ABS clumping

Hey all, I have a TAZ 3 that I am setting up. I am having a problem with the ABS “clumping” on the z calibration print. The extruder seems to be running okay, but the ABS is clumping together on the bed sometimes, particularly after the extruder has turned a corner or just stopped/started. Anybody got any thoughts on this?

We have seen this with our TAZ 2 printer as well. Would definitely like to hear if anyone knows what’s up with this.

It may be due to too low of a first layer height- the pressure builds until it’s released. Try turning the Z axis endstop adjustment screw clockwise (0.25 - .5 turns) to see if that helps.

also what temperature are you running your extruder at? You may also want to check that the small set screw in the small gear is down all the way tight. If that set screw is loose the gear will appear to turn some, but it won’t drive the main gear as far as it should be going, leading to lumpy extrusion. In this case though I would suspect layer height first.

I did some tweaking on the Z height adjustment, and that helped: definitely much less than it was. I had not realized that the Z height adjustment was quite so finnicky. I managed to find a spot between the clumping happening (too high? I guess so) and the nozzle catching on one of the other layers of plastic as it returned to the left side after the print had completed (too low), but it still happens a bit, which concerns me.

However, it is still happening, especially on the second pass for the outer square section of the bed calibration print. I took a macro shot to show the clumping. I think this is why my prints were failing: a clump on one of the small objects I was trying to print was catching on the nozzle, which was then getting blocked, leading to all the ABS coming out of the nozzle sticking together in a big, grungy lump.

The gcode file you are using is only a tool to visually see what areas of the bed need to be adjusted and has been cut in Slic3r with speed and ease of printing being the more important factors.

You can eliminate what you are seeing by adjusing a value in Slic3r at: Print Settings > Speed > External perimeter speed (50% is a good value to start with). By printing the external perimeter at a slower speed, you get a finer finish, and a more consistent extrusion edge.

For now, don’t worry about what you’re seeing, as you’ll take such things into consideration when cutting your personal models. The Slic3r settings we have here: https://www.lulzbot.com/support/taz-slic3r-profiles have the external perimeter speed set at a comfortable level, I would recommend starting with the Medium profiles- it’s more forgiving and should give you decent looking prints, in a reasonable amount of time.

Okay, I managed to figure out the problem. It was a combination of adjusting the Z switch, and clearing out small bits of filament stuck on the hobble wheel. When I took the extruder apart, I found that the grooves in the hobble wheel were filled with small pieces of filament, and that meant that the filament was slipping.

So, after clearing that out and resetting the Z level adjustment, no more clumping and the test print is nice and smooth.

However, I think this was caused by a design issue in the printer. The Pronterface software stops the extruder from extruding when it is cold, but the built-in controller doesn’t. So, what I think I did was to accidentally start a bed test print (which does not include commands to pre-heat the extruder and bed) without pre-heating the extruder. This meant that the hobble wheel was chewing away at the filament, which couldn’t go anywhere. Instead, it just gnawed off bits of filament and got clogged up.

My suggestion from this would be to either add pre-heating commands to the bed test print (and then create one for ABS and one for PLA), or add a check in the firmware that prevents the extruder from extruding when cold.

TL:DR - If you are getting globby, clumpy prints like mine, clean out your extruder and check your z height adjustment.

While you can specify bed temps and hot end temps in slic3d gcode files, doing so can be problematic, as you may be using a different material with different temps. We encounter less issues with things setup like this, rather than having people trying to use the wrong temperature with their desired filament choices.