Need help drilling a heatsink

I assume the fins are vertical to the baseplate. ;-) The idea with Cerrosafe (or some such like Wood's metal, Cerrobend etc.) sounds promising to me. When casting the metal between the fins, I would clamp some sheet on top of the fins and leave it there while drilling (even drill into that cover a bit). Don't forget to put some oil onto the fins, makes coming off the Cerrosave easier.

Nick

Nick Mueller fired this volley in news: snipped-for-privacy@mid.individual.net:

If I were going to use this method, I think I'd completely embed the object in the LMA. That way, it would be self-clamping, as it were.

I think I don't like this idea, at least for even small production quantites, as you're going to end up throwing away a lot of contaminated $30/lb. casting metal. You could re-melt and skimming all the chips, but I've had bad luck with contaminants affecting the surface-release properties of Cerro-Tru ... don't know about Cerro-Safe.

LLoyd

I would drill small clearance holes between fins and use a scroll saw dabbed with kerosene to cut out the 0.6" circles, fins down.

--Winston

What are you using to do the drilling? If you have a mill handy and can use power downfeed to control the feed rate, you might try an annular cutter. Jancy or Hougen are common brands. Crank up the RPM, LIGHT downfeed, plenty of lube/coolant.

I use them a lot in thin and fragile material with good results. Not as aggressive as a drill, and much more accurate than a hole saw.

.600 is a rather odd diameter. Can you use 5/8" (.625) or maybe 15mm (.591)????

Bill

Must be getting old. I know I found some simple way to do this but I can't remember which idea I used out of all the ones I thought of.

Probably it was clamping the heatsink to plywood with some cardboard in between to restrain the ends of the fins, and drilling with a sharp new endmill.

Gunner

I did that several times with embedded brass and aluminium. Used Ballistol as oil and had no problem skimming the chips. I even didn't pay attention when remelting to get the chips off before. I used something different as alloy. It melts at about 96°C (cadmium free).

Nick

Freeze it in a block of ice and use an end mill.

Pack the fins with modeling clay then use a two flute end mill instead of a drill.

Mike

Try packing the fins with brown sugar. Pack 'em good, the stuff will tamp a lot and become quite hard. After drilling (sharp endmil as Gunner suggests), you can dissolve the brown sugar in hot water.

How strong is tamped brown sugar? It's used to test prototype fuze electronics in artillery shells that experience over 20,000 G's when fired. Retreive round, soak in hot water to remove brown sugar, check the elex.

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.

LOL! Worth remembering!

Nick

If you are limited to materials that are available and acceptable at work, hot melt glue blobs between the fins might work. It doesn't stick to aluminum very well and you should be able to pry it out afterwards.

Jim Wilkins

!!!! Interesting !!!!

Miki, Unless you have Cerroxxx laying around, it's probably going to be cheaper in the long run to just wire EDM the part. DJ

If the fins happen to be the same thickness as the space between them, clamp two heatsinks fin-side-to-fin-side. This assumes you can live with a fin-width variation in hole location.

If they are not, perhaps you could find some sheets of thin sacrificial stuff (plastic, wood, soft aluminium) to take up the gap.

Thanks guys for all the suggestions and advice. I really appreciate it.

In the end I tried the brown sugar method, because we have plenty of it at the office coffee station. Long story short, it worked excellently well. ZERO distortion of the heatsink fins. We went with high speed and gentle feed.

I taped a cardboard form around the heatsink and tamped the brown sugar down with 1/4" parallels. After the sugar was packed in, I taped another cardboard piece to keep the sugar in the fins in case I thumped it between my office and the machine shop.

We don't have a lathe at work, but I have one at home, so I ground down a two-flute 5/8" endmill (based on Gunner's suggestion; improved by others' suggestions) on the home lathe to get the precise O.D. we need.

BTW, my company manufactures radio amps... the amp components all mount to the heatsink, and the 'sink mounts into a rackmount chassis. So our machine shop is somewhat limited. The 0.600" holes are for coax end connectors, this is a very tight build so the holes had to be relatively precise.

The purchasing department is going to wonder where all the brown sugar went...

That really is **such** a funny trick! Good to hear it worked so well.

Makes me smile! Thanks Don!

Nick

Bitte!