/* ================================================================
   Cable Grommet for Sheet Metal  —  TPU Print
   ================================================================
   Protects cable insulation from sharp drilled-hole edges.
   
   The grommet body fits inside the drilled hole while the two
   flanges seat flush against each face of the sheet metal,
   creating a smooth, rounded channel for the cable.

   INSTALLATION:
     Squeeze / fold the grommet (TPU flexibility makes this easy)
     and press it through the hole until both flanges snap flat
     against the sheet metal on each side.

   TIPS FOR TPU PRINTING:
     - 3–4 perimeters / walls for durability
     - 20–40% infill
     - No supports needed (prints flat on bottom flange)
     - Slow print speed recommended (≤ 30 mm/s) for clean bridges
   ================================================================ */


// ================================================================
//  USER PARAMETERS — edit these to match your application
// ================================================================

// Diameter of the hole drilled in the sheet metal (mm)
hole_diameter = 13;

// Thickness of the sheet metal (mm)
sheet_thickness = 1;

// Thickness of the grommet body wall (mm)
//   This directly sets how large the cable hole is:
//     cable hole = hole_diameter - 2 x wall_thickness
//   Decrease to widen the cable hole; increase to narrow it.
wall_thickness = 2.0;

// How far each flange lip extends beyond the hole edge (mm)
//   Larger value = more grip on the sheet metal.
flange_lips_overhang = 2.0;

// Thickness of each flange lip (mm)
flange_lips_thickness = 2.0;

// Chamfer radius at each cable entry/exit (mm)
//   This is the most important feature for insulation protection.
//   The chamfer creates a smooth funnel so the cable never contacts
//   a sharp edge even under vibration or flex.
cable_chamfer = 0;


// ================================================================
//  RENDERING QUALITY
// ================================================================
$fn = 128;


// ================================================================
//  DERIVED VALUES  (do not edit below this line)
// ================================================================
_body_d    = hole_diameter;
_flange_d  = hole_diameter + (2 * flange_lips_overhang);
_cable_d   = _body_d - (2 * wall_thickness);
_body_len  = sheet_thickness;
_total_h   = (2 * flange_lips_thickness) + _body_len;

// Sanity-check echoes (visible in OpenSCAD console)
echo(str("=== Cable Grommet Summary ==="));
echo(str("  Body outer diameter : ", _body_d,   " mm"));
echo(str("  Flange diameter     : ", _flange_d, " mm"));
echo(str("  Cable hole diameter : ", _cable_d,      " mm"));
echo(str("  Wall thickness      : ", wall_thickness, " mm"));
echo(str("  Total height        : ", _total_h,       " mm"));
if (wall_thickness < 1.5) {
    echo("  WARNING: Wall thickness is thin — consider increasing wall_thickness.");
}
if (_cable_d <= 0) {
    echo("  ERROR: wall_thickness is too large — cable hole is zero or negative.");
}
if (cable_chamfer > flange_lips_thickness) {
    echo("  WARNING: cable_chamfer is larger than flange_lips_thickness — chamfer will be clipped.");
}


// ================================================================
//  MODULE
// ================================================================
module grommet() {
    difference() {

        // ── OUTER SHELL ──────────────────────────────────────────
        union() {
            // Bottom flange
            // Wider at the sheet metal face, narrower at the outer (free) face.
            cylinder(d1 = _flange_d - 1.5, d2 = _flange_d, h = flange_lips_thickness);

            // Body — the section that lives inside the drilled hole
            translate([0, 0, flange_lips_thickness])
                cylinder(d = _body_d, h = _body_len);

            // Top flange
            // Wider at the sheet metal face, narrower at the outer (free) face.
            translate([0, 0, flange_lips_thickness + _body_len])
                cylinder(d1 = _flange_d, d2 = _flange_d - 1.5, h = flange_lips_thickness);
        }

        // ── CABLE BORE ────────────────────────────────────────────
        // Straight through-hole for the cable
        translate([0, 0, -0.01])
            cylinder(d = _cable_d, h = _total_h + 0.02);

        // ── BOTTOM ENTRY CHAMFER ──────────────────────────────────
        // Smooth funnel on the side the cable enters from.
        translate([0, 0, -0.01])
            cylinder(
                d1 = _cable_d + (2 * cable_chamfer),
                d2 = _cable_d,
                h  = cable_chamfer + 0.01
            );

        // ── TOP EXIT CHAMFER ──────────────────────────────────────
        // Mirror chamfer on the other side — equally important when
        // the cable flexes back toward the sheet metal.
        translate([0, 0, _total_h - cable_chamfer + 0.01])
            cylinder(
                d1 = _cable_d,
                d2 = _cable_d + (2 * cable_chamfer),
                h  = cable_chamfer + 0.01
            );
    }
}


// ================================================================
//  RENDER
// ================================================================
grommet();