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SoftFever
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# Belt printing for OrcaSlicer
This merges the `belt-printer` branch into `main`. It adds support for
conveyor-belt ("infinite Z") printers like the BabyBelt Pro, the
IdeaFormer IR3 V2 and the CR-30 family, along with the things that had
to grow around it: tilted-plane slicing, supports that terminate on the
belt, belt-aware brims, a purge tower that works without a flat bed,
multi-colour belt prints, a preview that shows the part the way it was
designed, and starter profiles.
It has been a long road (the first attempt was #12733 back in March, the
pipeline has been rebuilt twice since) and a lot of people have put work
into it. Credits are at the bottom; please tell me if I've missed
anyone.
Closes #2628, closes #11344, closes #6885, closes #9004, closes #14188.
---
## How belt printing works
Slicers assume the bed sits on the XY plane and layers stack along Z. A
belt printer breaks that in two ways at once: the belt is tilted
(usually 45°) and the axis that advances the belt is the printer's Z, so
the "bed" lives on the XZ plane and is, in principle, infinitely long.
<img width="6360" height="2702" alt="A flat bed vs a tilted belt"
src="https://github.com/user-attachments/assets/3f5542f2-6dab-42bf-9233-f96d863b40c8"
/>
Rather than teach every part of the slicer about tilted beds, the branch
leaves the slicing engine alone and transforms what goes in and what
comes out. The pipeline has five steps.
<details>
<summary><b>The five steps in detail</b></summary>
### 1. Pre-slice rotation
The mesh is rotated by the belt angle before slicing
(`BeltSliceStrategy`, `BeltTransform`), so that the ordinary horizontal
slicer produces layers that are actually tilted planes relative to the
part. Rotation is about X by default (belt along Y); Y rotation and a Z
lift are supported too. A "global" mode rotates every object about one
common origin, which is what keeps several parts on one belt consistent
with each other.
### 2. Slice
Nothing special. The mesh is rotated, the slicer does what it always
does. This is the reason most of Orca's features (walls, infill, seams,
ironing, painting, …) just work on a belt without belt-specific code.
### 3. Supports
Supports are generated after slicing against a virtual floor: the belt
surface, expressed in the rotated frame (`BeltFloorContext`). Normal,
tree and organic supports all terminate on that plane instead of on Z=0,
and nothing may be generated below it. Painted supports and seams are
transformed with the same `trafo_sliced()` as the layers.
### 4. G-code back-transform
The G-code is rotated back into the model's Cartesian frame
(`BeltBackTransform`). A nice side effect: with step 5 switched off you
can slice at a non-standard angle and print the result on a normal
printer. The first belt-sliced Benchy was printed exactly that way, on a
Sovol SV08.
### 5. Machine frame
The printer doesn't know its bed is tilted. To make straight walls come
out straight, the axes are remapped (the default mapping is X → reversed
X, Y → Z, Z → Y) and the result is sheared and scaled:
```math
\begin{bmatrix} X \\ Y \\ Z \end{bmatrix}
\longrightarrow
\begin{bmatrix} X \\ \dfrac{Y}{\cos\alpha} \\ Z + Y\cdot\tan\alpha \end{bmatrix}
```
This lives in `GCodeWriter` behind a small `MachineKinematics` strategy
(`BeltKinematics` on belts, identity otherwise), so the writer itself
has one code path. The slicing angle and the machine angle can differ if
you want to, e.g. slice at 30° on a 45° machine — mind your nozzle
clearance if you do.
</details>
A short recording of the back-transform from the original PR:
https://github.com/user-attachments/assets/cdb9cc83-711d-48b7-9d86-a014a32c5e8e
---
## What had to change to make it work
Belt mode is gated on the `belt_printer` printer setting; with it off,
every code path below is the old one.
<details>
<summary><b>Slicing and geometry</b></summary>
- `PrintObjectSlice` / `PrintObject`: the rotation, Z lift and
per-object layer-grid shift, plus the invalidation that goes with them.
Modifiers and painted volumes are transformed with the same matrix as
the model.
- `FirstLayerPlane`: "the first layer" on a belt is a band along the
belt, not the first slicing layer. First-layer speed, line width and the
fan band are measured against it.
- `Print::validate`: clearance checks against the gantry instead of the
printable height; skirt, raft, draft shield, the classic prime tower,
arc fitting, spiral vase with brim, and scarf-joint seams are refused or
disabled on belts because each of them either doesn't exist on a belt or
moves the belt the wrong way (a scarf seam starts one layer low, which
on a belt is a 0.28 mm back-step into the previous layer at every seam).
- Z-hop defaults to 0 on belt profiles; a lift on a belt is a belt move.
</details>
<details>
<summary><b>Supports</b></summary>
- `SupportMaterial`, `TreeSupport`, `TreeSupport3D`, `TreeModelVolumes`:
a shared `BeltFloorContext` provides the belt plane; supports clip to
it, extension layers are numbered sequentially, and the first-layer
flange that used to be stamped under everything is gone.
- `build_plate_tilt_x/y` (from #12733) is now derived from the slicing
rotation in `Print::apply`, so GUI and CLI agree; it's capped below 90°.
- Organic supports that reach the belt no longer produce negative flow.
</details>
<details>
<summary><b>Brims (#15155)</b></summary>
A belt first layer is effectively a single line of contact, so a brim
matters more than usual. `BeltBrim` generates per-layer bands along the
belt plus an "apron" ahead of the part, in the object's brim filament.
Two belt-specific settings came with it: **Leading edge brim length**
(more lines on the side printed first) and **Extra brim width** (across
the belt), plus a **Leading edge only** brim type.
<img width="1849" height="1043" alt="belt brim"
src="https://github.com/user-attachments/assets/f963ed8e-53e7-48f8-a495-123cb9ae27f7"
/>
</details>
<details>
<summary><b>Multi-colour: the belt purge tower</b></summary>
The classic wipe tower can't exist on a belt (its G-code bypasses the
transform and it needs a flat bed to stand on). Instead the GUI
generates a long, thin "purge prism" beside the parts, flush with the
far edge of the belt, one per plate (`BeltPurgeTower.cpp`). It is a real
model object, so it is sliced like everything else, and
`Print::_plan_belt_purge` routes every filament change into it via
`flush_into_objects`. It's sized from the flush matrix, split into one
island per simultaneous tool change, snapped onto the parts' layer grid,
cut off after the last colour change and stripped of infill no change
claimed, so what prints is a good deal smaller than the model you see in
Prepare.
</details>
<details>
<summary><b>G-code generation and cooling</b></summary>
- `GCodeWriter` + `MachineKinematics`/`BeltKinematics`: the
back-transform, axis remap, shear and scale, lifts that are belt moves,
and the first-layer travel speed.
- `GCode.cpp` / `BeltGCode`: a belt header (slicing rotation, remaps,
machine tilt) that the preview reads back; it is written outside the
optional header block so printers with a BTT TFT thumbnail still get it.
Exclude-object outlines are emitted in the plate frame.
- `CoolingBuffer`: the "first layers" the fan stays off for are a band
above the belt, marked per extrusion segment by the generator
(`;_BELT_BAND_START/END`) and honoured on every layer.
- `GCodeProcessor`: belt header parsing, start-G-code Z handling, and
height checks that don't compare belt travel against the printable
height.
- `ToolOrdering` / `BeltPurge`: filament changes are detected by
scanning the ordering (an apron layer never carries the first-layer
flag).
</details>
<details>
<summary><b>GUI</b></summary>
- Printer settings tab: the belt group (slicing rotation, angle, global
mode, infinite Y, purge tower, floor settings). The axis remap and
pre-slice remap options are Develop-mode only.
- `ConfigManipulation`: everything that doesn't apply on a belt is
greyed out (skirt, raft, draft shield, the wipe tower group, scarf
seams, …).
- Preview: a "designed view" that back-transforms the toolpaths onto the
model so you see the part upright, with `B` toggling the raw
machine-frame G-code (`GCodeViewer`, `Shortcuts`). The tilt comes from
the belt header, so imported G-code behaves.
- Arrange: parts are packed from the end of the belt that prints first,
colours are grouped into runs so each filament change happens once, the
purge tower's strip and the brim width are reserved, and piles aimed at
an off-centre `best_object_pos` are clamped to the bed (`Arrange.cpp`,
`ArrangeJob.cpp`, one clamp in `libnest2d`).
- `PartPlate`: plate icons stay in the gap between plates on a long,
narrow bed; the plate is open along Y for containment tests on an
infinite-Y belt.
- Calibration: a belt temperature tower (overhang variant) that slices
correctly on a tilt.
- The old tilted-bed rendering in Prepare was dormant and has been
removed; the bed is shown as the slicing pipeline treats it.
</details>
<details>
<summary><b>Config options</b></summary>
Printer: `belt_printer`, `belt_printer_infinite_y`,
`belt_slice_rotation`, `belt_slice_rotation_angle`,
`belt_slice_rotation_global`, `belt_preslice_global`,
`belt_frame_tilt_decouple`, `belt_frame_tilt_angle`,
`belt_support_floor_mode`, `belt_support_floor_offset`,
`belt_support_z_offset_mode`, `enable_belt_purge_tower`,
`first_layer_plane`, `first_layer_plane_offset`,
`first_layer_plane_thickness`, `build_plate_tilt_x/y`,
`gcode_back_transform`, `gcode_remap_x/y/z`, `preslice_remap_x/y/z`,
`preslice_remap_global`.
Process: `belt_purge_tower_width`, `leading_brim_length`,
`extra_brim_width`, brim type `leading_edge_only`. Object:
`belt_purge_tower_object`.
All of them have defaults that leave non-belt printers untouched, and
old `belt_support_floor_mode` values map to `none`.
</details>
<details>
<summary><b>Tests</b></summary>
`tests/libslic3r/test_belt_brim.cpp` and `test_arrange.cpp`, and belt
cases in `fff_print` (`test_print.cpp`, `test_skirt_brim.cpp`,
`test_gcodewriter.cpp`, `test_gcode_processor.cpp`): scarf gate, fan
band, gantry clearance, organic supports on the belt, brim with and
without the purge tower, apron widths, machine mapping at non-45°
angles, first-travel lift, start-G-code Z, arrange clamp and colour
grouping. All three suites pass on Linux, and the tree-wide profile
check passes.
</details>
---
## Starter profiles
Three vendors ship belt profiles. Belt mode needs the printer settings
at **Advanced** or above to show its group.
<img alt="advanced mode"
src="https://github.com/user-attachments/assets/7a519ce5-b3b5-400c-a914-4f208bb577b0"
/>
| Printer | Vendor bundle | Nozzles | Processes | Filaments |
|---|---|---|---|---|
| **Generic Belt Printer** (`MyBeltPrinter`) | Custom | 0.2, 0.4, 0.6,
0.8 | 0.20mm Standard, 0.12mm Fine | library |
| **BabyBelt Pro** (Printcepts) | Printcepts | 0.4 | 0.20mm Standard |
Generic PLA, Generic PETG, eSUN PLA |
| **IdeaFormer IR3 V2** | IdeaFormer | 0.4 | 0.20mm Standard | Generic
PLA, Generic PETG, eSUN PLA |
To set up a printer that isn't listed: pick **Generic Belt Printer**,
set the belt width and length, save the profile, then copy in your
machine's start/end G-code and limits and tune from there.
<img alt="generic belt printer"
src="https://github.com/user-attachments/assets/90134d55-d6fe-4dba-8695-5ea44e78ec2b"
/>
<details>
<summary>BabyBelt Pro</summary>
<img width="2467" height="1392" alt="BabyBelt Pro"
src="https://github.com/user-attachments/assets/2b448cee-339e-43c9-964b-1ee9044044c7"
/>
</details>
---
## Contributions
### @HarrierPigeon
***Majority of design & implementation***
I did most of the work here by myself with AI tools (primarily Claude,
some Codex.)
PRs #12733, #12998, #14385, #15155, #15361, #15156, #15526, #16127
### The @Unlayered3D Team
***Rotation-Mode Pipeline***
The initial version of this sheared the model in the pre-slice pipeline.
Talking with them convinced me to switch to the current
rotate->slice->unrotate-> remap & shear method, which had significant
immediate improvements. Working with them has been a blast.
### @tommasobbianchi
***IdeaFormer IR3V2 Profile, eSUN PLA Tuning, G-Code Render / Preview***
TommyB came in at the perfect time to help keep me motivated and
contributed several things I hadn't had the werewithal to implemement
yet. Without their contributions and encouragement, we wouldn't be here
yet.
### The BabyBelt Community
**BabyBelt Pro** — @rexit1982 for the profile, and @RobMink of
Printcepts for the printer and a lot of patient testing.
**Field reports** — Many members of the BabyBelt community helped,
testing on their machines, providing G-Code and examples of issues, and
encouraging me to keep working on it. Among them:
- @RobMink - creator of the BabyBelt
- @rexit1982 - initial BabyBelt Pro profile, bug hunter
- @shubhracc - found a *lot* of technical bugs
- @NeoDLC - bug hunter
and BabyBelt Discord members who found bugs & gave feedback in no
particular order:
- @horatio42 - also provided a build machine while mine was down
- @HotCubCar - requested belt printer brim support
- Swap_File
- @Nyctelios
- Sup
- @matschi140
- @Rise-Run
- @shooby-dooby
### OrcaSlicer Maintainers
**Generic belt printer** — @SoftFever
**Keeping on top of upstream** @RF47 & @HanifKoh
**Review and fixes** — @HanifKoh (#15685 and the review on this PR).
Among them: plates after the first printed off the bed on belts; painted
supports and seams ignored the belt transform; support generation failed
at a 90° tilt; the object table crashed on the Support column on every
printer because tilt keys were in the per-object tables; apron brims
printed in the wrong filament; `build_plate_tilt` went stale outside the
GUI; the CLI reserved a wipe tower on belts; every G-code file was
treated as belt G-code because the config block carries the angle; tests
didn't compile on Clang/MSVC; plus a long list of smaller clean-ups and
the review questions that led to the clearance check, the header length
fix, the retired floor modes and the removal of the diagnostic logging.
### Additional Thanks
A special thanks to LDO Motors, who provided equipment for validating
multicolor, and my wife, who not only put up with with this obsession,
and the addition of three belt printers to our home, but has encouraged
me to keep going ever since I started this project six months ago.
---
## Known Issues
- The purge prism's first tool is chosen by the shared `ToolOrdering`
logic; on some layouts the print opens on the wrong filament and makes
one extra change at the thin tip of the prism (the "cannot absorb the
full purge volume" warning at a low height).
- Colour grouping in arrange is a soft cost: when the belt is too short
for clean runs, colours overlap rather than spill onto another plate.
- Three OrcaFilamentLibrary filaments still carry `filament_z_hop` 0.4;
belt profiles override it to 0.
Also: slicing at an angle other than the machine's (decoupled frame
tilt) is supported but not something the starter profiles exercise.
OrcaSlicer tests
Building, running and writing tests is documented on the wiki, under How to Test.
Two files here rather than there, because coding agents only read what is in the repository: