Building the most accurate DIY CNC lathe in the world [video]

This guy is quite interesting, because he starts from scratch without reading or experience, so you end up with a really wonky machine, but it's wonky in unusual ways that really make you think. Like the sibling comment says, it's obvious he hasn't read the Gingery books. This sounds like I'm throwing shit, but I'm not - it's actually how I work a lot of the time. Making a mistake gives you a deeper understanding of the issue than you would typically get from doing things the right way. For example, he overheated the gravers while sharpening them, which made them soft, and now he gets to learn about annealing and temper. And indeed, in the comments, he gets:

>Just for future reference on making gravers, you were correct that you do not want to get the pre-hardened steel red hot or it will lose its heat treatment. However you have to go much further than that and not allow it to heat above the desired temper temperature. For instance if it was previously tempered to a straw (yellowish brown) color but then while grinding it the steel turns blue, that means you have reduced the temper to a lower hardness. So you need to keep the steel cool and never let the temperature go beyond the desired temper temperature. You can think of it this way, hardening the steel makes it as hard as it can get (but too brittle to be good for much), then tempering reduces the hardness but makes it stronger, and this effect continues the hotter you temper it.

n.b. this sort of thing is absolutely endemic in the world of 3D printing, which is why most videos are fairly useless to learn from, but the comments are invaluable.