Lots of people struggle to get a Celtic Knot or simply don't have the tools. Here is a simple little homemade tool that gives a similar pattern. All it is, is a mini holesaw. Take a piece of steel rod, drill a hole down the middle, cut a short slot in it with a junior hacksaw then file each side at an angle. The wood sample may not look great because I filled the voids with silver glitter and it appears ragged. I am doing another one that I will post later.
The holesaw is about 6mm dia
First attempt in an off cut of Bocote
The holesaw is about 6mm dia
First attempt in an off cut of Bocote