1. Got a question or need help troubleshooting? Post to the troubleshooting forum or Search the forums!

Partially Solved Ugly overhang

Discussion in 'Troubleshooting' started by Rod Smith, Nov 28, 2017.

  1. Rod Smith

    Rod Smith Member

    Joined:
    Nov 7, 2017
    Messages:
    87
    Likes Received:
    33
    Here's my latest problem:

    [​IMG]
    This photo is of a print of this temperature tower from Thingiverse. Compared to the photos of the same object on Thingiverse, the biggest problem I'm seeing is the ugly overhang. As the printer prints, it looks as if the overhanging area is bulging upward, so the print head gouges into the existing plastic and pushes it aside, leading to a ragged overhang and an edge that bulges upward. I've tried reducing the extrusion rate to 90% with no obvious effect. I don't see anything similar in other areas -- the base of the print, for instance, looks fine. It's just overhangs that are affected. Even then, the effect is often minor to nonexistent.

    This problem appears in other prints, too, but it's most dramatic in this one. (The prow of a 3D Benchy is another print that tends to show this problem a lot.)

    So, what might be causing this? What option should I be tweaking in my slicer (or firmware -- I've just upgraded to Marlin 1.1.6, but the problem occurs with both the stock Robo firmware and the Marlin 1.1.6 firmware). Thanks for any tips!
     
  2. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
    Staff Member

    Joined:
    Feb 21, 2013
    Messages:
    23,629
    Likes Received:
    7,312
  3. Rod Smith

    Rod Smith Member

    Joined:
    Nov 7, 2017
    Messages:
    87
    Likes Received:
    33
    Thanks for the pointers. I'm trying a print of two temperature towers simultaneously, with one rotated 180 degrees compared to the other, to see what happens with the overhang. I'm also looking into dual-fan options. There are several on Thingiverse, although of course I'd also need a new fan or two.
     
  4. Rod Smith

    Rod Smith Member

    Joined:
    Nov 7, 2017
    Messages:
    87
    Likes Received:
    33
    FWIW, I've printed a fan duct (this one) and, when I went to install it, discovered that the fan wasn't even working! I'm 100% certain that I'd checked the fan before, but it must have failed at some point -- perhaps after printing the fan duct, but probably before. I tested by swapping cables with the always-running fan that cools the cold part of the hotend, and the fault is definitely in the fan. This failure may well explain the cruddy overhangs I've been getting.

    I'd already ordered a couple of 40mm fans, with the intention of mounting one in the front, so I guess I'll wait for them to arrive and refrain from printing anything that requires delicate features until that time.
     
    Geof likes this.
  5. Rod Smith

    Rod Smith Member

    Joined:
    Nov 7, 2017
    Messages:
    87
    Likes Received:
    33
    I must take this back. I started a print running despite what I believed was the lack of a working bed fan, and discovered the fan was in fact working. I'd been testing the fan by issuing M106 commands, but it seems that either I'd done something wrong (typos, maybe) or the M106 command doesn't work until some other command is issued. I'll now try some tests to see if the single fan duct will help enough to satisfy me or if I'll need to install a second fan when the ones I bought arrive....
     
    WheresWaldo and mark tomlinson like this.
  6. Geof

    Geof Volunteer Moderator
    Staff Member

    Joined:
    Nov 9, 2015
    Messages:
    6,729
    Likes Received:
    2,330
    Add the front fan for sure if printing in pla then tune temps and speeds. Its a careful balance of temp speed and cooling to get great overhangs/bridges. More cooling and colder temps the better
     

Share This Page