Part Shrinkage For First 2 Inches Of Prints  

Part Shrinkage For First 2 Inches Of Prints

Hello everyone!

The lab I work out of recently purchased 2 Multi-Head Prusa XL's and have been trying to do multi-material printing of a air foil with TPU and PETG. However, we've been running into a really strange issue that we haven't seen before on our previous Prusa printers (Mk4 and Mk3). For some reason the first layer prints with the correct dimensions, then for the next ~2 inches of the print - in the Z axis - the print seems to shrink inwards but then continues to print perfectly for the rest of the print. The even stranger part about this issue is that the TPU sections of the print do not have this issue, only the PETG.  Our first attempt at this print is pictured below, these prints use Prusament Orange PETG and ESun Gray TPU.

After seeing this issue, we initially thought that it could be caused by the thinnish walls of this print causing warping. So, we ran test prints of a circular and square hollow tube of the same wall thickness with more Prusament PETG. Unfortunately these printed absolutely perfectly on both XL's

For a sanity check after this, we re-printed the exact same part, again with Prusament PETG and ESun TPU and ran into the exact same issue. 

As a final test before making this post, we thought that adding ribs to the outer walls of this print would help it keep strength and avoid and potential warping from heat. Unfortunately this still gave the exact same issue.

I'll attach the 3mf file below, any help or insight is really appreciated.

Thanks,

Zach

Compliant Wing