On Wednesday, April 15, 2015 at 2:15:11 PM UTC-7, 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


Countersinks are often required so that when the first threads gets pulled out from over-tightening, etc. it doesn't affect the surface.