Custom Bed Level Pattern size not calculated correctly

[yakoder]

It appears as if the Custom Bed Level Pattern size is calculated before removing any raft/brim, not after.

Steps:

• Set Build Plate Adhesion type to Raft and Raft Extra Margin of 5.0mm
• Add Custom Bed Level Pattern using 100% (number of rings 'should' be irrelevant, but I used only 1) [Tested with both Concentric Squares and Concentric Circles]
• Check reported model size (Cura lower left) (for my 235 x 235 printer bed, the model size is 224.0 x 224.0)
• Removed AutoTower Model (using 'A' button)
• Set Build Plate Adhesion type to None
• Add same Custom Bed Level Pattern as above
• Cura now reports model size different than previous test (for mine: 234.2 x 234.2) [Note: I actually expected 235x235, as that is the configured bed size. So this is a 2nd "error" in calculation that AutoTowers is subtracting twice the nozzle diameter. Put differently 100% is actually 99.66%.]
• Removed AutoTower Model (using 'A' button)
• Set Build Plate Adhesion type to Brim and Brim Width to 6.0mm
• Add same Custom Bed Level Pattern as above
• Cura now reports model size of 224.0 x 224.0
• Removed AutoTower Model (using 'A' button)
• Change Brim Width to 15mm
• Add Same pattern; Size is 224.0 x 224.0
• Remove Model; Change to Raft with 15mm extra margin; Size is now 204.2 x 204.2
• Remove Model; Change to Skirt with 3mm Skirt Distance; Size is now 228.2 x 228.2
• Remove Model; Change Skirt Distance to 15mm; Size is now 228.2 x 228.2

Conclusions:

• If a Brim is enabled, the Brim Width is not used for calculating the AutoTowers model width, but a "hard coded" value is used (e.g., bed_width - 11mm; or bed_width - 2 * 5.5mm)
• If a Raft is enabled, the Raft Extra Margin is used for calculating the AutoTowers model width.
• If a Skirt is enabled, the Skirt Distance is not used for calculating the AutoTowers model width, but a "hard coded" value is used (e.g., bed_width - 12mm; or bed_width - 2 * 3mm)
• If Skirt, Raft, or None is configured for Bed Adhesion Type, the Nozzle Diameter is used for calculating the AutoTowers model width

Expectation:

• If a model is set to 100%, that should exactly match the defined print bed dimensions without any adjustment for nozzle diameters or any margins/padding used by the skirt, brim, or raft that is being removed by this extension.

Rationale for wanting 100%: Verifying nozzle-to-bed alignment to discover if any nozzle X/Y offset is needed. (I had a large print result in multiple lines of a brim print off the right edge of the print bed.

Cura versions used: Ultimaker Cura 5.8.1; Elegoo Cura 5.6.0 build 231229

[yakoder]

Created "as-expected" model in OpenSCAD (below). Cura does not Auto Position the model on the build plate, nor does Arrange All Models (Ctrl+R) position the model, but "Center Selected" does put the model in the expected position.

Cura does report a size, for the below generated model, of 235.0 x 235.0 x 0.2 mm.

I tried reducing the model size by 1, 2, 3, and 4 times the nozzle width, and Cura didn't open the model positioned on the build plate with Build Plate Adhesion Type of 'None'. The model was opened in a correct position when 5 times the nozzle width was subtracted off the size of the model (resulting in a 233.0 x 233.0 x 0.2 mm model).

Conclusion: Cura has issues positioning models that exactly match are "too close" to the configured print bed size.

`noz = 0.4; lyr = 0.2; clr = 0.005; en3maxXY = 235;

difference() { cube([en3maxXY, en3maxXY, lyr]);

translate([noz, noz, -clr])
cube([en3maxXY-2*noz, en3maxXY-2*noz, lyr+2*clr]);

}`

Edit: I should have tried Slicing before posting. Cura refuses to slice any model that it cannot auto-position. Therefore, the maximum printable size appears to be bed_width - 5 * nozzle_diameter.

For my original need (verifying print bed size) Cura does slice a model that is 6 nozzles smaller (232.6 x 232.6) than the build plate with a brim width of 3.0 mm. (That, mathematically, produces a printed item of 235.0 x 235.0.)

The "Cura Sliceable Maximum" not matching the "Machine Build Plate Size" was a surprise, and might be the rationale behind some of the AutoTowers Bed Pattern Size "expected" vs "actual" differences.