On Wed, 15 Apr 2015 12:43:22 -0700 (PDT), whit3rd
wrote:

On Wednesday, April 15, 2015 at 6:26:25 AM UTC-7, Joe Gwinn wrote:
In article ,
Ignoramus18077 wrote:

On 2015-04-13, Don Foreman wrote:
On Sun, 05 Apr 2015 07:47:14 -0500, Ignoramus10114
wrote:

I have an aluminum heatsink that I need to tap , I wanted to know if I
should use 6-32 or some less coarse thread like 8-32 would be better?

I go the other way with aluminum -- I use forming taps, not cutting
taps, and lubricate with soft wax made for the purpose.

But, a heatsink might require a very flat top surface; a forming tap will raise
the surface slightly as it deforms the material, so it might not be suitable
for this particular application (unless a second operation follows, to
flatten the mating surface you've just disturbed).
let's just burn that straw man right now.. Debur or countersink /
chamfer the top of the hole and any possible "distortion" of the
extruded aluminum heat sink will be totally dealt with. You are
disturbing a few tens of thousandths of an inch of extruded aluminum
inside a drilled hole - it is not going to cause any flatness problems
beyond POSSIBLY raising a tiny ring at the top of the hole.