Had a talk with an old machinist that made me rethink my speeds

I was swapping stories with a guy named Pete at a supply house in Cleveland last week. He told me he runs his end mills at half the RPM I do but takes deeper passes and gets better surface finish. It goes against everything I learned in trade school but after trying it on a job, I have to admit the parts looked cleaner. Has anyone else experimented with really low spindle speeds for roughing?

2 comments

2 Comments

olivia_allen14d ago

Wait, are we sure the surface finish improvement isn't coming from the deeper passes and not the lower RPM itself? Like, if you're taking a deeper cut, the tool is engaging more of its edge and can actually dampen vibration better, which leads to that clean finish. I've seen some guys online argue that low RPM + high chipload can actually be way more efficient for roughing if your machine has the torque for it, especially on older manual mills. Plus, slower spindle speeds mean less heat buildup at the cutting edge, so the tool lasts longer and doesn't wear out as fast. Honestly, trade school teaches you textbook numbers, but guys like Pete have 40 years of real world experience, so it makes sense his rule of thumb works. Might have to try dropping my RPMs by like 40% and see if my inserts stop chipping on that stainless job.

graygonzalez14d ago

So my buddy tried this on a Bridgeport and snapped his endmill in three seconds flat?