Picked a Kennametal boring bar over a Sandvik on a tight ID job last week

I had to bore a 0.750 hole 4 inches deep in 4140 prehard. The Sandvik bar was shorter and stiffer but the Kennametal had a coolant-through option. I went with the Kennametal because the chips were piling up bad. It worked fine but the surface finish was a little rougher than I wanted. Has anyone else had to choose between rigidity and chip control like that?

2 comments

2 Comments

gavinhunt21d ago

Doubt it was that serious @ninal91, a few tenths change in surface finish on a boring bar that short is probably just a spring pass issue.

ninal9121d ago

Look at how the bar is clamping down in the holder... a split sleeve or a hydraulic holder can make a big difference in vibration on a long reach job like that. Sometimes the rigidity problem isn't the bar itself but how it's being held, especially when the coolant holes change the bar's wall thickness near the head. That rougher finish might've been chatter from the coolant passage weakening the bar's steel a bit more than you'd expect.