Shipping to up here sucks balls
I got tons of different kinds of aluminum as i work with it.
But i didnt have anything that looked like heat sink .
Just didnt know how big a difference the heat sink vs 1 big u channel with a smaller one inside like fins?
There is no big difference between a heatsink and a DIY heatsink. Calculate the surface area, you need ~110cm² per heatwatt for passive cooling(40cm² for active cooling). If you have a 50% efficient COB/strip running at 50w, it creates 25w of pure heat. To cool that passively multiply 25w by 110cm². A heatsink with 2750cm² can be used. For strips the needed area could be smaller(~90-100cm²), because strips radiate almost half of the heat fromtwise.
I did exactly what you described to cool my CRI90 COB's.
At first you compute all perpendicular and horizontal lengths together (Pic 1),
then multiply it by the length (Pic 2).
This heat sink of an 25x 35x 25x 2mm and an 20x 15x 20x 2mm channel with a length of 350mm offers approximately (246 x 350mm) 861cm² cooling surface.
Dividing this through 110cm² you get 7.82w of heat, which can be passively removed with it.
Say we, we use a 50% efficient COB (7,82:50x100=15,64w), then the surface of this DIY-heatsink is enough to passively cool a 16w COB without airflow.
Say we, we use a 60% efficient COB( 7,82:40x100=19,55w), then the surface is enough to cool a 20w COB.
Say we, we want to calculate it for active cooling(40cm²/heat watt). Surface area 861cm² : 40cm²/w = 21,5w heat.
With the same 60% efficient COB it would be enough to cool ~54w actively.(21,5:40x100=53,75w).
I just glued the little one in with the same thermal tape I'll use for the strips and it works very well!