diff --git a/sl2/slicer.pl b/sl2/slicer.pl
index 15e7a3b..58ecfe8 100755
--- a/sl2/slicer.pl
+++ b/sl2/slicer.pl
@@ -12,10 +12,19 @@
 #
 
 
-$epsilon = 0.0001;
+$epsilon = 0.0001;	# cutting offset
+$height = 10;		# height of workpiece
+$margin = 5;		# margin of workpiece box
+$end = 0;		# offset to add at the last layer
+$flip = 1;		# flip piece
+$z0 = -35;		# reference tool position
+$z_step = 1;
 
-$flip = 1;
 
+#----- Read the STL mesh ------------------------------------------------------
+
+
+$xmin = $xmax = $ymin = $ymax = $zmin = $zmax = undef;
 
 $v_n = 0;
 $e_n = 0;
@@ -35,21 +44,39 @@ while (<>) {
         if (/vertex\s+/) {
 		my @tmp = split(/\s+/, $');
 
-		if ($flip) {
-			push(@f, -$tmp[0], $tmp[1], -$tmp[2]);
-		} else {
-			push(@f, @tmp);
-		}
+		($tmp[0], $tmp[2]) = (-$tmp[0], -$tmp[2]) if $flip;
+
+		$xmin = $tmp[0] unless defined $xmin && $xmin < $tmp[0];
+		$xmax = $tmp[0] unless defined $xmax && $xmax > $tmp[0];
+		$ymin = $tmp[1] unless defined $ymin && $ymin < $tmp[1];
+		$ymax = $tmp[1] unless defined $ymax && $ymax > $tmp[1];
+		$zmin = $tmp[2] unless defined $zmin && $zmin < $tmp[2];
+		$zmax = $tmp[2] unless defined $zmax && $zmax > $tmp[2];
+
+		push(@f, @tmp);
                 next;
         }
 }
 
+print STDERR "bbox\t($xmin, $ymin, $zmin)\n\t($xmax, $ymax, $zmax)\n";
+
+
+#----- Calculate Z offset -----------------------------------------------------
+
+# align with bottom (zmin == 0), z_pos = height - zoff
+
+$z_off = $z0 - $zmin - $height;
+$z_pos = $height + $zmin;
+
+
+#----- Perform the slicing ----------------------------------------------------
+
 
 sub cut
 {
 	local ($z, $a, $b, @f) = @_;
 
-	if ($f[$a + 2] < $z &&$f[$b + 2] > $z) {
+	if ($f[$a + 2] < $z && $f[$b + 2] > $z) {
 		my $dx = $f[$b] - $f[$a];
 		my $dy = $f[$b + 1] - $f[$a + 1];
 		my $dz = $f[$b + 2] - $f[$a + 2];
@@ -57,7 +84,7 @@ sub cut
 		my $f = ($z - $f[$a + 2]) / $dz;
 		return [ $dx * $f + $f[$a], $dy * $f + $f[$a + 1] ];
 	}
-	if ($f[$a + 2] > $z &&$f[$b + 2] < $z) {
+	if ($f[$a + 2] > $z && $f[$b + 2] < $z) {
 		return &cut($z, $b, $a, @f);
 	}
 	return ();
@@ -78,46 +105,73 @@ sub remove
 }
 
 
-for $level (sort keys %z_level) {
-	my $z = $level + $epsilon;
+@z_levels = sort { $b <=> $a } keys %z_level;
+for $level (@z_levels) {
+	my $z_cut = $level + $epsilon;
 
-#	print STDERR "level = $level\n";
-	undef %next;
+	print STDERR "level $level (cut at $z_cut)\n";
+
+	undef %path;
 	for (@m) {
 		my @f = @{ $_ };
-		my @p = &cut($z, 0, 3, @f);
-		push(@p, &cut($z, 0, 6, @f));
-		push(@p, &cut($z, 3, 6, @f));
+		my @p = &cut($z_cut, 0, 3, @f);
+		push(@p, &cut($z_cut, 0, 6, @f));
+		push(@p, &cut($z_cut, 3, 6, @f));
 
 		next if $#p < 1;
 		die "BAD $#p" if $#p > 1;
 
 		my $a = "$p[0][0] $p[0][1]";
 		my $b = "$p[1][0] $p[1][1]";
-		push(@{ $next{$a} }, $b);
-		push(@{ $next{$b} }, $a);
+		push(@{ $path{$a} }, $b);
+		push(@{ $path{$b} }, $a);
 #		print STDERR "$z: ($a) to ($b)\n";
 	}
 
 	while (1) {
-		my @k = keys %next;
-
-		last if $#k == -1;
-		my $p0 = $k[0];
-		$p = $p0;
-		while (1) {
-			my $next = $next{$p}[0];
-
-			print "$p $z\n";
-#			print STDERR "at $p\n";
-#			print STDERR "\tnext $next\n";
-			die "open path" unless defined $next;	
-			&remove($p, $next);
-			&remove($next, $p);
-			last if $p0 eq $next;
-			$p = $next;
+		if (defined $z_step) {
+			$z_pos = $z_pos - $z_step > $level ?
+			    $z_pos - $z_step : $level;
+		} else {
+			$z_pos = $level;
 		}
-		print "$p0 $z\n";
-		print "\n";
+
+		my $z = $z_pos + $z_off;
+		$z += $end if $z_pos == $z_levels[$#z_levels];
+
+		print STDERR "\t$z_pos @ $z\n";
+		if (defined $margin) {
+			print $xmin - $margin, " ", $ymin - $margin, " $z\n";
+			print $xmax + $margin, " ", $ymin - $margin, " $z\n";
+			print $xmax + $margin, " ", $ymax + $margin, " $z\n";
+			print $xmin - $margin, " ", $ymax + $margin, " $z\n";
+			print $xmin - $margin, " ", $ymin - $margin, " $z\n\n";
+		}
+
+		%next = %path;
+		while (1) {
+			my @k = keys %next;
+
+			last if $#k == -1;
+
+			my $p0 = $k[0];
+			$p = $p0;
+			while (1) {
+				my $next = $next{$p}[0];
+
+				print "$p $z\n";
+#				print STDERR "at $p\n";
+#				print STDERR "\tnext $next\n";
+				die "open path" unless defined $next;	
+				&remove($p, $next);
+				&remove($next, $p);
+				last if $p0 eq $next;
+				$p = $next;
+			}
+			print "$p0 $z\n";
+			print "\n";
+		}
+
+		last if $z_pos == $level;
 	}
 }