Middle of prints shrinking

I just printed a few parts and noticed that they seem to be relatively close to the correct design dimensions at the bottom and top but the middle shrinks quite a lot. The OD of the cylinder should be 76.2mm but the print varies from 75.6mm (bottom) to 74.3mm (middle). Any recommendations?


I am printing with Overture PLA+
Recommended nozzle temp: 190-220
Recommended bed temp:25-60

Plastic shrinks as it cools, you may need to take this into account in your designs if tolerances across large dimensions are critical.

Before doing that the prerequisite is have a well calibrated printer where esteps and flow multiplier give you the exact single wall thickness commanded by the slicer within about +/-0.3mm. Additionally no under our over extrusion as that will affect wall thickness. And you are printing at the correct temperature with the correct cooling fire the particular part being printed as that will exacerbate dimensional changes.

Thanks, Brent. I have seen similar articles to what you linked. I recognize that shrinking is to be expected (this does fall within the 2-2.5% range) but what throws me off is the inconsistency from bottom to mid to top. I would think that the bottom might have the flaring since it is attached to the bed but would not expect the top to do the same. Because of the flaring at the top and bottom, I cannot compensate easily since it would be hard to only increase dimensions the mid section of the model. Unless I am still missing something? Thanks again for your input.

Likely temperature, cooling, or extrusion related.

Found the post below that covers e-step calibration. Mine was indeed off by quite a bit. I will try another print and see what the difference is before moving to flow control since wall thickness is within the tolerance you suggested. Also, linking your post that discusses your calibration steps for reference.

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@brent113
e-step changes alone made a significant difference. Last print OD came out ~76mm. Thank you!

@WilliamBosacker
Thanks for the input! I will try increasing the print speed. Wall thickness is set to 1.2mm. This is a spacer to keep a 1.5" PVC pipe centered inside a 3" PVC pipe.
Outer wall is 1.27mm
Inner wall is 2mm
Spokes are 3mm

Here is a link to the design:
https://a360.co/2SR8xup

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Generally speaking, and expanding on @WilliamBosacker’s point, many such parts will have huge strength increases when printed solid. You’ll find though that the sparse infill patterns give a lot of leeway for under or overextrusion as there are gaps for the extra filament to flow into. With solid parts, any calibration flaws will be brought to light.

Honestly, the standard calibration cube, printed solid, is a good test. If you have your flow multiplier set wrong or esteps is off you won’t get a good print with solid infill.

Specific strength is an interesting metric, maximum strength for a given weight of filament used: https://3dprinting.com/how-to/how-to-get-stronger-fdm-3d-prints/. Solid is the strongest overall, but uses the most filament. You can see in the specific strength graph that you’ll want the most perimeters, up to 6, with low infill for high strength-to-weight.

Not all of this applies to this specific part you’re making, just consideration for future projects.