diff --git a/package.json b/package.json
index 0e8743f5..f448a148 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
     "name": "grid-apps",
-    "version": "4.0.7",
+    "version": "4.0.8",
     "description": "grid.space 3d slice & modeling tools",
     "author": "Stewart Allen <sa@grid.space>",
     "license": "MIT",
diff --git a/src/geo/base.js b/src/geo/base.js
index e84b0f49..415d7c94 100644
--- a/src/geo/base.js
+++ b/src/geo/base.js
@@ -109,6 +109,25 @@ function sqr(v) {
     return v * v
 }
 
+// radians rotatition around origin
+function rotate(x,y,radians) {
+    return [
+        x * Math.cos(radians) - y * Math.sin(radians),
+        y * Math.cos(radians) + x * Math.sin(radians)
+    ];
+}
+
+const deg2rad = (Math.PI / 180);
+const rad2deg = (180 / Math.PI);
+
+function toRadians(degrees) {
+    return degrees * deg2rad;
+}
+
+function toDegrees(radians) {
+    return radians * rad2deg;
+}
+
 /**
  * return distance between two points
  */
@@ -576,6 +595,7 @@ base.util = {
     pwait,
     ptimer,
     flatten,
+    rotate,
     dist2D,
     distSq,
     distSqv2,
@@ -587,6 +607,8 @@ base.util = {
     offsetPrecision,
     circleCenter,
     numOrDefault,
+    toRadians,
+    toDegrees,
     thetaDiff,
     intersect,
     inRange,
diff --git a/src/geo/point.js b/src/geo/point.js
index 1bf6133b..0c857a89 100644
--- a/src/geo/point.js
+++ b/src/geo/point.js
@@ -551,6 +551,13 @@ class Point {
         this.z += delta.z;
         return this;
     }
+
+    // radians rotatition in XY around origin
+    rotate(angle) {
+        const { x, y } = this;
+        this.x = x * Math.cos(angle) - y * Math.sin(angle);
+        this.y = y * Math.cos(angle) + x * Math.sin(angle);
+    }
 }
 
 function dot(u, v) {
diff --git a/src/geo/polygon.js b/src/geo/polygon.js
index ee85691f..c251f66e 100644
--- a/src/geo/polygon.js
+++ b/src/geo/polygon.js
@@ -992,6 +992,20 @@ class Polygon {
         return this;
     }
 
+    /**
+     * @param {int[]} verts flat array of x,y,z vertices
+     */
+    addVerts(verts) {
+        for (let i=0; i<verts.length; ) {
+            this.add(
+                verts[i++],
+                verts[i++],
+                verts[i++]
+            );
+        }
+        return this;
+    }
+
     /**
      * append point to polygon and return point
      */
@@ -1080,6 +1094,7 @@ class Polygon {
         } else if (this.isClockwise() !== poly.isClockwise()) {
             this.reverse();
         }
+        return this;
     }
 
     /**
@@ -1091,6 +1106,7 @@ class Polygon {
         } else if (this.isClockwise() === poly.isClockwise()) {
             this.reverse();
         }
+        return this;
     }
 
     /**
diff --git a/src/main/mesh.js b/src/main/mesh.js
index 2913a3e5..a52644f1 100644
--- a/src/main/mesh.js
+++ b/src/main/mesh.js
@@ -20,7 +20,7 @@ const { broker } = gapp;
 const { moto } = root;
 const { space } = moto;
 
-const version = '1.3.0';
+const version = '1.4.0';
 const call = broker.send;
 const dbindex = [ "admin", "space" ];
 
diff --git a/src/mesh/api.js b/src/mesh/api.js
index b8347996..167ec308 100644
--- a/src/mesh/api.js
+++ b/src/mesh/api.js
@@ -318,6 +318,48 @@ let add = {
             });
             api.modal.bound.gencyl.focus();
         }
+    },
+
+    gear(opt = {}) {
+        function gengear(teeth, module, angle, twist, shaft) {
+            api.modal.hide();
+            worker.model_gen_gear({
+                teeth: parseInt(teeth),
+                module: parseFloat(module),
+                angle: parseFloat(angle),
+                twist: parseFloat(twist),
+                shaft: parseFloat(shaft),
+            }).then(gear => {
+                const nmdl = new mesh.model({ file: "gear", mesh: gear.toFloat32() });
+                const ngrp = group.new([ nmdl ]);
+                ngrp.floor();
+            });
+        }
+        api.modal.dialog({
+            title: "gear generator",
+            body: [ h.div({ class: "addgear" }, [
+                h.label('number of teeth'),
+                h.input({ value: opt.teeth || 20, size: 5, id: "gteeth" }),
+                h.label('module (diam / teeth)'),
+                h.input({ value: opt.module || 3, size: 5, id: "gmodule" }),
+                h.label('pressure angle'),
+                h.input({ value: opt.angle || 20, size: 5, id: "gangle" }),
+                h.label('twist angle'),
+                h.input({ value: opt.twist || 0, size: 5, id: "gtwist" }),
+                h.label('shaft diameter'),
+                h.input({ value: opt.shaft || 5, size: 5, id: "gshaft" }),
+                h.button({ _: "create", onclick() {
+                    gengear(
+                        api.modal.bound.gteeth.value,
+                        api.modal.bound.gmodule.value,
+                        api.modal.bound.gangle.value,
+                        api.modal.bound.gtwist.value,
+                        api.modal.bound.gshaft.value,
+                    )
+                } })
+            ]) ]
+        });
+        api.modal.bound.gteeth.focus();
     }
 };
 
diff --git a/src/mesh/build.js b/src/mesh/build.js
index 53255861..13ac1d36 100644
--- a/src/mesh/build.js
+++ b/src/mesh/build.js
@@ -118,7 +118,7 @@ const modal = api.modal = {
 let pinner;
 // transient logging window bottom/left
 const log = api.log = {
-    age: 10000, // age out lines more than 10 seconds old
+    age: 600000, // age out lines more than 10 minutes old
 
     data: [],   // last n messages
 
@@ -187,7 +187,9 @@ const log = api.log = {
 };
 
 // bind endpoint for worker to log in the ui
-gapp.broker.subscribe("mesh.log", log.emit);
+gapp.broker.subscribe("mesh.log", msg => {
+    log.emit(msg);
+});
 
 // welcome dialog
 api.welcome = function(version = "unknown") {
@@ -373,6 +375,7 @@ function ui_build() {
             h.div({ class: "pop"}, [
                 h.button({ _: 'cylinder', onclick: add.cylinder }),
                 h.button({ _: 'cube', onclick: add.cube }),
+                h.button({ _: 'gear', onclick: add.gear }),
                 devel ? h.button({ _: 'input', onclick: add.input }) : undefined
             ])
         ]),
diff --git a/src/mesh/tool.js b/src/mesh/tool.js
index 611a9bdc..f75c3438 100644
--- a/src/mesh/tool.js
+++ b/src/mesh/tool.js
@@ -737,6 +737,89 @@ mesh.tool = class MeshTool {
         }
         return out;
     }
+
+    // returns points array for a polygon
+    // extrusion and twist is handled in work.js
+    generateGear(numTeeth, module, pressureAngle) {
+        // Adapted from: Public Domain Parametric Involute Spur Gear by Leemon Baird, 2011, Leemon@Leemon.com http://www.thingiverse.com/thing:5505
+        // see also http://grabcad.com/questions/tutorial-how-to-model-involute-gears-in-solidworks-and-show-design-intent
+
+        // const pitch_radius = (numTeeth * module) / 2;
+        const pi = Math.PI;
+
+        // degrees to radians
+        function degrees_to_radians(theta) { return theta / 180 * pi; }
+
+        // polar to cartesian
+        function polar(r, theta) { return [r * Math.sin(theta), r * Math.cos(theta)]; }
+
+        // point on involute curve
+        function q6(b, s, t, d) { return polar(d, s * (iang(b, d) + t)); }
+
+        // unwind this many degrees to go from r1 to r2
+        function iang(r1, r2) { return Math.sqrt((r2 / r1) * (r2 / r1) - 1) - Math.acos(r1 / r2); }
+
+        // radius a fraction f up the curved side of the tooth
+        function q7(f, r, b, r2, t, s) { return q6(b, s, t, (1 - f) * Math.max(b, r) + f * r2); }
+
+        // lerp q7 0..1 with a given # steps
+        function qf(steps, r, b, r2, t, s) {
+            let res = [];
+            let step = 1/steps;
+            for (let f=0; f <= 1; f += step) {
+                res.push(q7(f, r, b, r2, t, s));
+            }
+            return res;
+        }
+
+        // rotate an array of 2d points
+        function rotate(points_array, angle) {
+            let answer = [];
+            for (let i = 0; i < points_array.length; i++) {
+                let x = points_array[i][0];
+                let y = points_array[i][1];
+                let xr = x * Math.cos(angle) - y * Math.sin(angle);
+                let yr = y * Math.cos(angle) + x * Math.sin(angle);
+                answer.push([xr, yr]);
+            }
+            return answer;
+        }
+
+        // gear parameter setup
+        let mm_per_tooth = module * pi; // mm size of one gear tooth
+        let clearance = 0.1; // freedom between two gear centers
+        let backlash = 0.1; // freedom between two gear contact points
+        let pressure_angle = degrees_to_radians(pressureAngle);
+        let gear = [];
+
+        // involute gear maker
+        {
+            let p = mm_per_tooth * numTeeth / pi / 2;         // radius of pitch circle
+            let c = p + mm_per_tooth / pi - clearance;        // radius of outer circle
+            let b = p * Math.cos(pressure_angle);             // radius of base circle
+            let r = p - (c - p) - clearance;                  // radius of root circle
+            let t = mm_per_tooth / 2 - backlash / 2;          // tooth thickness at pitch circle
+            let k = -iang(b, p) - t / 2 / p;                  // angle where involute meets base circle on side of tooth
+            let points = [                                    // [x,y] points for a single gear tooth
+                polar(r, -pi / numTeeth),
+                polar(r, r < b ? k : -pi / numTeeth),
+                ...qf(10, r, b, c, k, 1),
+                ...qf(10, r, b, c, k, -1).reverse(),
+                polar(r, r < b ? -k : pi / numTeeth),
+                // polar(r, 3.142 / numTeeth)                 // omit b/c overlaps start when rotated
+            ];
+
+            // create all gear teeth by rotating the first tooth
+            for (var i = 0; i < numTeeth; i++) {
+                gear.appendAll(rotate(points, -i * 2 * pi / numTeeth));
+            }
+
+            mesh.log(`gear pitch radius: ${p.round(3)}`);
+        }
+
+        return gear;
+    }
+
 };
 
 });
diff --git a/src/mesh/work.js b/src/mesh/work.js
index 313cdeb6..75afc371 100644
--- a/src/mesh/work.js
+++ b/src/mesh/work.js
@@ -21,9 +21,10 @@
 gapp.main("mesh.work", [], (root) => {
 
 const { Matrix4, Vector3, BufferGeometry, BufferAttribute, computeFaceNormal } = THREE;
-const { mesh, moto } = root;
+const { base, mesh, moto } = root;
 const { client, worker } = moto;
 const { util } = mesh;
+const { newPolygon } = base;
 const cache = {};
 
 // add scoped access to cache
@@ -397,6 +398,37 @@ let model = {
             log(`${id} | rebuild complete`);
             send.done({ lines: layers });
         });;
+    },
+
+    gen_gear(data, send) {
+        const { teeth, module, angle, twist, shaft, z } = data;
+        let points = new mesh.tool()
+            .generateGear(teeth, module, angle)
+            .map(v => [...v, 0]).flat();
+        let poly = newPolygon().addVerts(points);
+        if (shaft) {
+            poly.addInner(
+                newPolygon().centerCircle({
+                    x:0, y:0, z:0
+                }, shaft / 2, Math.min(20 + shaft,100))
+            );
+        }
+        let verts = poly.extrude(z || 15);
+        if (twist) {
+            let rad = base.util.toRadians(twist);
+            for (let i=0; i<verts.length; i += 3) {
+                if (Math.abs(verts[i+2]) < 0.001) {
+                    let [x, y] = base.util.rotate(
+                        verts[i],
+                        verts[i+1],
+                        rad
+                    );
+                    verts[i] = x;
+                    verts[i+1] = y;
+                }
+            }
+        }
+        send.done(verts);
     }
 };
 
diff --git a/src/moto/license.js b/src/moto/license.js
index da60adbc..4d5117e8 100644
--- a/src/moto/license.js
+++ b/src/moto/license.js
@@ -5,7 +5,7 @@
     let terms = {
         COPYRIGHT: "Copyright (C) Stewart Allen <sa@grid.space> - All Rights Reserved",
         LICENSE: "See the license.md file included with the source distribution",
-        VERSION: (is_self ? self : this).debug_version || "4.0.7"
+        VERSION: (is_self ? self : this).debug_version || "4.0.8"
     };
 
     if (typeof(module) === 'object') {
diff --git a/web/kiri/manifest.json b/web/kiri/manifest.json
index a207a50a..fc0a46cb 100644
--- a/web/kiri/manifest.json
+++ b/web/kiri/manifest.json
@@ -1,5 +1,5 @@
 {
-    "name": "Kiri:Moto 4.0.7",
+    "name": "Kiri:Moto 4.0.8",
     "short_name": "Kiri:Moto",
     "description": "Slicer for 3D printers, CNC mills, laser cutters and more",
     "start_url": "/kiri/",
diff --git a/web/mesh/index.css b/web/mesh/index.css
index 00c0cfab..bf3defb0 100644
--- a/web/mesh/index.css
+++ b/web/mesh/index.css
@@ -225,10 +225,20 @@ button:hover {
     gap: 4px;
 }
 
-.addact input {
+.addact input, .addgear input {
     text-align: center;
 }
 
+.addgear {
+    gap: 5px;
+    display: grid;
+    grid-template-columns: 1fr 50px;
+}
+
+.addgear button {
+    column-span: all;
+}
+
 .image-import {
     flex-direction: column;
     gap: 3px;