remove the box frame pieces, all pieces are of the extended lineage

Signed-off-by: Brian S. Stephan <bss@incorporeal.org>

src/frames/pieces/front-or-back-trapezoid.scad

@@ -0,0 +1,37 @@
+/*
+ * SPDX-FileCopyrightText: © 2024 Brian S. Stephan <bss@incorporeal.org>
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+include <parameters.scad>
+include <components.scad>
+use <front-or-back.scad>
+
+module clean_front_or_back() {
+	difference() {
+		front_or_back_frame_piece();
+		// chop off the lip we left on the basic piece
+		translate([-frame_x/2+frame_wall/2, 0, 0]) cube([frame_wall, frame_y, frame_z], center=true);
+	};
+}
+
+module bottom_piece_wall() {
+	// get a slice of the piece (before the bevel), to use it in extruding
+	projection(cut=true) rotate([-90, 0, 0]) translate([0, frame_y/2-(frame_wall-frame_bevel_height)*3/2, 0])
+		clean_front_or_back();
+}
+
+module bottom_piece_extension() {
+	// combine the original with a shrunken piece to "pull" the wall out
+	hull() {
+		linear_extrude(height=frame_extension_y) scale([1, 0.5, 1]) bottom_piece_wall();
+		linear_extrude(height=(frame_wall-frame_bevel_height)) bottom_piece_wall();
+	}
+}
+
+module front_or_back_trapezoid_frame_piece() {
+	clean_front_or_back();
+	translate([0, -frame_y/2+frame_wall, 0]) rotate([90, 0, 0]) bottom_piece_extension();
+}
+
+front_or_back_trapezoid_frame_piece();