diff --git a/bin/esbuild.config.mjs b/bin/esbuild.config.mjs
index 4881ab00..0cb973bb 100644
--- a/bin/esbuild.config.mjs
+++ b/bin/esbuild.config.mjs
@@ -12,7 +12,9 @@ const MESH_OUTFILE = 'src/pack/mesh-main.js';
 const MESH_EXTRAS = [ ];
 
 const KIRI_OUTFILE = 'src/pack/kiri-main.js';
-const KIRI_EXTRAS = [ ];
+const KIRI_EXTRAS = [
+    'src/ext/base64.js'
+];
 
 async function appendExtraModules(extras, outfile, minify = false) {
     const files = await glob(extras);
diff --git a/notes.md b/notes.md
index a7036e77..5efbac1a 100644
--- a/notes.md
+++ b/notes.md
@@ -31,6 +31,10 @@
 * `B` multi-extruder rendering of raft fails to offset the rest of the print
 * `B` multi-extruder purge blocks fail to generate properly for rafts
 
+* `F` min layer time
+* `F` separate bridging speed / fan control
+* `F` elephant foot compensation
+* `F` inner / outer perimeter compensation
 * `F` better thin-wall (like arachne)
 * `F` add scarf seams
 * `F` add 'random' and 'seam' start point options
diff --git a/src/geo/polygon.js b/src/geo/polygon.js
index 38957f46..846515f9 100644
--- a/src/geo/polygon.js
+++ b/src/geo/polygon.js
@@ -258,9 +258,10 @@ export class Polygon {
     // of the polygon with the noodle removed (for the next pass)
     noodle(width) {
         let clone = this.clone(true);
-        let ins = clone.offset(width);
+        let ins = clone.offset(width) ?? [];
+        let remain = ins.clone(true);
         let nood = POLY.nest(POLY.flatten([ clone, ...ins ], [], true));
-        return { noodle: nood, remain: ins };
+        return { noodle: nood, remain };
     }
 
     // generate center crossing point cloud
diff --git a/src/kiri/core/init.js b/src/kiri/core/init.js
index 36a68da0..02dd0a55 100644
--- a/src/kiri/core/init.js
+++ b/src/kiri/core/init.js
@@ -1323,7 +1323,8 @@ function init_one() {
             yr = ((tl && yc) || (!tl && yt) ? ra : 1),
             zr = ((tl && zc) || (!tl && zt) ? ra : 1);
         // prevent null scale
-        if (xr * yr * zr === 0) {
+        if (xv * xr < 0.1 || yv * yr < 0.1 || zv * zr < 0.1) {
+            api.alerts.show('invalid scale value');
             return;
         }
         selection.scale(xr,yr,zr);
@@ -1350,7 +1351,11 @@ function init_one() {
             xr = ((tl && xc) || (!tl && xt) ? ra : 1),
             yr = ((tl && yc) || (!tl && yt) ? ra : 1),
             zr = ((tl && zc) || (!tl && zt) ? ra : 1);
-
+        // prevent null scale
+        if (xv * xr < 0.1 || yv * yr < 0.1 || zv * zr < 0.1) {
+            api.alerts.show('invalid scale value');
+            return;
+        }
         selection.scale(xr,yr,zr);
         ui.scaleX.was = ui.scaleX.value = xv * xr;
         ui.scaleY.was = ui.scaleY.value = yv * yr;
@@ -1362,6 +1367,7 @@ function init_one() {
         e.target.value = val;
     }
 
+    // on enter but not on blur
     space.event.onEnterKey([
         ui.scaleX,        selectionScale,
         ui.scaleY,        selectionScale,
@@ -1369,6 +1375,9 @@ function init_one() {
         ui.sizeX,         selectionSize,
         ui.sizeY,         selectionSize,
         ui.sizeZ,         selectionSize,
+    ]);
+    // on enter and blur
+    space.event.onEnterKey([
         ui.toolName,      updateTool,
         ui.toolNum,       updateTool,
         ui.toolFluteDiam, updateTool,
diff --git a/src/kiri/core/print.js b/src/kiri/core/print.js
index 848229f3..d0487b52 100644
--- a/src/kiri/core/print.js
+++ b/src/kiri/core/print.js
@@ -362,14 +362,11 @@ class Print {
                 // if( axis == 'I' || axis == "J") return
                 if (abs) {
                     pos[axis] = val;
-                    
                     if (axis == "X") point.x = factor * pos.X + xoff.x + off.x
                     else if (axis == "Y") point.y = factor * pos.Y + xoff.y + off.y
                     else if (axis == "Z") point.z = factor * pos.Z + xoff.z + off.z + dz
-                    
-
                 } else {
-                    mov[axis] = val;
+                    // mov[axis] = val;
                     pos[axis] += val;
                 }
                 // console.log("position updated",structuredClone(pos))
@@ -393,7 +390,6 @@ class Print {
                 center = center.add(prevPoint);
                 center.setZ((prevPoint.z+point.z)/2+dz);
             }
-            
             return {
                 center,
                 point,
@@ -402,10 +398,8 @@ class Print {
         }
 
         function outputPoint(point,lastP,emit,{center,arcPoints,retract}) {
-            
             // non-move in a new plane means burp out
             // the old sequence and start a new one
-            
             if (newlayer || (autolayer && seq.z != point.z)) {
                 newlayer = false;
                 let dz = point.z - seq.z;
diff --git a/src/kiri/mode/cam/cl-tab.js b/src/kiri/mode/cam/cl-tab.js
index 8237065e..0cda4f12 100644
--- a/src/kiri/mode/cam/cl-tab.js
+++ b/src/kiri/mode/cam/cl-tab.js
@@ -61,7 +61,7 @@ export function createTabBox(iw, ic, n) {
     const { camZBottom, camStockIndexed } = process;
     const sz = stock.z || bounds.max.z;
     const zto = sz - iw.track.top;
-    const zp = (env.camZBottom || camStockIndexed ? env.camZBottom : sz - track.box.d - zto) + (camTabsMidline ? 0 : camTabsHeight / 2);
+    const zp = (camZBottom || camStockIndexed ? camZBottom : sz - track.box.d - zto) + (camTabsMidline ? 0 : camTabsHeight / 2);
     ic.x += n.x * camTabsDepth / 2; // offset from part
     ic.z -= n.y * camTabsDepth / 2; // offset swap z,y
     ic.y = zp; // offset swap in world space y,z
diff --git a/src/kiri/mode/cam/op-outline.js b/src/kiri/mode/cam/op-outline.js
index 270f4c64..c9b7e275 100644
--- a/src/kiri/mode/cam/op-outline.js
+++ b/src/kiri/mode/cam/op-outline.js
@@ -100,6 +100,11 @@ class OpOutline extends CamOp {
         // extend cut thru (only when z bottom is 0)
         if (workarea.bottom_z < 0) {
             let last = slices[slices.length-1];
+            // when step down > full cut depth, clear slices and
+            // leave only the cut-thru pass(es)
+            if (op.down > workarea.top_stock - workarea.bottom_part) {
+                slices.length = 0;
+            }
             for (let zneg of base_util.lerp(0, -workarea.bottom_cut, op.down)) {
                 if (!last) continue;
                 let add = last.clone(true);
diff --git a/src/kiri/mode/cam/op-rough.js b/src/kiri/mode/cam/op-rough.js
index 341f56d8..beb24827 100644
--- a/src/kiri/mode/cam/op-rough.js
+++ b/src/kiri/mode/cam/op-rough.js
@@ -32,11 +32,12 @@ class OpRough extends CamOp {
         let roughStock = op.all && isIndexed;
         let toolDiam = new Tool(settings, op.tool).fluteDiameter();
         let trueShadow = process.camTrueShadow === true;
+        let cutThruBypass = op.down > workarea.top_stock - workarea.bottom_part;
 
         updateToolDiams(toolDiam);
 
         // clear the stock above the area to be roughed out
-        if (workarea.top_z > workarea.top_part) {
+        if (workarea.top_z > workarea.top_part && !cutThruBypass) {
             let shadow = state.shadow.base.clone();
             let step = toolDiam * op.step;
             let inset = roughStock ?
@@ -258,6 +259,12 @@ class OpRough extends CamOp {
 
         let last = slices[slices.length-1];
 
+        // when step down > full cut depth, clear slices and
+        // leave only the cut-thru pass(es)
+        if (cutThruBypass) {
+            slices.length = 0;
+        }
+        // add cut thru passes
         if (workarea.bottom_z < 0)
         for (let zneg of base_util.lerp(0, -workarea.bottom_cut, op.down)) {
             if (!last) continue;
diff --git a/src/kiri/mode/cam/op-trace.js b/src/kiri/mode/cam/op-trace.js
index 7b759316..52481169 100644
--- a/src/kiri/mode/cam/op-trace.js
+++ b/src/kiri/mode/cam/op-trace.js
@@ -38,7 +38,7 @@ class OpTrace extends CamOp {
         let cutdir = ov_conv;
         let polys = [];
         let reContour = false;
-        let canRecontour = offset !== 'none' && down === 0;
+        let canRecontour = offset !== 'none' && down < 0;
         let stockRect = stock.center && stock.x && stock.y ?
             newPolygon().centerRectangle({x:0,y:0}, stock.x, stock.y) : undefined;
         updateToolDiams(toolDiam);
@@ -57,6 +57,7 @@ class OpTrace extends CamOp {
             let max = Math.max(...zs);
             if (max - min > 0.0001 && canRecontour) {
                 reContour = true;
+                down = 0;
             }
         }
         if (false) newSliceOut(0).output()
diff --git a/src/kiri/mode/cam/tools.js b/src/kiri/mode/cam/tools.js
index 9552fccb..8c6b43d2 100644
--- a/src/kiri/mode/cam/tools.js
+++ b/src/kiri/mode/cam/tools.js
@@ -4,6 +4,7 @@ import { $ } from '../../../moto/webui.js';
 import { api } from '../../core/api.js';
 import { consts } from '../../core/consts.js';
 import { settings as setconf } from '../../core/settings.js';
+import { calcTaperLength, calcTaperAngle } from './tool.js';
 
 const DEG2RAD = Math.PI / 180;
 
@@ -44,7 +45,7 @@ function selectTool(tool) {
     ui.toolMetric.checked = tool.metric;
     ui.toolType.selectedIndex = toolNames.indexOf(tool.type);
     if (tool === 'tapermill') {
-        ui.toolTaperAngle.value = kiri.driver.CAM.calcTaperAngle(
+        ui.toolTaperAngle.value = calcTaperAngle(
             (tool.flute_diam - tool.taper_tip) / 2, tool.flute_len
         ).round(1);
     } else if(tool === 'drill'){
@@ -208,16 +209,15 @@ export function updateTool(ev) {
     selectedTool.metric = ui.toolMetric.checked;
     selectedTool.type = toolNames[ui.toolType.selectedIndex];
     if (selectedTool.type === 'tapermill') {
-        const CAM = kiri.driver.CAM;
         const rad = (selectedTool.flute_diam - selectedTool.taper_tip) / 2;
         if (ev && ev.target === ui.toolTaperAngle) {
             const angle = parseFloat(ev.target.value);
-            const len = CAM.calcTaperLength(rad, angle * DEG2RAD);
+            const len = calcTaperLength(rad, angle * DEG2RAD);
             selectedTool.flute_len = len;
             ui.toolTaperAngle.value = angle.round(1);
             ui.toolFluteLen.value = selectedTool.flute_len.round(4);
         } else {
-            ui.toolTaperAngle.value = CAM.calcTaperAngle(rad, selectedTool.flute_len).round(1);
+            ui.toolTaperAngle.value = calcTaperAngle(rad, selectedTool.flute_len).round(1);
         }
     } else {
         ui.toolTaperAngle.value = 0;
diff --git a/src/kiri/mode/fdm/driver-be.js b/src/kiri/mode/fdm/driver-be.js
index 397670e2..f1164acc 100644
--- a/src/kiri/mode/fdm/driver-be.js
+++ b/src/kiri/mode/fdm/driver-be.js
@@ -1,7 +1,7 @@
 /** Copyright Stewart Allen <sa@grid.space> -- All Rights Reserved */
 
 import { util } from '../../../geo/base.js';
-import { fdm_slice } from './slice.js';
+import { fdm_slice, sliceAll } from './slice.js';
 import { fdm_prepare } from './prepare.js';
 import { fdm_export } from './export.js';
 
@@ -39,6 +39,7 @@ export const FDM = {
     extrudePerMM,
     extrudeMM,
     slice: fdm_slice,
+    sliceAll: sliceAll,
     prepare: fdm_prepare,
     export: fdm_export
 };
diff --git a/src/kiri/mode/fdm/post.js b/src/kiri/mode/fdm/post.js
index bbc088fc..a2222402 100644
--- a/src/kiri/mode/fdm/post.js
+++ b/src/kiri/mode/fdm/post.js
@@ -2,7 +2,7 @@
 
 import '../../../ext/jspoly.js';
 import { base } from '../../../geo/base.js';
-import { newPolygon } from '../../../geo/polygon.js';
+import { newPolygon, Polygon } from '../../../geo/polygon.js';
 import { polygons as POLY, fillArea } from '../../../geo/polygons.js';
 import { getRangeParameters } from './driver.js';
 import { slicer } from '../../../geo/slicer.js';
@@ -163,25 +163,47 @@ function thin_type_2(params) {
 }
 
 function thin_type_3(params) {
+    // offsetN usually = extrusion width (nozzle diameter)
     let { z, top, count, offsetN, last, gaps } = params;
-    top.thin_fill = [];
-    top.fill_sparse = [];
 
+    // produce trace from outside of poly inward no more than max inset
     let { noodle, remain } = top.poly.noodle(offsetN * count);
-    top.shells = noodle;
+
+    // top.shells = noodle;
     top.gaps = last = remain;
 
-    let thin = top.thin_fill;
-    let scale = 5000;
+    let thin = top.thin_fill = [];
+    let sparse = top.fill_sparse = [];
+    let scale = 1000;
     let minR = offsetN / 2;
     let maxR = minR * 1.5;
-    let minSpur = 0; // offsetN * 3;
+    let minSpur = offsetN * 2;
+
+    let showNoodle = false;
+    let mergeChains = true;
+    let interpolateShortSpur = true;
+    let showChainRawPoints = false;
+    let showChainInterpPoints = true;
+    let showMidline = true;
+    let showMidPoints = false;
+    let showMidNormals = false;
+    let showMidRadii = true;
+    let showNexuses = false;
 
     let pointMap = new Map();
     let lineMap = new Map();
 
+    function pointDist(p0, p1) {
+        return Math.hypot(p0.x-p1.x, p0.y-p1.y);
+    }
+
+    function point2key(point) {
+        return `${(point.x*100)|0}|${(point.y*100)|0}`;
+    }
+
+    // convert point to deduplicated / unique point record
     function pointToRec(point) {
-        let key = `${(point.x*100)|0}|${(point.y*100)|0}`;
+        let key = point2key(point);
         let rec = pointMap.get(key);
         if (!rec) {
             rec = {
@@ -196,6 +218,7 @@ function thin_type_3(params) {
         return rec;
     }
 
+    // convert line to unique line record. matches reversed and duplicate lines
     function pointsToLine(p0, p1) {
         p0 = pointToRec(p0);
         p1 = pointToRec(p1);
@@ -219,6 +242,9 @@ function thin_type_3(params) {
 
     let chains = [];
 
+    // for each standalone noodle, construct medial axis
+    // map medial axis points into de-duplicated segments
+    // which will be re-connected into chains
     for (let poly of noodle) {
         // scale the polygon (including inners) so the medial axis code works properly
         poly = poly.clone(true).scale({ x:scale, y:scale, z:scale });
@@ -231,69 +257,84 @@ function thin_type_3(params) {
         for (let { point0, point1 } of ma) {
             pointsToLine(point0, point1);
         }
-        for (let seg of lineMap.values()) {
-            let { p0, p1 } = seg;
-            let len = seg.len = Math.hypot(p0.x-p1.x, p0.y-p1.y);
-            // filter out lines where both points' radii are under the
-            // minR threshold. shorten and fixup lines where minR falls
-            // somewhere along the gradient between ends.
-            if (p0.r < minR || p1.r < minR) {
-                if (p0.r > minR && len > minSpur) {
-                    // move p1 toward p0 until minR met
-                    let pct = (minR - p1.r) / (p0.r - p1.r);
-                    let dx = p1.x - p0.x;
-                    let dy = p1.y - p0.y;
-                    p1.x -= dx * pct;
-                    p1.y -= dy * pct;
-                    p1.r = minR;
-                    pointMap.delete(p1.key);
-                } else if (p1.r > minR && len > minSpur) {
-                    // move p0 toward p1 until minR met
-                    let pct = (minR - p0.r) / (p1.r - p0.r);
-                    let dx = p0.x - p1.x;
-                    let dy = p0.y - p1.y;
-                    p0.x -= dx * pct;
-                    p0.y -= dy * pct;
-                    p0.r = minR;
-                    pointMap.delete(p0.key);
-                } else {
-                    lineMap.delete(seg.key);
-                    continue;
-                }
+    }
+
+    // connect segments into chains
+    for (let seg of lineMap.values()) {
+        let { p0, p1 } = seg;
+        let len = seg.len = pointDist(p0, p1);
+        // filter out lines where both points' radii are under the
+        // minR threshold. shorten and fixup lines where minR falls
+        // somewhere along the gradient between ends.
+        if (interpolateShortSpur)
+        if (p0.r < minR || p1.r < minR) {
+            if (p0.r > minR && len > minSpur) {
+                // move p1 toward p0 until minR met
+                let pct = (minR - p1.r) / (p0.r - p1.r);
+                let dx = p1.x - p0.x;
+                let dy = p1.y - p0.y;
+                p1.x -= dx * pct;
+                p1.y -= dy * pct;
+                p1.r = minR;
+                pointMap.delete(p1.key);
+            } else if (p1.r > minR && len > minSpur) {
+                // move p0 toward p1 until minR met
+                let pct = (minR - p0.r) / (p1.r - p0.r);
+                let dx = p0.x - p1.x;
+                let dy = p0.y - p1.y;
+                p0.x -= dx * pct;
+                p0.y -= dy * pct;
+                p0.r = minR;
+                pointMap.delete(p0.key);
+            } else {
+                // both points eliminated
+                pointMap.delete(p0.key);
+                pointMap.delete(p1.key);
+                lineMap.delete(seg.key);
+                continue;
             }
-            // for each line segment either add it to a chain or start a new chain
-            let add;
-            for (let chain of chains) {
-                if (p0.count === 2 && p0.key === chain[0].key) {
-                    chain.splice(0,0,{...p1, len});
-                } else if (p0.count === 2 && p0.key === chain.peek().key) {
-                    chain.peek().len = len;
-                    chain.push({...p1});
-                    add = true;
-                } else if (p1.count === 2 && p1.key === chain[0].key) {
-                    chain.splice(0,0,{...p0, len});
-                    add = true;
-                } else if (p1.count === 2 && p1.key === chain.peek().key) {
-                    chain.peek().len = len;
-                    chain.push({...p0});
-                    add = true;
-                }
-                if (add) {
-                    chain.total += len;
-                    break;
-                }
+        }
+        // for each line segment either add it to a chain or start a new chain
+        let add;
+        for (let chain of chains) {
+            if (p0.count === 2 && p0 === chain[0]) {
+                // prefix chain with p1
+                chain.splice(0,0,p1);
+                add = true;
+            } else if (p0.count === 2 && p0 === chain.peek()) {
+                // append chain with p1
+                chain.push(p1);
+                add = true;
+            } else if (p1.count === 2 && p1 === chain[0]) {
+                // prefix chain with p0
+                chain.splice(0,0,p0);
+                add = true;
+            } else if (p1.count === 2 && p1 === chain.peek()) {
+                // append chain with p0
+                chain.push(p0);
+                add = true;
             }
-            if (!add) {
-                chains.push([ {...p0 ,len}, {...p1} ]);
-                chains.peek().total = len;
+            if (add) {
+                chain.total += len;
+                break;
             }
         }
+        if (!add) {
+            chains.push([ p0, p1 ]);
+            chains.peek().total = len;
+        }
     }
 
-    let showMid = false;
-    let showCross = false;
-    let showRad = true;
+    // todo: merge chains at next of 3 or more preferencing
+    // merging longer chains. then shorten remaining nexus chain
+    // intersections by minR
 
+    // render inset "noodle"
+    if (showNoodle) {
+        top.shells.appendAll(noodle);
+    }
+
+    // divide a segment/redius into 1 or more equal subsegments
     function div(cr) {
         if (cr <= maxR) {
             return [ cr ];
@@ -311,71 +352,249 @@ function thin_type_3(params) {
         }
     }
 
-    // add chains to thinwall output for visualization
-    if (showRad) {
-        top.shells = [];
-    }
-    for (let chain of chains.filter(c => c.total >= minR)) {
-        // chain reduction by merging short segments
-        let end = chain[0];
-        let nuchain = [ end ];
-        for (let point of chain.slice(1)) {
-            if (point.len === undefined || point.len + end.len >= minR) {
-                nuchain.push(point);
-                end = point;
-            } else {
-                end.len += point.len;
+    // filter chains that are too short from consideration
+    chains = chains.filter(c => c.total >= minR);
+    chains.sort((c1,c2) => c2.total - c1.total);
+
+    function merge1chain() {
+        let clen = chains.length;
+        for (let i=0; i<clen; i++) {
+            let ci = chains[i];
+            if (!ci) continue;
+            for (let j=i+1; j<clen; j++) {
+                let cj = chains[j];
+                if (!cj) continue;
+                if (ci[0] === cj[0]) {
+                    ci.reverse().appendAll(cj)
+                    ci.total += cj.total;
+                    cj.merged = true;
+                    chains[j] = undefined;
+                    return true;
+                } else if (ci.peek() === cj.peek()) {
+                    ci.appendAll(cj.reverse());
+                    ci.total += cj.total;
+                    cj.merged = true;
+                    chains[j] = undefined;
+                    return true;
+                } else if (ci.peek() === cj[0]) {
+                    ci.appendAll(cj);
+                    ci.total += cj.total;
+                    cj.merged = true;
+                    chains[j] = undefined;
+                    return true;
+                } else if (ci[0] === cj.peek()) {
+                    cj.appendAll(ci);
+                    cj.total += ci.total;
+                    ci.merged = true;
+                    chains[i] = undefined;
+                    return true;
+                }
             }
         }
-        chain = nuchain;
-        // emit chain with subdivision for long segments
-        for (let i=0; i<chain.length-1; i++) {
-            // medial axis segment
-            if (showMid) {
-                thin.push(new Point(chain[i].x, chain[i].y));
-                thin.push(new Point(chain[i+1].x, chain[i+1].y));
+        return false;
+    }
+
+    // map chains to nexus via endpoints
+    let nexus = {};
+    function addEp(point, chain) {
+        let key = point.key;
+        let rec = nexus[key];
+        if (!rec) rec = nexus[key] = { point, chains: [] };
+        if (rec.chains.indexOf(chain) < 0) rec.chains.push(chain);
+    }
+    // since chains are sorted longest to shortest,
+    // they will appear in the nexus record longest to shortest
+    for (let chain of chains) {
+        addEp(chain[0], chain);
+        addEp(chain.peek(), chain);
+    }
+
+    // connect chains end to end following nexus branches that result
+    // in the longest final merged chain (open or closed)
+    // map chain endpoints to nexus points
+    while (mergeChains && merge1chain()) ;
+
+    // filter out null chains that were merged into other chains
+    chains = chains.filter(chain => chain);
+
+    // filter dup points from connecting ends
+    chains = chains.map(chain => chain.filter((v, i) => i === 0 || v !== chain[i - 1]));
+
+    // mark closed chains
+    // todo use exact point match by eliminating slice above
+    // then later removing repeated points in the resulting chain from merges
+    for (let chain of chains) {
+        chain.closed = (chain[0] === chain.peek());
+        console.log(chain.closed ? 'closed' : 'open');
+        if (chain.closed) chain.pop();
+    }
+
+    // shorten chain length by minR distance by popping or moving points
+    function shorten(chain) {
+        for (let rem=0, i=chain.length-1; i>=1 && rem < minR; i--) {
+            let c1 = chain[i];
+            let c2 = chain[i-1];
+            let d = pointDist(c1,c2);
+            if (rem + d <= minR) {
+                chain.pop();
+                rem += d;
+            } else {
+                let diff = minR - rem;
+                // move c1 toward c2
+                let pct = diff / d;
+                let dx = c1.x - c2.x;
+                let dy = c1.y - c2.y;
+                chain[i] = {
+                    x: c1.x - dx * pct,
+                    y: c1.y - dy * pct,
+                    r: c1.r
+                };
+                rem = 0;
+                break;
             }
-            // compute medial axis segment cross section
+        }
+    }
+
+    // shorten chains terminating at nexus by midR
+    for (let rec of Object.values(nexus)) {
+        let { point } = rec;
+        rec.shorts = 0;
+        if (rec.chains.length < 3) continue;
+        for (let chain of chains.filter(c => !c.closed)) {
+            if (pointDist(chain[0], point) < minR) {
+                chain.reverse();
+                shorten(chain);
+                chain.reverse();
+                rec.shorts++;
+            } else if (chain.peek() === point) {
+                shorten(chain);
+                rec.shorts++;
+            }
+        }
+    }
+
+    if (showNexuses)
+    for (let rec of Object.values(nexus)) {
+        let { point } = rec;
+        top.shells.push(newPolygon().centerCircle(point, 0.2, 6 - rec.shorts));
+    }
+
+    function renderPointNormal(pt, ndx, ndy) {
+        if (showMidNormals) {
+            let xo = ndx * pt.r;
+            let yo = ndy * pt.r;
+            thin.push(new Point(pt.x + yo, pt.y - xo));
+            thin.push(new Point(pt.x - yo, pt.y + xo));
+        }
+        if (showMidRadii) {
+            const Sx = pt.x + ndy * pt.r;
+            const Sy = pt.y - ndx * pt.r;
+            const circ = top.shells;
+            const pop = div(pt.r);
+            let acc = 0;
+            for (let r of pop) {
+                const t = acc + r;
+                const px = Sx + -ndy * t;
+                const py = Sy + ndx * t;
+                circ.push(newPolygon().centerCircle({x:px, y:py}, r, 10));
+                acc += r * 2;
+            }
+        }
+}
+
+    // gather point offsets into shells
+    let zi = z;
+    for (let chain of chains) {
+        // zi += 0.1;
+        if (showChainRawPoints)
+        for (let pt of chain) {
+            top.shells.push(newPolygon().centerCircle(pt, pt.r ?? 0.1, 10));
+        }
+        // draw medial axis chain
+        let { closed, length } = chain;
+        let term = closed ? length : length - 1;
+        let segs = [];
+        for (let i=0; i<term; i++) {
             let p0 = chain[i];
-            let p1 = chain[i+1];
+            let p1 = chain[(i+1) % length];
+            let len = pointDist(p0, p1);
+            // medial axis segment
+            if (showMidline) {
+                thin.push(new Point(p0.x, p0.y, zi));
+                thin.push(new Point(p1.x, p1.y, zi));
+            }
+            // compute medial axis segment normal
+            let offs = len <= offsetN ? [ 0 ] : base.util.lerp(0, len, offsetN, true);
+            let step = 1 / offs.length;
             let dr = (p1.r - p0.r);
             let dx = (p1.x - p0.x);
             let dy = (p1.y - p0.y);
-            let ndx = dx / p0.len;
-            let ndy = dy / p0.len;
-            let offs = p0.len <= offsetN ? [ 0.5 ] : base.util.lerp(0, p0.len, offsetN, true);
-            let indx = 0;
-            let step = 1 / offs.length;
-            // interpolate across the length of the chain segment
-            for (let off of offs) {
-                let inc = (indx++ * step);
-                let cr = p0.r + dr * inc;
-                let cx = p0.x + dx * inc;
-                let cy = p0.y + dy * inc;
-                let xo = ndx * cr;
-                let yo = ndy * cr;
-                if (showCross) {
-                    thin.push(new Point(cx + yo, cy - xo));
-                    thin.push(new Point(cx - yo, cy + xo));
+            let ndx = dx / len;
+            let ndy = dy / len;
+            segs.push({ p0, p1, offs, step, dr, dx, dy, ndx, ndy });
+        }
+        console.log({ segs });
+        // compute chain subdivisions
+        let slen = segs.length;
+        for (let si=0; si<slen; si++) {
+            let seg = segs[si];
+            let segp = segs[(si - 1 + slen) % slen];
+            let { p0, p1, offs, step, dr, dx, dy, ndx, ndy } = seg;
+            let first = si === 0;
+            let last = si === slen - 1;
+            let mid = !(first || last);
+            // for length 2, first and last segment are the same
+            if (showMidPoints) {
+                if (first) {
+                    // todo: handle closed
+                    top.shells.push(newPolygon().centerCircle(p0, 0.08, 10));
                 }
-                if (showRad) {
-                    let circ = top.shells;
-                    let pop = div(cr);
-                    let sx = cx + yo;
-                    let sy = cy - xo;
-                    let m = 1;
-                    for (let r of pop) {
-                        sx -= (r/cr) * yo * m;
-                        sy += (r/cr) * xo * m;
-                        circ.push(newPolygon().centerCircle({ x:sx, y:sy }, r, 10));
-                        m = 2;
+                if (mid) {
+                    // mid segments
+                    top.shells.push(newPolygon().centerCircle(p0, 0.08, 10));
+                }
+                if (last) {
+                    // todo: handle closed
+                    top.shells.push(newPolygon().centerCircle(p0, 0.08, 10));
+                    if (closed) {
+                        console.log('closed');
+                    } else {
+                        top.shells.push(newPolygon().centerCircle(p1, 0.08, 10));
                     }
-                    // console.log(pop);
                 }
             }
+            {
+                // todo: handle closed
+                if (first) {
+                    renderPointNormal(p0, ndx, ndy);
+                }
+                if (mid) {
+                    renderPointNormal(p0, ((ndx + segp.ndx)/2), ((ndy + segp.ndy)/2));
+                }
+                if (last) {
+                    renderPointNormal(p1, ndx, ndy);
+                }
+            }
+            // interpolate across the length of the chain segment
+            if (showChainInterpPoints)
+            for (let indx = 1; indx < offs.length; indx++) {
+                const inc = indx * step;
+                const cr = p0.r + dr * inc;
+                const cx = p0.x + dx * inc;
+                const cy = p0.y + dy * inc;
+                const xo = ndx * cr;
+                const yo = ndy * cr;
+                if (showMidPoints) {
+                    top.shells.push(newPolygon().centerCircle({ x:cx, y:cy }, 0.05, 10));
+                }
+                renderPointNormal({ x:cx, y:cy, r:cr }, ndx, ndy);
+            }
         }
     }
 
+    POLY.setZ([...thin, ...top.shells], z);
+    // POLY.setZ([...top.shells], z);
+
     return { last, gaps };
 }
 
diff --git a/src/kiri/run/engine.js b/src/kiri/run/engine.js
index 00824cbe..5b9d7008 100644
--- a/src/kiri/run/engine.js
+++ b/src/kiri/run/engine.js
@@ -156,7 +156,7 @@ class Engine {
     }
 
     slice() {
-        this.widget.setTopZ(this.settings.stock.z - (this.topOffset || 0));
+        this.widget.setTopZ((this.settings?.stock?.z || 0) - (this.topOffset || 0));
         return new Promise((accept, reject) => {
             client.clear();
             client.sync([this.widget]);