I machined an O-ring groove located a little too close to a part’s inner corner for using my old lathe O-ring cutting tool. I tried running the lathe in reverse so I could approach the O-ring groove from the more narrow side of my O-ring cutting tool but still not enough room for the tool.
I have been wanting a more universal O-ring cutting tool so I ground a new O-ring cutting tool made from an old blank of Rex AAA HSS. The tool cutting face width is 0.095” and 0.5” long (to the shoulder) and ground at an offset of 30 degrees from the center line to provide better access. In addition to using the cutting tool for making O-ring grooves, it is also does a great job as a trepanning tool. I used it recently to remove a 3.5” diameter center section from a plate of T-304 stainless steel. The Rex AAA HSS had no trouble trepanning the stainless steel. I included some photos of the tool at work.