Kossel print "lurches"

I have a DIY "micro" kossel that has worked fine for many months. To get more Z height, I put a new end effector on it. Did all the usual tuning, Z height setting et. al. I replaced a simple "hang below" Kossel effector with an FLSun one that I fixed in place because I don't care for the "auto" cal thing it did. It's size and complexity were perfect for this application. My first few prints were just fine, a little scale tuning and things looked great.

Then, "something" happened.

Now when I print to it, it "lurches". The print head acts like it is catching on something and lurching to catch up. It will travel at one speed for a second, then much faster, then slow down, then more of the same. Sometimes the filament comes out faster, sometimes not much. I am getting thin spots, globby spots. When I print from stuff that I have on the SD card, I get the thin/thick problem, but not so much the speed-up, slow down. It seems like something has dorked all of the stepper actions - But the firmware and hardware are unchanged. It could be that the stuff on the SD card being smaller than what I tried to print, didn't cause the motion issues. But, I am clueless here.

This printer worked great until I changed the end effector. What terrible thing could I have done to cause this? Has anyone seen this kind of thing before and corrected it? I look forward to adding to my knowledge, because I am without a clue what to do next.

Many thanks,
DLC

Edited 1 time(s). Last edit at 03/01/2018 12:02AM by dlc60.

The grub screw of the filament drive gear might have come loose? That would cause uneven extrusion, which leads to the nozzle dragging through blobs. Your hole printer-mechanic accumulates the dragging force until the nozzle is free and the effector jumps forward.

Quote
o_lampe
The grub screw of the filament drive gear might have come loose? That would cause uneven extrusion, which leads to the nozzle dragging through blobs. Your hole printer-mechanic accumulates the dragging force until the nozzle is free and the effector jumps forward.

Good thought, I have seen that one before, and it was a puzzle. This time the slow-fast... movement is happening on the first layer before anything has been put down yet.

thanks,
DLC