diff --git a/example/save.js b/example/save.js
index f7dc831..37bfb70 100644
--- a/example/save.js
+++ b/example/save.js
@@ -16,7 +16,11 @@ jsonLoader.load('models/airplane.json', async geometry => {
   geometry.computeFaceNormals();
 
   const slicer = new Slicer().setGeometry(geometry);
-  const gcode = slicer.sliceSync(settings);
+  const gcode = await slicer.slice(settings)
+    .progress(({ done, total, action }) => {
+      const percentage = `${(done / total * 100).toFixed()}%`
+      document.write(`<p>${action}, ${percentage}</p>`);
+    });
 
   const file = new File([gcode], 'gcode.gcode', { type: 'text/plain' });
   saveAs(file);
diff --git a/jspm.config.js b/jspm.config.js
index 5c47273..ea1ba2b 100644
--- a/jspm.config.js
+++ b/jspm.config.js
@@ -151,11 +151,12 @@ SystemJS.config({
     "github:*/*.json"
   ],
   map: {
+    "progress-promise": "npm:progress-promise@0.0.6",
     "text": "github:systemjs/plugin-text@0.0.11",
     "js-yaml": "npm:js-yaml@3.9.0",
     "clipper-js": "github:Doodle3D/clipper-js@1.0.2",
     "three.js": "github:mrdoob/three.js@r83",
-    "assert": "npm:jspm-nodelibs-assert@0.2.0",
+    "assert": "github:jspm/nodelibs-assert@0.2.0-alpha",
     "buffer": "github:jspm/nodelibs-buffer@0.2.0-alpha",
     "child_process": "npm:jspm-nodelibs-child_process@0.2.0",
     "constants": "npm:jspm-nodelibs-constants@0.2.0",
diff --git a/package.json b/package.json
index c388e0b..10d7f62 100644
--- a/package.json
+++ b/package.json
@@ -10,6 +10,7 @@
       "clipper-js": "github:Doodle3D/clipper-js@1.0.2",
       "js-yaml": "npm:js-yaml@^3.9.0",
       "json": "github:systemjs/plugin-json@^0.1.2",
+      "progress-promise": "npm:progress-promise@^0.0.6",
       "text": "github:systemjs/plugin-text@^0.0.11",
       "three.js": "github:mrdoob/three.js@r83",
       "worker": "github:casperlamboo/plugin-worker@master"
@@ -27,7 +28,7 @@
       "zlib": "npm:jspm-nodelibs-zlib@^0.2.0"
     },
     "peerDependencies": {
-      "assert": "npm:jspm-nodelibs-assert@^0.2.0",
+      "assert": "github:jspm/nodelibs-assert@^0.2.0-alpha",
       "buffer": "github:jspm/nodelibs-buffer@^0.2.0-alpha",
       "child_process": "npm:jspm-nodelibs-child_process@^0.2.0",
       "constants": "npm:jspm-nodelibs-constants@^0.2.0",
diff --git a/src/Slicer.js b/src/Slicer.js
index 658c191..2e2be20 100644
--- a/src/Slicer.js
+++ b/src/Slicer.js
@@ -1,6 +1,7 @@
 import * as THREE from 'three.js';
 import slice from './sliceActions/slice.js';
 import SlicerWorker from './slicerWorker.js!worker';
+import ProgressPromise from 'progress-promise';
 
 export default class {
   setMesh(mesh) {
@@ -27,15 +28,15 @@ export default class {
 
     return this;
   }
-  sliceSync(settings) {
-    return slice(this.geometry, settings);
+  sliceSync(settings, onprogress) {
+    return slice(this.geometry, settings, onprogress);
   }
   slice(settings) {
     const slicerWorker = new SlicerWorker();
 
     const geometry = this.geometry.toJSON();
 
-    return new Promise((resolve, reject) => {
+    return new ProgressPromise((resolve, reject, progress) => {
       slicerWorker.onerror = reject;
 
       slicerWorker.addEventListener('message', (event) => {
@@ -47,9 +48,8 @@ export default class {
             break;
           }
           case 'PROGRESS': {
-            if (this.onprogress) {
-              this.onprogress(data);
-            }
+            progress(data);
+            break;
           }
         }
       });
diff --git a/src/sliceActions/addBrim.js b/src/sliceActions/addBrim.js
index 285d94f..33d2475 100644
--- a/src/sliceActions/addBrim.js
+++ b/src/sliceActions/addBrim.js
@@ -8,8 +8,6 @@ const offsetOptions = {
 };
 
 export default function addBrim(slices, settings) {
-  console.log('add brim');
-
   let { brim: { offset: brimOffset } } = settings;
   brimOffset /= PRECISION;
 
diff --git a/src/sliceActions/calculateLayersIntersections.js b/src/sliceActions/calculateLayersIntersections.js
index fcc198b..b8d3aa8 100644
--- a/src/sliceActions/calculateLayersIntersections.js
+++ b/src/sliceActions/calculateLayersIntersections.js
@@ -1,8 +1,6 @@
 import * as THREE from 'three.js';
 
 export default function calculateLayersIntersections(lines, settings) {
-  console.log('calculating layer intersections');
-
   const { layerHeight, dimensions: { z: dimensionsZ } } = settings;
 
   const numLayers = Math.floor(dimensionsZ / layerHeight);
diff --git a/src/sliceActions/createLines.js b/src/sliceActions/createLines.js
index 4984ca9..b7f1e6e 100644
--- a/src/sliceActions/createLines.js
+++ b/src/sliceActions/createLines.js
@@ -15,8 +15,6 @@ function addLine(geometry, lineLookup, lines, a, b, isFlat) {
 }
 
 export default function createLines(geometry, settings) {
-  console.log('constructing unique lines from geometry');
-
   const lines = [];
   const lineLookup = {};
 
diff --git a/src/sliceActions/detectOpenClosed.js b/src/sliceActions/detectOpenClosed.js
index 443e103..1e7449e 100644
--- a/src/sliceActions/detectOpenClosed.js
+++ b/src/sliceActions/detectOpenClosed.js
@@ -1,6 +1,4 @@
 export default function detectOpenClosed(lines) {
-  console.log('detecting open and closed lines');
-
   const pools = getPools(lines);
   const openLines = lines.map(line => line.connects.length === 2);
 
diff --git a/src/sliceActions/generateInfills.js b/src/sliceActions/generateInfills.js
index 7d1d43e..f9ec418 100644
--- a/src/sliceActions/generateInfills.js
+++ b/src/sliceActions/generateInfills.js
@@ -3,8 +3,6 @@ import getFillTemplate from './getFillTemplate.js';
 import Shape from 'Doodle3D/clipper-js';
 
 export default function generateInfills(slices, settings) {
-  console.log('generating infills');
-
   let {
     layerHeight,
     fill: { gridSize: fillGridSize },
diff --git a/src/sliceActions/generateInnerLines.js b/src/sliceActions/generateInnerLines.js
index 6ead645..a25550d 100644
--- a/src/sliceActions/generateInnerLines.js
+++ b/src/sliceActions/generateInnerLines.js
@@ -8,8 +8,6 @@ const offsetOptions = {
 };
 
 export default function generateInnerLines(slices, settings) {
-  console.log('generating outer lines and inner lines');
-
   // need to scale up everything because of clipper rounding errors
   let { layerHeight, nozzleDiameter, shell: { thickness: shellThickness } } = settings;
   nozzleDiameter /= PRECISION;
diff --git a/src/sliceActions/generateSupport.js b/src/sliceActions/generateSupport.js
index 8ea06d1..2a1a01e 100644
--- a/src/sliceActions/generateSupport.js
+++ b/src/sliceActions/generateSupport.js
@@ -3,8 +3,6 @@ import Shape from 'Doodle3D/clipper-js';
 import { PRECISION } from '../constants.js';
 
 export default function generateSupport(slices, settings) {
-  console.log('generating support');
-
   if (!settings.support.enabled) return;
 
   let {
diff --git a/src/sliceActions/intersectionsToShapes.js b/src/sliceActions/intersectionsToShapes.js
index fbd4903..06c5f79 100644
--- a/src/sliceActions/intersectionsToShapes.js
+++ b/src/sliceActions/intersectionsToShapes.js
@@ -2,8 +2,6 @@ import * as THREE from 'three.js';
 import Shape from 'Doodle3D/clipper-js';
 
 export default function intersectionsToShapes(layerIntersectionIndexes, layerIntersectionPoints, lines, settings) {
-  console.log('generating slices');
-
   const layers = [];
 
   for (let layer = 1; layer < layerIntersectionIndexes.length; layer ++) {
diff --git a/src/sliceActions/optimizePaths.js b/src/sliceActions/optimizePaths.js
index 638ae76..071cc50 100644
--- a/src/sliceActions/optimizePaths.js
+++ b/src/sliceActions/optimizePaths.js
@@ -2,8 +2,6 @@ import * as THREE from 'three.js';
 import Shape from 'Doodle3D/clipper-js';
 
 export default function optimizePaths(slices, settings) {
-  console.log('optimize paths');
-
   const start = new THREE.Vector2(0, 0);
 
   for (let layer = 0; layer < slices.length; layer ++) {
diff --git a/src/sliceActions/removePrecision.js b/src/sliceActions/removePrecision.js
index 0b05d35..ec02f25 100644
--- a/src/sliceActions/removePrecision.js
+++ b/src/sliceActions/removePrecision.js
@@ -3,8 +3,6 @@ import { PRECISION } from '../constants.js';
 const inversePrecision = 1 / PRECISION;
 
 export default function removePrecision(slices) {
-  console.log('remove precision');
-
   for (let layer = 0; layer < slices.length; layer ++) {
     const slice = slices[layer];
 
diff --git a/src/sliceActions/slice.js b/src/sliceActions/slice.js
index 8a68d59..2042875 100644
--- a/src/sliceActions/slice.js
+++ b/src/sliceActions/slice.js
@@ -13,51 +13,53 @@ import applyPrecision from './applyPrecision.js';
 import removePrecision from './removePrecision.js';
 
 export default function(geometry, settings, onProgress) {
-  const totalStages = 12;
-  let current = 0;
-  const progressMessage = () => {
+  const totalStages = 11;
+  let current = -1;
+  const updateProgress = (action) => {
     current ++;
-    // postMessage({ message: 'PROGRESS', data: { done: current, total: totalStages } });
+    if (onProgress) onProgress({ done: current, total: totalStages, action });
   };
 
   geometry.computeFaceNormals();
 
   // get unique lines from geometry;
+  updateProgress('Constructing unique lines from geometry');
   const lines = createLines(geometry, settings);
-  progressMessage();
 
+  updateProgress('Detecting open vs closed shapes');
   const openClosed = detectOpenClosed(lines);
-  progressMessage();
 
+  updateProgress('Calculating layer intersections');
   const {
     layerIntersectionIndexes,
     layerIntersectionPoints
   } = calculateLayersIntersections(lines, settings);
-  progressMessage();
 
+  updateProgress('Constructing shapes from intersections');
   const shapes = intersectionsToShapes(layerIntersectionIndexes, layerIntersectionPoints, lines, settings);
-  progressMessage();
 
   applyPrecision(shapes);
 
+  updateProgress('Constructing slices from shapes');
   const slices = shapesToSlices(shapes, settings);
-  progressMessage();
 
+  updateProgress('Generating inner lines');
   generateInnerLines(slices, settings);
-  progressMessage();
+  updateProgress('Generating infills');
   generateInfills(slices, settings);
-  progressMessage();
+  updateProgress('Generating support');
   generateSupport(slices, settings);
-  progressMessage();
+  updateProgress('Adding brim');
   addBrim(slices, settings);
-  progressMessage();
+  updateProgress('Optimizing paths');
   optimizePaths(slices, settings);
-  progressMessage();
-  removePrecision(slices);
-  progressMessage();
 
+  removePrecision(slices);
+
+  updateProgress('Constructing gcode');
   const gcode = slicesToGCode(slices, settings);
-  progressMessage();
+
+  updateProgress('Finished');
 
   return gcode;
 }
diff --git a/src/sliceActions/slicesToGCode.js b/src/sliceActions/slicesToGCode.js
index 9d65318..7268ae3 100644
--- a/src/sliceActions/slicesToGCode.js
+++ b/src/sliceActions/slicesToGCode.js
@@ -1,8 +1,6 @@
 import GCode from '../GCode.js';
 
 export default function slicesToGCode(slices, settings) {
-  console.log('slices to gcode');
-
   const gcode = new GCode(settings);
 
   for (let layer = 0; layer < slices.length; layer ++) {
diff --git a/src/slicerWorker.js b/src/slicerWorker.js
index 451456a..78e6654 100644
--- a/src/slicerWorker.js
+++ b/src/slicerWorker.js
@@ -3,6 +3,13 @@ import * as THREE from 'three.js';
 
 const loader = new THREE.JSONLoader();
 
+const onProgress = progress => {
+  self.postMessage({
+    message: 'PROGRESS',
+    data: progress
+  });
+}
+
 self.addEventListener('message', (event) => {
   const { message, data } = event.data;
   switch (message) {
@@ -11,7 +18,7 @@ self.addEventListener('message', (event) => {
 
       const { geometry } = new loader.parse(JSONGeometry.data);
 
-      const gcode = slice(geometry, settings);
+      const gcode = slice(geometry, settings, onProgress);
 
       self.postMessage({
         message: 'SLICE',