Death of a tool bit

[Robin Hewitt]

I thought this looked interesting so I pointed a camera at it..

Pic 1: Same program, two different metals. HE20 cuts nicely, pure aluminium creates an enormous burr. Proving the cutter can handle a bit of extrusion.

Pic 2: HE20 aluminium, 6mm HSS cutter, 1250 rpm, 0.1mm off final size, feed 2.5 mm/s, 2mm DOC, good flow of suds.

It enters the picture top right and you can see it already in trouble because it is only cutting on the leading edge. It has picked up metal on it's flutes, it's bending in to the cut and has gone past depth.

It slows up at the corner and things get worse, it is now barely cutting. It passes a hole and veers towards it, it is now bent in two directions, it tries to recover but everything gets too much for it.

I haven't got a clue why it suddenly decided to pick up metal, I dropped the DOC to 1.5mm and finished the job without losing another. A bit of a fudge, I hate not understanding.

Unrelated but I popped three 6mm cutters one ofter the other last week. Didn't make it an inch in to the slot. Problem was a new draw bar which bottomed out on it's thread. The collet chuck felt firm but it obviously wasn't. That had me scratching my head until I thought, what has changed?