25mm dia countersink

I have an alpha 025 hss cse-25 countersink bit. (3 flutes)

I tried for the first time today, pushing it into a 12mm dia through hole in mild steel on the cnc mill. I used 250rpm (my cnc mill lowest rpm). Surface speed of 20m/min - plunge rate of 64mm/min . That's what fusion through out. I'm using flood coolant

I pulled it up half way on each hole to remove swarf and continued. Ok until I got 2/3rds of the way in. It sounded like it was rubbing - then pushed up further into the ER32 collet and span in the collet. Now got to order a new collet.

Was I way out on the feeds/speeds ?

That's a plunge rate of >1mm per second. That might be ok for the first mm or so but with a countersink, the spindle load increases proportional to the depth.

When countersinking (chamfering) a hole under CNC control, I always run the tool around the hole, using it as a milling cutter rather than a countersink. And rather than use a large 25mm countersink tool, I'd use a smaller (eg 6mm) chamfer mill. For a hole that isn't close to any vertical features that might interfere, you could still use the large countersink but I'd recommend using a profile toolpath rather than a drill cycle.

When generating a chamfer (actually 2D profile) toolpath in Fusion, you either model the feature without the chamfer then add the chamfer in CAM - or you model the chamfer and run the chamfer toolpath in CAM (2D profile etc) without any additional chamfer "depth" programmed.

Like this:
https://www.youtube.com/watch?v=hwB55zDl45U

Nice, sounds the way to go. After I thought of boring the countersink hole with a 10mm carbide endmill at 0.5mm step-downs so most of the material is gone then using the countersink bit, which prob would have been much kinder on my cnc. But your way seems a huge improvement on that. The countersink had to be around 10mm deep, so the full flute of the 25mm tool had to be in the hole.