diff --git a/cameo/Makefile b/cameo/Makefile
index d1b4b86..549e649 100644
--- a/cameo/Makefile
+++ b/cameo/Makefile
@@ -15,7 +15,8 @@ PREFIX ?= /usr/local
 SHELL=/bin/bash
 
 MAIN=cameo
-OBJS=cameo.o excellon.o gerber.o gnuplot.o ops.o path.o lex.yy.o y.tab.o
+OBJS=cameo.o excellon.o gerber.o gnuplot.o ops.o path.o shape.o \
+     lex.yy.o y.tab.o
 
 CFLAGS_WARN=-Wall -Wshadow -Wmissing-prototypes \
             -Wmissing-declarations -Wno-format-zero-length
diff --git a/cameo/README b/cameo/README
index e6b1de1..6e3216b 100644
--- a/cameo/README
+++ b/cameo/README
@@ -136,3 +136,11 @@ Concave corners on an outside path are normally cut such that the corner
 is round, leaving material at and near the corner point. The option "dog"
 changes this to cutting a "dogbone" hole such that material is also
 removed up to the corner point.
+
+
+Drill/mill substitution:
+
+  drill <min-diameter> <max-diameter>
+  mill <diameter> <step>
+  remainder
+  empty
diff --git a/cameo/lang.l b/cameo/lang.l
index 9356334..4e1bd72 100644
--- a/cameo/lang.l
+++ b/cameo/lang.l
@@ -42,8 +42,12 @@ NUM	-?[0-9]+\.?[0-9]*
 				  return TOK_ALIGN; }
 <INITIAL>array			return TOK_ARRAY;
 <INITIAL>clear			return TOK_CLEAR;
-<INITIAL>reset			return TOK_RESET;
+<INITIAL>drill			return TOK_DRILL;
+<INITIAL>empty			return TOK_EMPTY;
+<INITIAL>mill			return TOK_MILL;
 <INITIAL>offset			return TOK_OFFSET;
+<INITIAL>remainder		return TOK_REMAINDER;
+<INITIAL>reset			return TOK_RESET;
 <INITIAL>translate		return TOK_TRANSLATE;
 <INITIAL>z			return TOK_Z;
 
diff --git a/cameo/lang.y b/cameo/lang.y
index f382736..a960996 100644
--- a/cameo/lang.y
+++ b/cameo/lang.y
@@ -25,6 +25,7 @@
 
 static double xo = 0, yo = 0, zo = 0;
 static struct path *paths = NULL;
+static struct path *remain = NULL;
 
 
 #define MIL2MM(mil)	((mil)/1000*25.4)
@@ -108,6 +109,33 @@ static void align(int ref, double x, double y)
 }
 
 
+static void clear_paths(void)
+{
+	struct path *next;
+
+	while (paths) {
+		next = paths->next;
+		path_free(paths);
+		paths = next;
+	}
+}
+
+
+static struct path **classify(struct path **anchor, struct path *path)
+{
+	struct path **walk, *next;
+
+	if (!path)
+		return &(*anchor)->next;
+	for (walk = &paths; *walk; walk = &(*walk)->next);
+	*walk = path;
+	next = (*anchor)->next;
+	path_free(*anchor);
+	*anchor = next;
+	return anchor;
+}
+
+
 %}
 
 
@@ -121,7 +149,8 @@ static void align(int ref, double x, double y)
 };
 
 
-%token		TOK_ALIGN TOK_ARRAY TOK_CLEAR TOK_RESET TOK_OFFSET
+%token		TOK_ALIGN TOK_ARRAY TOK_CLEAR TOK_DRILL TOK_EMPTY
+%token		TOK_MILL TOK_OFFSET TOK_REMAINDER TOK_RESET
 %token		TOK_TRANSLATE TOK_Z
 %token		TOK_GERBER TOK_GNUPLOT TOK_EXCELLON TOK_WRITE
 %token		TOK_DOG TOK_INSIDE
@@ -166,13 +195,7 @@ command:
 		}
 	| TOK_CLEAR
 		{
-			struct path *next;
-
-			while (paths) {
-				next = paths->next;
-				path_free(paths);
-				paths = next;
-			}
+			clear_paths();
 		}
 	| TOK_RESET
 		{
@@ -218,6 +241,38 @@ command:
 			gnuplot_write($2, paths);
 			translate(0, 0, -zo);
 		}
+	| TOK_DRILL dimen dimen
+		{
+			struct path **walk;
+
+			remain = paths;
+			paths = NULL;
+			walk = &paths;
+			while (*walk)
+				walk =
+				    classify(walk, try_drill(*walk, $2, $3));
+		}
+	| TOK_MILL dimen dimen
+		{
+			struct path **walk;
+
+			remain = paths;
+			paths = NULL;
+			walk = &paths;
+			while (*walk)
+				walk = classify(walk, try_mill(*walk, $2, $3));
+		}
+	| TOK_REMAINDER
+		{
+			clear_paths();
+			paths = remain;
+			remain = NULL;
+		}
+	| TOK_EMPTY
+		{
+			if (paths)
+				yyerror("path list is not empty");
+		}
 	;
 
 opt_filename:
diff --git a/cameo/ops.c b/cameo/ops.c
index 74c4cfa..f73f396 100644
--- a/cameo/ops.c
+++ b/cameo/ops.c
@@ -11,7 +11,10 @@
  */
 
 
+#include <stddef.h>
+
 #include "path.h"
+#include "shape.h"
 #include "ops.h"
 
 
@@ -54,3 +57,34 @@ void tool_comp_paths(struct path *paths, int dog_bone, int all_inside)
 				tool_comp_1(path, 0, dog_bone);
 	tool_comp_1(leftmost, !all_inside, dog_bone);
 }
+
+
+struct path *try_drill(struct path *path, double d_min, double d_max)
+{
+	struct path *new;
+
+	if (path->r_tool*2 < d_min || path->r_tool*2 > d_max)
+		return NULL;
+	if (!path->first || path->first != path->last)
+		return NULL;
+	new = path_new((d_min+d_max)/2); /* @@@ fishy */
+	path_add(new, path->first->x, path->first->y, path->first->z);
+	return new;
+}
+
+
+struct path *try_mill(struct path *path, double diam, double step)
+{
+	if (path->r_tool*2 < diam)
+		return NULL;
+	if (!path->first)
+		return NULL;
+	if (path->first == path->last)
+		return circle(path->first->x, path->first->y, path->first->z,
+		    path->r_tool, diam/2, step);
+	if (path->first->next == path->last)
+		return slot(path->first->x, path->first->y,
+		    path->first->next->x, path->first->next->y,
+		    path->first->z, path->r_tool, diam/2, step);
+	return NULL;
+}
diff --git a/cameo/ops.h b/cameo/ops.h
index a40fcf9..ad20b1e 100644
--- a/cameo/ops.h
+++ b/cameo/ops.h
@@ -14,10 +14,11 @@
 #ifndef OPS_H
 #define OPS_H
 
-
 #include "path.h"
 
 
 void tool_comp_paths(struct path *paths, int dog_bone, int all_inside);
+struct path *try_drill(struct path *path, double d_min, double d_max);
+struct path *try_mill(struct path *path, double diam, double step);
 
 #endif /* !OPS_H */
diff --git a/cameo/shape.c b/cameo/shape.c
new file mode 100644
index 0000000..e8c1819
--- /dev/null
+++ b/cameo/shape.c
@@ -0,0 +1,83 @@
+/*
+ * shape.c - Toolpaths for basic shapes
+ *
+ * Written 2010 by Werner Almesberger
+ * Copyright 2010 Werner Almesberger
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+
+#include <math.h>
+
+#include "path.h"
+#include "shape.h"
+
+
+static struct path *path;
+
+
+static double arc2angle(double arc, double r)
+{
+	return acos(1-arc*arc/(r*r)/2);
+}
+
+
+static void half_circle(double cx, double cy, double rx, double ry, double z,
+    double s)
+{
+	double m[4];
+	double x = rx, y = ry, tmp;
+	double a;
+
+	m[0] = cos(s);
+	m[1] = -sin(s);
+	m[2] = -m[1];
+	m[3] = m[0];
+
+	for (a = 0; a < M_PI; a += s) {
+		path_add(path, cx+x, cy+x, z);
+		tmp = x*m[0]+y*m[1];
+		y = x*m[2]+y*m[3];
+		x = tmp;
+	}
+	path_add(path, cx-rx, cy-ry, z);
+}
+
+
+struct path *slot(double xa, double ya, double xb, double yb, double z,
+    double sr, double tr, double step)
+{
+	double dx = xb-xa;
+	double dy = yb-ya;
+	double s = arc2angle(step, sr);
+	double nx, ny;
+	double f;
+
+	f = (sr-tr)/hypot(dx, dy);
+	nx = -dy*f;
+	ny = dx*f;
+
+	path = path_new(tr);
+	half_circle(xa, ya, nx, ny, z, s);
+	half_circle(xb, yb, -nx, -ny, z, s);
+	path_add(path, xa+nx, ya+ny, z);
+	return path;
+}
+
+
+struct path *circle(double cx, double cy, double cz, double cr, double tr,
+    double step)
+{
+	double s = arc2angle(step, cr);
+	double a;
+
+	path = path_new(tr);
+	for (a = 0; a < 2*M_PI; a += s)
+		path_add(path, cx+(cr-tr)*cos(a), cy+(cr-tr)*sin(a), cz);
+	path_add(path, cx+(cr-tr), cy, cz);
+	return path;
+}
diff --git a/cameo/shape.h b/cameo/shape.h
new file mode 100644
index 0000000..98e280f
--- /dev/null
+++ b/cameo/shape.h
@@ -0,0 +1,25 @@
+/*
+ * shape.h - Toolpaths for basic shapes
+ *
+ * Written 2010 by Werner Almesberger
+ * Copyright 2010 Werner Almesberger
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+
+#ifndef SHAPE_H
+#define SHAPE_H
+
+#include "path.h"
+
+
+struct path *slot(double xa, double ya, double xb, double yb, double z,
+    double sr, double tr, double step);
+struct path *circle(double cx, double cy, double cz, double cr, double tr,
+    double step);
+
+#endif /* !SHAPE_H */