threadlib: An OpenSCAD repository from mjstn

threadlib is a library of standard threads for OpenSCAD. It is based on Helges excellent threadprofile.scad to create nice threads with lead-in / lead-out tapers. Check out his article on generating nice threads on Hackaday.

In contrast to other thread libraries such as openscad-threads, yet another thread library, threads for screws and nuts V1, and threading.scad, threadlib does not make you look up diameters and pitches and maybe even thread-profiles in tables and norms: It has these tables built in.

Creating a thread is as simple as

use <threadlib/threadlib.scad>
thread("G1/2-ext", turns=10);

to create a British Standard Pipe parallel external thread.

Why you may want to use threadlib

really easy to use
creates nice threads
configurable higbee arc
creates working threads (clearances are left for production tolerances)
flexible:
- choose the $fn you need to fit the rest of your design
- let threadlib tell you the thread specs so you can do with them what you want
extensible: Add your own threads
tried and tested in the real world: Well, partly. Given the sheer number of threads, this is only possible with your help! Any feedback regarding working (or not working) threadlib-threads is appreciated.

Installation

Prerequisits:

Save all of these into your OpenSCAD library folder

threadlib:

Clone threadlib into the folder 'threadlib' inside your OpenSCAD library folder

Your libraries folder should now look similar to this:

libraries
├── list-comprehension-demos/
├── scad-utils/
├── thread_profile.scad
└── threadlib/

Usage

Before you start: threadlib is designed in millimeters (not meters, not inches). Make sure that your units are set accordingly or scale the output of threadlib to match the units you use in your project!

To create a bolt (without head) with 5 turns of M4 thread:

bolt("M4", turns=5, higbee_arc=30);

See these nice lead-in / lead-out tapers? Try a nut (this time using the default argument for higbee_arc):

nut("M12x0.5", turns=10, Douter=16);

Note that for a nut you also have to specify an outer diameter. The inner diameter is implicitly given by the thread designator ("M12x0.5" in this case).

To make a threaded hole (e.g. in a plate), an intuitive approach would be to create the difference of the plate and a bolt. However, this part would not work well in practice: You need a little space around the bolt to avoid collisions. threadlib's solution is to provide the tap module:

tap("G1/2", turns=5);

The tap shown above is intended for use like this and has accounted for the allowances needed in practice. Also, it will create the tapers:

difference() {
     part_to_be_tapped_here();
     tap("G1/2", turns=5);
}

Make sure that the tap extends a tiny bit out of the part to be tapped. Otherwise, you will end up with infinitely thin artifacts covering the entrance of your tapped hole.

If you only need the threads alone:

thread("G1/2-ext", turns=5);

(Note: You need to specify whether you want internal ("-int") or external ("-ext") thread here.) Then, add the support you want. In the simplest case, a cylinder (which is what nut(...) uses):

specs = thread_specs("G1/2-ext");
P = specs[0]; Rrot = specs[1]; Dsupport = specs[2];
section_profile = specs[3];
H = (5 + 1) * P;
translate([0, 0, -P / 2])
    cylinder(h=H, d=Dsupport, $fn=120);

Here, we have used the function thread_specs(...) to look up the threads specifications - including the recommended diameter of the support structure.

List of supported threads

Currently, threadlib knows these threads:

Metric threads (coarse, fine, and super-fine pitches) M0.25 to M600.
Unified Inch Screw Threads (UNC, UNF, UNEF, 4-UN, 6-UN, 8-UN, 12-UN, 16-UN, 20-UN, 28-UN, and 32-UN). All threads are class 2 threads.
BSP parallel thread G1/16 to G6. All threads are class A threads.
PCO-1881 (PET-bottle thread)

Extensibility

Don't find some of the threads you need for your project? Don't worry: You can add your own:

use <threadlib/threadlib.scad>

MY_THREAD_TABLE = [
                   ["special", [pitch, Rrot, Dsupport,
                   [[r0, z0], [r1, z1], ..., [rn, zn]]]]
                   ];

thread("special", turns=15, table=MY_THREAD_TABLE);

Care to share? Safe others from repeating the valuable work you have already accomplished and get the fame you deserve: Send in your tried and tested threads for addition to threadlib! See Design of Threadlib for help on how to hack your own thread as shown above and Creating Thread Specs for an introduction on how to contribute entire thread classes to threadlib.

Still reading?

If you read this far, you're probably not here for the first time. If you use and like threadlib, would you consider giving it a Github Star? (The button is at the top of this website.)

Change Log

0.4: PCO-1810. tap module. Fixes bug with $fn in straight_thread(). Lists metric threads under short designator and full designator.
0.3: Unified Inch Screw Threads (UNC, UNF, UNEF, 4-UN, 6-UN, 8-UN, 12-UN, 16-UN, 20-UN, 28-UN, and 32-UN. Fixed problem with PCO-1881-int. Fixed problem with G-ext threads. New build system.
0.2: Metric threads, PCO-1881
0.1: Initial release supporting BSP parallel thread

mjstn/threadlib