First iteration, lets see if it works.

crystal-drill-guide.scad

@@ -0,0 +1,35 @@
+// Cut size
+_cutwidth = 40;
+_cutlength = 40;
+
+// Base size
+height = 10;
+width = 117+4;
+length = _cutlength+4;
+
+difference () {
+    
+    linear_extrude (height) {
+        difference () {
+            square([width,length], center=false); //Base
+        };
+    };
+    translate ([(2),0,2])
+    linear_extrude (height) {
+        difference () {
+            square([width-4,length], center=false);
+        };
+    };
+    
+    translate ([(width/2-_cutwidth/2),(2)])
+    linear_extrude (2) {
+        difference () {
+            square([_cutwidth,_cutlength], center=false);
+        };
+    };
+
+    difference () {
+    
+    };
+    
+};