# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1412951084 -7200
# Node ID 8334ce389108c2bc0137862d4d227773636749bd
# Parent  5dda66a506fa17812cf3d5b05599ff19e20ae1c9
Fixed the edge connector tab alignment. Separated the back payload and connector
sections of the cartridge, providing more internal depth in the payload section.

diff -r 5dda66a506fa -r 8334ce389108 cartridge.scad
--- a/cartridge.scad	Wed Oct 08 13:54:46 2014 +0200
+++ b/cartridge.scad	Fri Oct 10 16:24:44 2014 +0200
@@ -128,14 +128,16 @@
 	/* Internal dimensions. */
 
 	int_width = 86.0;
-	int_depth = 11.0;
+	int_payload_depth = 12.5;	/* maximum depth in the payload section */
+	int_connector_depth = 11.0;	/* maximum depth in the connector section */
 	int_payload_height = 50.8;	/* space between the top and the floor */
 	int_connector_height = 13.5; 	/* vertical offset of bottom/floor of payload area */
 
 	/* Side thicknesses. */
 
 	front = 2;
-	back = 3.5;
+	payload_back = 2;		/* in the payload area the thickness is reduced */
+	connector_back = 3.5;		/* the back cavity requires a thicker back wall */
 	top = 3;
 	side = 2; 			/* increased from 1.5 for 3D printing reliability */
 	bottom = 1;			/* thickness of floor of payload area */
@@ -150,14 +152,17 @@
 
 	int_front_depth = 4.5;
 	front_depth = int_front_depth + front;
-	int_back_depth = int_depth - int_front_depth + front_back_overlap;
-	back_depth = int_back_depth + back;
+	int_payload_back_depth = int_payload_depth - int_front_depth + front_back_overlap;
+	int_connector_back_depth = int_connector_depth - int_front_depth + front_back_overlap;
+	back_depth = int_payload_back_depth + payload_back;
 
 	/* Cartridge dimensions. */
 
 	width = int_width + side + side;
-	height = top + int_payload_height + bottom + int_connector_height;
-	depth = int_depth + front + back;
+	payload_height = top + int_payload_height;
+	connector_height = bottom + int_connector_height;
+	height = payload_height + bottom + int_connector_height;
+	depth = int_payload_depth + front + payload_back;
 	int_payload_upper_extent = height / 2 - top;
 	int_payload_lower_extent = -height / 2 + int_connector_height + bottom;
 
@@ -249,15 +254,6 @@
 	inner_front_edge_depth = 1.5;
 
 	/*
-	The cutouts in the floor of the front of the cartridge that produce a
-	kind of tab that guides the edge connector into place in the back cutout.
-	*/
-
-	edge_connector_cutout_front_offset = 1.0;
-	edge_connector_cutout_front_depth = front_back_overlap;
-	edge_connector_cutout_front_width = 15.0;
-
-	/*
 	The cutout in the floor of the back of the cartridge that accommodates
 	the edge connector.
 	*/
@@ -266,6 +262,14 @@
 	edge_connector_cutout_back_width = 57.5;
 
 	/*
+	The cutouts in the floor of the front of the cartridge that produce a
+	kind of tab that guides the edge connector into place in the back cutout.
+	*/
+
+	edge_connector_cutout_front_depth = front_back_overlap;
+	edge_connector_cutout_front_width = (int_width - edge_connector_cutout_back_width) / 2;
+
+	/*
 	Edge connectors are themselves 0.05" or approximately 1.27mm in
 	thickness according to the Acorn Electron Cartridge Interface Specification
 	(Acorn Support Application Group Note 014).
@@ -452,7 +456,7 @@
 						edge_connector_cutout_front_depth,
 						bottom,
 						1, -1, 1,
-						-width / 2 + edge_connector_cutout_front_offset,
+						-int_width / 2,
 						0,
 						-height / 2 + int_connector_height);
 
@@ -462,7 +466,7 @@
 						edge_connector_cutout_front_depth,
 						bottom,
 						-1, -1, 1,
-						width / 2 - edge_connector_cutout_front_offset,
+						int_width / 2,
 						0,
 						-height / 2 + int_connector_height);
 				}
@@ -597,9 +601,20 @@
 				/* Back portion. */
 
 				if (BACK_SURFACE) {
-					cube_at(width, back, height,
-						0, 1, 0,
-						0, int_back_depth, 0);
+
+					/* Payload section of back surface. */
+
+					cube_at(width, payload_back, payload_height,
+						0, 1, 1,
+						0, int_payload_back_depth, int_payload_lower_extent);
+
+					/* Connector section of back surface overlapping the floor. */
+
+					cube_at(width, connector_back, connector_height,
+						0, 1, 1,
+						0, int_connector_back_depth, -height / 2);
+
+					/* Sides of back piece. */
 
 					cube_at(back_left, back_depth, height,
 						-1, 1, 0,
@@ -609,6 +624,8 @@
 						1, 1, 0,
 						int_width / 2, 0, 0);
 
+					/* Top of back piece. */
+
 					cube_at(width, back_depth, top,
 						0, 1, 1,
 						0, 0, int_payload_upper_extent);
@@ -651,7 +668,7 @@
 
 					/* Floor of cartridge. */
 
-					cube_at(int_width, int_back_depth, bottom,
+					cube_at(int_width, int_connector_back_depth, bottom,
 						0, 1, 1,
 						0, 0, -height / 2 + int_connector_height);
 
@@ -755,7 +772,7 @@
 
 			/* Inner back cavities. */
 
-			translate([0, int_back_depth, -height / 2])
+			translate([0, int_connector_back_depth, -height / 2])
 				linear_extrude(height = int_connector_height)
 					translate([-int_width / 2, 0, 0])
 						polygon([
@@ -766,7 +783,7 @@
 							[0, inner_back_slope_depth]
 							]);
 
-			translate([0, int_back_depth, -height / 2])
+			translate([0, int_connector_back_depth, -height / 2])
 				linear_extrude(height = int_connector_height)
 					translate([int_width / 2, 0, 0])
 						polygon([
@@ -780,7 +797,7 @@
 			/* Inner back edge cavity. */
 
 			translate([inner_back_edge_width / 2,
-				int_back_depth + inner_back_edge_depth, -height / 2])
+				int_connector_back_depth + inner_back_edge_depth, -height / 2])
 				rotate([0, -90, 0])
 					linear_extrude(height = inner_back_edge_width)
 						polygon([