this particular part (the attached factory was just a slice), but I could reduce those.
dkightley wrote:My closing comment.....think about what is actually going on at the exit of the nozzle and try to understand why the plastic is doing what it is doing.....and then work back through the mechanics to find out what to change. Scouring through gcode and comparing setting values, in my opinion, is not the quickest way to diagnose the problem.
I'm probably going about it backwards, but I'm trying to correlate behavior within the file with a defect. The main reason I was pointing out the gcode lines was because the problem is happening at a specific point - looking at another test print, confirms a bump appears whenever the extruder switches to a fast travel move, which I'm hoping will help point out where in the settings the problem is. Ideally it would give me a better understanding of what the nozzle is physically doing, but I often attack a problem from outside in (if that even makes sense
However, I'm probably done for the day so will think about this, maybe read up a bit on nozzle dynamics, and try to think through what it might be doing.