Love all the new goodies introduced in PreForm 2.18. I noticed one of the modifications reads:
Early layer unioning improves adherence when printing without a raft.
And according to your latest supports documentation:
PreForm automatically revises the first 0.75 mm of all on-build-platform prints to increase adhesion. “Early layer unioning” combines and extrudes the shapes - the perimeter and fill area - of all layers contained in the first 0.75 mm to ensure that printed parts have a completely flat surface in contact with the build platform.
I realize a substantial number of those first few layers will get eaten up by compression. However the 0.75mm figure strikes me as being tuned to the “lowest common denominator” across all your printers (i.e. closer to worst-case-scenario).
I’ve done a LOT of direct-on-base printing (on older Preforms / firmwares). My general approach has been to manually extrude a vertical portion like that seen below, for adhesion and to act as a “sacrificial stub” to offset compression. I tune the stub height to the printer and build platform being used (sometimes even to the location on the platform). With care, I’m able to achieve a very smooth bottom surface.
For my own equipment my best results tend to settle closer to 0.45mm.
Any chance we could get a knob under Advanced support settings (or under Printer Fine Tuning) to adjust the amount of layer unioning?