Had a part shift mid-cycle and it taught me a hard lesson about soft jaws

I was running a batch of 304 stainless flanges last Wednesday on my Haas VF-2. Everything was going fine until I heard that sick grinding sound and looked over to see the part had shifted about 0.015 in the jaws. The whole setup felt solid when I checked it but I guess the cutting pressure was just too much for my soft jaws. I stopped the machine right away and realized I hadn't put any serrations or grooves in those jaws to grip the part better. Ended up scrapping 3 parts from that run and losing about $200 in material plus my afternoon. Now I always cut a little crosshatch pattern into the face of any new soft jaws before I put them to work. Has anyone else had luck with a specific jaw prep method for stainless jobs?

2 comments

2 Comments

green.mason4d agoTop Commenter

Have you ever tried milling a little ridge right at the OD of the soft jaws before you cut the bore? I do that on all my stainless jobs now, it creates a tiny raised ring that digs in just enough without marking up the part too bad. That crosshatch pattern you mentioned works good for sure, but I find a single sharp ridge gives more bite with less stress on the jaw screws. Also keep in mind that 304 work hardens like crazy, so if your insert gets even a little dull the cutting force jumps way up and that's usually what causes the shift in the first place.

morgan.cameron4d ago

Yeah I mean a 0.015 shift and three scrapped parts? That's annoying but not the end of the world. $200 is like a decent dinner out not a life changing loss. I've had parts walk way worse and just re-indicated and kept going. Soft jaws are supposed to be soft they're not going to hold like a vise. Serrations help sure but if your feed and speed are dialed in right you shouldn't need much. Sounds like maybe your insert was getting dull like green.mason said. I've run 304 for days with smooth bored soft jaws and zero issues. Just saying maybe the setup wasn't as solid as you thought.