diff --git a/src/sliceActions/createLines.js b/src/sliceActions/createLines.js
index 0c8cf20..7dcb51b 100644
--- a/src/sliceActions/createLines.js
+++ b/src/sliceActions/createLines.js
@@ -1,6 +1,6 @@
 import { normalize } from './helpers/vector2D.js';
 
-function addLine(geometry, lineLookup, lines, a, b, faceIndex) {
+function addLine(vertices, lineLookup, lines, a, b, faceIndex) {
   let index;
   if (typeof lineLookup[`${b}_${a}`] !== 'undefined') {
     index = lineLookup[`${b}_${a}`];
@@ -8,7 +8,10 @@ function addLine(geometry, lineLookup, lines, a, b, faceIndex) {
     index = lines.length;
     lineLookup[`${a}_${b}`] = index;
 
-    const line = { start: geometry.vertices[a], end: geometry.vertices[b] };
+    const start = { x: vertices[a * 3], y: vertices[a * 3 + 1], z: vertices[a * 3 + 2] };
+    const end = { x: vertices[b * 3], y: vertices[b * 3 + 1], z: vertices[b * 3 + 2] };
+
+    const line = { start, end };
     const faces = [];
     lines.push({ line, faces });
   }
@@ -22,8 +25,17 @@ export default function createLines(geometry, settings) {
   const lines = [];
   const lineLookup = {};
 
-  for (let i = 0; i < geometry.faces.length; i ++) {
-    const { normal, materialIndex: objectIndex, a, b, c } = geometry.faces[i];
+  for (let i = 0; i < geometry.objectIndexes.length; i ++) {
+    const i3 = i * 3;
+    const objectIndex = geometry.objectIndexes[i];
+    const normal = {
+      x: geometry.faceNormals[i3],
+      y: geometry.faceNormals[i3 + 1],
+      z: geometry.faceNormals[i3 + 2]
+    };
+    const a = geometry.faces[i3];
+    const b = geometry.faces[i3 + 1];
+    const c = geometry.faces[i3 + 2];
 
     // skip faces that point up or down
     if (normal.y > .999 || normal.y < -.999) {
@@ -31,9 +43,9 @@ export default function createLines(geometry, settings) {
       continue;
     }
 
-    const indexA = addLine(geometry, lineLookup, lines, a, b, i);
-    const indexB = addLine(geometry, lineLookup, lines, b, c, i);
-    const indexC = addLine(geometry, lineLookup, lines, c, a, i);
+    const indexA = addLine(geometry.vertices, lineLookup, lines, a, b, i);
+    const indexB = addLine(geometry.vertices, lineLookup, lines, b, c, i);
+    const indexC = addLine(geometry.vertices, lineLookup, lines, c, a, i);
 
     const flatNormal = normalize({ x: normal.z, y: normal.x });
     const lineIndexes = [indexA, indexB, indexC];
diff --git a/src/sliceActions/slice.js b/src/sliceActions/slice.js
index 8a36539..516864b 100644
--- a/src/sliceActions/slice.js
+++ b/src/sliceActions/slice.js
@@ -65,8 +65,9 @@ export default function(settings, geometry, openObjectIndexes, constructLinePrev
   updateProgress('Finished');
 
   // if (constructLinePreview) gcode.linePreview = createGcodeGeometry(gcode.gcode);
-  // gcode.gcode = gcodeToString(gcode.gcode);
-  // return gcode;
+
+  gcode.gcode = gcodeToString(gcode.gcode);
+  return gcode;
 }
 
 const PRECISION_INVERSE = 1 / PRECISION;
diff --git a/src/slicer.js b/src/slicer.js
index 7ee9723..79590cb 100644
--- a/src/slicer.js
+++ b/src/slicer.js
@@ -23,13 +23,38 @@ export function sliceGeometry(settings, geometry, materials, matrix, sync = fals
     throw new Error('Geometry is not an instance of BufferGeometry or Geometry');
   }
 
-  if (geometry.faces.length === 0) {
-    throw new Error('Geometry does not contain any data');
-  }
+  if (matrix && matrix.isMatrix4) geometry.applyMatrix(matrix);
+  geometry.computeFaceNormals();
 
-  if (matrix && matrix.isMatrix4) {
-    geometry.applyMatrix(matrix);
-  }
+  const vertices = geometry.vertices.reduce((array, { x, y, z }, i) => {
+    const i3 = i * 3;
+    array[i3] = x;
+    array[i3 + 1] = y;
+    array[i3 + 2] = z;
+    return array;
+  }, new Float32Array(geometry.vertices.length * 3));
+  const faces = geometry.faces.reduce((array, { a, b, c }, i) => {
+    const i3 = i * 3;
+    array[i3] = a;
+    array[i3 + 1] = b;
+    array[i3 + 2] = c;
+    return array;
+  }, new Uint32Array(geometry.faces.length * 3));
+  const faceNormals = geometry.faces.reduce((array, { normal: { x, y, z } }, i) => {
+    const i3 = i * 3;
+    array[i3] = x;
+    array[i3 + 1] = y;
+    array[i3 + 2] = z;
+    return array;
+  }, new Float32Array(geometry.faces.length * 3));
+  const objectIndexes = geometry.faces.reduce((array, { materialIndex }, i) => {
+    array[i] = materialIndex;
+    return array;
+  }, new Uint8Array(geometry.faces.length));
+
+  if (faces.length === 0) throw new Error('Geometry does not contain any data');
+
+  geometry = { vertices, faces, objectIndexes, faceNormals };
 
   const openObjectIndexes = materials instanceof Array ? materials.map(({ side }) => {
     switch (side) {
@@ -95,11 +120,12 @@ function sliceAsync(settings, geometry, openObjectIndexes, constructLinePreview,
       }
     });
 
-    // send geometry and settings to worker to start the slicing progress
-    geometry = geometry.toJSON();
+    const { vertices, faces, objectIndexes, faceNormals } = geometry;
+    const buffers = [vertices.buffer, faces.buffer, objectIndexes.buffer, faceNormals.buffer];
+
     slicerWorker.postMessage({
       message: 'SLICE',
       data: { settings, geometry, openObjectIndexes, constructLinePreview }
-    });
+    }, buffers);
   });
 }
diff --git a/src/slicer.worker.js b/src/slicer.worker.js
index c43f88a..4ebcb50 100644
--- a/src/slicer.worker.js
+++ b/src/slicer.worker.js
@@ -1,6 +1,5 @@
 import 'core-js'; // polyfills
 import slice from './sliceActions/slice.js';
-import * as THREE from 'three';
 
 const onProgress = progress => {
   self.postMessage({
@@ -9,14 +8,11 @@ const onProgress = progress => {
   });
 }
 
-const loader = new THREE.JSONLoader();
-
 self.addEventListener('message', (event) => {
   const { message, data } = event.data;
   switch (message) {
     case 'SLICE': {
-      const { settings, geometry: JSONGeometry, constructLinePreview, openObjectIndexes } = data;
-      const { geometry } = loader.parse(JSONGeometry.data);
+      const { settings, geometry, constructLinePreview, openObjectIndexes } = data;
 
       const gcode = slice(settings, geometry, openObjectIndexes, constructLinePreview, onProgress);