Drill square hole

I have the need to make some rectangular holes with good precision between 3-4mm. I have a G0704 and do not want to broach or file the hole. I see there are end mills made for making a square hole after pre-drilling. If I use a center cutting helix square end mill like https://www.mscdirect.com/product/details/78598356, will I be fine with a fixed chuck/arbor or do I need one that gives in a circular motion? My apologies if I'm not using the right terminology but most of the videos I see have a rotating motion on not just the end mill. I also saw something that said the number of flutes should be 1 less than the corners you're trying to cut. Would I still be able to do square corners with a 4 flute end mill?

There are 3 flute drills that are designed to make a square(ish) hole. I have never used one, but I think they need to be able to walk around a bit. You might look up some Youtube videos on this subject.

With an end mill, you can not make a corner radius that is smaller than the end mill radius. The only way to really create a square corner is to broach.

Possiblity #1 - Wobble broach. Google it. You'd need a custom-ground broach and I'm not sure how you'd orient the broach - maybe hand-file a matching rectangle in a bit of material and clamp it to the top of the part so the wobble broach starts appropriately.

Possibility #1 - single-point broach. Grind a HSS tool with appropriate reliefs and a sharp corner and use your Z-axis like a CNC shaper. Take a bite of about 0.001 or 0.002, back off a bit, advance for another bite. Lather, rinse repeat. You could probably do two corners at once stepping over if you gind the tool to final hole width. If not, then do all four corners individually. I played around with it a bit and you need fairly fast Z-axis (150-200IPM) movement to make clean cuts. Doesn't work well for pockets even with a chip relief hole - but through holes and keyways work like a charm.

Looks like the biggest, stupidest sewing machine ever when it's running.