304 versus 17-4 on a hitting surface

17-4 PH is a precipitation-hardening stainless that takes a carbide flute the way a good fixture should. It cuts clean, holds an edge, and still has a corner in March if you did not get greedy with the facing pass. A lot of better muscle and cavity irons use something in this family, or close enough that Reed’s spark and a file will agree. When we see it, Keiko writes a climb mill in the neighborhood of 0.35 mm stepover, four-flute, and a feed that does not make the spindle sound like a violin. The Ra sled then lands in the band we like for irons. That is the happy path. It is not the only path that arrives on Olive Street.

304 stainless is softer, cheaper to stamp in volume, and common on heads that were never meant to be recut. It will mill. It wants a gentler feed and a smaller ego. Push it like 17-4 and the wall smears instead of shearing. The smear looks like a finish until the first wet collar loads it, and then the smear is a ramp that helps rye stay. We drop feed, sometimes drop flute count in the CAM, and we tell the golfer the edge will not last as many Pacific rounds. That sentence is not an upsell. It is metallurgy. If they want a longer corner, the honest next object is a different blank, not a second mill on the same soft face.

Chrome on a game-improvement cavity is a third object pretending to be steel. The cap can peel if you treat it as homogeneous stock. We have a small graveyard of chips that are shiny on one side and dull on the other. When Reed sees that sandwich, the job becomes a conversation about veto. Sometimes a groove-edge restore is still kind, because it stays in the wall and does not try to resurface the window. Sometimes the honest answer is “do not mill this.” Paying for a map that ends in a no is cheaper than paying for a cut that leaves a blister in the chrome and a lawsuit in the inbox.

There is a fourth visitor: a face that has already been milled by someone who did not write a ticket. Thickness is then a rumor. 17-4 that is already thin is still 17-4; it is also closer to a crack. 304 that is already thin is closer to foil. We mic three spots. If the number is a problem, the 4-iron stays ugly and we mill the 7 that still has budget. Golfers hate this. Heads last longer because of it. The spark test is not theater. Reed does it on a belt toward the chip tray so the mark does not live on the back of a cavity you will still show your friends.

If you want a practical rule for the drive over from Springfield: tell us what you think the head is, then let the spark argue. Bring any old paper from a prior recut. If there is no paper, assume we will treat the blank as guilty until the mic says otherwise. And do not ask us to mill 304 to the same Ra as a 17-4 wedge you saw on a phone. The phone is not holding a flute at 4,800 rpm in a humid room. The flute is.

Alloy first. Ticket second. Catalog year never. That order is how we still have thickness to mill next winter, which in this valley is not a hypothetical season. It is the default setting of the grass.

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