Material shrinkage pulling in vertical side walls  

RE: Material shrinkage pulling in vertical side walls

Are you referring to the change in the vertical walls? Do you get the same variations when printing a perfectly vertical surface like a cube? If you see variations in solid prints like a cube, it could be a hardware issue (e.g., bearings causing layer shift). I don't think that's the case here. There is a common phenomenon that you'll encounter as vertical surfaces vary ever so slightly during a print. This was given the unfortunate name of "buldge" in earlier posts. Deviations in wall thickness can occur as layers transition:

• Between solid infill and sparse infill. (I think this is what you're seeing.)
• Between sparse infill and gap fill
• When the number of perimeters increases or decreases between layers.

• Thread one - Buldge when print reaches "solid" layers.
• Thread two - Any tips to get rid of the bulge?
• Thread three - Mitigate wall bulge.
• The Prusa Benchy hull line notes might also be interesting.

• Be sure you're not just seeing the effect of minor warping/lifting/curling along edges or in corners. This can really throw troubleshooting off. Rotate the print and verify the problem occurs in the same place.
• Slow down external perimeter speeds (and all speeds in general). If the nozzle is moving a bit too fast, you get slight under extrusion on some layers. These are apparent as adjacent layers print with slightly different extrusion rates. I use 25mm/s for external perimeters when appearance is important.
• Calibrate your extrusion multiplier for each filament. Any slight over or under extrusion can produce very small but noticeable variations in layers with different features (e.g. infill, gap fill, top solid infill). The closer your slicer settings match your actual printer and filament, the more accurate the gcode will be.
• Calibrate linear advance (LA) for each filament. LA adjusts the flow of filament to compensate for acceleration and deceleration. If it's not right, you may see artifacts even away from features such as bumps or hole on the same layer. In some cases, a hole on one wall causes imperfections on the far side of the print.
• Add an external perimeter if vertical walls allow it. The thicker combined perimeter allows the filament flow to even out.
• Tweak perimeter extrusion widths. The problem can appear when the slicer switches between gap fill, sparse infill, and solid or top infill. If you can find a multiple of perimeter widths that minimizes these transitions, it can work for a specific print.
• If you are the part designer, make vertical free-standing walls thicker. IME, at 1.5mm thick, the problem is less noticeable. You can try for a multiple of extrusion widths, although be aware the PrusaSlicer does some internal calculations for overlap between extrusions that can throw you off. PrusaSlicer gives hints about optimal thin (free standing) wall thicknesses for different print parameters.
• Check cooling. Variations in fan speeds can cause changes in print appearance.

RE: Material shrinkage pulling in vertical side walls

@bobstro

Thank you very much for your detailed reply. I have read through your comments and followed the links that you provided. I had not previously seen the info from Prusa on their research into the "Benchy Hull Line" and I am sure that this is my issue.

Do you know if the Benchy Hull Line and the "Buldge" issues are the the same issue, two different issues or two different but potentially related issues?

Thanks again

RE: Material shrinkage pulling in vertical side walls

Posted by: @brad-3

[...] Do you know if the Benchy Hull Line and the "Buldge" issues are the the same issue, two different issues or two different but potentially related issues?

I'd put this in the category of "things to be aware of". There are a LOT of different things that can cause similar-looking problems. The "buldge" category -- at least as I'm defining it -- is really about minute extrusion deviations within a layer. If you transition from, for example, sparse infill to solid, or if there's a change in the speed or direction it takes to print a layer (e.g., there's a hole in a wall), the small changes in speed and extrusion can create very small (sub-mm) but perceptible variations in wall appearance. Each layer is calculated independently by the slicer, so there can be very small but noticeable variations between layers depending on what else is going on within the layer. A print feature (opening, floor, etc.) on one side of a print can shift a flat wall on another side.

There are other problems that can look very similar:

• Temperature deviations can cause variations in wall thickness. If you print in a drafty area, this can be a problem.
• Z binding can cause variations in vertical walls. These will tend to show repeating patterns (e.g., every X mm a bulge) regardless of the underlying print shape.
• Belt tension can cause irregular patterns. These may cause patterns independent of the print shape, or cause dramatic layer shifts once in a while.
• Loose belt and idler screws.
• Cats.

They key characteristic of the "buldge" issues (it's a stupid name, but it sure is easy to search for) is that irregularities show in relation to the print itself. You'll see odd lines on the side opposite an opening or transition to solid infill for example.

Don't get hung up on the name. It's just a silly shorthand way of saying "deviations in vertical print surfaces based on internal features" or something like that. 😀 

RE: Material shrinkage pulling in vertical side walls

@bobstro

Thanks again.

As you say - cats most certainly can cause a deviation. My daughter’s 3D printer deviated to the dustbin via the floor (she could no longer level the bed after the cat had knocked it off of the table so she threw the printer out). Fortunately, not a Prusa though!

RE: Material shrinkage pulling in vertical side walls

@bobstro

Why the hate on cats 🙂  I'm sure dogs could do the same!   I do have to keep my rubbish bin with a top on it because the cats like to get in and pull the skirts from my prints out and play with them.   I keep my printers in enclosures and the cats seem to steer clear lol

RE: Material shrinkage pulling in vertical side walls

Suggest we use the term "caht" to make feline-induced print anomalies easier to search for. Or "catdge"?

One evening I tossed a whiffle ball for my 65lb bulldog to chase, not thinking much about it. I rounded the corner to my office to catch him as he was preparing to jump up on my desk to fetch it. I think that'd be a different category of print defect.

RE: Material shrinkage pulling in vertical side walls

@bobstro

you were lucky.  it would be a shame to have to wait months to get a new printer!

RE: Material shrinkage pulling in vertical side walls

Posted by: @ssill2

[...] you were lucky.  it would be a shame to have to wait months to get a new printer!

This guy has caused a couple of layer shifts...

RE: Material shrinkage pulling in vertical side walls

@bobstro

I'm sure he has!

RE: Material shrinkage pulling in vertical side walls

@bobstro

Looks like trouble