Radius breaking off threading insert!

[northernmach]

I am using valenite brand threading inserts and cutting a 1" - 14 tpi thread in 4150 PH. The radius of the tool is breaking off, most of the time right on the first piece. I am using a laydown style insert with profile for 14 tpi. I have also tried using a v-loc style insert and I am having the same issue but lasts a bit longer. Does any one know the possible cause of this. Chatter does not seem to be a problem until the tip breaks. Speeds and feeds are from valenite Tech support and I have also gone slower and faster than there recomended. I am using G76 cycle and have worked my way down to .003 on first pass to get some life out of the insert. Any feedback is welcome.

Thanks,
Chad

www.northernmachininginc.com

[ghyman]

1. 4150 sucks.
2. Use a very fine stone to put a light (<.0005") edge break all the way around the tip... typically, the tool will:
heat up,
fracture the coating,
flake off
generate more heat
break
The edge break will help prevent the fracturing, which will in turn help with everything that follows.
3. If possible, use a cutting fluid that has chlorine and / or sulfur.
4. LOTS of coolant!
5. Check the center height of the insert and tool holder -- make sure the tip is on center; too high or low will cause breakage every time!
6. Check the material hardness, there may be some work hardening going on from the finish pass (unlikely, but always possible).

I will never badmouth a specific manufacturer; Valenite has some excellent milling and turning tools. But I have always gone with Sandvik's top-lock for single-point threading.

Beyond that, play with speeds and depth of cut... good luck!

[northernmach]

I will definately try the edge break. Sounds like a great idea that I haven't tried yet. I have gone through all other steps you have recomended though.

Thanks
Chad