On Wed, 15 Apr 2015 17:15:10 -0400, "Jim Wilkins"
wrote:

"whit3rd" wrote in message
...
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).

http://www.katonet.com/article/mindrilltapping.html
"Good machining practice dictates that a countersink be provided at
the top of the tapped hole. Countersinking is recommended before
tapping to create a good starting thread."

Easier said than done, though.

-jsw

easier said than done? How? Hit the top of the hole with a
countersink, or a drill a few sizes bigger than the hole if you can't
afford (or can't find ) a countersink. Best done in the drill press,
but for crying out loud it's "just" aluminum - you can do it with the
drill bit in your bare hand if you have to.