diff --git a/src/Slicer.js b/src/Slicer.js
index 280a6df..f3f802d 100644
--- a/src/Slicer.js
+++ b/src/Slicer.js
@@ -7,9 +7,7 @@ export default class {
   setMesh(mesh) {
     mesh.updateMatrix();
 
-    this.setGeometry(mesh.geometry, mesh.matrix);
-
-    return this;
+    return this.setGeometry(mesh.geometry, mesh.matrix);
   }
   setGeometry(geometry, matrix) {
     if (geometry.isBufferGeometry) {
@@ -20,7 +18,7 @@ export default class {
       throw new Error('Geometry is not an instance of BufferGeometry or Geometry');
     }
 
-    if (matrix) {
+    if (typeof matrix !== 'undefined') {
       geometry.applyMatrix(matrix);
     }
 
@@ -32,13 +30,16 @@ export default class {
     return slice(this.geometry, settings, onprogress);
   }
   slice(settings) {
-    const slicerWorker = new SlicerWorker();
-
-    const geometry = this.geometry.toJSON();
+    if (!this.geometry) {
+      throw new Error('Geometry is not set, use Slicer.setGeometry or Slicer.setMesh first');
+    }
 
     return new ProgressPromise((resolve, reject, progress) => {
+      // create the slicer worker
+      const slicerWorker = new SlicerWorker();
       slicerWorker.onerror = reject;
 
+      // listen to messages send from worker
       slicerWorker.addEventListener('message', (event) => {
         const { message, data } = event.data;
         switch (message) {
@@ -54,6 +55,8 @@ export default class {
         }
       });
 
+      // send geometry and settings to worker to start the slicing progress
+      const geometry = this.geometry.toJSON();
       slicerWorker.postMessage({
         message: 'SLICE',
         data: { geometry, settings }
diff --git a/src/sliceActions/generateInfills.js b/src/sliceActions/generateInfills.js
index f9ec418..e959475 100644
--- a/src/sliceActions/generateInfills.js
+++ b/src/sliceActions/generateInfills.js
@@ -26,8 +26,8 @@ export default function generateInfills(slices, settings) {
 
     let surroundingLayer;
     if (layer - bottomSkinCount >= 0 && layer + topSkinCount < slices.length) {
-      const downSkin = slices[layer - bottomSkinCount].getOutline();
-      const upSkin = slices[layer + topSkinCount].getOutline();
+      const downSkin = slices[layer - bottomSkinCount].outline;
+      const upSkin = slices[layer + topSkinCount].outline;
       surroundingLayer = upSkin.intersect(downSkin);
     }
 
diff --git a/src/sliceActions/generateOutlines.js b/src/sliceActions/generateOutlines.js
new file mode 100644
index 0000000..d98ccdf
--- /dev/null
+++ b/src/sliceActions/generateOutlines.js
@@ -0,0 +1,12 @@
+import Shape from 'Doodle3D/clipper-js';
+
+export default function calculateOutlines(slices, settings) {
+  for (let layer = 0; layer < slices.length; layer ++) {
+    const slice = slices[layer];
+
+    slice.outline = slice.parts.reduce((shape, part) => {
+      if (part.outerLine) shape.join(part.outerLine);
+      return shape;
+    }, new Shape([], true));
+  }
+}
diff --git a/src/sliceActions/generateSupport.js b/src/sliceActions/generateSupport.js
index 6996450..d8d2e37 100644
--- a/src/sliceActions/generateSupport.js
+++ b/src/sliceActions/generateSupport.js
@@ -30,7 +30,7 @@ export default function generateSupport(slices, settings) {
     if (supportAreas.length > 0) {
 
       if (layer >= supportDistanceLayers) {
-        var sliceSkin = slices[layer - supportDistanceLayers].getOutline();
+        var sliceSkin = slices[layer - supportDistanceLayers].outline;
         sliceSkin = sliceSkin;
 
         var supportAreasSlimmed = supportAreas.difference(sliceSkin.offset(supportMargin));
@@ -52,7 +52,7 @@ export default function generateSupport(slices, settings) {
       }
     }
 
-    var supportSkin = slices[layer + supportDistanceLayers - 1].getOutline();
+    var supportSkin = slices[layer + supportDistanceLayers - 1].outline;
 
     var slice = slices[layer + supportDistanceLayers];
     for (var i = 0; i < slice.parts.length; i ++) {
diff --git a/src/sliceActions/helpers/Slice.js b/src/sliceActions/helpers/Slice.js
index c9a1ea3..4e1002e 100644
--- a/src/sliceActions/helpers/Slice.js
+++ b/src/sliceActions/helpers/Slice.js
@@ -4,12 +4,6 @@ export default class {
   constructor() {
     this.parts = [];
   }
-  getOutline() {
-    return this.parts.reduce((shape, part) => {
-      if (part.outerLine) shape.join(part.outerLine);
-      return shape;
-    }, new Shape([], true));
-  }
   add(shape) {
     const part = { shape };
 
diff --git a/src/sliceActions/slice.js b/src/sliceActions/slice.js
index 2042875..e0d63e1 100644
--- a/src/sliceActions/slice.js
+++ b/src/sliceActions/slice.js
@@ -2,6 +2,7 @@ import calculateLayersIntersections from './calculateLayersIntersections.js';
 import createLines from './createLines.js';
 import generateInfills from './generateInfills.js';
 import generateInnerLines from './generateInnerLines.js';
+import generateOutlines from './generateOutlines.js';
 import generateSupport from './generateSupport.js';
 import intersectionsToShapes from './intersectionsToShapes.js';
 import addBrim from './addBrim.js';
@@ -13,7 +14,7 @@ import applyPrecision from './applyPrecision.js';
 import removePrecision from './removePrecision.js';
 
 export default function(geometry, settings, onProgress) {
-  const totalStages = 11;
+  const totalStages = 12;
   let current = -1;
   const updateProgress = (action) => {
     current ++;
@@ -27,7 +28,7 @@ export default function(geometry, settings, onProgress) {
   const lines = createLines(geometry, settings);
 
   updateProgress('Detecting open vs closed shapes');
-  const openClosed = detectOpenClosed(lines);
+  detectOpenClosed(lines);
 
   updateProgress('Calculating layer intersections');
   const {
@@ -45,6 +46,8 @@ export default function(geometry, settings, onProgress) {
 
   updateProgress('Generating inner lines');
   generateInnerLines(slices, settings);
+  updateProgress('Generating out lines');
+  generateOutlines(slices, settings);
   updateProgress('Generating infills');
   generateInfills(slices, settings);
   updateProgress('Generating support');
diff --git a/src/slicerWorker.js b/src/slicerWorker.js
index 369e4b3..ff1797e 100644
--- a/src/slicerWorker.js
+++ b/src/slicerWorker.js
@@ -16,7 +16,7 @@ self.addEventListener('message', (event) => {
     case 'SLICE': {
       const { geometry: JSONGeometry, settings } = data;
 
-      const { geometry } = new loader.parse(JSONGeometry.data);
+      const { geometry } = loader.parse(JSONGeometry.data);
 
       const gcode = slice(geometry, settings, onProgress);