Please help...Blobbing vs Stringing and tempature vs retract settings.

Hello All,

I seem to be having a problem that I can't seem to solve. I am using a makergear kit, so their extruder as well. PLA 1.75 mm filament. All tempatures are barrel temps measured using a K thermocouple. 0.2mm layers.

So no matter what I do I get either stringing or blobing. There is no in between.
170 appears to be my lower temp limit, below this I can't generate enough force to extrude without loosing steps.

If I Print at 170-175 deg I get serious stringing to the point there is actually small raised nipples coming off the part.
If I print at 175-180 I get blobs everywhere it changes layers.

I am using a retract speed of 10mm/s. Based on every test I throw at it, it is not loosing steps in the retract.
For length. 1.5mm. I was told not to exceed 2mm because I will get air. A retract of 1mm makes both problems worse, up to 2mm doesn't improve the problem either.

I have tried going through the temps 170-180 in 1 deg increments and can not get it to stop.

In my mind if stringing is caused by too low of a temp I should raise the temp. Alternatively blobing appears to be caused by oozing out from too much pressure. While the later change happens. Am I wrong?

I am at a loss of what to adjust or how to fix this. Any suggestions or ideas?

Thank you for your time and help.

Edited 1 time(s). Last edit at 07/26/2012 10:55AM by tjhj2.

Perhaps your PLA has absorbed moisture. You could try drying it either by warming it in an oven below 50C or in a sealed container with desiccant.

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[www.hydraraptor.blogspot.com]

It looks like your extruder filament drive is direct mounted. If that's correct then the "not more than 2mm" rule is probably good.

(If it's on a Bowden cable then the springiness of the long tube and the filament in the tube means that you can probably retract 3-4mm before you get air sucked back up. This is what I found with my Ultimaker.)

I run a retract speed of 30-40mm/s on my Prusa Mendels, and could probably go faster. Generally, faster is better so long as you're not loosing steps. I strongly suspect that your blobbing is happening because your retract is taking too long, and the blob forms as the retraction is happening. Try boosting the retraction speed.

Please let us know how you get on (others will be having the same problem).

Cheers,

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Leo

leo@RepRapKit.com
[RepRapKit.com]

What tip size are you using. I find I have to use less/more retract depending on size. I am willing to bet a good starting point for the 1.75 tube is going to be .75mm retract @ 25mm/s (assuming a .35 nozzle). Although, I am basing this on wade's extruder experience...some have found different settings for the direct drives.

Another thing to check is make sure your retract/restart distance is the same (visually). Quite often blobbing/stringing has been traced back to too high of retract acceleration in firmware. I personally find marlin to be too high by quite a bit.
If the accel is too high it can skip in retract but not restart causing blobbing...or in restart causing holes.

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