That old machinist who told me to quit chasing tenths on rough parts

Ngl I was at a job shop in Cleveland last month and this guy in his 60s watched me spend 10 minutes trying to dial in a dimension to within 0.0002 inches on a raw aluminum block. He just laughed and said 'kid you're fighting the material, not the machine.' I thought he was just old school but he showed me how the stock itself had internal stress and would move after I cut it. Honest to god I checked the part 20 minutes later and it had shifted by 0.001 inches on its own. Made me realize I was wasting time chasing numbers that were never gonna hold. Has anyone else had a veteran machinist drop some wisdom that totally changed how you approach a setup?

3 comments

3 Comments

lisab321d agoMost Upvoted

Rough it hot, let it cool, then take your finish pass.

kimblack1d ago

Wait, the part actually moved by itself after you cut it? That's wild, I never knew the material could change shape like that just from sitting.

dianawilson1d ago

Kimblack, you're right that it's wild when that happens, but it's actually pretty common with certain metals. If you don't stress relieve a part after rough machining, the internal tension can twist it like a pretzel once you break through the surface. Best thing you can do is rough it, heat treat it, then finish cut.