Skip to bottom for short and sweet version about the rotor material and drilling tips.
I talked to one of the machinists at work about helping me plot my drill pattern, and he naturally asked about the material I was looking to drill. I explained that no one really knew what it was, but it was some sort of stainless steel. He then told me that stainless steel has high heat retention, so he thought it was odd that they used it and said it's probably low quality. I told him that it was, because it was stainless, but it was also magnetic. This made something click for him, and he told me that it's probably what they call a "hardenable stainless", it can be heat treated and annealed. This made a lot of sense to me because a lot of people have had varying results while trying to drill the rotors, and this would explain why. The people with the correct tools and knowledge have an easy time of it because they know and can control exactly what they are doing. The average person doesn't have access to that stuff and ends up doing it incorrectly. He said you should be at like 350rpm while drilling this stuff, otherwise you are just going to end up work hardening(heat treating and hardening the rotor with the drill bit) the hole you are trying to drill, and then you have to try to drill hardened stainless, which is extremely difficult. He told me what alloy he thought it was, but I didn't catch it.
Talking to a machinist, the material is probably what they call a "hardenable stainless". Martensitic stainless is what I think the actual name is. I did not catch exactly what alloy he thought it was. He suggested about 350rpm for a drilling speed. If your RPMs are too high, you can harden the material in the hole you are trying to drill, which makes it MUCH harder to drill. He also said that stainless retains a lot of heat, which means that drilling holes the same size, or smaller then the thickness of the rotor would be beneficial because it creates more surface area(the walls of the hole), therefore promoting cooling
