[BUG] worm_gear(): backlash parameter has no effect — not passed to _gear_tooth_profile()

[chertykov]

Describe the bug
The backlash parameter in worm_gear() is accepted, validated via assert, but never forwarded to the internal _gear_tooth_profile() call. As a result, _gear_tooth_profile() always uses its default value backlash=0.0, and the gear tooth geometry is identical regardless of what backlash value the user specifies.

Code To Reproduce Bug

include <BOSL2/std.scad>
include <BOSL2/gears.scad>

// Render these side by side — they produce identical geometry
up(4) worm_gear(mod=0.8, teeth=120, worm_diam=14, worm_starts=1, worm_arc=60, backlash=0.0, slices=30, $fn=60);
down(4) worm_gear(mod=0.8, teeth=120, worm_diam=14, worm_starts=1, worm_arc=60, backlash=1.0, slices=30, $fn=60);

Expected behavior
backlash=1.0 should produce noticeably thinner teeth compared to backlash=0.0, creating clearance between meshing teeth — consistent with how backlash works in spur_gear(), rack(), and other gear modules.

Screenshots

Actual Behavior
Both models are identical. Changing backlash from 0 to any value has zero visual or geometric effect.

Root Cause
In gears.scad, inside the worm_gear() function body, the call to _gear_tooth_profile() is missing the backlash argument:

// gears.scad, inside function worm_gear(), approximately line 2188
full_tooth = path3d(reverse(zrot(90, _gear_tooth_profile(
                                         circ_pitch, teeth=teeth,
                                         pressure_angle=PA,
                                         profile_shift=profile_shift,
                                         clearance=clearance, shorten=.3,
                                         helical=helical, internal=false,
                                         // backlash is NOT passed here
                                         center=true)))),

Suggested Fix
Add backlash=backlash to the _gear_tooth_profile() call:

 full_tooth = path3d(reverse(zrot(90, _gear_tooth_profile(
                                          circ_pitch, teeth=teeth,
                                          pressure_angle=PA,
                                          profile_shift=profile_shift,
                                          clearance=clearance, shorten=.3,
+                                         backlash=backlash,
                                          helical=helical, internal=false,
                                          center=true)))),

Version
OpenSCAD version 2021.01

[adrianVmariano]

Worm gears are generally a bit broken right now. If you create a worm gear and it's mating worm they tend to self-intersect and I don't know how to fix this. I can enable backlash, but there are still problems.

[chertykov]

This is a bug that can be fixed.
Please fix it.