Old timer at my shop corrected my spindle speed chart reading

Had a retired guy stop by to pick up a used vise last month, and he watched me set up a job for about a minute. He pointed at my speed chart and said that feed rate looks too hot for that insert, you're going to burn the corners off it. I argued back since my numbers matched the book, but he insisted the book assumes a rigid machine, not our 20 year old mill with a worn drawbar. I dropped the RPM by 30% and the surface finish came out way better than my usual parts. That one comment stuck with me more than any online tutorial or manual section. Anyone else had a random visitor point out something so obvious you missed it for years?

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brookerobinson22d ago

My buddy runs a little one man shop in Ohio, and he had a similar thing happen with an old tool and die guy who came in to sell him a box of end mills. The guy watched him roughing out a part in some 4140 and just said "your speed is too high for that holder, it's singing." My buddy brushed it off because he had the numbers right off the insert box. But he tried dropping it 200 RPM just to shut the guy up, and the chatter disappeared completely. That old timer didn't even look at a chart, he just listened to the machine for maybe ten seconds. My buddy says he still thinks about that every time he sets up a job now, because the book never accounts for wear or vibration in older machines.