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Old 16th February 2009, 08:26 AM   #1
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Default metal resurfacing question

I may build a Pass F1 and want to mount the fets on a 1/4" 2"X12" copper block as a heat spreader attatched to the heatsink. But the surface is rather rough. I figure I would need
to remove about 1/100" to make it smothe and flat. Any easy
way to do this without expensive tools?
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Old 16th February 2009, 08:29 AM   #2
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Sandpaper
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Old 16th February 2009, 08:36 AM   #3
AndrewT is offline AndrewT  Scotland
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silicon carbide paper. called wet or dry and also called wet and dry.

Easily available in grades from 180grit to 600grit. 1000grit and 1200grit also available.

Use it wet, after removing most of the imperfections
and make sure the sheet of W&D is on a flat surface.
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Old 16th February 2009, 09:04 AM   #4
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Quote:
Originally posted by AndrewT
...make sure the sheet of W&D is on a flat surface.
This is most important. If you just rub away freehand you can actually reduce the flatness while improving the superficial shine.

If you have ever tried using car bodyfiller you will understand. You need a flat support for the abrasive sheet.

w
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Old 16th February 2009, 10:53 AM   #5
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Thanks for all the replys. That was what I was planning on
just wanted to double check before I started.
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Old 16th February 2009, 02:36 PM   #6
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Glass sheet to support the abrasive, after you have it fairly flat.
Thick glass...

Or a precision metal surface, but if you don't have any precision power tools, you won't have that handy...

Or, just bring it to a local machine shop and see if someone will take a quick pass on the milling machine with a fly cutter for you...
Maybe will cost you a few bux, but save a lot of work...

oh, you had best have something as a barrier between the copper and the aluminum...


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Old 16th February 2009, 10:14 PM   #7
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Quote:
Originally posted by bear

oh, you had best have something as a barrier between the copper and the aluminum...


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Regular thermal paste will do for that purpose, and that's needed there anyway.


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Old 16th February 2009, 10:39 PM   #8
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You are assuming zero contact through the thermal compound, a bad assumption, imho.

And, what about screws?

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Old 16th February 2009, 10:49 PM   #9
Magura is offline Magura  Denmark
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Quote:
Originally posted by bear
You are assuming zero contact through the thermal compound, a bad assumption, imho.

And, what about screws?

_-_-bear

No, but it takes quite humid conditions, to make anything galvanic happen, and if you have some thermal compound in between the copper and the aluminum, nothing will happen.

I know this from experience, as I use copper and aluminum in combination frequently.

About the screws, again, you need to add water to the equation, and quite a bit of it, so a little grease, and it's gonna be fine as well.

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Old 17th February 2009, 02:36 PM   #10
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I think you are incorrect.

But if you count the life of the unit in terms of a relatively short span - like most products today - ur ok.

I'd still be very cautious about copper and aluminum (or other metals) being in contact even with the grease... Ymmv.

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