7/16 slot in CR Mild Steel. 1.625 deep.

[Houndogforever]

The part has a flat square bottom thru the center of some 3/4" cold rolled material. Looks like 1018.

Since it needs a flat square bottom, I was thinking of a HFM mill to rough slot it out.

My question, 1) is this a workable idea?
2) when using a solid carbide HFM end mill to rough a 7/16 slot, would I want to use a 3/8 cutter, go down center and back on each edge?
Or maybe a 1/4" cutter taking a full width cut on first pass and a 80% width of cut going back?
or 5/16 ? I dunno, haven't done this much.

Oh, and as to the suggestion of use a big indexable slotting cutter, yeah, I have a Speedio and a Fadal3016.

 

[F35Machinist]

I would just use a regular 4 flute 3/8" end mill with a pilot hole. I have both of those machines as well and it should work fine with either. 1.625" isn't too deep for 3/8 diameter. I find it is easier and faster to use tools I have in stock than special orders. I don't think high feed mills would be much faster in this case anyway since you would need to finish with a normal end mill anyway.