I want to print worm gears for my robot arm. I would like to design it in FreeCAD. Normally, I would use involute gear for regular gears. However, this tool cannot be used for worm gears. I can't find any add-ons for this.
Is it possible to produce a worm gear automatically? If not, how can I make it manually?
As far as I know there is not a workbench capable of producing the design you want with a single click "new worm gear". But it is a rather simple affair to create the part you want from scratch.
What you want to do is to sweep a sketch along a helix. It is a very similar process to the one you would follow to create a thread documented in the official tutorial (it's the "method #3" on that page). This is how it should look like:
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Since helices are subject to a few limitation in FreeCAD, I recommend to read the section called "tricks to success" and the following tips, as it is very likely you will incur in problems otherwise.