Parametric Adapter

// ============================================================================
//  Adapter: 3/4" GHT Female  →  1/2" NPT Male
//  Units: millimeters
//  Library: BOSL2  (https://github.com/BelfrySCAD/BOSL2)
// ============================================================================
//  Install BOSL2 into your OpenSCAD libraries folder, then open this file.
//  Preview with F5; render with F6.  Enable "thrown-together" view to inspect
//  internal threads and the gasket seat.
// ============================================================================

include <BOSL2/std.scad>
include <BOSL2/threading.scad>

$fn = $preview ? 72 : 144;

// ── Scale helpers ──────────────────────────────────────────────────────────
IN = 25.4;

// ─── 3/4" GHT (Garden Hose / 3/4-11.5 NH) ──────────────────────────────────
// Straight thread.  Female receives a standard male garden-hose coupling
// and seals on a flat washer seat below the threads.
GHT_MAJOR     = 1.0625 * IN;   // 26.9875 mm – nominal major diameter
GHT_PITCH     = IN / 11.5;     // ≈ 2.209 mm  (11.5 TPI)
GHT_THREAD_L  = 12.5;          // usable female thread depth
GHT_SEAT_H    = 3.0;           // solid washer-seat land under the threads
GHT_OD        = 32.0;          // outer diameter of the female socket
GHT_ENTRY_CH  = 1.5;           // lead-in chamfer depth at the open end

// ─── 1/2" NPT Male ─────────────────────────────────────────────────────────
// Tapered National Pipe Thread.  BOSL2 encodes the 1:16 taper, TPI, and
// major diameter for standard pipe sizes.
NPT_SIZE      = 1/2;           // nominal size passed to npt_threaded_rod()
NPT_LEN       = 15.0;          // external thread length (typical engagement ≈ 13 mm)

// ─── Body / wrench flats ───────────────────────────────────────────────────
HEX_AF        = 27.0;          // hex across-flats (≈ 1-1/16")
HEX_H         = 9.0;           // hex section height
BORE          = 15.5;          // through-bore ≈ schedule-40 1/2" ID
BORE_CHAMFER  = 1.2;           // entry chamfer on both open ends

// ─── Derived layout (Z builds upward from the NPT tip) ─────────────────────
Z_NPT_TOP     = NPT_LEN;
Z_HEX_TOP     = Z_NPT_TOP + HEX_H;
Z_GHT_BOT     = Z_HEX_TOP;                       // GHT body starts on top of hex
Z_SEAT        = Z_GHT_BOT + GHT_SEAT_H;           // washer-seat face (Z of seat plane)
Z_GHT_TOP     = Z_SEAT + GHT_THREAD_L;            // open mouth of female GHT
TOTAL_H       = Z_GHT_TOP;

// ============================================================================
//  Adapter
// ============================================================================
module ght_npt_adapter() {
    difference() {
        // ── Outer solid ────────────────────────────────────────────────────
        union() {
            // Male 1/2" NPT (tapered external threads, tip at Z=0)
            npt_threaded_rod(
                size   = NPT_SIZE,
                l      = NPT_LEN,
                bevel1 = true,       // lead-in bevel at the tip
                bevel2 = false,
                anchor = BOTTOM
            );

            // Hex wrench section
            up(Z_NPT_TOP)
                linear_extrude(height = HEX_H)
                    hexagon(id = HEX_AF);

            // Female socket cylinder (GHT outer body)
            up(Z_GHT_BOT)
                cyl(d = GHT_OD, h = GHT_SEAT_H + GHT_THREAD_L, anchor = BOTTOM);

            // Small blend under the socket (helps print orientation / strength)
            up(Z_HEX_TOP)
                cyl(d1 = HEX_AF * cos(30) * 0.95, d2 = GHT_OD, h = 1.5, anchor = BOTTOM);
        }

        // ── Through-bore ───────────────────────────────────────────────────
        cyl(d = BORE, h = TOTAL_H + 2, anchor = BOTTOM);

        // Bore entry chamfer – NPT end
        up(-0.01)
            cyl(d1 = BORE + 2 * BORE_CHAMFER, d2 = BORE, h = BORE_CHAMFER + 0.01, anchor = BOTTOM);

        // Bore exit chamfer – GHT seat (also helps define the washer ID)
        up(Z_SEAT + 0.01)
            cyl(d1 = BORE, d2 = BORE + 2 * BORE_CHAMFER, h = BORE_CHAMFER, anchor = TOP);

        // ── Internal 3/4" GHT thread ───────────────────────────────────────
        // Thread starts above the washer seat.  A slight extra length guarantees
        // a clean cut through the open end of the body.
        up(Z_SEAT - 0.05)
            threaded_rod(
                d           = GHT_MAJOR,
                l           = GHT_THREAD_L + 1.0,
                pitch       = GHT_PITCH,
                internal    = true,
                blunt_start = true,
                bevel       = false,
                anchor      = BOTTOM
            );

        // ── Lead-in chamfer at the female mouth ────────────────────────────
        up(Z_GHT_TOP + 0.01)
            cyl(
                d1 = GHT_MAJOR + 0.4,
                d2 = GHT_MAJOR + 0.4 + 2 * GHT_ENTRY_CH,
                h  = GHT_ENTRY_CH + 0.01,
                anchor = TOP
            );

        // Slight relief under the seat thread start so the first thread
        // doesn't crash into a hard shoulder (helps mate with male GHT).
        up(Z_SEAT)
            cyl(d = GHT_MAJOR - 1.6, h = 0.8, anchor = BOTTOM);
    }
}

// ============================================================================
//  Optional dimensional tags (preview only)
// ============================================================================
module _label(txt, pos, ang = [90, 0, 0]) {
    if ($preview)
        translate(pos)
            rotate(ang)
                color("DarkSlateGray")
                    linear_extrude(0.3)
                        text(txt, size = 2.2, halign = "center", valign = "center");
}

// ============================================================================
//  Build
// ============================================================================
ght_npt_adapter();

// Dimension callouts (visible in preview, ignored in STL)
_label("1/2\" NPT M",  [0, -HEX_AF/2 - 3, NPT_LEN/2], [90, 0, 0]);
_label("3/4\" GHT F",  [0, -GHT_OD/2 - 3, (Z_SEAT + Z_GHT_TOP)/2], [90, 0, 0]);
_label(str("H≈", TOTAL_H, " mm"), [HEX_AF/2 + 4, 0, HEX_H/2 + Z_NPT_TOP], [90, 0, 90]);