Homemade Dovetail Cutter, Not so Great

 Made an "insert" dovetail cutter over the past two days, just an hour or two a day of course. The shank was turned 3/8" diameter, drilled and tapped 10-32 UNF for a set screw. The set screw is threaded in and locktited in place, with about 1/8" of it sticking out. The cutter insert then screws onto the set screw sticking out.

Why did you use a set screw instead of simply single point threading the end? If I single pointed this very short thread, I would be relying on the low quality "cheese grade" a36 hot rolled steel to hold the insert.With a hardened steel screw, it's much stronger. It also eliminates the need for a thread relief, making the attachment even stronger.

Why did you make an insert tool and holder, instead of buying some O1 rod online and making a solid tool? I think the better question is "Why are you asking yourself questions in third-person on a longer-than-needed blog article about something that failed in the first place?"

Because I didn't have any rod on hand, only rectangle plate.

 The teeth were first broached on the lathe above center, to give the effect of positive rake when the tooth tip reaches center line. I then finished by milling it true, so all the teeth were square and Kosher. I only rough indexed them on the lathe. After the teeth were cut, I went back to the lathe for ideal work holding, and gave the teeth some edge relief using a triangular file. I stayed just a hair away from the edge, and just a little filing is needed.

 The insert, is made from O1, or what I thought was O1. Heat treated twice, red hot on the stove and quenched in motor oil. I made a tin foil "kiln" for it to keep the heat in best I could. I then stoned the bottom and tempered it light straw. Some more stoning on the bottom and it wad ready to test. Since I gave it some end relief on the lathe, the stone only touched the teeth on the bottom. That's okay. I did not stone the teeth, It felt sharp enough, and as you can see in the video, it cut aluminum very well. I didn't even remove the oxide scale, so it's still a very pretty blue/black. As long as it looks good, right?

 Here are some pictures and the short, shaky video showing it on aluminum. After I turned the camera off I tried some mild steel, and the teeth just wore off. Maybe it wasn't O1 after all! I can always re-anneal it, turn it to a smaller diameter, file more edge relief, and re-harden and temper and keep it just for aluminum.

Note these pictures were taken after the tips were destroyed.

I'm still not sure why I wrote such a long article on this, but I did, so thanks for reading!