[Amps] attaching a heat spreader to a heat sink

[kg7hf at comcast.net]

If it is an aluminum head sink, why not just plane it?  As long as your using carbide or heat treated cutters, a regular benchtop planer should work fine (make many fine passes).  I've never run a heat sink through my planer, but I've run a few pieces of aluminum stock through it.  Obviously, not treated, aircraft hardend aluminum, but taking small areas off at a time should be fine.  You can check your run out before you do it on a few pieces of hardwood stock like Jabota (brazillian cherry), which in my opinion is way harder than aluminum and would be a good test (jatoba really makes my planer strain).  If you still have too much runout, you should be able to correct it with the flat plate glass trick already mentioned.  

I would think that might be overkill, because when you bolt the spreader to the heat sink, the two pieces are going to conform to each other, in fact, they are going to expand and contract as the heat is applied and dissipated anyway.