Add parametric pivot mount assembly and welding jig

Introduces a fully parametric, replaceable pivot mount assembly for the loader arm, including new OpenSCAD modules for the assembly, arm plate slot, and bolt pattern. Updates arm plate and loader arm modules to support the new assembly, with non-uniform bolt spacing and proper clearances. Adds a 3D printed welding jig for accurate fabrication. All relevant parameters are centralized in lifetrac_v25_params.scad for consistency and easier modification.

Author: dorkmo

LifeTrac-v25/mechanical_design/openscad/3d_printed_welding_jigs/pivot_mount_welding_jig.scad

@@ -0,0 +1,286 @@
+// pivot_mount_welding_jig.scad
+// 3D Printed Welding Jig for Pivot Mount Assembly
+// Part of LifeTrac v25 OpenSCAD design
+//
+// This jig holds the two circular plates and DOM tube in proper alignment
+// during welding. It ensures:
+// - Correct spacing between plates (arm tube width)
+// - DOM tube centered on both plates
+// - Plates perpendicular to DOM tube
+// - Access for welding around the DOM-to-plate joints
+
+include <../lifetrac_v25_params.scad>
+
+// =============================================================================
+// JIG PARAMETERS
+// =============================================================================
+
+// Inherit from params file
+// JIG_WALL_THICKNESS = 4;   // Standard wall for 3D printed parts
+// JIG_CLEARANCE = 0.5;      // Fit clearance
+
+// Pivot mount dimensions (use params if available, else fallback)
+_JIG_PIVOT_PLATE_DIA = is_undef(PIVOT_MOUNT_PLATE_DIA) ? 152.4 : PIVOT_MOUNT_PLATE_DIA;
+_JIG_PIVOT_PLATE_THICK = is_undef(PIVOT_MOUNT_PLATE_THICK) ? PLATE_1_4_INCH : PIVOT_MOUNT_PLATE_THICK;
+_JIG_PIVOT_WIDTH = is_undef(PIVOT_MOUNT_WIDTH) ? TUBE_2X6_1_4[0] : PIVOT_MOUNT_WIDTH;
+_JIG_PIVOT_BOLT_CIRCLE_DIA = is_undef(PIVOT_MOUNT_BOLT_CIRCLE_DIA) ? 114.3 : PIVOT_MOUNT_BOLT_CIRCLE_DIA;
+_JIG_PIVOT_CLEARANCE = is_undef(PIVOT_MOUNT_CLEARANCE) ? 25.4 : PIVOT_MOUNT_CLEARANCE;
+
+// Jig dimensions
+JIG_BASE_THICK = 8;                     // Base plate thickness
+JIG_SUPPORT_HEIGHT = 30;                // Height of plate supports
+JIG_FINGER_COUNT = 6;                   // Number of support fingers around plate
+JIG_FINGER_WIDTH = 20;                  // Width of each support finger
+JIG_FINGER_THICKNESS = JIG_WALL_THICKNESS;
+
+// DOM alignment features
+DOM_CRADLE_DEPTH = 15;                  // How deep the DOM sits in cradle
+DOM_CRADLE_ANGLE = 120;                 // Arc angle of DOM cradle (degrees)
+
+// Clearance for welding access
+WELD_ACCESS_GAP = 25;                   // Gap between jig parts for welder access
+
+// =============================================================================
+// JIG BASE PLATE MODULE
+// =============================================================================
+
+module jig_base_plate() {
+    // Base plate that sits under the assembly
+    // Has cradle for DOM tube and supports for circular plates
+    
+    base_length = _JIG_PIVOT_WIDTH + _JIG_PIVOT_PLATE_DIA + 40;
+    base_width = _JIG_PIVOT_PLATE_DIA + 40;
+    
+    difference() {
+        union() {
+            // Main base plate
+            translate([-base_length/2, -base_width/2, 0])
+                cube([base_length, base_width, JIG_BASE_THICK]);
+            
+            // DOM tube cradle (V-shaped supports at ends)
+            // Left cradle
+            translate([-_JIG_PIVOT_WIDTH/2 - 10, 0, JIG_BASE_THICK])
+                dom_cradle_support();
+            
+            // Right cradle  
+            translate([_JIG_PIVOT_WIDTH/2 + 10, 0, JIG_BASE_THICK])
+                dom_cradle_support();
+        }
+        
+        // Cutout center for weight reduction and ventilation
+        translate([0, 0, -1])
+            cylinder(d=_JIG_PIVOT_PLATE_DIA - 60, h=JIG_BASE_THICK + 2, $fn=48);
+    }
+}
+
+// =============================================================================
+// DOM CRADLE SUPPORT MODULE
+// =============================================================================
+
+module dom_cradle_support() {
+    // V-shaped cradle to hold DOM tube at correct height
+    // DOM center should be at plate center height
+    
+    cradle_height = DOM_PIPE_OD/2 + DOM_CRADLE_DEPTH;
+    cradle_width = DOM_PIPE_OD + JIG_WALL_THICKNESS * 2;
+    
+    difference() {
+        // Outer block
+        translate([-15, -cradle_width/2, 0])
+            cube([30, cradle_width, cradle_height]);
+        
+        // DOM tube cutout (with clearance)
+        translate([0, 0, cradle_height])
+            rotate([0, 90, 0])
+            cylinder(d=DOM_PIPE_OD + JIG_CLEARANCE*2, h=50, center=true, $fn=48);
+        
+        // V-notch for easier tube placement
+        translate([0, 0, cradle_height + 10])
+            rotate([0, 90, 0])
+            cylinder(d=DOM_PIPE_OD * 1.5, h=50, center=true, $fn=48);
+    }
+}
+
+// =============================================================================
+// PLATE ALIGNMENT RING MODULE
+// =============================================================================
+
+module plate_alignment_ring(inner=false) {
+    // Ring that fits around the circular plate edge
+    // Holds plate perpendicular and centered
+    // Has gaps for welding access
+    
+    ring_id = _JIG_PIVOT_PLATE_DIA + JIG_CLEARANCE * 2;
+    ring_od = ring_id + JIG_WALL_THICKNESS * 2 + 10;
+    ring_height = _JIG_PIVOT_PLATE_THICK + JIG_SUPPORT_HEIGHT;
+    
+    // Support ledge for plate to sit on
+    ledge_height = JIG_SUPPORT_HEIGHT;
+    ledge_width = 8;
+    
+    difference() {
+        union() {
+            // Main ring
+            difference() {
+                cylinder(d=ring_od, h=ring_height, $fn=64);
+                translate([0, 0, -1])
+                    cylinder(d=ring_id, h=ring_height + 2, $fn=64);
+            }
+            
+            // Inner support ledge (plate sits on this)
+            translate([0, 0, 0])
+            difference() {
+                cylinder(d=ring_id, h=ledge_height, $fn=64);
+                translate([0, 0, -1])
+                    cylinder(d=ring_id - ledge_width*2, h=ledge_height + 2, $fn=64);
+            }
+        }
+        
+        // Welding access gaps (4 equally spaced)
+        for (i = [0:3]) {
+            angle = i * 90 + 45;
+            rotate([0, 0, angle])
+            translate([0, 0, ledge_height])
+                cube([ring_od + 2, WELD_ACCESS_GAP, ring_height], center=true);
+        }
+        
+        // Center hole for DOM tube (with clearance)
+        translate([0, 0, -1])
+            cylinder(d=DOM_PIPE_OD + JIG_CLEARANCE * 4, h=ring_height + 2, $fn=48);
+        
+        // Bolt hole clearances (so jig doesn't interfere with bolt holes)
+        for (i = [0:5]) {
+            angle = i * 60;
+            bx = (_JIG_PIVOT_BOLT_CIRCLE_DIA / 2) * cos(angle);
+            by = (_JIG_PIVOT_BOLT_CIRCLE_DIA / 2) * sin(angle);
+            translate([bx, by, -1])
+                cylinder(d=BOLT_DIA_1_2 + 5, h=ring_height + 2, $fn=24);
+        }
+    }
+}
+
+// =============================================================================
+// COMPLETE JIG ASSEMBLY MODULE
+// =============================================================================
+
+module pivot_mount_welding_jig_assembly(show_parts=true) {
+    // Complete jig showing all components
+    // Set show_parts=true to see the pivot mount parts in position
+    
+    color("Orange", 0.8) {
+        // Base with DOM cradles
+        jig_base_plate();
+        
+        // Left plate alignment ring
+        translate([-_JIG_PIVOT_WIDTH/2 - _JIG_PIVOT_PLATE_THICK, 0, JIG_BASE_THICK])
+        rotate([0, 90, 0])
+            plate_alignment_ring();
+        
+        // Right plate alignment ring
+        translate([_JIG_PIVOT_WIDTH/2, 0, JIG_BASE_THICK])
+        rotate([0, 90, 0])
+            plate_alignment_ring();
+    }
+    
+    // Show the parts in position
+    if (show_parts) {
+        // DOM tube cradle height
+        dom_z = JIG_BASE_THICK + DOM_PIPE_OD/2 + DOM_CRADLE_DEPTH;
+        
+        color("SteelBlue", 0.6) {
+            // DOM tube
+            translate([0, 0, dom_z])
+            rotate([0, 90, 0])
+            difference() {
+                cylinder(d=DOM_PIPE_OD, h=_JIG_PIVOT_WIDTH, center=true, $fn=48);
+                cylinder(d=DOM_PIPE_ID, h=_JIG_PIVOT_WIDTH + 2, center=true, $fn=48);
+            }
+            
+            // Left plate
+            translate([-_JIG_PIVOT_WIDTH/2, 0, dom_z])
+            rotate([0, 90, 0])
+            difference() {
+                cylinder(d=_JIG_PIVOT_PLATE_DIA, h=_JIG_PIVOT_PLATE_THICK, $fn=64);
+                cylinder(d=DOM_PIPE_OD, h=_JIG_PIVOT_PLATE_THICK + 1, $fn=48);
+            }
+            
+            // Right plate
+            translate([_JIG_PIVOT_WIDTH/2 - _JIG_PIVOT_PLATE_THICK, 0, dom_z])
+            rotate([0, 90, 0])
+            difference() {
+                cylinder(d=_JIG_PIVOT_PLATE_DIA, h=_JIG_PIVOT_PLATE_THICK, $fn=64);
+                cylinder(d=DOM_PIPE_OD, h=_JIG_PIVOT_PLATE_THICK + 1, $fn=48);
+            }
+        }
+    }
+}
+
+// =============================================================================
+// INDIVIDUAL PRINTABLE COMPONENTS
+// =============================================================================
+
+module jig_base_printable() {
+    // Base plate oriented for printing (flat on bed)
+    jig_base_plate();
+}
+
+module jig_ring_printable() {
+    // Alignment ring oriented for printing
+    // Printed standing up for strength
+    plate_alignment_ring();
+}
+
+// =============================================================================
+// EXPLODED VIEW FOR DOCUMENTATION
+// =============================================================================
+
+module pivot_mount_welding_jig_exploded() {
+    explode = 80;
+    
+    color("Orange", 0.8) {
+        // Base
+        jig_base_plate();
+        
+        // Left ring (exploded)
+        translate([-_JIG_PIVOT_WIDTH/2 - _JIG_PIVOT_PLATE_THICK - explode, 0, JIG_BASE_THICK])
+        rotate([0, 90, 0])
+            plate_alignment_ring();
+        
+        // Right ring (exploded)
+        translate([_JIG_PIVOT_WIDTH/2 + explode, 0, JIG_BASE_THICK])
+        rotate([0, 90, 0])
+            plate_alignment_ring();
+    }
+}
+
+// =============================================================================
+// RENDER PREVIEW
+// =============================================================================
+
+$fn = 32;
+
+echo("=== PIVOT MOUNT WELDING JIG SPECIFICATIONS ===");
+echo("Jig Base Thickness:", JIG_BASE_THICK, "mm");
+echo("Support Ring Height:", JIG_SUPPORT_HEIGHT, "mm");
+echo("Wall Thickness:", JIG_WALL_THICKNESS, "mm");
+echo("DOM Cradle Depth:", DOM_CRADLE_DEPTH, "mm");
+echo("Weld Access Gap:", WELD_ACCESS_GAP, "mm");
+echo("");
+echo("Parts to print:");
+echo("  1x Base plate");
+echo("  2x Alignment rings");
+
+// Show complete assembly with parts
+pivot_mount_welding_jig_assembly(show_parts=true);
+
+// Show individual printable parts below
+translate([0, -250, 0]) {
+    translate([-100, 0, 0])
+        jig_base_printable();
+    
+    translate([100, 0, 0])
+        jig_ring_printable();
+    
+    translate([100, 100, 0])
+        jig_ring_printable();
+}

LifeTrac-v25/mechanical_design/openscad/lifetrac_v25_params.scad

@@ -127,6 +127,81 @@ DOM_PIPE_ID = 38.1; // ID matching 1.5" pivot pin
 JIG_WALL_THICKNESS = 4; // Standard wall thickness for 3D printed jigs
 JIG_CLEARANCE = 0.5; // Clearance for fit
 
+// Tube bolt hole positioning
+TUBE_BOLT_INSET = 50.8;                 // 2" distance from tube edge to NEAREST bolt
+
+// =============================================================================
+// PIVOT MOUNT ASSEMBLY PARAMETERS
+// =============================================================================
+// Replaceable pivot mount assembly that slides into arm from bottom
+// Consists of 2 circular plates welded to a DOM tube section
+
+PIVOT_MOUNT_PLATE_DIA = 152.4;          // 6" = 152.4mm diameter circular plates
+PIVOT_MOUNT_PLATE_THICK = PLATE_1_4_INCH; // 1/4" plate thickness
+PIVOT_MOUNT_BOLT_COUNT = 5;             // Number of bolts per plate
+PIVOT_MOUNT_BOLT_DIA = BOLT_DIA_1_2;    // 1/2" mounting bolts
+PIVOT_MOUNT_BOLT_CIRCLE_DIA = 114.3;    // 4.5" bolt circle diameter
+
+// Slot position and NON-UNIFORM bolt spacing
+// Slot is at bottom (270°) for DOM to slide in from below
+// In arm plate coordinates: 0°=right (toward arm tip), 90°=up, 180°=left, 270°=down (toward slot)
+PIVOT_MOUNT_SLOT_ANGLE = 270;           // Angle where DOM slot is located (bottom)
+PIVOT_MOUNT_BOLT_SLOT_CLEARANCE = 127;  // 5" total arc clearance across slot for bolts (2.5" each side)
+
+// Calculate slot gap angle from clearance distance
+// Arc length = radius × angle(radians), so angle(deg) = clearance / radius × 180/π
+_pivot_bolt_radius = PIVOT_MOUNT_BOLT_CIRCLE_DIA / 2;  // 57.15mm
+PIVOT_MOUNT_SLOT_GAP_ANGLE = PIVOT_MOUNT_BOLT_SLOT_CLEARANCE / _pivot_bolt_radius * 180 / PI;  // ~50.9° for 2"
+
+// Non-uniform spacing: slot gap is larger, remaining bolts are closer
+// With N bolts: 1 slot gap + (N-1) regular gaps = 360°
+// regular_gap = (360° - slot_gap) / (N-1)
+_pivot_regular_gap = (360 - PIVOT_MOUNT_SLOT_GAP_ANGLE) / (PIVOT_MOUNT_BOLT_COUNT - 1);
+
+// Calculate bolt angles array
+// Two bolts flank the slot at: slot_angle ± half_slot_gap
+// Bolt A (CCW from slot): slot_angle - half_gap = 270° - 25.45° ≈ 244.55°
+// Bolt B (CW from slot):  slot_angle + half_gap = 270° + 25.45° ≈ 295.45°
+// Remaining bolts fill in with regular spacing going CCW from Bolt B
+_half_slot_gap = PIVOT_MOUNT_SLOT_GAP_ANGLE / 2;
+_bolt_A_angle = PIVOT_MOUNT_SLOT_ANGLE - _half_slot_gap;  // ~244.55° (lower-left, just before slot)
+_bolt_B_angle = PIVOT_MOUNT_SLOT_ANGLE + _half_slot_gap;  // ~295.45° (lower-right, just after slot)
+
+// Build array: start at Bolt B (after slot), go CCW around, end at Bolt A (before slot)
+PIVOT_MOUNT_BOLT_ANGLES = [
+    for (i = [0:PIVOT_MOUNT_BOLT_COUNT-1])
+        _bolt_B_angle + i * _pivot_regular_gap
+];
+// Result for 5 bolts: [295.45, 372.7, 449.9, 527.2, 604.4] = [295.45°, 12.7°, 89.9°, 167.2°, 244.4°]
+// Bolt 0 (295.45°) and Bolt 4 (244.4°) flank the 270° slot
+
+// Echo clearance info for verification
+echo("=== PIVOT MOUNT BOLT PATTERN ===");
+echo(str("Slot at: ", PIVOT_MOUNT_SLOT_ANGLE, "° (bottom of arm)"));
+echo(str("Slot gap: ", round(PIVOT_MOUNT_SLOT_GAP_ANGLE * 10) / 10, "° (", 
+         round(PIVOT_MOUNT_BOLT_SLOT_CLEARANCE * 10) / 10, "mm arc)"));
+echo(str("Regular gap: ", round(_pivot_regular_gap * 10) / 10, "°"));
+echo(str("Bolt flanking slot (CCW): ", round(_bolt_A_angle * 10) / 10, "° (lower-left)"));
+echo(str("Bolt flanking slot (CW):  ", round(_bolt_B_angle * 10) / 10, "° (lower-right)"));
+echo("All bolt angles (raw): ", PIVOT_MOUNT_BOLT_ANGLES);
+
+PIVOT_MOUNT_WIDTH = TUBE_2X6_1_4[0];    // Assembly width = arm tube width (50.8mm/2")
+PIVOT_MOUNT_DOM_LENGTH = PIVOT_MOUNT_WIDTH; // DOM tube length between plates
+PIVOT_MOUNT_CLEARANCE = 25.4;           // 1" clearance from plate OD to tube start
+
+// Weld parameters - torus (donut) shape at DOM-to-plate joints
+PIVOT_MOUNT_WELD_DIA = 6.35;            // 0.25" diameter of weld bead (torus cross-section)
+// Weld torus center is at DOM OD radius, so weld OD = DOM_OD + weld_dia
+PIVOT_MOUNT_WELD_OD = DOM_PIPE_OD + PIVOT_MOUNT_WELD_DIA;  // ~57.15mm
+
+// Slot cutout diameter = weld OD + 1/4" clearance
+PIVOT_MOUNT_WELD_SLOT_CLEARANCE = 6.35; // 0.25" clearance around weld in slot cutout
+PIVOT_MOUNT_SLOT_DIA = PIVOT_MOUNT_WELD_OD + PIVOT_MOUNT_WELD_SLOT_CLEARANCE;  // ~63.5mm
+
+// Calculate tube start offset from pivot center
+// Tube starts at: plate radius + clearance = 76.2 + 25.4 = 101.6mm
+PIVOT_MOUNT_TUBE_START = PIVOT_MOUNT_PLATE_DIA/2 + PIVOT_MOUNT_CLEARANCE;
+
 // Define ARM_MIN_ANGLE and ARM_MAX_ANGLE later after geometry is calculated
 // ARM_MIN_ANGLE = -ARM_GROUND_ANGLE;     // Lowest position (at ground)
 // ARM_MAX_ANGLE = 60;                     // Maximum raised position
@@ -323,7 +398,9 @@ _bend_rad = (180 - ARM_SHAPE_ANGLE);
 _geom_correction = _tube_offset * (sin(_bend_rad) - (1 - cos(_bend_rad)) / tan(_bend_rad));
 
 // Set Lengths
-ARM_OVERLAP = 76.2; 
+// ARM_OVERLAP defines how far the plate extends behind the tube start
+// Updated to account for 6" pivot mount plate + 1" clearance
+ARM_OVERLAP = PIVOT_MOUNT_PLATE_DIA/2 + PIVOT_MOUNT_CLEARANCE; // 76.2 + 25.4 = 101.6mm
 ARM_MAIN_LEN = _L_main_kinematic - ARM_OVERLAP + _geom_correction; 
 
 ARM_DROP_EXT = 80;