Old timer told me my speeds were way off on a stainless job

Been running CNC mills for about 4 years now and always thought I had a decent handle on feeds and speeds. Last month I was machining some 304 stainless for a medical parts order and kept getting terrible surface finish and tool chatter. A guy who's been running machines since the 80s walked by, looked at my program, and said I was running the spindle way too fast for that diameter end mill. He told me to drop my RPM from 4000 down to 1800 and bump up the feed rate by about 20%. I figured he was just old school and wrong, but I tried it on a test part and the finish came out glass smooth with no vibration at all. Never realized how much I was leaving on the table by just trusting default speeds from the CAM software. Has anyone else had an old school machinist bust your assumptions about something you thought you knew?

2 comments

2 Comments

michael6931mo ago

Ain't that just trusting your gut over a calculator though?

henryreed1mo ago

More like trusting my gut over a calculator that's been drinking. My gut's made a few bad calls before. Told me that second slice of pizza was a good idea. Calculator never lies about math but it sure doesn't know how I'm feeling. So yeah, my gut's a messy tracker but it's the one I've got.