diff --git a/src/bevel_gear.rs b/src/bevel_gear.rs
index cb5fefe..c8173f8 100644
--- a/src/bevel_gear.rs
+++ b/src/bevel_gear.rs
@@ -1,6 +1,6 @@
-use std::f32::consts::{FRAC_PI_2, PI};
+use std::f32::consts::PI;
 
-use glam::{Affine3A, FloatExt, Quat, Vec2, Vec3, Vec3Swizzles, vec3};
+use glam::{Affine3A, Vec2, Vec3, Vec3Swizzles, vec3};
 
 use crate::{crown_gear::CrownGearDesc, profile::Profile, render::mesh::MeshIndexed};
 
@@ -55,34 +55,29 @@ impl BevelGearShape {
 			.map(move |(k, r)| Vec2::from_angle(k as f32 * angle) * r)
 	}
 
-	pub fn cut(&mut self, offset_teeth: f32) {
+	pub fn cut(&mut self, cutter_tfm: Affine3A) {
 		let cutter = self.desc.cutter();
-		let crown_skip_teeth = cutter.pitch_radius.floor();
-		let crown_turns = (offset_teeth.fract_gl() + crown_skip_teeth) / (2. * cutter.pitch_radius);
-		let cutter_tfm = Affine3A::from_rotation_translation(
-			Quat::from_rotation_y(FRAC_PI_2 + self.desc.cone_halfangle)
-				* Quat::from_rotation_z(2. * PI * crown_turns),
-			vec3(0., 0., self.desc.pitch_distance()),
-		);
 		let z_proj = self.desc.pitch_distance();
-		let cutting_line = cutter.to_shape(0.375..0.725, 200);
+		let cutting_line = cutter.to_shape(0.375..0.625, 200);
 		let cutting_line: Vec<_> = cutting_line
 			.into_iter()
 			.map(|pt| {
 				let pt_3d = cutter_tfm.transform_point3(pt);
-				let pt_2d = -pt_3d.xy() * (z_proj / (z_proj - pt_3d.z));
+				let pt_2d = pt_3d.xy() * (z_proj / (z_proj - pt_3d.z));
 				pt_2d
 			})
 			.collect();
-		let len = self.points.len();
+		let angle = 2.0 * PI / self.points.len() as f32;
 		for (k, pt) in self.points.iter_mut().enumerate() {
-			let dir = Vec2::from_angle(
-				2.0 * PI * (k as f32 / len as f32 - offset_teeth / self.desc.teeth as f32),
-			);
+			let dir = Vec2::from_angle(k as f32 * angle);
 			for line in cutting_line.iter().zip(&cutting_line[1..]) {
-				if line.0.dot(dir.perp()) >= 0. && line.1.dot(dir.perp()) <= 0. {
-					*pt = pt.min(f32::min(line.0.length(), line.1.length()));
+				if line.0.dot(dir) <= 0. || line.1.dot(dir) <= 0. {
+					continue;
 				}
+				if line.0.dot(dir.perp()) < 0. || line.1.dot(dir.perp()) > 0. {
+					continue;
+				}
+				*pt = pt.min(f32::min(line.0.length(), line.1.length()));
 			}
 		}
 	}
diff --git a/src/crown_gear.rs b/src/crown_gear.rs
index 40d3169..0918aed 100644
--- a/src/crown_gear.rs
+++ b/src/crown_gear.rs
@@ -21,6 +21,10 @@ pub struct CrownGearVisual {
 }
 
 impl CrownGearDesc {
+	pub fn teeth(&self) -> f32 {
+		2. * self.pitch_radius
+	}
+
 	pub fn to_shape(&self, part: Range<f32>, sides: usize) -> Vec<Vec3> {
 		let teeth = 2.0 * self.pitch_radius;
 		let mut ret = Vec::new();
diff --git a/src/lib.rs b/src/lib.rs
index 280ee13..ef6b81f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -3,7 +3,7 @@ use std::{
 	f32::consts::{FRAC_PI_2, PI},
 };
 
-use glam::{FloatExt, Mat4, Quat, UVec2, Vec3, Vec4, vec3, vec4};
+use glam::{Affine3A, FloatExt, Mat4, Quat, UVec2, Vec3, Vec4, vec3, vec4};
 
 use crate::render::mesh::GpuParams;
 
@@ -156,6 +156,21 @@ impl Core {
 		}
 	}
 
+	fn gear_tfm(&self) -> Affine3A {
+		let turns = -self.t / self.bevel_gear_desc.teeth as f32;
+		Affine3A::from_rotation_translation(Quat::from_rotation_z(2. * PI * turns), Vec3::ZERO)
+	}
+
+	fn cutter_tfm(&self) -> Affine3A {
+		let skip_teeth = self.crown_gear_desc.pitch_radius.floor();
+		let turns = (self.t.fract_gl() + skip_teeth) / self.crown_gear_desc.teeth();
+		Affine3A::from_rotation_translation(
+			Quat::from_rotation_y(FRAC_PI_2 + self.bevel_gear_desc.cone_halfangle)
+				* Quat::from_rotation_z(2. * PI * turns),
+			vec3(0., 0., self.bevel_gear_desc.pitch_distance()),
+		)
+	}
+
 	fn render(&self, output: &wgpu::Texture, args: &RedrawArgs) {
 		let y_frac = {
 			let size = output.size();
@@ -184,30 +199,17 @@ impl Core {
 			},
 		);
 
-		let turn_teeth = self.t;
-		let bevel_turns = 0.5 - turn_teeth / self.bevel_gear_desc.teeth as f32;
-		let crown_skip_teeth = self.crown_gear_desc.pitch_radius.floor();
-		let crown_turns =
-			(turn_teeth.fract_gl() + crown_skip_teeth) / (2. * self.crown_gear_desc.pitch_radius);
-
 		self.params_gear.set(
 			&self.queue,
 			render::mesh::ObjectParams {
-				transform: Mat4::from_rotation_translation(
-					Quat::from_rotation_z(2. * PI * bevel_turns),
-					Vec3::ZERO,
-				),
+				transform: self.gear_tfm().into(),
 				color: srgba_to_linear(vec4(0.2, 0.8, 0.1, 1.0)),
 			},
 		);
 		self.params_cutter.set(
 			&self.queue,
 			render::mesh::ObjectParams {
-				transform: Mat4::from_rotation_translation(
-					Quat::from_rotation_y(FRAC_PI_2 + self.bevel_gear_desc.cone_halfangle)
-						* Quat::from_rotation_z(2. * PI * crown_turns),
-					vec3(0., 0., self.bevel_gear_desc.pitch_distance()),
-				),
+				transform: self.cutter_tfm().into(),
 				color: srgba_to_linear(vec4(0.8, 0.2, 0.1, 1.0)),
 			},
 		);
@@ -302,7 +304,8 @@ impl Core {
 	///
 	/// [`Self::configure`] must be called at least once before this.
 	pub fn redraw(&mut self, args: &RedrawArgs) {
-		self.bevel_gear_shape.cut(self.t);
+		self.bevel_gear_shape
+			.cut(self.gear_tfm().inverse() * self.cutter_tfm());
 		let output = self.surface.get_current_texture().unwrap();
 		self.render(&output.texture, args);
 		output.present();