[QUOTE=cropwell;85406
Any suggestions ?

* the ali plate is probably as soft as poodle poo, I don't know what grade it is.

[/QUOTE]

Pic of it would help but you have probably answered your own question. Soooooo many times i see you guys posting about ally cutting problems and nearly all of the problems are because you do not use grades that are machinable. Use the correct grades that ARE machinable. if you don't you will always have these continuing problems of one sort or another.

Countersink with a very crispy sharp countersink, if the bur is peeling up on one side then you will have a problem of the burr shoving the csk offset and it will be hard to get a neat csk. If the burr is uniform then it should be ok. With very soft materials like this the tendency is to shove the material out of the way as apposed to cutting which itself gives problems even when countersinking because the edge of the hole can not resist the cutting force and the burr wont shear and therefore can also push that burr partially in the hole. It may be an idea to do as mentioned and try a rubbing block to get most of the bur off as possible then csk the hole.

The right material again will save you all this nonsense you are experiencing.