Somewhere along the way, I lost part of the constellation of settings that produce a properly sized first layer. While looking for something else, I discovered that the Z-axis level started at half the expected 0.25 mm:
(<layer> 0.125 ) (<skirt>) G1 X-13.25 Y29.2675 Z0.125 F15000.0
The key turned out to be (re?)enabling the Skeinforge Bottom setting:
- Additional Height over Layer Thickness: 1.0
- Altitude: 0.0
Then it comes out right:
(<layer> 0.25 ) (<skirt>) G1 X-13.25 Y29.2675 Z0.25 F15000.0
The excellent illustrations at the bottom of the Official Documentation (which I don’t recall seeing before) show you what’s going on; you really can’t deduce the geometry from the parameter names alone.
The first layers were still within ±0.05 mm of 0.25 mm, which suggests the plastic squooshes out around the nozzle and rebounds to nearly the correct thickness, but they tended toward consistently too thin rather than OK-on-average. The first trial with the proper Bottom setting came out spot on at 0.25 mm around the Skirt thread, so it’s back on track.
The first layer comes out at 20 mm/s and sticks like glue to the Kapton tape. The remaining layers run at 40 mm/s for infill and 20 mm/s for perimeters, producing spot-on dimensions, with 250 mm/s traverses between printed sections. It’d be nice to run faster, but accuracy has its benefits for mechanical parts.
That’s with a 2.95 mm Filament Diameter setting closely matching the average actual diameter and a 0.95 Filament Packing Density. I think the Density is slightly too low, so I’ll bump that to 1.0 for the next object.