Boring 4130 and getting chatter

[crashman5468]

I have a 2.175" bore to make 6" deep in 4130 hardened to 22 rockwell. I am using a kennametal 1" diameter boring bar that is 12" OAL and I have around 8" hanging out of my tool turret. I have tried between 300-675 sfm at .01-.015"ipr. but I keep getting a diamond pattern rough chatter. can anyone offer any input? thanks

[Geof]

Pull your boring bar back. If you are going 6" deep you do not need 8" hanging out.

You don't mention the depth of cut. Sometimes it is possible to reduce chatter by taking a healthy cut at a healthy feed.

Of course the obvious is to check if the tool is on center or even a bit above.

[robertproff]

There are several things to consider about your boring bar. First a boring bar is designed to be used at a depth of 4Xdia. Sometimes you can get satisfactory results by taking a heavy finish cut to load up your bar, but if you have to rerun the bore then you are probably going to get chatter. Also, it is important what radius insert you are using, if you are using a 1/32R insert and only finishing .01 per side then you will have a hard time eliminating chatter especially at that depth. Kennametal offers a devibe bar that works very well for cutting depths up to 10Xdia, but I think the smallest bar that they offer is 1.25", the also offer a heavy bar which IMO works very well. I would think with your setup I would try about 100SFM and feed of .006-.010 if using a .015R I would leave .02 to .04 per side to finish. Sometimes it works and sometimes it doesn't. It usually takes a little playing with to get something to work.