This is a template for making celtic or pictish knot patterns. I have attached a completed knot as an example.
The source software is Rhino 5 and I have attached the template file for you to play with. You can get an evaluation copy of Rhino for free for 90 days and the educational licenses are pretty reasonable after that. But you can get a lot done in 90 days.
To use the tool, drag and drop the 2D pattern and the corresponding 3D pattern across onto the grid. It is a bit clunky, but it allows you to visualise your pattern in 2D which is clear while you assemble the 3D knot. At the end I Boolean the 3D components together and export the whole pattern with 0.01mm resolution as a binary STL.
You can scale the complete pattern to you heart's desire to make it deeper or wider or whatever. I use scale 1D.
If you find this useful, I would appreciate a tip.