I need to cut an internal (female) seal gland with a square cross section 2.5 inches down a bore that is 0.875 inches in diameter. The gland itself doesn't need to be particularly deep (~0.1 inches) but it is the depth inside the bore that is giving me trouble. Ordinarily, a woodruff cutter would work fine, but all of the ones I have seen are far too short. Has anyone done this type of job before? I am aware of the products made by PH Horn, but just the tool holder costs ~$280 and that is a bit too expensive.
Make an extension bar (or buy an extension collet/toolholder) for the woodruff cutter and cut gently.
You could also grind a single point HSS tool and put it in a boring bar and interpolate the cut (cheapest and slowest option).