diff --git a/js/kiri-slicer.js b/js/kiri-slicer.js
index 3d9f832d..91009b0e 100644
--- a/js/kiri-slicer.js
+++ b/js/kiri-slicer.js
@@ -257,15 +257,11 @@ var gs_kiri_slicer = exports;
             }
         }
 
-/* -- synchronous slice -- can't be cancelled --
         // create a Slice for each z offset in the zIndexes array
         for (var i = 0; i < zIndexes.length; i++) {
             // slice next layer and add to slices[] array
             sliceZ(zIndexes[i], zHeights[i]);
-            // kill slicing if onupdate() returns 42
-            if (onupdate(i / zIndexes.length) === 42) {
-                return ondone(null);
-            }
+            onupdate(i / zIndexes.length);
         }
 
         // for cam, mark top and bottom as mandatory (hasFlats)
@@ -284,39 +280,6 @@ var gs_kiri_slicer = exports;
 
         // pass Slices array back to ondone function
         ondone(slices);
-*/
-
-        var sliceIndex = 0;
-
-        function kickSlice() {
-            sliceZ(zIndexes[sliceIndex], zHeights[sliceIndex]);
-            // kill slicing if onupdate() returns 42
-            if (onupdate(sliceIndex / zIndexes.length) === 42) {
-                return ondone(null);
-            }
-            if (++sliceIndex < zIndexes.length) {
-                setTimeout(kickSlice, 0);
-            } else {
-                // for cam, mark top and bottom as mandatory (hasFlats)
-                if (options.cam && slices.length > 0) {
-                    slices[0].hasFlats = true;
-                    slices[slices.length-1].hasFlats = true;
-                }
-
-                // connect slices into linked list for island/bridge projections
-                for (i=1; i<slices.length; i++) {
-                    slices[i-1].up = slices[i];
-                    slices[i].down = slices[i-1];
-                }
-
-                slices.slice_time = time() - timeStart;
-
-                // pass Slices array back to ondone function
-                ondone(slices);
-            }
-        }
-
-        kickSlice();
 
         /** ***** SLICING FUNCTIONS ***** */
 
diff --git a/js/kiri-widget.js b/js/kiri-widget.js
index d6bfb241..36827d75 100644
--- a/js/kiri-widget.js
+++ b/js/kiri-widget.js
@@ -87,8 +87,6 @@ var gs_kiri_widget = exports;
             progress: 0
         };
         this.saved = false;
-        // cancel slice/print ops
-        this.cancel = false;
     }
 
     /** ******************************************************************
@@ -530,7 +528,6 @@ var gs_kiri_widget = exports;
             startTime = UTIL.time();
 
         widget.settings = settings;
-        widget.cancel = false;
 
         onupdate(0.0001, "slicing");
 
@@ -548,10 +545,9 @@ var gs_kiri_widget = exports;
                 if (reply.slices) { widget.clearSlices(); widget.slices = [] };
                 if (reply.slice) widget.slices.push(KIRI.codec.decode(reply.slice, {mesh:widget.mesh}));
                 if (reply.error) {
-                    widget.cancel = true;
                     ondone(false, reply.error);
                 }
-                if (reply.done && !widget.cancel) {
+                if (reply.done) {
                     widget.modified = false;
                     ondone(true);
                 }
@@ -577,12 +573,6 @@ var gs_kiri_widget = exports;
 
             var catchupdate = function(progress, message) {
                 onupdate(progress, message);
-                if (widget.cancel) {
-                    ondone("canceled");
-                    return 42;
-                } else {
-                    return 0;
-                }
             };
 
             var driver = null;
diff --git a/js/kiri-work.js b/js/kiri-work.js
index 4446850e..4d0732fe 100644
--- a/js/kiri-work.js
+++ b/js/kiri-work.js
@@ -16,7 +16,8 @@ if (self.window) {
         BASE = self.base,
         seqid = 1,
         running = {},
-        worker = new Worker(pre + "/code/worker.js/" + exports.VERSION);
+        slicing = {},
+        worker = null;
 
     // new moto.Ajax(function(body) {
     //     console.log({body:body});
@@ -24,20 +25,6 @@ if (self.window) {
     //     worker = new Worker(URL.createObjectURL(blob));
     // }).request(pre + "/code/worker.js/");
 
-    worker.onmessage = function(e) {
-        var now = time(),
-            reply = e.data,
-            record = running[reply.seq],
-            onreply = record.fn;
-
-        if (reply.done) delete running[reply.seq];
-
-        // calculate and replace recv time
-        reply.time_recv = now - reply.time_recv;
-
-        onreply(reply.data, reply);
-    };
-
     function send(fn, data, onreply, async, zerocopy) {
         var seq = seqid++;
 
@@ -52,6 +39,32 @@ if (self.window) {
     }
 
     KIRI.work = {
+        restart : function() {
+            if (worker) worker.terminate();
+
+            for (var key in slicing) {
+                slicing[key]({error: "cancelled"});
+            }
+            slicing = {};
+            running = {};
+
+            worker = new Worker(pre + "/code/worker.js/" + exports.VERSION);
+
+            worker.onmessage = function(e) {
+                var now = time(),
+                    reply = e.data,
+                    record = running[reply.seq],
+                    onreply = record.fn;
+
+                if (reply.done) delete running[reply.seq];
+
+                // calculate and replace recv time
+                reply.time_recv = now - reply.time_recv;
+
+                onreply(reply.data, reply);
+            };
+        },
+
         decimate : function(vertices, callback) {
             var vertices = vertices.buffer.slice(0);
             send("decimate", vertices, function(output) {
@@ -65,18 +78,16 @@ if (self.window) {
             });
         },
 
-        cancel : function(widget) {
-            send("cancel", widget ? {id:widget.id} : {});
-        },
-
         slice : function(settings, widget, callback) {
             var vertices = widget.getGeoVertices().buffer.slice(0);
+            slicing[widget.id] = callback;
             send("slice", {
                 id: widget.id,
                 settings: settings,
                 vertices: vertices,
                 position: widget.mesh.position
             }, function(reply) {
+                if (reply.done || reply.error) delete slicing[widget.id];
                 callback(reply);
             }, null, [vertices]);
         },
@@ -115,6 +126,9 @@ if (self.window) {
         }
     };
 
+    // start first worker
+    KIRI.work.restart();
+
 } else {
 
     module = { exports: {} };
@@ -164,19 +178,6 @@ if (self.window) {
             send.done(vertices);
         },
 
-        cancel: function(data) {
-            if (data.id) {
-                var widget = cache[data.id];
-                if (widget) widget.cancel = true;
-            } else {
-                for (var id in cache) {
-                    if (cache.hasOwnProperty(id)) {
-                        cache[id].cancel = true;
-                    }
-                }
-            }
-        },
-
         slice: function(data, send) {
             var settings = data.settings,
                 vertices = new Float32Array(data.vertices),
diff --git a/js/kiri.js b/js/kiri.js
index 9e5b2d7d..6f1aefb7 100644
--- a/js/kiri.js
+++ b/js/kiri.js
@@ -2551,7 +2551,7 @@ self.kiri.license = exports.LICENSE;
                     // hide all dialogs
                     hideDialog();
                     // cancel slicing
-                    KIRI.work.cancel();
+                    KIRI.work.restart();
                     break;
             }
             return false;