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Comment by DebtDeflation | Hacker News Reader

Was going to say. I graduated high school 33 years ago. Was one of the last cohorts that had wood shop and metal shop. It was fun, but even back then the tools and presses we used hadn't been relevant to industry for awhile. If you want shop to be relevant to modern industry you would need to teach robotics, CAD/CAM, CNC, 3D printing, etc.

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> If you want shop to be relevant to modern industry you would need to teach robotics, CAD/CAM, CNC, 3D printing, etc.

Uhh.. what? A CNC mill is, fundamentally, a mill. A CNC lathe is a lathe. You're not absolved from knowing how to use a manual lathe or a manual mill even if you use CNC machines all day long. Where do you develop an intuition for feeds, speeds, finishes, tolerances, etc if not by spending hours and hours doing it by hand?

A classic machinist apprentice task is to take a rough steel cube and make the sides flat and smooth using a hand file. That teaches you how steel behaves and can be worked. Life was slower a century ago.

High school students can learn CNC with smaller machine tools. There are little desktop CNC machines in the US$1000 range. You can cut aluminum, brass, and plastics, but not steel. They talk the same G-code as the big machines. You design jobs for them the same way you do for the big machines. At that scale you can usually avoid coolant, oily rags, oily chip disposal, and the general mess of a real machine shop.

Taking that lesson to its extreme you realize there's a rounding effect where seemingly no matter how carefully you hold the file, the edges of the face are cut down more than the center. To combat this you might discover you can use the end of the file (like the last tooth) as a scraper. You can use a gauge block and some blue ink to discover the high spots and repeatedly work them until it's flat. Congratulations! You've just discovered how to make a lathe bed.

I tried to learn machining on a CNC mill. it went ok, I guess. but I ruined a lot of tools, had to do a lot of polishing passes, and didn't really understand why my tolerances were so off. things like the flycutter mystified me, and using the boring head was deeply frustrating since it didn't have a tiny little servo. aligning the vice was something I dreaded, took me a good hour for some reason. 4 jaw chuck? maybe you use that if you need to drill off center or work on square stock.

couple of decades later I only use manual machines (with power feeds and DROs), and I'm really a lot faster and more consistent.

CNC is cool, and you can do some pretty amazing things e.g. with a 4 or 5 axis machine, but ultimately the value is in repeatably churning out the same part over and over again. The industrial utility is obvious, but there's not a lot of pedagogical utility and to a hobbyist or prototyper it's generally just not worth the overhead.

I learned CNC by hand writing G code. I think it was valuable.

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