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blobs and top layer probs

Posted by stu121 
blobs and top layer probs
September 09, 2012 11:46AM
hi, printing with prusa mendel, at 2.5 lh, I am getting little blobs all over my prints, i have increased retractions from 1 to 2mm with no difference, retraction speed is at 30, should I change these some more or is my problem something else?

also can not get a good top on this vader head, first I tried with 3 top layers and then this was 5 and a little better. have turned my top layer speed down and can print a cube quite nicely, just not this.

printing here with .2 infil, in 3mm pla with slic3r 092

any help much appreciated

thanks, Stu
open | download - IMG_20120909_163704.jpg (597.3 KB)
Re: blobs and top layer probs
September 11, 2012 12:01AM
A couple thoughts as I have had similar issues:

-check your extruder steps calibration...could be too much plastic
-check to see when the blobs occur; i believe those may be occurring after the completion of the perimeter and before moving to infill. If so, a fan may help (still testing this myself). hard to tell how much infill is in that model as i havent printed it myself.

If the blobs aren't occurring before infill, then I would check how much you are restarting after retraction. I believe little restart, if any, is needed. But would be curious to hear others thoughts on this.
Re: blobs and top layer probs
September 11, 2012 04:02AM
All my small blobs seem to form during non-printing moves, when the nozzle moves from one part of a print to another. It seems to me that the oozing (although small) is just enough to cause this type of 'blobbing'. I haven't tried to adjust the retract setting yet, but I think that will help you out on the first problem.
Re: blobs and top layer probs
September 12, 2012 03:25PM
It may be a mechanical issue like temprature or it seems that you keep print in front of a blowing fan.
Re: blobs and top layer probs
December 09, 2012 03:28AM
Are you printing your "quite nice cube" with .2 infill or 1.0 infill?

The top looks like it's concave a bit - i.e. there's not enough support underneath it?

As for the sides, I have similar issues so I'll be following this thread for now - Temperature can control the ooze (which I suspect is the problem) and so can retracting, but sometimes you don't have much choice with temperature, and I use skeinforge and can't figure out how to retract and control ooze yet...

*runs off to google*

Try the model again with 1.0 infill? Is it the "concave-ness" that you're worried about or the "coarseness"? cos if it's the coarseness it's only fixable using smaller resolution:

*Smaller nozzle
*Smaller layer height
*Smaller edge width

Also worth checking your extruder idler pressure - I've been having a hectic time getting my prints to be uniform, found that when I put a bit more pressure on the idler it helped - I guess the hobbed bolt was just sliiiiightly slipping - was good 99% of the time but occasionally it would skip a fraction of a thread and had funny results...

Let us know if you get it working and what worked for you!

- JazzyB
Re: blobs and top layer probs
December 28, 2012 11:28PM
I've encountered what I like to call "looping" when the extrusion speed exceeds the travel rates ability to keep the same diameter line. Try reducing your extrusion speed or increasing your travel rate while extruding.
This can also happen if there are blockages in the nozzle itself because the extruder gears push the plastic through into the liquification chamber at a set rate, but it isn't extruding. Hydraulic pressure builds up and it rushes out, creating a "loop" of material.
Try running a bunch of PLA through it for around 300s extrude (yes i know..a long time) and running your fingers over the filament and inspecting it visually. Are there small bubbles or imperfections? Sometimes a junk roll of plastic or old ones can cause issues like this.

If you care to provide more details I'm glad to help you troubleshoot!

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