From 2021b75cebcf239010e28df8e9483101fdd8eb33 Mon Sep 17 00:00:00 2001
From: Bryan Varner <1652015+bvarner@users.noreply.github.com>
Date: Wed, 8 Jul 2020 11:02:22 -0400
Subject: [PATCH] In trying to convert some of my existing openscad projects
 over to this module I ran across the mental block of adding interior threads
 to a pre-cut hollow, which broke my brain a bit.

I find it more natural to think of adding a threaded hole to a solid as a 'tap' or difference() operation, rather than differencing a hollow and then adding interior threads to it.

For this reason I've created the, `tap(...)` module, which creates a positive of the internal threads suitable for differencing to produce a threaded tap hole.
---
 threadlib.scad | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/threadlib.scad b/threadlib.scad
index 132efb5..b94a08a 100644
--- a/threadlib.scad
+++ b/threadlib.scad
@@ -62,3 +62,17 @@ module nut(designator, turns, Douter, higbee_arc=20, fn=120, table=THREAD_TABLE)
             };
     };
 };
+
+module tap(designator, turns, higbee_arc=20, fn=120, table=THREAD_TABLE) {
+    difference() {
+        specs = thread_specs(str(designator, "-int"), table=table);
+        P = specs[0]; Dsupport = specs[2];
+        H = (turns + 1) * P;        
+
+        translate([0, 0, -P / 2]) {
+            cylinder(h=H, d=Dsupport, $fn=fn);
+        };
+        
+        thread(str(designator, "-int"), turns=turns, higbee_arc=higbee_arc, fn=fn, table=table);
+    };
+}