diff --git a/src/kiri/mode/cam/op-lathe.js b/src/kiri/mode/cam/op-lathe.js
index b1b5349a..275b6906 100644
--- a/src/kiri/mode/cam/op-lathe.js
+++ b/src/kiri/mode/cam/op-lathe.js
@@ -2,7 +2,7 @@
 
 import { CamOp } from './op.js';
 import { Tool } from './tool.js';
-import { Topo4 } from './topo4.js';
+import { generate as topo4_generate } from './topo4.js';
 import { newPoint } from '../../../geo/point.js';
 
 function createFilter(op) {
@@ -39,7 +39,7 @@ class OpLathe extends CamOp {
         let { addSlices } = state;
         let filter = createFilter(op);
 
-        this.topo = await Topo4({
+        this.topo = await topo4_generate({
             op,
             state,
             onupdate: (pct, msg) => {
diff --git a/src/kiri/mode/cam/topo3.js b/src/kiri/mode/cam/topo3.js
index 4116ac21..d45ae043 100644
--- a/src/kiri/mode/cam/topo3.js
+++ b/src/kiri/mode/cam/topo3.js
@@ -11,7 +11,7 @@ import { Tool } from './tool.js';
 const RAD2DEG = 180 / Math.PI;
 const DEG2RAD = Math.PI / 180;
 
-class Topo {
+export class Topo {
     constructor() { }
 
     async generate(opt = {}) {
diff --git a/src/kiri/mode/cam/topo4.js b/src/kiri/mode/cam/topo4.js
index 2a430dce..7a4c39c6 100644
--- a/src/kiri/mode/cam/topo4.js
+++ b/src/kiri/mode/cam/topo4.js
@@ -17,7 +17,7 @@ function scale(fn, factor = 1, base = 0) {
     }
 }
 
-class Topo {
+export class Topo {
     constructor() { }
 
     async generate(opt = {}) {
@@ -296,7 +296,7 @@ class Topo {
     }
 
     async latheWorker(onupdate) {
-        const { sliced, tool, zoff, leave } = this;
+        const { sliced, tool, zoff, leave, linear } = this;
 
         const rota = this.angle * DEG2RAD;
         const steps = (Math.PI * 2) / rota;
@@ -319,19 +319,32 @@ class Topo {
             onupdate(count / steps);
         }
 
-        count = recs[0].heights.length / 3;
+        count = linear ? recs.length : recs[0].heights.length / 3;
+        // count = recs[0].heights.length / 3;
         while (count-- > 0) {
             let slice = newSlice(count);
             slice.camLines = [ newPolygon().setOpen() ];
             paths.push(slice);
         }
 
-        for (let rec of recs) {
-            const { degrees, heights } = rec;
-            [...heights].group(3).forEach((a,i) => {
-                // progress each path 360 degrees to prevent A rolling backwards
-                paths[i].camLines[0].push( newPoint(a[0], a[1], a[2] + leave).setA(degrees + i * -360) );
+        if (linear) {
+            recs.forEach((rec,i) => {
+                const { degrees, heights } = rec;
+                [...heights].group(3).forEach((a) => {
+                    paths[i].camLines[0].push( newPoint(a[0], a[1], a[2] + leave).setA(degrees) );
+                });
+                if (i % 2 === 1) {
+                    paths[i].camLines[0].reverse();
+                }
             });
+        } else {
+            for (let rec of recs) {
+                const { degrees, heights } = rec;
+                [...heights].group(3).forEach((a,i) => {
+                    // progress each path 360 degrees to prevent A rolling backwards
+                    paths[i].camLines[0].push( newPoint(a[0], a[1], a[2] + leave).setA(degrees + i * -360) );
+                });
+            }
         }
 
         for (let slice of paths) {
@@ -395,8 +408,6 @@ class Topo {
         await Promise.all(promises);
         recs.sort((a, b) => { return b.angle - a.angle });
 
-        // let linear = true;
-
         count = linear ? recs.length : recs[0].heights.length / 3;
         while (count-- > 0) {
             let slice = newSlice(count);
@@ -468,6 +479,6 @@ export function rotatePoints(lines, rot) {
     new THREE.BufferAttribute(lines, 3).applyMatrix4(rot);
 }
 
-export function Topo4(opt) {
+export async function generate(opt) {
     return new Topo().generate(opt);
 };
diff --git a/src/kiri/run/minion.js b/src/kiri/run/minion.js
index 6d97d0c4..ae1c2920 100644
--- a/src/kiri/run/minion.js
+++ b/src/kiri/run/minion.js
@@ -15,7 +15,7 @@ import { sliceZ, sliceConnect } from '../../geo/slicer.js';
 import { Slicer as cam_slicer } from '../mode/cam/slicer.js';
 import { Slicer as topo_slicer } from '../mode/cam/slicer_topo.js';
 import { Probe, Trace, raster_slice } from '../mode/cam/topo3.js';
-import { Topo4, rotatePoints } from '../mode/cam/topo4.js';
+import { Topo as Topo4, rotatePoints } from '../mode/cam/topo4.js';
 import { wasm_ctrl } from '../../geo/wasm.js';
 
 const clib = self.ClipperLib;
@@ -54,9 +54,13 @@ function debug() {
     // console.log(`[${name}]`, ...arguments);
 }
 
+let invalid = 0;
 const funcs = self.minion = {
     invalid(data, seq, cmd) {
-        console.error({ invalid_minion_command: cmd, data });
+        if (invalid++ < 20) {
+            // prevent flooding console and killing session
+            console.error({ invalid_minion_command: cmd, data });
+        }
         reply({ seq, error: `invalid command (${cmd})` });
     },