1 Topic by dkeeling728

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Topic: overextrusion "bumps" when changing level

Looked through the forum to see if i can find an example of what im experiencing, or at least learn what its called. but no luck.

its not a major problem, just an annoyance on an otherwise perfect print. but i get noticeable bumps on my models where the extruder changes levels or lines in perimeters. ive tried increasing the retraction amount and that seems to make it worse (huh?). i've done all the calibration steps and have everything else as close to perfect as i have the patience to get it till i get ready to do some high resolution prints. just this one little issue annoying me. lol

setting it to randomize start locations tends to help a bit, but then i get little plastic pimples all over the model instead of in uniform locations. its not a big deal to me for now since im just printing utility parts and upgrades for the printer, but i defiantly need some ideas to help fix it before i start printing stuff that i want to look pretty smile.

2 Reply by lawsy

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Re: overextrusion "bumps" when changing level

dkeeling728 wrote:

ive tried increasing the retraction amount and that seems to make it worse (huh?).

I've noticed this too. I think that the retraction makes the nozzle pause for a split second longer in that spot.

Even though the filament in the hot end is retracted, the bit at the tip is melted to the model so won't go anywhere. This split second extra wait means more deposits into the bumps.

Try speeding up the retraction rate, rather than increasing the distance. You may need to set the max retraction speed higher in the Repetier-Host EEPROM menu.

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3 Reply by op7ical

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Re: overextrusion "bumps" when changing level

I turned off the setting which makes it retract on a layer change.  I noticed a large reduction in defects at the location where it pauses, since it idles for a much shorter period of time.

4 Reply by dkeeling728

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Re: overextrusion "bumps" when changing level

op7ical wrote:

I turned off the setting which makes it retract on a layer change.  I noticed a large reduction in defects at the location where it pauses, since it idles for a much shorter period of time.

not sure if that would help this problem, since it seems to be more an issue of perimeters. for instance, when printing several items on a plate, it gives me bumps at the places where it finishes the external perimeter on that part and moves on to the next. i do believe disabling retraction on layer change would help a lot if you were printing only one item at a time/large items.

lowering the retraction speed is something i never thought to try, but now that it was mentioned, it makes perfect sense! i will have to try it! as soon as this 6 hour print is done... wish i would have remembered to check the forum earlier.

5 Reply by IanJohnson

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Re: overextrusion "bumps" when changing level

You can also try speeding up the max feed rate for Z a bit in the EEPROM so it spends less time changing layers.

6 Reply by dkeeling728

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Re: overextrusion "bumps" when changing level

hmm, tried messing with retraction amount and speed, as well z travel speed, and now im getting a weird irregular blob on some corners and more stringing. the blobs are inconsistant, so i dont think its a backlash issue, but i'll be toning down all the changes i made to test. also, the "warts" seem to have gotten more extreme, if that was possible. tried 2 different rolls of ABS, so i dont think its the plastic, though the white seems worse than the black.

bah, one of those things that was probably better off left alone

7 Reply by Downeasta

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Re: overextrusion "bumps" when changing level

I saw this on youtube searching for other solidoodle info.  Alas it sounds like they want money for the discovery.

I am an open book, write on my pages that I may learn the wisdom that you posses.

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8 Reply by IanJohnson

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Re: overextrusion "bumps" when changing level

Those overhangs aren't a challenge, they are so short.  You run the speed a little higher and the flow a little lower on bridges so the thread is stretched, and stays tight from shrinkage as it cools.

9 Reply by Downeasta

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Re: overextrusion "bumps" when changing level

That makes sense.  Alot better than the above vid that says it is a "unique algorithm".

Have (to Ian Johnson) you an updated slic3r vid for version 85 of repetier host?  I would like to see it, and yes I am a subscriber.

I am an open book, write on my pages that I may learn the wisdom that you posses.

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10 Reply by dkeeling728

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Re: overextrusion "bumps" when changing level

Looks like i had developed a partial clog causing those bumps... that or my hot end was shifting in the jigsaw extruder. had a PLA peek jam this morning while trying to change filaments, so i took the orotundity to switch to my mk4 that i printed weeks ago, and now, with the same filament, im no longer getting the extra warts on corners and on external perimeters. just poked the end of the nozzle with a small straight pin i had laying around as good measure, seemed to do the trick! haha.

gonna raid my guitar parts stash for an old high E string to use to keep the boogers cleaned out.

11 Reply by Shameless

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Re: overextrusion "bumps" when changing level

If your lines are starting out with a thicker blob then going back to the normal width they need to be (would look like a q-tip from a top down view), this is what I found most effective:

for slic3r: printer settings -> extruder 1 -> extra length on restart, and set it to a negative value like -0.1 or -0.2, it will pull a little filament back up when it starts a new layer or perimeter.

for skeinforge: dimension tab then restart extra distance, same dealio.