Deep Slot Milling in Aluminium - Optimum Cutter Diameter

[JAZZCNC]

I won't go more than 1mm cut depth for a slot. As I'm not cutting for cash, I don't mind high cycle times and although my machine is capable of cutting deep pockets in Al, I don't want to risk any more carbide cutters.

There's part of your problem straight away, Carbide likes to be pushed hard and 1mm Doc isn't enough with a 6mm tool. Could easily double this and more without breaking the tool.
Next is the intermittent cut caused by the holes you drilled, Carbide doesn't like shocks and intermittent cutting, I would stop doing this.

I find Mist cooling with plenty of air is better than flood for slots.

[guy_]

To be honest, I'm not sure what you mean when you say that carbide likes to be pushed hard. I know that it can be pushed hard and my DOC could be bigger but I'm just getting to grips with what my machine is comfortable with. The intermittent cutting is really the same as any stepover. I know carbide is brittle but I haven't seen any damage to my bits from doing this.