On 2007-12-18, Miki wrote:
Hi guys,

I have a project at work, it involves drilling two .600" holes into
the backplate of a heatsink and through the fins.

On the first try I plunged a .600" drill into the base plate. When
the drill was through the base plate and touched the fins, the fins
wanted to wrap around the drill and tear out of the base plate.

Drill bits are a bit too aggressive for the task.

I have had good luck with a milling machine, milling from the
top of the fins downward -- slowly, and with the heatskink firmly
gripped end on in the milling vise, which offers some extra support for
the fins at the ends. This needs to be a center-cutting end mill,
obviously.

Of course -- a 0.600" end mill may be difficult to find. How
accurate does this need to be? Or could you use the end mill somewhat
oversized, say 0.750", and switch to a drill once you have started
facing the horizontal surface?

Or a 5/8" end mill is only 0.025" oversized. Perhaps you could
live with that?

Or -- you could set up a horzontal mill with cutters spaced the
same as the fins to make something which would hold the top 1/4" of the
fins clamped down onto the heatsink. Make it a fixture which will hold
the sinks in the same place (assuming more than one heatsink to drill),
and make it of a material which you can drill into with the endmill so
you can get the full length of the fins -- or through the fixture from
the top.

For one only, you might be able to get away with clamping it
firmly to a soft wood or plastic so the fins embed on their own and get
sufficient lateral support from that.

Good Luck,
DoN.

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