I'm lucky that my best friend is a machinist. He has milled down the length of several stems and quill adapters for me. That said they were all high quality, Nitto, Cinelli etc. You just have to make sure the milled angle is the same as the original and that new marks are made for minimum insertion based on the previous ones. Cutting the bolt and cleaning up the end is no big deal. On every one we did the wall thickness was measured and there was never a deviation.