Problems with bad layers in a print

[nerys]

I am printing a model and the single perimeter section keeps coming out bad (voids in layers) rendering the part worthless

I now know what it is doing but not the "why" or how to correctly stop it from doing this.

I was watching it print and I finally actually saw it screw up.

its the start of an extrusion. when it moves from one discrete extrusion to another discrete extrusion it moves to a point in the print and then it begins.

I noticed it was "incomplete" it was NOT smoothly extruding until it had move about 2 inches on the model then the filament was extruding smoothly.

obviously this is causing my voids since there is no plastic in that 2 inch long segment or just little bits of plastic. not a solid line.

my retraction is .75mm I have no stringing at all and my restart retraction is 0

suggestions? what is causing this and what setting do I change to alter this behaviour.

I have a feeling it happens more than I think but its hidden in multiple perimeters OR it does not happen in "single part" prints but only when it moves from part to part.

for it I print ONE part it prints fine though the problem may persist and just be less of a problem with less transit movement between a stop and retract and a restart.

Here is a video. I did it in 720 so it will upload fast (about 3 minutes till finished)

suggestions?

https://www.youtube.com/watch?v=PfxvHk3bBdI

[nerys]

OK I think I fixed it. I still don't know fully why it was happening but I think I got a fix.

coast is not what I thought it was this should be clarified in the description. I thought coast meant extrude a layer stop extruding and then keep going x distance.

what it really does is coast x distance at -x distance from actual end of layer. Very very big difference :-) its not a nozzle coast its a EXTRUSION coast. makes much more sense now (no this was not the problem it was just something I tried using to fix it)

I set retraction to 1mm (no string) then restart retraction to .2mm.

then I turned on a 3mm wipe. this did what I wanted. finished layer then "kept going" past end point for 3mm.

the .2mm restart solved the missing filament at restart but left a tiny blob (any less than .2mm and I got intermittent missing extrusion it had to be .2mm minimum. the wipe then "smoothes" out the blob enough that I don't mind it now.

looking good so far. now to restart the 23 hour print for the 4th time. :-) hehehe

I would still like to know what was going wrong the first time around. seems to me I am "patching" the real problem with a bandaid.

or is this kind of thing normal?

while this work around works for outside opaque models it won't work for illuminated models as those blobs and imperfections this bypass makes are glaringly visible as imperfections in the print.

[Heutinck]

It sounds like its a retraction issue. what happens is when you move between parts its preforming retraction, and then when it reprimes the nozzle. it doesn't push enough filament into the nozzle so you get a gap. This is where the extra restart distance comes into affect. if you set this to say +.2 with a retraction distance of .75 like you had mentioned, then when retraction occurs it will retract .75 mm and at restart it will feed .95 mm before starting to print.

You just need to play with the numbers until you get it right, you mentioned that .2 is the minimum you can add to the restart value, so you may need to increase the retraction to say .80 mm to effectively get .15 extra restart distance.

[nerys]

not minimum as in I can not go lower but minimum as in any less and I get voids.

longer normal retraction does not seem to effect. this. I have not messed with it more since its "working" and I am getting acceptable results.

when time allows I am going to try some micro adjustments. like .09 .08 and see if its capable of that and what it does.