I wanted to test the physical guide instead of continuing to reason about it only from OpenSCAD. So I generated the Uncial 3 mm guide, printed it, and used that first print to find the next design problem. This is the workflow I used; it is a real test, not a universal printer profile.
Context
The first guide I printed was the 180 × 36.8 × 2 mm Uncial 3 mm model. I used ordinary Elegoo PLA. In PrusaSlicer I used a 0.15 mm quality profile, 15% infill, no supports and no brim. The slicer estimated about 1 hour 25 minutes and roughly 15 g of filament; the actual print took about 1.25 hours. Those values describe this particular print and printer setup; another printer, nozzle, material or speed profile will change them.
What actually worked
I downloaded the SCAD file from CalligraphyToolkit and opened it in OpenSCAD. I pressed F6 to do a full render, then exported the rendered model as STL. OpenSCAD distinguishes the fast preview from the full render; the official manual also documents rendering before STL export. I then opened the STL in PrusaSlicer, selected the printer and PLA profiles, sliced it, checked the layer preview and sent the resulting file to the printer.
The steps I use
1. Generate the model and save the .scad file. 2. Open it in OpenSCAD. 3. Press F6 and wait for the render to finish. 4. Export the rendered geometry as STL. 5. Open the STL in PrusaSlicer. 6. Confirm the physical dimensions and orientation. 7. Slice the model. 8. Inspect the first layer, bridges and any unsupported geometry in Preview. 9. Export or send the print file to the printer. For the flat practice guide I did not need supports or a brim.
What the first print taught me
The legacy guide printed correctly, but the straight narrow slots demanded a very thin pencil. That is exactly the kind of problem that is difficult to notice on screen. It led to Guide R3, where the tracing openings use a V/funnel profile: wider at the top and narrower close to the paper so a normal conical pencil or pen can reach farther into the guide.
Keep the model identity
Before printing I now check the model code, physical revision and app version engraved in the generated model. The downloaded SCAD filename also includes the script, nib width, x-height, revision, model code and app version. If I print several variants, I can tell them apart without measuring every one again.