# Level shafts, direct linkage screws, separate rectangular shims

Implemented 2026-09-18 from the recessed-horn design and its level-shaft demo.

## Open and inspect

`Ainekio-Level-Shafts-Direct-Screws.blend` contains:

- **01 - Implemented level-shaft leg:** the complete assembly. Frame 1 is neutral;
  Space plays the retained eight-second illustrative loop.
- **02 - Print parts and rectangular shims:** separate printable meshes laid flat.

The existing robot file and earlier demo file are preserved. When installed into
the live session with the demo scene present, the installer also writes
`Before-Implementation-Demo.blend` before adding the revised scenes.

## Changes

- Both servo shafts are at the same height, with 12.5 mm horizontal spacing.
- The 24 mm input, 24 mm pickup, 41 mm rod, 40 mm carrier and 60 mm distal
  dimensions are retained.
- Three added M3 nuts and the hex nut pockets in Parts 009, 023 and 027 are
  removed. Their plain nominal **3 mm** linkage bores match the original source
  geometry. The later 3.2 mm clearance bores are reduced to that source size.
- The three long joint screw/bolt references are replaced by **M3 x 6 mm screw
  envelopes**, entering the printed supports directly, without separate nuts.
  Nominal support engagement is 2.7 mm after the bearing and washer stack.
- Recessed horn screw heads, horn pockets, bearing seats, short support collars
  and the inner connecting rod are retained.
- Part_027's round pickup eye now blends into the shaft over a smooth 10 mm
  taper, replacing the abrupt circular shoulder. Its 10 mm eye diameter, 3 mm
  hole, pivot positions and underside joint support are preserved; the new
  outline retains the 0.5 mm edge bevel.
- Parts_009 and _023 have matching smooth 10 mm transitions into their curved
  shafts, with 0.5 mm edge bevels. Joint locations, 3 mm bores, support collars,
  shaft slots, horn pockets and screw recesses are retained. Both assembly and
  print-layout meshes, source arrays and STL exports include this revision.
- Part_003 is restored from the original mount mesh, removing the two added
  circular offset pads. Small zero-area source triangles were cleaned up.
- Two identical, separate rectangular shims maintain the refined **5.25 mm** servo006
  offset along its shaft. Each is **12.4 x 4.2 x 5.25 mm**, with a **2.2 mm** mounting
  screw clearance hole. Use one beneath each mounting ear. Their compact shape
  avoids adding a connecting bar through the adjacent servo/case space.
- Bearing-support refinement: three **5.1 mm** support collars with **6 mm**
  flared roots; **5 mm** Part 026 with unchanged rod bearing-stop datums; outer
  leg moved outward **0.5 mm**. The input/output/knee plate gaps are **0.25 mm**.
  See `bearing-support-refinement-20260918/REFINEMENT.md` for the measured stack.
- Part_026's middle is widened from **5.015 to 7.015 mm**. Its sides now use
  continuous circular arcs (24.019 mm inner radius, 49.623 mm outer radius)
  tangent to the round ends, replacing the earlier bulged taper. Its oval
  cutouts, bearing seats, 41 mm joint spacing and 5 mm axial thickness are unchanged.
  See `../robot-part026-smooth-curve-20260918/` for the generator and comparison.

## Printable files

`STLs-mm/` contains six STL files in millimeters:

1. Part_003.stl — original mount; print one.
2. Part_003_Rectangular_Shim_5p25mm.stl — print **two**.
3. Part_009.stl — input crank; print one.
4. Part_023.stl — carrier; print one.
5. Part_026.stl — connecting rod; print one.
6. Part_027.stl — lower leg; print one.

The shims have flat faces and straight through holes. Other source part features
remain; this does not establish support-free printing for the whole assembly.

## Scope

All seven printable assembly meshes (including both shim instances) are checked
as one closed component each, with positive volume and no zero-area triangles.
The animation solves the unchanged linkage closure and retains the concept path.
No new full-range collision, torque, load, or hardware qualification was run.

**Screw fit:** the original nominal 3 mm holes are faithfully restored, without
modeled threads. That nominal diameter alone does not demonstrate thread grip
for an actual M3 screw. Match the print/actual screws before loading the leg;
no different pilot size has been silently substituted. Hardware meshes are
clearance references rather than manufactured thread models.

The calculated planar workspace remains that of the equal-height 24/24/41
linkage. Actual usable travel still depends on assembled clearance and servo
calibration; the retained animation is not a maximum-range test.

## Sources and reproduction

- `build_geometry.py`: regenerates the part meshes and STL files from the saved
  recessed-horn mesh arrays and original RR mesh snapshot.
- `install_blender.py`: installs the isolated assembly/print scenes and writes
  the standalone Blender file. Run inside Blender's Python environment.
- `design-report.json`: dimensions, removed hardware and basic mesh results.
- `index.json`, `geometry.npz`: generated source geometry.
- `smooth_driven_arms.py`: end-profile construction for Parts 009 and 023.
- `Parts_009_023-transition-before-after.png`: comparison of their revised ends.
- `bearing-support-refinement-20260918/`: preserved user edits, dimensional
  refinement generator, configuration and saved-artifact checks.

Run the geometry generator using a Python environment with NumPy, trimesh,
Shapely and manifold3d. It does not run or edit Blender. The Blender installer reads this
folder and adds new scenes without modifying existing robot geometry.