Drilling Heatsinks

[wes-ninja250]

Hey, All!

I accidentally wound up with a heat sink which is nearly perfect for what I want to use it for -- except it needs a couple of holes for M6 screw heads, right in the middle.

Ideally, I would like two holes about 12mm diameter (1/2") through the fins, with 6mm (1/4") holes all the way through the plates. That would allow me to use existing hardware to secure it.. securely.. to where it needs to be.


(See http://www.bgmicro.com/prodinfo.asp?prodid=ACS1430).

Has anybody ever tried to drill through a delicate heat sink like this? Is there a technique for making through-holes in one without ruining the fins? How about clamping it down to drill in the first place??

If I can't figure out how to make the holes, I'm probably going to wind up slicing it in half. *eek*

Tools at my disposal -- nice drill press, titanium nitride drill bits, dremel and basic accessories, perserverence.

Thanks,
Wes

[wes-ninja250]

Youch.

Just got home and made some measurements -- the only way I can see it's going to work for my app is to saw the sucker right in half, perpendicular to the (bonded) fins. Then drill and tap some not-through holes in the base.

Anybody gonna try and stop me? I've never tried to slice up a head sink through the fins before.

Wes

[lgreen]

Hey stop! Why don't you think about it a little more? Or you could drill and tap holes in the heatsink to attach a mounting bracket or something in order to mount the heatsink to where it needs to be.

[BWRX]

Originally posted by wes-ninja250
the only way I can see it's going to work for my app is to saw the sucker right in half, perpendicular to the (bonded) fins. Then drill and tap some not-through holes in the base.

This sounds much better (and easier) than your first idea! I've tried to do this once before but bent the fins more than I would have liked because I was a little too forceful with the hacksaw. After finishing the job (I hate it when good ideas come to you after you botch something up) I thought of something that could have helped to keep the fins more in order. Find some basswood sheets or some other semi hard and thin material of just the right thickness at a craft store/hobby shop to place in between all of the fins to keep them properly separated and more rigid while cutting through them. I'll bet this would keep them from bending or deforming while cutting. Let us know how it turns out when you're all done!

[ctardi]

Drill through from the back with a 1/4" bit...

This would work well if you used wood between the fins as suggested above. Then you can use the dremel to carve away the fins.

[wes-ninja250]

Hey guys!

Thanks for the feedback. I wound up getting impatient after I had an idea -- and I think it's worth sharing!

Side note - I'll be drilling and tapping the base to mount the heat sink, but I had to have the space (originally the holes) in the middle, to accomodate the M6 screws which in turn bolt some 1.25" steel tubing a roughly 18 awg stainless steel plate. It's needed to hold things together. Now the mounting hardware will peek out from between the two halves of the heatsink; I had to cut it because it wasn't long enough to reach the screw holes for the two chipamps anyhow (they are about 3.75" apart).

Anyhow, the wood idea is superb, but it turns out to be unnecessary with my solution -- which worked out ALMOST perfectly. It would have been perfect if I had been less impatient -- It turns out that my cut wasn't perfectly square, because I started it with my dremel tool, which doesn't have a long enough shank for the job. So the cutting wheel was spinning at a bit of an angle. It's only about 10 degrees off, though; no worries.

I noticed that the heatsink came in a nice plastic box, in which it fit very snugly, flat-side-up. So, I clamped the whole shooting match to my work bench, and simply started cutting. Eventually, when I figured out the dremel tool wasn't the way to go, I got out my hack saw, and made my way through the thick base to the fins -- cutting right through the plastic box as I went along.

You'll know right away when you hit the fins, the sound changes dramatically. Try to cut as level as possible, so as to hit all the fins at the same time, same amount. I think the hacksaw blade I was using was 30 tpi; might have been 32. Quite fine, anyhow.

The real key to getting them to cut cleanly, other than the plastic box, was using the barest amount of pressure on the saw to make it cut, and (get this) tapping lube to keep the blade moving smoothly. I also found out that stopping was a BIG mistake!

When I got VERY close to the end, the heat sink sort of collapsed in on itself. This made moving the saw difficult. The solution is to clamp BOTH sides of the heatsink/box to the bench, not just one! Also, putting a spare hacksaw blade into the slot above the working blade might help.

When I was done, I had some minor rough edges which I cleaned up with a small cylindrical grinding stone at mid RPM (8000?) on the Dremel. Using the lightest touch possible, you can follow the fins, grinding several at one, and do a passable job cleaning them up. They now feel smooth, although they reflect light differently than the undamaged sections. Also, I cleaned up the edges where I cut with the grinding stone and some sand paper to make sure I wasn't going to get any "lift".

Now, each half of this heat sink will augment a chassis heat-sink solution for my LM3886s, giving me a little piece of mind.

Conclusion: If you can have a saw guide at each end which is firmly clamped to the heatsink, which is firmly clamped to your bench on each side, you can do this with lots of lube and a hand-held hacksaw.

But it takes like two hours.

Wes

[lgreen]

sounds good. 2 hours is not much compared to the amount of time you think about the problem and try to come up with something. Reminds me of using a small file to fix mounting holes in thick metal, it can be done but takes time and effort.

[wes-ninja250]

Yeah. I should have used a small file to make the slots in my 1/4" steel mounting rails; I got impatient and used a dremel grinding bit. Wore it right down 'till it broke.

Luckily, the slots were *just* big enough when it broke.

Wes