Subject: Re: Looking for ev6 or later workstation..
To: None <>
From: Miles Nordin <carton@Ivy.NET>
List: port-alpha
Date: 02/18/2007 11:33:17
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>>>>> "eef" == Erik E Fair <> writes:

   eef> you can find the right kind of heat sink,how hard could it be
   eef> to drill a couple of holes in it ... ?

quite hard because the edges of the holes need to be completely
smooth.  This is actually a big deal with heatsinks in general.  If
you find a big one with holes pre-drilled (ex., one for transistors),
you'll see it's no ordinary hole: the (component side only) of the
hole probably has a conical taper about a quarter millimeter deep,
presumably made with something besides an ordinary drill like a
``reamer'' or some other fancy metalworking thing, just to make sure
the contact surface is completely burr-free, scratch-free,
wobble-free.  Also if you heat the metal too much I think it could
warp or something---you often see discoloration around a hole drilled
in metal.  so you have to use cutting oil and a drill press and go

The problem of drilling holes in heatsinks is one reason you often se
TO-220 transistors mounted with clips instead of screws.  It looks
like they're being cheap to use some strip of bent metal instead of an
actual screw, but it actually has more consistency in the thermal
performance across all the devices than drilling a hole in any
affordable way (and along with it you get the springyness, so it's
less likely to loosen under thermal cycling.  it's not _just_ because
holse are hard to drill.).  I'm not an expert on this, but I read this
whole chapter about different styles of heatsink once at the beginning
of this MOSFET data book, and they spent a couple pages on holes.

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