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Hi everyone,

I've been experimenting recently after I noticed that retraction causes blobs in my print. The unusual thing is that it depends on which slicing program I use. If I slice with Cura, nothing bad happens on retracts. But when I slice with Slic3r, my Steve's extruder makes a grinding noise and forces a bunch of filament out, which blobs my prints. The filament never gets retracted; the extruder just kind of vibrates for a fraction of a second while it's supposed to be pulling the filament back from the extruder, then it pushes out the filament that was supposed to be retracted in the first place. It doesn't matter how low I set my retraction speed and acceleration.

I'm using a Steve's extruder with 1000 for acceleration and 20 start speed. In Cura, I have my retract speed set to 50 mm/s and it works just fine with no problems at all. In Slic3r I have tried setting the retraction speed between 50 and 5, and no matter how slow I make it, it always grinds and blobs. So basically I can't make anything with slic3r because of the terrible retracts and blobs. Cura can make small parts, but anything that takes too long to print causes the stopped printer problem (which I just found out 47 seconds ago it caused by the pre-2014 version of repetier host firmware). Hopefully the new firmware will fix that.

Has anyone else had problems with retracts using Slic3r?

Generic Default wrote:Hi everyone,

I've been experimenting recently after I noticed that retraction causes blobs in my print. The unusual thing is that it depends on which slicing program I use. If I slice with Cura, nothing bad happens on retracts. But when I slice with Slic3r, my Steve's extruder makes a grinding noise and forces a bunch of filament out, which blobs my prints. The filament never gets retracted; the extruder just kind of vibrates for a fraction of a second while it's supposed to be pulling the filament back from the extruder, then it pushes out the filament that was supposed to be retracted in the first place. It doesn't matter how low I set my retraction speed and acceleration.

I'm using a Steve's extruder with 1000 for acceleration and 20 start speed. In Cura, I have my retract speed set to 50 mm/s and it works just fine with no problems at all. In Slic3r I have tried setting the retraction speed between 50 and 5, and no matter how slow I make it, it always grinds and blobs. So basically I can't make anything with slic3r because of the terrible retracts and blobs. Cura can make small parts, but anything that takes too long to print causes the stopped printer problem (which I just found out 47 seconds ago it caused by the pre-2014 version of repetier host firmware). Hopefully the new firmware will fix that.

Has anyone else had problems with retracts using Slic3r?

The Steve's extruder has been replaced with the EZStruder. If it is possible for you to replace the Steve's with the EZStruder, that is one of the first things I would do.
All the gears in the Steve's can introduce backlash and other problems and the direct drive EZStruder does not have the gears. I am not saying that the problems you are
having cannot be fixed while using the Steve's but I think it would be much easier to troubleshoot if the EZStruder does not fix the retraction problems.

There is a very good chance that 50mm/s is too fast for a Steve's extruder, depending on how it was assembled, and how much pressure is on the roller, back it way down to say 15 or 20 verify it's OK at that speed then increase until you have issues.
My experience is Steve's extruder is heavilly over engineered and difficult to get the roller pressure corect for printing, in short an excercise in frustration. The EZ struder is a lot easier to work with, or print one like the Airtripper extruder.

Generic Default, what you describe is a known symptom on the Steve's extruder. A simple test - make a black mark with a Sharpie on the small gear attached to the stepper. Now watch that mark when you print. On a retraction, it should reverse some # of degrees (depends on your retraction length, etc). And then, when it restarts, it should move back to the exact same location. I bet you will see that the mark does not move on retraction and then advances before printing. This usually means that you are overdriving the retraction by either having it's retract speed too fast, or acceleration too large, or you need to lower the current to the stepper (or all of these). I am sure I have more info in my long Rostock build thread, but the fix is to find the #define for the extruder in your firmware (or EEPROM) and reduce the extruder acceleration and max feedrate.

My bet is that your acceleration is too high, I seem to recall that the default setting was too high.

I used to keep a black mark on all of my Steve's just so I could watch this.

cheers,
Michael

Thanks for the advice guys!

The thing that's strange about it is that it has no problem doing retracts from Cura gcode, but nearly identical gcode generated by Slic3r messes it up regardless of how low I have my retraction speed or acceleration set.

I did design and print a very simple direct drive extruder that I'll be testing soon. I just hope the ball bearing is pressed against the filament hard enough with the spring I have.