Sharp Overhang blobbing


PLA - recommendedmodified.ini (3.14 KB)
Every time I try and print object with sharp corners that are also overhangs, I get upward curling on the tips of the bends as soon as they are printed. Eventually it builds on itself and gets to a point where the nozzle will run over the large bump and I have to stop it. However, the side of the model that has the fan directly blowing on it turns out perfectly.

I am printing in PLA using the recommended fast settings on a TAZ4. I’ve tried changing the temperature, extrusion rate, speeds, and an external fan blowing on the print. Nothing seems to help it much.

Thanks!
startest filleted.stl (735 KB)

I’d drop the temperature of your hot end from 185 to 180, or use another fan blowing on that side of the print.

I tried the 180 temperature as well. No change. Could I try going lower than that?

And about the fan, I’ve already printed a mirror image of the fan duct that also blows on the heatsink, and I have a fan to go on it, but in the X home position, the fan/duct will run into the left wall of the printer. Is there a design that I could print that is made to fit that opposite side? That would be great.

I was also thinking of designing a cup around the nozzle that would have regulated low air pressure from my pneumatic line blowing on the print, that way air could be blowing equally from all sides, and the duct could be much smaller. :smiley:

Besides Orias’ advise, which is solid, i’ve found that a lower layer height can help this failure mode. It has a lot to do with the overhang distance per layer.

Something like this?
TAZ_Fan_Dual_Duct_mirrored_extended.STL (572 KB)

I printed that fan duct out. Am I missing a spacer between the inserts on the print head and the fan duct or something? It doesn’t fit properly. It also still seems like it will run into the left side of the printer when I put the fan on.

My thought was that by moving the fan forward it would clear the screw. Do you have a TAZ 3 or TAZ 4 or otherwise?

I have a TAZ 4. I got some standoffs and attached the fan duct to the head. As expected, the fan runs into the Z axis home microswitch specifically. The fan still needs around 3/4" of clearance before I can home the x axis without it crashing into the side. I could shorten the standoffs slightly, but the problem is the fan duct would run into the hot end, and the hot end heatsink.

Just curious, where did you get this stl for the mirrored curved fan duct?






Thanks a lot for the testing and feedback! I dl’d the original file from the forum, translated and rotated parts of the mesh with proportional editing enabled in blender. The reason things aren’t lined is because I forgot the buda isn’t centered on the exturuder mount.

I tried something similar to this once on a taz 3 and it crashed into the screw, but the TAZ 4 has a totally different setup. Fingers crossed that this will clear everything. :ugeek:


secondary_fan_mount_3_ss.1.stl (1.33 MB)