That old timer told me to trust my ears over the readout and he was dead wrong

I had a guy named Pete who's been running CNC since the 80s tell me last year that I should ignore the digital readout for chatter detection and just listen to the machine. He said the readouts lie sometimes and your ears know better after enough time. So I tried his way on a big 304 stainless job for a local aerospace supplier, running a 3/4 inch four flute end mill at 3500 RPM. Machine sounded fine to me, no screaming or weird harmonics, but the readout showed a 0.0025 inch deflection spike every few passes. I kept going because I trusted Pete and ended up scrapping four parts worth about $800 each because the surface finish went to hell on the last pass. Next time I ran the same job I set up a vibration sensor and split the difference between the readout alerts and my ears, zero issues. Has anyone else ever been given advice by a veteran that just plain backfired on a specific part or material?

3 comments

3 Comments

rileygarcia1mo ago

Read an article saying harmonics change with tool wear, so both were kinda right maybe.

samflores1mo ago

I had a two-week stretch where my CNC started sounding like a dying cat every time I cut 6061. I checked everything - speeds, feeds, coolant, even blamed the phase converter. Finally swapped out the end mill and bam, back to a nice smooth hum. That taught me real quick that tool wear and harmonics are best friends. Made a whole chart of sound frequencies for different tools now. Maybe I'm overdoing it but hey, beats crashing another $100 tool.

max2231mo ago

DUDE yeah @rileygarcia you're totally onto something. I remember cutting some aluminum parts and my machine started making this weird high pitched whine halfway through. Turned out my end mill was getting dull and the harmonics shifted enough to mess with surface finish. Swapped it out and the noise went away plus parts came out cleaner. So yeah tool wear definitely changes harmonics for real.