Sources for cheap threadmill bits?

[Jlabine]

This is what i did
I used a grade 5 bolt (1 dollar)
Machined teeth onto it then heat treated it

[hfjbuis]

Start with outer threading. Use an old drill bit any size will do. Take a grinder or a dremel and cutoff disk. Flat the tip of the bit. Then grind the tip in 60°, tilt the tip a bit to get clearence. For the 60° make a holder, for the tilt make two holders (about 6°). stack the 3 together. You have to tilt from front to back for the nose clearance, You have to tilt from left to right/right to left for the left/right side.
For inner threading, the nose clearance should be larger. I do 16°.
Threading is not rocket science. Grinding tool bits is easy especially if you only have to grind flats.
For inner threading,

Below a small threading tool based on a 4.1 mm HSS rod, tip heated red, bend 90°, quenched in water, grinded using a dremel and holder made in MDF. Can do threads 7 mm and higher