Took me 3 years to admit an older machinist was right about speeds and feeds

I always ran my feeds as fast as the machine would go. Thought slower was for old guys who didn't know better. Then I got a job in Denver running a bunch of 304 stainless parts. The chatter was bad and I kept breaking inserts every 20 parts. My boss finally made me drop the RPM from 4000 to 2600 and cut the feed rate by 30%. Surface finish came out mirror smooth and that same insert is still going after 150 parts. Has anyone else had a similar wake up call about running too fast?

2 comments

2 Comments

christopher3851mo ago

3500 rpm on a 2 inch facemill in 316L taught me the hard way. I was getting this awful squeal and thought it was the holder flexing. Swapped to a brand new Sandvik insert and same noise. Dropped the spindle from 3500 to 2200 and the feed from 15 IPM to 12 IPM and it ran SILENT for 8 hours straight. I still think there's a middle ground though. Your old machinist was right for that setup but I've seen guys run way too slow for modern carbide too. Hardox 450 at 800 rpm will just rub the coating off and kill your tool life faster than running it hot. The real game changer for me was learning to read the chip color and adjust from there.

simonw411mo ago

What speed were you at before you dropped it down? I had a similar issue on a 3 inch facemill in 304. I was running 3000 rpm and it sounded like a banshee. Dropped to 1800 and bumped the feed up a tiny bit and it was like a different machine. Chip color is huge too. I look for that straw color on stainless. If I see blue I know I'm burning the edge off. Took me years to stop guessing and just listen to what the cut is telling me.