Lightweight grids

README.md

@@ -56,6 +56,9 @@ For inserting magnets, check out [the jig](#jig).
     - [None](#none)
     - [Integer Fraction](#integer-fraction)
     - [Dynamic](#dynamic)
+  - [Lightweight](#lightweight)
+    - [Wall thickness](#wall-thickness)
+    - [Bottom lip](#bottom-lip)
   - [Corner radius](#corner-radius)
   - [Alignment](#alignment)
   - [Custom cell size](#custom-cell-size)
@@ -462,6 +465,39 @@ If you wish to only create larger cells, not smaller cells, you can set the mini
 <!-- openscad -o docs/images/filler-dynamic-expand-always.png --camera=0,0,0,40,0,10,150 -D plate_size='[120, 42]' -D filler_x=2 -D filler_minimum_size=[42,42] -->
 <img src="docs/images/filler-dynamic-expand-always.png" alt="Dynamic filler always expanded" />
 
+## Lightweight
+
+`hollow` skeletonizes the baseplate: instead of solid material between the cells, only a thin wall following the Gridfinity profile is printed. Neighbouring cells share a hollow channel, open towards the bed and closed at the top by a self-supporting 45° roof. Without magnets this roughly halves filament use and print time — a 4x4 plate drops from 20.6cm³ to 10.5cm³.
+
+<!-- openscad -o docs/images/lightweight.png --camera=0,0,0,150,0,25,260 -D plate_size='[84, 84]' -D hollow=true -D connector_intersection_puzzle=false -D numbering=false -->
+<img src="docs/images/lightweight.png" alt="Lightweight baseplate, seen from below" />
+
+The same plate without `hollow`, also seen from below:
+
+<!-- openscad -o docs/images/lightweight-off.png --camera=0,0,0,150,0,25,260 -D plate_size='[84, 84]' -D hollow=false -D connector_intersection_puzzle=false -D numbering=false -->
+<img src="docs/images/lightweight-off.png" alt="Standard baseplate, seen from below" />
+
+The top surface, the outer wall of each segment and the puzzle connectors stay solid, so segments link up the same way and the plate looks unchanged from above.
+
+> [!NOTE]
+> Hollow mode is incompatible with magnets, `solid_base` and the click latch — there is no material left to hold them, and GridFlock refuses to render that combination.
+
+### Wall thickness
+
+`hollow_wall` sets the wall thickness. It is a *horizontal* thickness, which is what the slicer sees on each layer, so setting it to your nozzle diameter prints the plate as a single wall with no infill. The default 0.8mm is one wall on a 0.8mm nozzle, two to three on a 0.4mm nozzle.
+
+<!-- openscad -o docs/images/lightweight-wall.png --camera=0,0,0,150,0,25,260 -D plate_size='[84, 84]' -D hollow=true -D hollow_wall=1.6 -D connector_intersection_puzzle=false -D numbering=false -->
+<img src="docs/images/lightweight-wall.png" alt="Lightweight baseplate with thicker walls" />
+
+### Bottom lip
+
+The Gridfinity profile ends in a 0.7mm lip that slopes back inwards. It is not functionally required; `remove_bottom_lip` replaces it with a straight continuation of the vertical section. This saves a little filament, removes the overhang where two cells meet, and gives the first layer a flat contact area instead of a knife edge.
+
+<!-- openscad -o docs/images/bottom-lip.png --camera=0,0,0,150,0,25,140 -D plate_size='[42, 42]' -D remove_bottom_lip=true -D connector_intersection_puzzle=false -D numbering=false -->
+<img src="docs/images/bottom-lip.png" alt="Baseplate with the bottom lip removed" />
+
+It can be used on its own, and is always enabled in hollow mode, where the inward slope would taper the horizontally measured walls to nothing at the first layer.
+
 ## Corner radius
 
 GridFlock generates plates with a corner radius of 4mm by default. This matches the Gridfinity corner radius, so when the plate size is a perfect multiple of 42, there is no gap.

editor.toml

@@ -14,10 +14,11 @@ description-extra-html = """
 <br>Apr 8: Glue-in magnets now have a release slot, which can be disabled by setting magnet_release_width to 0.
 <span style="display: none" class="alert alert-warning" data-display-condition="click && click_style == 0">The click latch can deform over time, especially if made of PLA. Prefer other materials like PETG.</span>
 <span style="display: none" class="alert alert-warning" data-display-condition="click && click_style == 1">The click latch can deform over time if used with non-ClickGroove bins, especially if made of PLA. Prefer other materials like PETG if you plan to use such bins.</span>
+<span style="display: none" class="alert alert-danger" data-display-condition="hollow && (magnets || solid_base > 0 || click)">Hollow mode only leaves a thin wall around the gridfinity profile, so it cannot be combined with magnets, a solid base or the click latch.</span>
 <span style="display: none" class="alert alert-warning" data-display-condition="connector_intersection_puzzle && connector_edge_puzzle">You have enabled both the edge and intersection puzzle connectors. While technically possible, it is better to focus on and tune one connector type.</span>
 """
 umami-track-render = []
-umami-track-export = ["magnets", "magnet_style", "connector_intersection_puzzle", "connector_edge_puzzle", "bed_size", "click", "click_style", "filler_x", "filler_y", "stacked_print", "adapter_mode"]
+umami-track-export = ["magnets", "magnet_style", "connector_intersection_puzzle", "connector_edge_puzzle", "bed_size", "click", "click_style", "filler_x", "filler_y", "stacked_print", "adapter_mode", "hollow"]
 
 [model.param-metadata.bed_size.presets]
 text = "Printer Presets"
@@ -129,6 +130,18 @@ display-condition = {js = "filler_x == 1 || filler_y == 1"}
 help-link = "https://github.com/yawkat/GridFlock/blob/main/README.md#dynamic"
 display-condition = {js = "filler_x == 2 || filler_y == 2"}
 
+[model.tab-metadata."Lightweight"]
+control-boolean = "hollow"
+description-html = "Skeletonize the baseplate so only thin walls are printed. This roughly halves filament use and print time, but leaves no material for magnets, a solid base or the click latch."
+help-link = "https://github.com/yawkat/GridFlock/blob/main/README.md#lightweight"
+[model.param-metadata.hollow]
+display-condition = {fixed = false}
+[model.param-metadata.hollow_wall]
+help-link = "https://github.com/yawkat/GridFlock/blob/main/README.md#wall-thickness"
+[model.param-metadata.remove_bottom_lip]
+help-link = "https://github.com/yawkat/GridFlock/blob/main/README.md#bottom-lip"
+display-condition = {js = "!hollow"}
+
 [model.tab-metadata."Numbering"]
 help-link = "https://github.com/yawkat/GridFlock/blob/main/README.md#numbering"
 collapsed = true

gridflock.scad

@@ -103,6 +103,15 @@ filler_minimum_size = [15, 15];
 // Padding alignment. The first value is the x direction (east/west), the second value the y direction (north/south). When padding is added to the build plate, this alignment is used to distribute it. A lower value will move the grid towards the west/south direction, adding more padding to the east/north
 alignment = [0.5, 0.5]; // [0:0.1:1]
 
+/* [Lightweight] */
+
+// Skeletonize the baseplate: instead of solid material between the cells, only a thin wall following the gridfinity profile is printed. This roughly halves filament use and print time. Incompatible with magnets, a solid base and the click latch
+hollow = false;
+// Wall thickness in hollow mode. This is a horizontal thickness, which is what the slicer sees on each layer, so a value matching your nozzle diameter prints as a single wall
+hollow_wall = 0.8; // 0.05
+// Remove the bottom lip of the gridfinity profile, extending the vertical section of the profile straight down instead. The lip is not functionally required; removing it saves filament, removes the overhang between neighbouring cells, and widens the first layer. Always enabled in hollow mode
+remove_bottom_lip = false;
+
 /* [Numbering] */
 
 // Enable numbering of the segements, embossed in a corner
@@ -256,6 +265,10 @@ assert(!magnets || magnet_frame_style != _MAGNET_SOLID || magnet_style != _MAGNE
 
 assert(!thumbscrews || solid_base > 0 || (magnets && magnet_frame_style == _MAGNET_SOLID), "Thumbscrew holes require some sort of solid base, such as magnet_style solid, or an explicit solid_base.");
 
+assert(!hollow || (!magnets && solid_base == 0 && !click), "Hollow mode only leaves a thin wall around the gridfinity profile, so there is nothing left to hold magnets, a solid base or a click latch.");
+
+assert(hollow_wall > 0, "hollow_wall must be positive.");
+
 _OPENGRID_LITE = 1;
 _OPENGRID_DIRECTIONAL = 2;
 _OPENGRID_VERTICAL = 4;
@@ -276,6 +289,12 @@ _magnet_extraction_dim_negative = [magnet_release_width, magnet_diameter/2];
 _profile_height_raw = 4.65;
 // for stacked prints, we cut off a sliver at the top to get a better contact area
 _profile_height = _profile_height_raw - top_slice - (stacked_print ? stacked_print_slice : 0);
+// The lip slopes inward, so in hollow mode it would taper the horizontally measured shell to nothing
+_remove_bottom_lip = remove_bottom_lip || hollow;
+// Horizontal distance from the sweep path to the vertical (waist) section of the gridfinity profile
+_profile_waist_offset = BASEPLATE_INNER_RADIUS + _BASEPLATE_PROFILE[1].x;
+// Height of the bottom lip of the gridfinity profile
+_profile_lip_height = _BASEPLATE_PROFILE[1].y;
 // height of the magnet level
 _magnet_level_height = (magnet_style != _MAGNET_GLUE_TOP ? magnet_top : 0) + (magnet_style != _MAGNET_GLUE_BOTTOM ? magnet_bottom : 0) + magnet_height;
 // total height of the non-bin levels (magnets, solid base). These are placed at z<0
@@ -373,6 +392,24 @@ module cutter(size, below=0) {
             }
         }
     }
+    // Extend the waist straight down, removing the lip and the overhang between neighbouring cells
+    if (_remove_bottom_lip) {
+        floor = -below - 0.001;
+        translate([0, 0, floor]) linear_extrude(_profile_lip_height - floor) offset(_profile_waist_offset)
+            square([size.x - BASEPLATE_OUTER_DIAMETER, size.y - BASEPLATE_OUTER_DIAMETER], center=true);
+    }
+}
+
+/**
+ * @Summary The interior volume of a cell that hollow mode removes, leaving a hollow_wall shell
+ * @param unit_size Size of the cell, in grid units, in each direction
+ */
+module cell_core(unit_size=[1, 1]) {
+    size = [BASEPLATE_DIMENSIONS.x*unit_size.x, BASEPLATE_DIMENSIONS.y*unit_size.y];
+    difference() {
+        translate([-size.x/2, -size.y/2, -0.001]) cube([size.x, size.y, _total_height + 0.002]);
+        cutter([size.x + hollow_wall*2, size.y + hollow_wall*2]);
+    }
 }
 
 /**
@@ -1024,6 +1061,33 @@ function compute_segment_size(trace, padding) = [
     BASEPLATE_DIMENSIONS.y * cumulate(trace.y)[len(trace.y)] + padding[_NORTH] + padding[_SOUTH],
 ];
 
+/**
+ * @Summary Decide how a single cell is rendered, from cell_override
+ * @param index Index of the cell within the segment
+ */
+function cell_style(index, global_cell_index, global_cell_count) = let(
+    seq_index = (index.y + global_cell_index.y) * ceil(global_cell_count.x) + (index.x + global_cell_index.x)
+) len(cell_override) > seq_index ? cell_override[seq_index] : _CELL_STYLE_NORMAL;
+
+/**
+ * @Summary The union of the cell cores, clipped so the outer wall and its puzzle connectors stay solid
+ */
+module segment_core(trace, size, padding, connector, global_cell_index, global_cell_count) {
+    last = [len(trace.x)-1, len(trace.y)-1];
+    intersection() {
+        translate([0, 0, -_extra_height]) linear_extrude(height = _total_height)
+            offset(-hollow_wall) segment_rectangle(size, connector, include_wall=false);
+        union() {
+            for (ix = [0:1:last.x]) for (iy = [0:1:last.y]) navigate_cell(size, trace, padding, [ix, iy]) {
+                cell_size = [trace.x[ix], trace.y[iy]];
+                if (cell_style([ix, iy], global_cell_index, global_cell_count) == _CELL_STYLE_NORMAL) {
+                    cell_core(cell_size);
+                }
+            }
+        }
+    }
+}
+
 /**
  * @Summary Model a segment, which is piece of the plate without breaks
  * @param trace The cell sizes, in grid units, on each axis
@@ -1061,21 +1125,20 @@ module segment(trace=[[1], [1]], padding=[0, 0, 0, 0], connector=[false, false,
                     for (ix = [0:1:last.x]) for (iy = [0:1:last.y]) navigate_cell(size, trace, padding, [ix, iy]) {
                         cell_size = [trace.x[ix], trace.y[iy]];
 
-                        seq_index = (iy + global_cell_index.y) * ceil(global_cell_count.x) + (ix + global_cell_index.x);
-                        cell_style = len(cell_override) <= seq_index ? _CELL_STYLE_NORMAL : cell_override[seq_index];
-                        if (cell_style == _CELL_STYLE_NORMAL) {
+                        style = cell_style([ix, iy], global_cell_index, global_cell_count);
+                        if (style == _CELL_STYLE_NORMAL) {
                             at_edge = [iy == last.y, ix == last.x, iy == 0, ix == 0];
                             cell(
                                 cell_size, 
                                 connector=[for (direction = [0:3]) connector[direction] && at_edge[direction]], 
                                 bottom_chamfer_takes=[for (direction = [0:3]) at_edge[direction] && !connector[direction] ? max(0, bottom_chamfer[direction] - padding[direction]) : 0]
                             );
-                        } else if (cell_style == _CELL_STYLE_EMPTY) {
-                        } else if (cell_style == _CELL_STYLE_SOLID) {
+                        } else if (style == _CELL_STYLE_EMPTY) {
+                        } else if (style == _CELL_STYLE_SOLID) {
                             dim = [BASEPLATE_DIMENSIONS.x * cell_size.x, BASEPLATE_DIMENSIONS.y * cell_size.y];
                             translate([-dim.x/2, -dim.y/2, -_extra_height]) cube([dim.x, dim.y, _total_height]);
                         } else {
-                            assert(false, str("Unknown cell style: '", cell_style, "'"));
+                            assert(false, str("Unknown cell style: '", style, "'"));
                         }
                     };
                 };
@@ -1222,6 +1285,8 @@ module segment(trace=[[1], [1]], padding=[0, 0, 0, 0], connector=[false, false,
         translate([0, -size.y/2]) rotate([0, 0, 180]) horizontal_screws(_SOUTH, padding, trace = trace.x, connector = connector);
         translate([-size.x/2, 0]) rotate([0, 0, 90]) horizontal_screws(_WEST, padding, trace = trace.y, connector = connector);
         translate([size.x/2, 0]) rotate([0, 0, -90]) horizontal_screws(_EAST, padding, trace = trace.y, connector = connector);
+
+        if (hollow) segment_core(trace, size, padding, connector, global_cell_index, global_cell_count);
     }
 }