[EricH]

Originally Posted by Boe

i guess... we have a manuel mill though so it would have been alot harder

Nah, not a lot harder. Just means you have to take a bit more time and care, that's all.

Here's a CNC comparison of tolerances. I'm speaking for a shop at my college here, but the absolute best they can get out of a high-quality 3D printer is a .007" print head (at least, with what they have), but they typically run a .010" head. Figure at least .0035" of "slop" with the smaller head. The CNC machines can go to .002".

Now, let's say I'm on a manual mill. I can't consistently get to .002" of tolerance--nowhere near enough practice. But I can hold .010" just fine; more than likely I can hit .005" without too much stress. And that's me--I have limited mill experience, and I'm a bit rusty. A shop teacher who's been doing this for years could probably hit the .005" just about every time it's needed, and tighter if absolutely needed.

Of course, the "if needed" part begs the question: How tight does your tolerance really need to be? .100"? .010"? .005"? .002"? Tighter? Looser? And that's not a question that is easily answered. Just trust me on that one. I had to wrestle through that on more than one occasion this last semester. And only on a couple of parts...