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Old 03-30-2013, 08:38 PM #1
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Default Simple compression shrink fitting tutorial

Do you want to press fit your module into a heat sink, but come to find that it's just a tad too bog for the hole? Don't drill it out, make it even stronger!

I couldn't find anyone talking about it here before, so I thought I'd share it. It can be very useful at times and can make your normal press fit a bit easier.

This should work if your module is within .000 and .001''(.025mm) distance without too much trouble. At the .001'' it'll be very difficult to ever get apart. Personally I'd try and stay low though, because as the metal contracts it'll cause some stress, and if it's too much you'll end up with a warped or broken heat sink or module... or both.
================================================== ==========
What you'll need:

Heat sink and module
Pliers or Tongs (to keep your hands away from the hot parts)
Welding gloves would probably be a good idea
Oven
Freezer
and possibly a hammer and something to tap your parts with if needed.


Step one:
Look at this chart and see what kind of expansion your dealing with, aluminum is a good use for this, but keep in mind it expands more than copper. Remember, what your using will change the amount of distance and stresses your part can handle.
Edit: I forgot to link to the chart,
Here you go: Coefficients of Linear Thermal Expansion

Step two:
Heat your oven somewhere between 350F and the melting point of your heat sink, 400F should be good for most though. Then put your heat sink in there on a cookie rack or something and let heat up.

Step three:
put your module in the freezer, this should contract it a bit and help things from getting too hot when you put them together. You may want to later transfer this to a bowl of ice on the counter for speed, but keep it from getting wet... use a baggy or something, and maybe put salt on the ice.

If you have dry ice or liquid nitrogen you could probably do this with out the oven (still requires gloves though)


Step four:
when the parts are to there respective temperatures, QUICKLY take them to the counter. depending on how good your heat sink is you may only have seconds. For something like a maglite adapter heat sink you should have a fair amount of time though

Step five:
The ideal positioning for this would be If your wanted your heat sink and module to be flush with each other. Then you can just have both of those sides face down on the table and push the cold module into the hot heat sink, if your lucky it'll just drop right in and you can let them cool. if not you'll need that hammer and... i don't know, a wooden dowel, a metal rod, whatever you can find to push it with.

Lets say the grey is your heat sink, the red is the module, and the black is the cookie sheet.

In the end, you end up with a perfect press fit and your original sized heat sink (if you did it right)

If this is not the configuration of your heat sink, you'll probably need ceramic spacers or something... good luck if you dare

================================================== =========

Just remember to find everything before hand.
Also, you should remember you run the risk of permanently ruining whatever you do here, so no diodes, no expensive lenses, and no getting mad at me if something comes out crooked or broken.

This should create the tightest press fit you could ever hope for, just hope you want it to stay that way

Well that's all I have for now, I don't think I missed anything, but let me know if I did. Hope you get some use outta this.
Presentteck
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Last edited by Presentteck; 03-30-2013 at 10:34 PM.
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Old 04-01-2013, 01:37 AM #2
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Default Re: Simple compression shrink fitting tutorial

Quote:
Originally Posted by Presentteck View Post
as the metal contracts it'll cause some stress, and if it's too much you'll end up with a warped or broken heat sink or module... or both.
Aluminum and copper are both very soft (as far as metals go) and brass isn't far behind, so the chances of something breaking are pretty much zero. Since the heat sinks are circular, there won't be any warping either. The stress is radial. Inflating a tire doesn't make it lop-sided because the pressure pushes everywhere equally. If any damage is done here, it'll be because of excessive force and/or the wrong tools.
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Old 04-01-2013, 03:08 AM #3
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Default Re: Simple compression shrink fitting tutorial

Well if you did this with a difference of say >.5mm the stresses would be fairly large. If there were any faults they could have problems, but I see what your saying. I guess it wouldn't break. Some undesirable warping could occoure though.

It might cause problems with the thredding if there is too much pressure though. And probably be hard to press fit the diodes in.


Thanks for the feedback though
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