Lathe Boring 316 Stainless - Getting Chips to Break

[BernieB]

For the low price, Korloys king drills are pretty great. Travers has 1.25" 3xD for $365, comes with a nice case and 2 boxes of inserts. 5xD is $507.
I use a smaller one in duplex often.

Sandvik had a nice sale on their newer DS drills in september but that's over now. Their old 880's are good too.
Don't worry about breaking a chip so long as the chips make it out of the hole its fine, around .0032" feed and good through coolant to get the chips out. I use a 880 .937" up to 4.5" deep in 316, Duplex, 625 Inconel, no problem at all. Insert life isn't too good in inconel but in stainless it'll drill all day long without changing edge.

I’ll try it with a 1.25“ 880 drill. Looks like 2044 and 1144 for inserts? Is that what you’ve been using in stainless? Thanks again for the help!

 

[SND]

Those are the grades I use yeah, works good in stainless, duplex, inconel.
I was using my new DS20 1.312" going 6.2" deep in 316 a few days ago, 1150rpm and .0035 feed was about 64% on the Z thrust load of my Lynx2100LB, spindle was 38%. 145psi, more pressure would be nice bit this gets the chips out ok enough. now I'm debating getting a 1.75", looks like the machine can handle it.

 

[rwskinner]

Think I'll get a bigger insert drill to simplify it all. Any recommendations on drill and insert for this material in 1.25" size? The 1" insert drill I have has similar issue to the boring bar. Chips don't want to break, unless I really get after it with the feed, and at the point the inserts don't last more than a hole or 2 without chipping.

I use a 1" insert drill in 316 all the time and then I use the same insert drill to open the hole up to whatever size needed. Nice finish, no chatter, and saves a tool change.

 

[nissan300ztt]

I know this is an older post. But in my experience at pretty much working with any 300 series stainless is to push it fast and hard. So when im using a Carbide boring bar and the chips wont break I just increase my RPMs and feed rate. I have a great luck. If the SFM calls out 400 go to 450 or even 500 and they will break. And for the finish id minus my tool about .005" to get rid of any chatter marks and recut with the .005 back into it. Smooth as glass most of the time.

 

[TommyGunzz]

I have a job boring a bunch of 316 stainless, and am having a really hard time getting the chips to break. They ratsnest in the hole, and break insert after insert. I first drill a 1" hole with an insert drill, and am following it up with a 3/4" diameter carbide boring bar. Bore needs to end up 1.32" +- .01, surface finish not important. Anyone have recommendations for inserts and/or strategy for getting these chips to break, and getting them out of the hole? I have ccmt 3252 inserts for the boring bar, and have tried every insert I have with no luck. Surface speed at 300sfm. Tried both a bit more and less. Feed I've tried everything from .005" per rev to .015" per rev. DOC everywhere from .005 to .040. Wondering if there isn't a specific chipbreaker / coating / some other magic juju that'll help me get these f!@#$%g chips to break. I've tried feeding +Z direction too with shallow DOC as an experiment, and that didn't seem to work either... Surely there's a way....

I just ran into this running some parts on mazak lathe. Material is 17-4. Finished bore size is .938 +/-.001 and we are pre drilling with a 13/16 insert drill .800 deep and boring .650 deep I believe. The part gets parted off at .6. Initially we were roughing the bore out going all the way into our .650 depth but we were getting a lot of chips packing up at the bottom and it sounded horrible so we changed it to bore to .400 deep first out to the .938 diameter and then went the other .250 deep after and have had 0 issues. We are using a 3/4 boring bar to rough and a 1/2 boring bar to finish. Speed and feed on rough boring bar is 275sfm and .01 feed per rev at .03 doc I believe.

 

[Fancuku]

we are pre drilling with a 13/16 insert drill

We are using a 3/4 boring bar to rough

That first roughing pass must have sounded pretty crunchy.