Cutter notes · 21 Jun 2026
CAM will draw a pretty wall with any flute you pick. The metal will not. A 10 mm square-end cannot live in a score line that a 6 mm can, and the land that remains is the difference between a family of irons and a set of mismatched knives.
Facing a window and restoring a groove are two tools. Golfers see one spindle and assume one cutter. Keiko does not. The facing pass wants a square-end large enough to be stiff, small enough to follow a cavity’s slight bulge without digging a trench at the toe. On many 17-4 irons that is a 10 mm neighborhood. The groove wall wants a flute that can enter the score line without eating the land. That is a smaller tool, slower feed, different CAM origin. If you try to do both jobs with the facing cutter, you round the land into a ramp. The ramp packs rye. We know, because we did it once in 2021 and kept the head as a warning, not as inventory.
Land width is the unglamorous spec. Too narrow and the wall is a razor that chips. Too wide and the groove is a suggestion. Factory lands vary by year, by cavity, by whether the head was milled at all. We measure what is on the blank, then we decide whether a restore will respect that width or whether a full recut has to redraw it. A 6 mm flute with a programmed wall can leave a land the 10 mm never could. That is not magic. That is diameter. The larger tool’s corner radius, even on a “sharp” square-end, occupies space the score line does not have to spare.
There is a temptation to use a tiny flute for everything because it photographs as precision. Tiny flutes chatter on a facing pass. Chatter is a washboard. Washboard is spin scatter. So we do not face a 7-iron with a groove tool, and we do not groove a 7-iron with a facing tool. Two passes, two diameters, one ticket. If a shop shows you a single toolpath screenshot and a finished face, ask which flute did the walls. If they cannot answer, the lands are an accident.
Cavity irons complicate the vise. The back of the head is a pocket, the face has a bulge, the score lines may not be parallel to anything a mill table respects. Soft jaws and an indicator sweep matter more than the brand of CAM. A 10 mm that is 0.2 mm off origin will still face a pretty window and then leave the toe land fat and the heel land starved when the smaller flute follows a bad map. That is how a set becomes a collection. We would rather spend twelve minutes indicating than twelve months explaining why the 8-iron grabs and the 6-iron does not.
Hybrid faces, for completeness, rarely get the small flute at all. Most do not have score lines worth restoring. Putter mills use a facing logic closer to the iron window and nothing like a wedge wall. Wedges get the small flute as the star of the show. Knowing which diameter is the star is the job. The gantry will spin whatever you put in the collet. The collet does not have taste. The machinist has to.
If you like hardware: we keep the facing cutters and the wall cutters in separate foam so a hurried Saturday cannot grab the wrong one. That foam is more important than a new monitor. The ball never asked what computer we owned. It asked what corner we left. Diameter is how a corner gets a chance to exist.