What countersink bit for M3 screws into aluminium?

[Eusebius]

I'm building some amplifiers which have an aluminium top plate and I want to countersink M3 screws so they are flush with the top. I have one basic countersink bit, the serrated all the way round kind. It leaves serration marks in the hole, though it's better if you dip it in meths each time, which is time consuming. I have several holes to countersink.

Suggestions for a good bit that suits M3 screws?

[Martin Brown]

Aluminium is soft and tends to clog some countersink bits but the serration marks you describe could be because you are applying the wrong pressure and the job is bouncing away from the tool.

Trying another bit with fewer cutting edges might help you control the cut better. I've never found countersinking aluminium too difficult. YMMV

[Colin Bignell]

Also, paraffin is much better lubricant for aluminium than meths. Keep the meths to clean off any paraffin residue afterwards.

[Rob Morley]

Some machinists reckon WD40 is good for aluminium.

[Rob Morley]

You may be pressing too hard. Using a bench drill rather than hand-held, and setting the depth stop, can help reduce the chatter.

[Colin Bignell]

It contains paraffins.

[wasbit]

Use a small snail countersink to give a near polished finish. They can be used on wood & mild steel.

£14.98 from Axminster tools. See if you can find cheaper elsewhere. - One theory is that countersinks should have an odd number of cutting edges to prevent chatter.

[Ian Jackson]

It has the advantage of being the sort of thing that most DIYers have a can of, often within easy reach on a shelf.

[Colin Bignell]

I have a can of paraffin available, but no WD40. I've never been impressed by WD40.