Inconsistent Alloy In Cpu Heatsinks?

Hi Folks,

Ran across an odd problem.

I buy these types of heatsisnks for filthy cheap:
www.build-your-own-computer.net/image-files/cpu-cooling-01.jpg

What I do is remove the clip and fan, saw in half along the space for the clip, clean the edges with a belt sander and voila! I have high power heatsinks for transistor projects.

Normally I drill and tap where I need; 4-40 for the devices and 6-32 for the mounting holes.

Until last night when I ran across a half of a heatsink that refused to be drilled.

Normally I drill with a pilot bit, usually tungsten carbide, then the tap hole with a cobalt bit. I do it gentle and add oil as I go.

Well, I start with my tungsten bit... *clink*



OK, old and tired or I went too fast. Get my last tungsten bit, move over 2mm and start again... slower.

*clink*



*iss on it. I'll go in with the 7/32" cobalt bit and lube the heck out of it...

*clink*



$50 of bits dead so far and one left... a Chinese made, dollar store bit I got in a pack of 24 bits for a buck. Yep, a BUCK!

Went through it like butter.



Someone tell me what just happened? All the other sinks went fine

Cheap HSS is plenty hard for aluminium.

Harder stuff isn't really going to have much advantage, and will have the disadvantage of being brittle

Some kind of hard spot at an angle that shoved the bit sideways and made it snap?

I imagine heat sinks are just alum scrap. Maybe a bottle cap shoved its way into a can and made it into the pot, or a chip of such.

How cheap is cheap btw, for the heatsinks?

That's what I was thinking.

The last batch I got new for $0.50 each at Princess Auto

There were only two left. though.

Local computer shops sometimes give me a box of used ones as most users want the funky vapour cooler types.

yeah ... it might be a piece of hard stuff in the pour mix or a harder section of the alloy (temp/solubility differential) .
i have seen hard spots in aluminum and steel ... the stuff was not cheap stock .
move away from the spot a half inch and no problems drilling .

I actually doubt there's much as far as inclusions. Those are all extruded, and you have to have homogeneous alloy to extrude it right. Wrong, and the extrusion warps and twists and bends and you waste a lot of material. Supposedly, if there are scratches on the billet before extrusion, they can be tracked to blemishes on the finished product!

Geek: sure you didn't just... erm... well I'm sure you've drilled holes before with those bits, but, you aren't using a hand drill or anything are you? Carbide requires a drill press; even a real steady hand will break bits.

Tim

Drill press.

Drilled hundreds of holes in aluminum with them, including about a dozen of these exact sinks.

I had that kindof problem too not so long ago.
Actualy i was intrested after leaving the WTF phase.
wanted to drill 4 holes on a cheapo alum cpu heatsink to mount it on my adsl modem.
it goes wacky afer a few hours, throwing away connection.
it is a heat related issue, namely the lack of heatsinking.
while the holes are on the pcb to allow a heatsink.

anyways.. i broken 2 drills before i went mad about it.
i cut the heatsink with a saw made to cut iron.
what i found are small non-aluminium particles, like quarter of a head of a match.
something hard, that broke the drills. it was like a milimeter deep.

if i have to guess the same happened. i think these cheapo heatsinks are made out of not so pure material. i do not know exactly how they managed to mold it, and how come the foreign material did not surface -stayd within the aluminium- but made in china sticker usualy means.. anything is possible. somehow.

if you are that intrested you might try to cut the heatsink to see.

hmmm ...
ya might want to take a geiger counter to those chunks of cut aluminum .

GAH! So I'm not crazy

Do I really want to?

A year or two ago,I was drilling some of the newer style Intel OEM heatsinks,with the copper slug in the center. Broke about 3 bits. I guess copper is too gummy to try to drill half-assed with a hand drill.

Bah, screw it. After that experience, I'm going to order from Heatsink USA. This is as close to what I was getting surplus:
http://www.heatsinkusa.com/5-375-wide-extr...minum-heatsink/

That's a whole 'nuther topic...

Bookmarked the sink-link btw (thanks).

often to heatsink something i just use a U profile.
many times its actualy a lot cheaper.
sure, alum is better than steel.
then again, depends on application

Hit it with WD-40 while you're drilling.

Yeah, so do I.

I have a little metal shop and I could crank out a zillion of those in a day, but a lot of times on the commissions, I need to dissipate 20+W of heat in a few sq. inches with a temp rise that won't burn customers fingers.... that can only be done with thick bases and good fins for convection

Hit it with WD-40 while you're drilling.

I think I was using ATF..