diff --git a/src/geo/polygon.js b/src/geo/polygon.js
index 3efe4504..a99d38b2 100644
--- a/src/geo/polygon.js
+++ b/src/geo/polygon.js
@@ -1495,7 +1495,6 @@ class Polygon {
 
     toClipper(inout) {
         let poly = this,
-            cur = [],
             out = inout || [];
         out.push(poly.points.map(p => p.toClipper()));
         if (poly.inner) {
@@ -1519,6 +1518,37 @@ class Polygon {
         return POLY.expand([this], -offset, this.getZ(), output);
     }
 
+    /**
+     * ofsetting an open line uses a different procedure and options
+     *
+     * @param {number} distance
+     * @param {'square'|'round'|'miter'} type
+     * @returns {Polygon[]}
+     */
+    offset_open(distance, type = 'miter') {
+        if (this.isOpen()) {
+            let cjnt = clib.JoinType,
+                cety = clib.EndType,
+                coff = new clib.ClipperOffset(),
+                ctre = new clib.PolyTree(),
+                entt = {
+                    'square' : cety.etOpenSquare,
+                    'round' : cety.etOpenRound,
+                    'miter' : cety.etOpenSquare
+                }[type] || cety.etOpenSquare,
+                jntt = {
+                    'square': cjnt.jtSquare,
+                    'round': cjnt.jtRound,
+                    'miter': cjnt.jtMiter
+                }[type] || cjnt.jtMiter;
+                coff.AddPaths(this.toClipper(), jntt, entt);
+                coff.Execute(ctre, distance * config.clipper);
+            return POLY.fromClipperTree(ctre, this.getZ(), null, null, 0);
+        } else {
+            return this.offset(distance);
+        }
+    }
+
     /**
      * todo need something more clever for polygons that overlap with
      * todo differing resolutions (like circles)
diff --git a/src/geo/polygons.js b/src/geo/polygons.js
index 53debbe3..dfd9fe11 100644
--- a/src/geo/polygons.js
+++ b/src/geo/polygons.js
@@ -34,7 +34,7 @@ const POLYS = base.polygons = {
     offset,
     trimTo,
     expand,
-    expand_lines,
+    // expand_lines,
     points,
     length,
     route,
@@ -508,18 +508,18 @@ function sumCirc(polys) {
  * @param {number} distance offset
  * @param {number} [z] defaults to 0
  */
-function expand_lines(poly, distance, z) {
-    let fact = config.clipper,
-        cjnt = clib.JoinType,
-        cety = clib.EndType,
-        coff = new clib.ClipperOffset(),
-        ctre = new clib.PolyTree();
+// function expand_lines(poly, distance, z) {
+//     let fact = config.clipper,
+//         cjnt = clib.JoinType,
+//         cety = clib.EndType,
+//         coff = new clib.ClipperOffset(),
+//         ctre = new clib.PolyTree();
 
-    coff.AddPaths(poly.toClipper(), cjnt.jtMiter, cety.etOpenSquare);
-    coff.Execute(ctre, distance * fact);
+//     coff.AddPaths(poly.toClipper(), cjnt.jtMiter, cety.etOpenSquare);
+//     coff.Execute(ctre, distance * fact);
 
-    return fromClipperTree(ctre, z, null, null, 0);
-}
+//     return fromClipperTree(ctre, z, null, null, 0);
+// }
 
 /**
  * @param {Polygon[]} polys
diff --git a/src/kiri-mode/cam/client.js b/src/kiri-mode/cam/client.js
index da44193d..101bf540 100644
--- a/src/kiri-mode/cam/client.js
+++ b/src/kiri-mode/cam/client.js
@@ -123,6 +123,11 @@ CAM.init = function(kiri, api) {
         const layers = new kiri.Layers();
         for (let poly of open) {
             layers.setLayer("open", {line: 0xff8800}, false).addPoly(poly);
+            let diam = poly.tool?.shape?.diameter;
+            if (diam) {
+                const exp = poly.offset_open(diam, 'round');
+                layers.setLayer("open2", {line: 0xff5555}, false).addPolys(exp);
+            }
         }
         for (let poly of closed) {
             layers.setLayer("close", {line: 0xff0000}, false).addPoly(poly);
diff --git a/src/load/gbr.js b/src/load/gbr.js
index d919b35a..a70c9122 100644
--- a/src/load/gbr.js
+++ b/src/load/gbr.js
@@ -44,7 +44,7 @@ function toMesh(text, opt = { z: 1 }) {
         return [];
     }
 
-    // copper traces
+    // copper pads
     const mid = [];
     for (let poly of flat.filter(p => p.depth === 1)) {
         mid.push(poly.extrude(z1, z0 - z1));
@@ -55,10 +55,24 @@ function toMesh(text, opt = { z: 1 }) {
         return top[0];
     }
 
-    // inner polys for traces which we will punch thru for vias
+    // copper traces (expand first since open)
+    const open_exp = open.map(poly => {
+        const diam = poly.tool?.shape?.diameter;
+        return diam ? poly.offset_open(diam, 'round') : null;
+    }).filter(p => p).flat();
+
+    // union open trace expansions
+    const opn = [];
+    for (let poly of POLYS.union(open_exp)) {
+        const tool = poly.tool;
+        opn.push(poly.extrude(z0));
+    }
+
+    // inner polys for traces which we add back to the top
+    // and (optionally) remove from the bottom for making vias
     const low = [];
     for (let poly of flat.filter(p => p.depth === 2)) {
-        low.push(poly.extrude(z0));
+        low.push(poly.extrude(z1, z0 - z1));
     }
 
     // convert vertex arrays to csg mesh definitions
@@ -66,17 +80,21 @@ function toMesh(text, opt = { z: 1 }) {
     const midMesh = mid.map(v => CSG.fromPositionArray(v));
 
     // subtract mid from top
-    const v0Mesh = CSG.subtract(topMesh, ...midMesh);
+    let meshOut = CSG.subtract(topMesh, ...midMesh);
 
-    if (low.length === 0) {
-        return CSG.toPositionArray(v0Mesh);
+    if (opn.length) {
+        // add back raised traces (before removing vias)
+        const opnMesh = opn.map(v => CSG.fromPositionArray(v))
+        meshOut = CSG.union(meshOut, ...opnMesh);
     }
 
-    // subtract low (vias) from remaining
-    const lowMesh = low.map(v => CSG.fromPositionArray(v))
-    const v1Mesh = CSG.subtract(v0Mesh, ...lowMesh);
+    if (low.length) {
+        // subtract low (vias) from remaining
+        const lowMesh = low.map(v => CSG.fromPositionArray(v))
+        meshOut = CSG.union(meshOut, ...lowMesh);
+    }
 
-    return CSG.toPositionArray(v1Mesh);
+    return CSG.toPositionArray(meshOut);
 }
 
 function parse(text) {