The chip load calculator is useless if you ignore tool deflection

I keep seeing guys here running feeds and speeds straight from a chart without accounting for how much the tool is bending, especially on deep slots. Last week a buddy snapped a 1/2" endmill taking a full axial depth on a hardened steel job because he didn't factor in the stickout past the holder. Has anyone else found a good rule of thumb for adjusting based on tool length?

2 comments

2 Comments

angela_grant1d ago

Yeah, ignoring tool deflection is a recipe for snapping tools. A buddy of mine was running a 3/4" endmill with about 3 inches of stickout and it started singing loud, then bam - shattered the shank and took a chunk out of the part.

patricia_schmidt141d ago

Wait, are you sure it was the stickout that caused it? I've ran a 3/4 endmill with way more than 3 inches out on aluminum with no issues, so I'm thinking it might've been the speed or feed rate that was the real problem. If your buddy was pushing it too hard with that much stickout, yeah, it's gonna sing and snap eventually. But respectfully, I feel like tool deflection gets blamed for stuff that's actually just bad cutting parameters or a dull tool. I've seen guys run the same setup with lighter chips and get through it just fine, so the stickout alone isn't always the enemy.