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Threads: a taper thread's groove follows its crest cone across the section, so no sliver of the flanks is left

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The groove's section was cut square a fixed margin past the crest. The crest cone changes 1 in 32
along the axis across the section's own width, so for NPT (margin 0.015 mm against a 0.028 mm
rise) the section's deeper corner stopped under the cone and each tooth kept a sliver of its
flank: 0.94 mm3 too much on a 1/2-14 NPT. The section's edge now follows the cone at the same
margin.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
This commit is contained in:
jyviko
2026-10-29 18:40:16 -04:00
committed by Irakli Kourtis
parent 023017747b
commit 6af622978a
1 changed files with 40 additions and 22 deletions
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crates/doc/src/eval_thread.rs
+40 -22
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@@ -461,21 +461,44 @@ fn thread_grooves(
format!("this {shown} mm shaft is too thin for a modelled {m} thread: {cut}; make the shaft {} mm for {m}{alt}", show_mm(d))
}));
}
// The section's radial span: from the root out past the surface (external), or from inside
// the hole wall out to the root (internal), so the cut leaves no skin.
// The section: from the root out past the surface (external), or from inside the hole wall
// out to the root (internal), so the cut leaves no skin, its flanks the groove's.
// A taper thread's crests are cut by its major cone (external) or minor cone (internal),
// as the die or tap cuts them ([`taper_envelope`]): its groove reaches just past the crest,
// by as much as narrows the tooth's crest flat by a quarter (NPT's flat is 0.038 P).
let past = |g: &crate::thread_forms::GrooveProfile| 0.25 * g.crest_flat / (g.flank_lo.tan() + g.flank_hi.tan());
let span = |g: &crate::thread_forms::GrooveProfile| match (taper.is_some(), t.internal) {
(true, true) => (g.crest_r - past(g), g.root_r),
(true, false) => (g.root_r, g.crest_r + past(g)),
(false, true) => (radius.min(g.crest_r) - 0.1 * p, g.root_r),
(false, false) => (g.root_r, radius.max(d / 2.0) + 0.05 * p),
// as the die or tap cuts them ([`taper_envelope`]): its groove reaches past the crest by as
// much as narrows the tooth's crest flat by a quarter (NPT's flat is 0.038 P). The cone
// changes 1 in 32 along the axis (`major_at`) across the section's own width, so its edge
// there follows the cone at that margin rather than being cut square: square, its deeper
// corner stops short of the cone and leaves a sliver of each flank.
let cone = taper.map_or(0.0, |_| (major_at(t.start + 1.0) - major_at(t.start)) / 2.0);
let section_of = |g: &crate::thread_forms::GrooveProfile| -> (Vec<Vec2>, f64) {
let (tl, th) = (g.flank_lo.tan(), g.flank_hi.tan());
if taper.is_none() {
let (r0, r1) = if t.internal {
(radius.min(g.crest_r) - 0.1 * p, g.root_r)
} else {
(g.root_r, radius.max(d / 2.0) + 0.05 * p)
};
let ((lo0, hi0), (lo1, hi1)) = (g.extents(p, r0), g.extents(p, r1));
let wide = g.width(p, if t.internal { r0 } else { r1 });
return (vec![Vec2::new(r0, -lo0), Vec2::new(r1, -lo1), Vec2::new(r1, hi1), Vec2::new(r0, hi0)], wide);
}
// Depth from the root, out towards the crest: d(z) = dc + q·z along the edge, which
// meets the flanks z = −(h + d·tl) and z = h + d·th.
let o = if t.internal { -1.0 } else { 1.0 };
let q = o * cone;
let h = g.width(p, g.root_r) / 2.0;
let dc = o * (g.crest_r - g.root_r) + 0.25 * g.crest_flat / (tl + th);
let (z_lo, z_hi) = (-(h + dc * tl) / (1.0 + q * tl), (h + dc * th) / (1.0 - q * th));
let r = |z: f64| g.root_r + o * (dc + q * z);
let (root, edge) = ([Vec2::new(g.root_r, -h), Vec2::new(g.root_r, h)], [Vec2::new(r(z_lo), z_lo), Vec2::new(r(z_hi), z_hi)]);
// In the order the square section has: the inner radius's corners first.
let pts = if t.internal { vec![edge[0], root[0], root[1], edge[1]] } else { vec![root[0], edge[0], edge[1], root[1]] };
(pts, z_hi - z_lo)
};
let (r0, r1) = span(&g);
let wide = if t.internal { r0 } else { r1 };
if g.width(p, wide) >= p * 0.98 {
let (mut section, wide) = section_of(&g);
let radii = |s: &[Vec2]| s.iter().fold((f64::INFINITY, f64::NEG_INFINITY), |(a, b), v| (a.min(v.x), b.max(v.x)));
let (r0, r1) = radii(&section);
if wide >= p * 0.98 {
// The groove would be wider than a pitch: the face is far inside the thread (a hole
// narrower than its minor diameter, a shaft thicker than its major one, #2688).
let (m, dia) = (&t.designation, 2.0 * radius);
@@ -488,9 +511,6 @@ fn thread_grooves(
format!("this {shown} mm shaft is too thick for a modelled {m} thread; make the shaft {} mm for {m}{alt}", show_mm(d))
}));
}
let (lo0, hi0) = g.extents(p, r0);
let (lo1, hi1) = g.extents(p, r1);
let mut section = vec![Vec2::new(r0, -lo0), Vec2::new(r1, -lo1), Vec2::new(r1, hi1), Vec2::new(r0, hi0)];
if !(r0.is_finite() && r1.is_finite() && r0 > 0.0) {
return Err(DocError::Invalid("thread dimensions are out of range".into()));
}
@@ -503,7 +523,8 @@ fn thread_grooves(
// the material (an external thread's away from the axis, past the surface; an internal
// one's towards it, into the hole) as it turns. It lies past the full-form length, up to the
// shoulder's clearance; at a free end, inside the face, the groove reaching nothing there.
let (w_lo, w_hi) = (lo0.max(lo1), hi0.max(hi1));
// How far the section reaches each way along the axis.
let (w_lo, w_hi) = section.iter().fold((0.0_f64, 0.0_f64), |(a, b), v| (a.max(-v.y), b.max(v.y)));
let s0 = match (ends[0], ease[0] > 0.0) {
(End::Free, false) => t.start - p,
(End::Free, true) => t.start,
@@ -528,11 +549,8 @@ fn thread_grooves(
let mut r0 = r0;
let taper_rate = match taper {
Some(_) => {
let gb = profile(major_at(s0));
let (a, b) = span(&gb);
let ((l0, h0), (l1, h1)) = (gb.extents(p, a), gb.extents(p, b));
section = vec![Vec2::new(a, -l0), Vec2::new(b, -l1), Vec2::new(b, h1), Vec2::new(a, h0)];
r0 = a;
section = section_of(&profile(major_at(s0))).0;
r0 = radii(&section).0;
(major_at(s0 + lead) - major_at(s0)) / 2.0
}
None => 0.0,