Rich
How about showing us how you make them
The only trick is finding a triangular file of the right size. Small but not needle file size.
Clamp it in the vise with some sticking out and snap off any extra length with a hammer.
Heat it to orange with a torch in a little brick cubby and back the torch off slowly, allowing it to turn black. Keep the torch on it backing off slowly. The slower temp drop will help anneal it.
File or grind the teeth completely off. Square up the end. Decide which flat will be the top flat.
Clamp in the vise with the tip pointing right at you. Now take another triangular file and file a V trough in the top flat. Keep it straight. Now this is a half hour job. Take your time. Use magnification. Look at the face and see if your v trough is even relative to the sides of the v file. The v trough you are filing tapers and is widest and deepest at the face.
Unless you do a great job of filing the v trough the parting tool will be lousy. Any irregularities of the v trough at the face will make it impossible to sharpen it well and get a clean cut. The V trough is the whole key to a good parting tool.
After filing you want to polish the v trough. Pick your poison. A triangular stone will work as will a stick filed into a triangle and loaded with fine grit polishing compound.
Ok let’s say you’ve got the v trough done such that there’s about 0.030” of “wall” to the edge of the file. It’s a V with the walls 0.030” wide. Now you need to file the heel. Basically mark about 1/8” back from the edge and file from there to the face under magnification. Leave a smidge of thickness to sharpen after hardening and tempering.
Now you will see that the trough is slightly rounded at the bottom. It’s not a perfect v. You have to file the sides AND the bottom of the tool to establish the edge.
LRB is right- one can do much better. But now I heat the front 2” of the tool to orange and quench in brine. I wash it off, polish it in and out, and stick it in the oven at 450 degrees for an hour and turn the oven off.
When it’s cool, I clean it and put a handle on it and sharpen it. Below is one of my tools plus a couple small triangular files. One is too big in my opinion.
Of course some folks are used to a different size or length and this would not work for them.