Extruder shooting out a ton of plastic all at once

I just built a Prusa i3 using an i3 rework kit from Replikeo (Arduino Mega + RAMPS 1.4 + Stepstick), and I am getting a very strange extrusion behavior over here, but only in *some* prints. I am using Simplify3D for slicing and also to drive the printer over USB (I don't have an SD card slot on it yet). While printing the first layer of the raft, when it's laying down horizontal lines of thick plastic, sometimes it will stop extruding for a whole row, then at the end of the row stop moving and squirt out an entire row's worth of plastic all at once. This even just now resulted in the extruder gear spinning freely, causing the hobbed bolt to lose its grip, and the filament just fell right out of the extruder!

Since I'm driving the printer over USB it could be a serial issue or something. I don't think the Arduino can receive faster than 115200 baud so until I can work out an SD slot I might not be able to fix this. The strange thing is that it's not every print that does it, only certain prints. I had this happen before with a filament spool bracket i was trying to print, consistently happening every time I tried to print it, and then I printed five plant pots with no issues whatsoever, now I'm having the issue again with a piece I designed myself.

Does anyone have any idea what might be causing this other than the SD card slot? My plan is to add an SD card slot but I don't want to have to immediately.

Your nozzle is to close to the bed. And maybe the bed is uneven.
Repeat the same print with the nozzle in the air and see if it happens again.
-Olaf

I set my Z endstop a few mm higher and it's still happening. I don't dispute that my build plate might be a little uneven but I don't think that's what's causing this problem.

Attaching a photo of a raft I discarded, showing the missing row of filament and the glob of filament at the ends.

Does the printer stopped and continuously extrudes plastic at that point? I think that may be due to heavy process on your pc, try not to do anything cpu intensive while doing 3d printing

It could be an error in the slicer's gcode. Maybe try the same stl using a different slicer.
Could also be a buffering issue with the USB/serial.
Steve

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My updated Instructable on our Prusa i3 Build
[www.instructables.com]

The Arduinos run fine at 250000 - I have never run slower, and never have comm issues.

- Tim

Thanks everybody! I had better results running the 3D printer off a laptop that wasn't doing anything else. I think I'll also renice Simplify3D to have a higher CPU priority than other tasks but it's a little hard to believe that with 8 cores on my CPU I'm having process-contention issues. I'll try a few prints at 250Kbaud and report back with my findings.

Are you running I7 cpu? I don't think that's octa core, most likely it's just quad core with threads on each cores.

Well, I ran into printer stuttering during printing from my laptop while doing something, more than 3 times actually and some times destroyed my prints because the laptop unable to send gcode data to the printer even though pronterface are set to highest priority. With sd print, it is also the same like printing through usb, the pc reads from sd card, then sends back to the printer to print (correct me on this). I thought it will print directly from sdcard once I unplugged the usb but the printer just failed to move

I print, slice, compile, whatever simultaneously on my Linux laptop with zero issues . . . Swapping can really bog things down - how much memory do you have?

- Tim

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tadawson
I print, slice, compile, whatever simultaneously on my Linux laptop with zero issues . . . Swapping can really bog things down - how much memory do you have?

- Tim

Mine? 4gb with 64bit win7 I5. That time I was using abbyy finereader to recognize those documents, so it's quite cpu intensive process

It´s not about CPU power but the mainboards-CPU bridge ( chipset ) that can cause a "traffic-jam" .Furthermore some virus scanners dramatically increase the latency in data transactions. Also the PC thinks after a few minutes without mouse movement, the PC is "idling" and starts some background tasks, like harddrive defragmentation a.s.o.
-Olaf

I see, I have lcd 2004a, but didn't show a thing when turning the pot, so I bought another for replacement recently, plugged to spare board I have (I'm away from my printer now), it shows block characters. I guess I only able to use usb printing as of now until I change board for pwm fan and lcd. 2004 lcd seems quite troublesome.

sarf2k4 you are correct that it's quad-core with threads, but it still should be able to handle serial communications. I've hooked the 3D printer up to a PC that has nothing better to do right now and hopefully that resolves it. The reason for my delay on an SD card slot is that my RAMPS board is mounted on the frame in such a way that if I added an SDramps, it would be in the way of the X-axis stepper motor as it travels upward during a print. So sometime soon I will figure out a way to mount it maybe with a ribbon connector or something instead of the headers it comes with.

For what it's worth, I sliced the file I'm trying to print in Simplify3D as usual and then just loaded the GCODE file on my PC using Pronterface and so far (fingers crossed, knock on wood, etc) the printer hasn't gone rogue on me. If it completes the print this way, this'll be my stopgap until I have some time to get an SD card slot on there.