When faced with any problem, a time tested approach is to break it down into it’s smallest components and determine what you know and don’t know about each. This can eliminate a lot of unnecessary effort and help you focus on finding the root issue. If you are seeing odd print artifacts in your parts and have worked through and are an ardent practitioner of my guide Strategies for Obtaining Great Prints , you can use the following strategies to track down and erradicate print artifacts. In this case, you can break the problem down into six categories:
- first layer problems
first layer problems
- perimeter problems
- top layer problems
- fill problems
- overhang problems
and for each of these there can be:
A) slicing problems
B) mechanical problems
(of course I’ve simplified this, the model itself (see #6) could be a problem as could electrical issues, etc. But for the majority of the cases, these two will suffice.)
You can attack 1 through 6 in order - and, of course, you might not experience all of these. Here are some strategies:
1) First Layer Problems - follow the recommendations in my Guide and use the single layer object until you can print it reliable and perfectly. If slowing down, adjusting extrusion, using the lowest filament melt temperature, etc don’t work to eliminate the artifacts you are observing or if you see artifacts that indicate a mechanical problem, then you need to turn your attention to the mechanical aspects of the machine and work through those until you find and resolve the problem. You can use the recommendations in #2 below to solve these first layer issues too.
2) Greater than First Layer Problems - if you nail the first layer, it goes down nice and smooth without significant artifacts predictably and reliably but are seeing issues in the second or higher layers, this is almost always related to a mechanical problem and not a slicing problem. Think about it, once the first layer is down it has created a “raft” for the next layer and the top surface of that raft should be precisely parallel at any point on the surface to the nozzle tip’s motion. In other words, the next bead should go down perfectly. If not, start with the nozzle itself. Polish the tip, check the bore to make sure it is round and has no burrs or significant scratches in it (hold up to light and look through). If you have a spare nozzle, polish it up and try it. Once the nozzle has been eliminated (and nozzle issues would also be prime suspects for #3, #4 and possibly #5) next check the hot end itself. Make sure it is tight with NO WIGGLE whatsoever. One easy test is to re-orient the hot end in its holder (rotate it 90° or 120°) and test print. Does the issue show up in exactly the same place? If so, it is not the hot end, if not, then you have narrowed it down a bit. Don’t forget to use the slicer rotate feature to rotate the part, say 90°, and test. The results of this can help determine which axis of motion (typically X or Y) might be contributors.
Think about the Cartesian geometry and how artifacts in the part relate to that geometry. Most of the time, a defect will be aligned with either X or Y and that provides valuable information on where to check. Artifacts that are not aligned most likely have contributors from both the X and Y axis motion. This is a powerful realization as it allows you to start thinking about the relationship of the printer axis movements to the part geometry. For instance, if you have print artifacts that are precisely aligned with the Cartesian Y axis no matter how you rotate the part or hot end, that should be screaming “There is a problem along the Y axis mechanical path.” Don’t forget the belt, stepper pulley and idler pull at the top. A small piece of debris on these parts can cause the belt to stretch slightly as it goes around the pulley and this can result in a print artifact. A good thing to do is to clean everything carefully (I use Windex and clean lint-free paper towels) and re-test. It is also a good idea to tighten the pulley grub screws - I can’t tell you how many times that has been the issue. If you can’t determine an alignment with X or Y, try rotating the part in your slicer and rechecking. Move the part closer to the “0” end of the bed and the maximum end of the bed on both the X and Y axes and reprint and check. This is why I like a simple, small part to test - you might be making a lot of prints and you want to get the data as quickly as possible.
If you discover a relationship, investigate the suspect axes for misalignment, loose belts, backlash, etc. One technique I use is to apply pressure from my finger on the extruder mount aligned with the direction of the suspect axes while it is printing. First towards “0” end then towards “max”. This eliminates backlash in the system and can help identify issues. You can do both directions on a single print so you get a twofer on this test!
3) Perimeter Problems - these could be caused by either slicing or mechanical problems. Here it is important to think about what could cause the observed artifact. Is it a blob? If so, that is most likely a slicing issue and you should turn your attention to tuning the slicing parameters. Is it a dislocation, i.e. corners or long edges are not completely aligned one on top of each other? If so, that is a mechanical issue and you can use the strategies in #2 above to identify which axis is contributing to the problem.
4) Top Layer Problems - these are somewhat related to #2 in that the top layer is being laid down on what should be a near perfect base. Nozzle imperfections are a prime suspect as is a loose hot end - see the tests and recommendations in #2.
5) Fill Problems - fill problems are more unusual and are almost always a slicing issue. Once you have the first layer and perimeters nailed, squirting the plastic inside to fill the part is usually not a problem. Overfilling that causes bulges in higher layers can be an issue. This can be addressed with calibrating the extruder, filament extrusion temperature, infill extrusion width and even infill density.
6) Overhang Problems - firstly, realize there are geometry limitations on what can be printed with a FFF printer! The laws of physics still apply to 3D printing. Overhang issues are almost always related to slicing. There are many different types of overhangs and bridges so I’m not going to attempt them all here. However, a common one is worth discussing. Think about an inverted pyramid - the sides slope up and out creating an overhang. Most slicers default to printing perimeters outside-in. Think about that. What is that outside perimeter going to adhere to? Depending on the slope of the wall, there may be very little plastic underneath from the previous layer. I like to print these inside-out. Think about that. Now, the first inner perimeter will be printed securely on a solid base. The outermost layer will have the advantage of a neighboring layer to stick to, helping prevent it from sagging.