FreeCAD threads: Five Ways to Fail, With Workarounds
Channel: Bradford Needham
Date: 18/02/2021

In this video I show five ways I've failed while making threads in FreeCAD 0.19, and how I've worked around those problems. TL;DR - you can watch the under-7-minute version that just tells you what do: https://youtu.be/wsfLP7pLsSg "How to Make Threads in FreeCAD 0.19 (the quick version)"

I've learned the hard way how to make threads in FreeCAD, from various projects I've designed and 3D printed. Some techniques in this video apply to any CAD application, but others are workarounds for FreeCAD's specific quirks and bugs.

I started from the FreeCAD tutorial text, https://wiki.freecadweb.org/Thread_for_Screw_Tutorial. Its "Method 3. Sweeping a vertical profile" is a good start, but I found it wasn't obvious how to avoid some of the issues it describes.

Index of this video:
00:00 Introduction: I'm using FreeCAD 0.19 pre from February 14, 2021.
00:39 Starting to make a thread.
07:09 Problem: the Helix isn't part of the Body I want to edit. Solution: Use a Shape Binder.
08:37 Problem: Sweep failed. Solution: Make the thread profile overlap with the cylinder wall.
10:23 Problem: Sweep failed. Solution: Make the thread profile shorter than the pitch, to avoid making a self-intersecting thread.
12:21 Problem: Sweep fails after Refine Shape. Solution: rotate the thread profile and helix to avoid the cylinder's seam.
15:38 Problem: Sweep still fails after Refine Shape. Solution: Reduce Helix height to cross the cylinder's seam only once.
18:21 Problem: Multiple turn threads fail. Solution: Make a one-turn thread and use a Linear Pattern Feature to duplicate it.
20:57 Problem: The Linear pattern fails after Refine Shape. Solution: Make a slightly-less than one turn thread to avoid a self-intersecting linear pattern.
23:42 Problem: A large-scale thread could fail to print. Solution: Make the thread's angles 45° or less from vertical.
25:49 Problem: I don't like the sharp edge of the thread. Solution: Make the thread profile a trapezoid.
28:25 The 3D printed result. Yay!