That's a good analogy. Essentially project to surface moves the selected geometry in a straight line towards a surface until all points of the geometry make contact with that surface. Looking at the profile of a cylinder creates a rectangular boundary. Any geometry that lies within the boundary will project down to the visible half of the cylinder without issue. Anything lying outside that boundary will not project to the cylinder, because when moving in a straight line it'll never touch the cylinder.

I guess I'm somewhat immune to this since I machine HPDC parts and we have our own foundry and die casting in-house. Customers send us a cast and machined models. We source dies for the customer, to ensure they fit our die casting machines and verify them once they arrive. If any cast features are out of spec. when we PPAP the parts the whole die goes back to the manufacturer to be fixed or replaced. As dies age, they will inevitably get less consistent, but we run in-process CMM checks on every part. If we see dimensions going out of spec. we will stop production and pull the die out to repair it. We do simple repairs in-house. and major repairs go back to the manufacturer. We try to make sure the parts are good throughout the process and not just when they leave our dock.

If SwiftCarb doesn't have anything standard you can use, TMA Tools is a small manufacturer that specializes in custom tools. I've been using them for almost 4 years now, mostly for double-margin drills, but whenever I stop by I see racks of endmills in process for a local transmission manufacturer. They're website isn't much to look at, but they're reasonably priced and decent lead times for custom tools.

The class at the tech. school was Hand Tool Operations, the most useless class I have ever taken. The apprenticeship however wasn't just for machining, it was a tool and die apprenticeship. My first three months I didn't touch a machine manual or CNC with the exception of a bandsaw to cut my stock, and I think it's exactly how the apprenticeship should've been. Those three months weren't about teaching me anything, it was to show our instructor who we were as students. We were a team of six apprentices, not because they needed six, but because they never expected all of us to make it. The first task we were given was to use a hacksaw and cut shims out of 1080 hot rolled C-channel. Each shim had to be 2mm thick +/-0.5mm. We had to continue cutting shims until we had 3 that were within spec. It served no purpose other than demonstrating who really wanted it. Who was determined and who had a good work ethic. The company is headquartered in Germany and as far as I know that plant still teaches their apprentices the same way, and I had heard from many of the Germans at that plant, that the apprenticeship in Germany was more difficult and even included learning how to hand scrape machine ways. I apprenticed in 2011, I didn't have to weld my own blade, but when I was finally allowed to use the lathe I had to grind my own tools first.

This is the post that finally gets me to stop lurking and actually comment. As I read this, I was reminded of the time when I was an apprentice tool and die maker. The company I worked for was, on top of the apprenticeship, also sending me to tech. school for programming and mechatronics in the evening. One evening I was at school and we were working on a project, if you can call it that, where had to take a piece of 1018 square stock, and file the edge cut by the bandsaw until it was flat and square to the sides. A teacher, who wasn't even teaching this class, decided to share his expertise on filing with us. He proceeded to show the class how to "saw horse" file. I told him that my apprenticeship instructor told me that saw horse filing is an improper technique and he took me to his office which was near the machining area and actually took his engineering degree off the wall and shoved it in my face yelling at me. Saying that he graduated top of his class with honors and that he wasn't going to be disrespected by some kid he was just trying to "help out". I was so dumbfounded by the situation I didn't even know what to say, so I just turned and walked out of his office.