Need to countersink holes in CF, which bit do I need?

[simplechamp]

I need to drill 4 (or possibly 8) holes in the bottom of a CF chassis for mounting lipo trays. The screws are M3, and I already have a 3mm pure carbide bit for drilling the holes, but I also need a bit to countersink the holes.

Can anyone suggest the bit I should use? I would like to find something cheap, even if that means tossing it out after I'm done. I know the CF dulls tools fast.

[PBO]

Just a regular CSK bit will work fine for 4 holes

[simplechamp]

Do I need a certain angle or anything? Or are metric flatheads a standard angle on the head?

EDIT: Wikipedia says "Countersink cutters are manufactured with six common angles, which are 60°, 82°, 90°, 100°, 110°, or 120°, with the two most common of those being 82° and 90°. Countersunk-head screws that follow the Unified Thread Standard very often have an 82° angle, and screws that follow the ISO standard very often have a 90° angle."

So which do I need?

[PBO]

Originally Posted by simplechamp

Do I need a certain angle or anything? Or are metric flatheads a standard angle on the head?

EDIT: Wikipedia says "Countersink cutters are manufactured with six common angles, which are 60°, 82°, 90°, 100°, 110°, or 120°, with the two most common of those being 82° and 90°. Countersunk-head screws that follow the Unified Thread Standard very often have an 82° angle, and screws that follow the ISO standard very often have a 90° angle."

So which do I need?

Well, do you now the CSK angle of the screw head? that would be the answer

I wouldn't worry too much about pressure angles unless the tensile load is extreme. If you want to be certain, bed the screws in with epoxy - this will allow mirrored pressure angles

[mjderstine]

the most common at 82. so unless you got goofy screws you should be fine!

[simplechamp]

Just using standard M3x0.5 flatheads. I didn't know if they are Unified Thread Standard or ISO like the Wikipedia entry mentioned. Just did a bit more searching and looks like they are ISO so I'm going to use a 90° countersink

[brushlessboy16]

Originally Posted by mjderstine

the most common at 82. so unless you got goofy screws you should be fine!

Metrics use 90 degree IIRC

[pb4ugo]

BB16 is right--metrics are 90 and standards are 82. I've had difficulty finding 90 deg countersinks locally, so the best setup I've found is a 90 deg carbide router bit. If only four, you could get away with HSS, but the carbide isn't too much more in router bits.

[brushlessboy16]

Mcmaster carr
P/n 3013A43

[mjderstine]

oh, my bad, i have been using 82 on metrics for a while now without an issue... just torque em down :) :)