I'm a machinist. Currently working in a pretty large operation.
I'm running a small Okuma MX45VAE three axis cnc vertical machining center (mill). I do exclusively hard milling on heat treated A2, D2, and S7 tool steel parts. These parts are 54-58 Rockwell and chew up the tooling.
About half of my work I finish, mostly thread milling and helical milling slip fit dowel holes (+/- .002", +.005"/-0, etc). The other half of my work is "semi-finishing" parts for the jig grinder, which finish the press fit dowel holes +.0002"/-0.
I have to hold parts to pretty tight locational tolerances however. +/-.0002" very common, occasionally +/-.0005" or +/-.002".
Each part usually takes more time to indicate than run. In a production setting this gets tedious. I have only worked in job shops in the past, with a much wider variety of work, so this is a change.
For example, parts I ran today are precision ground adapter discs. They have a variety of different types of holes in a circle, dowel holes, tapped holes, counterbored holes, etc. I first put an undersize gage pin in my drill chuck, and lower it into hole I will cut, which roughly clocks the part. The part is unclamped and against stops, just move til the pin drops.
I then screw in two widgets called thread locators into two tapped holes (assuming they will thread in, threads do weird stuff in heat treat, thats why I have an assortment of carbide taps). These locators have a threaded end, a small knurled ring, and then a small precision ground post that lets you accurately indicate tapped holes. I indicate these posts alternately and give the part small taps until posts are on location within .005", and then I clamp the part down.
Then get a different indicator and pick up the datum (usually a ground ID or OD) and try to get as close to dead nuts as I can. The best I've seen is about .0001" TIR, I don't know if the grinders can do any better. Set that point as zero, and hit cycle start. Then 5 minutes later...do it again.
Pardon the rambling.
