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What's a good insert for dry turning 304 stainless?

Rocketdc

Aluminum
Joined
May 24, 2020
Having a little trouble getting a decent finish on some 304 weldments I need to turn down. Parts have a brushed/satin finish so the surface doesn't have to be perfect, but the smoother it is the easier it is to apply the brushed finish.

I tried some ccmt and cnmg inserts with mixed to bad results so I was looking for recommendations for a good insert for dry turning as well as any advice on feed/speed. My lathe is a manual 1440 and one of the calculators I was using gave me a f/min around 300 with a .006 chip which didn't work well. I just plugged the info into a different calculator which spec'd 100 f/min, which I haven't tried yet, so it's possible I was just running it too fast. I already screwed up a few of these so I was hoping to get some advice before I try a few more.
 

BT Fabrication

Stainless
Joined
Nov 3, 2019
300! on a small lathe. it doesn't have the rigidity to do well. but 80-100 is close.
but saying its a ccmt or cnmg doesn't say much, as there are hundreds of sizes and radius and chip breaker and coating and manufacturers combinations out there.
 

Rocketdc

Aluminum
Joined
May 24, 2020
The ccmt is a 32.51 PVD coated and the cnmg are 432 with a gold coating, don't have anything that says which specific coating it is.

I have a coolant pump that works, but I haven't been running it because I don't have a splash guard on the lathe. Maybe I should get that taken care of and run them with coolant. I had to start using flood coolant on the knee mill because the end mills were getting fried milling pockets in 304 SS.
 

LOTT

Hot Rolled
Joined
Nov 28, 2016
Brushing on oil might help, in the absence of flood coolant. Oil doesn't seem to thermally shock carbide, IME.
 

BT Fabrication

Stainless
Joined
Nov 3, 2019
The ccmt is a 32.51 PVD coated and the cnmg are 432 with a gold coating, don't have anything that says which specific coating it is.

I have a coolant pump that works, but I haven't been running it because I don't have a splash guard on the lathe. Maybe I should get that taken care of and run them with coolant. I had to start using flood coolant on the knee mill because the end mills were getting fried milling pockets in 304 SS.
dang that is a big insert for a small lathe.
what is the grade of it? PM25?
 

Gordon Heaton

Stainless
Joined
Feb 19, 2007
Location
St. George, Utah
Just a side note, if you're going for a Sandvik insert, their stainless grades are the 2000 series grades.
Yeah, I use the one I linked to as an all-purpose insert. I do a fair amount of 304L, and tried it since it was on hand. I was quite happy with the performance other than chip control. But then I've never had any luck with chipbreaking turning 304. I should have also mentioned that my shop is all manual.
 

BT Fabrication

Stainless
Joined
Nov 3, 2019
Yeah, I use the one I linked to as an all-purpose insert. I do a fair amount of 304L, and tried it since it was on hand. I was quite happy with the performance other than chip control. But then I've never had any luck with chipbreaking turning 304. I should have also mentioned that my shop is all manual.
i do a ton of 304 L expecially after welding. I have i believe it was an 8625 grade from iscar? on a wnmg 431 size.
 








 
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