Custom Aluminum Heatsink

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Custom Aluminum Heatsink

Postby Rando » Thu Mar 08, 2018 8:30 pm


Sometimes, you just want to carve out your OWN heatsink design, right? Part fun, part needing to get the vises back onto the machine bed, and part honestly needing to change the direction of airflow inside an electronics enclosure, well, you might get something like this:



This project is part of a larger project to design an aftermarket Diesel engine fuel regulator. This is the heatsink for the power-converter in there. The assembly is more just a platform for development and testing, but the generated heat is enough that we're looking at maybe needing a fan. The heatsink design started with the rest of the design in Fusion360, was saved as a STEP file and imported into BobCAD/CAM, then through my special post-processing, and on to my Shark HD2+. It's 2.4x2.6x0.6", and used the following: Bottom-side = 1/4" radiused endmill to remove 0.08" from the 0.75" stock, 1/4" 90-degree spot drill for the 4 clearance holes for M3x0.5 screws; Top-side = 1/8"D 2FL 0.50"LOC 0.020"R endmill for roughing, 1/8" 3F BALL 0.5"LOC for finishing. Can you say "bottom radiusing for free!" and "no broken endmill tips!" :ugeek: I sure do love those radiused endmills. MAN do they last forever with the right F&S!

Ahem, sorry...Total processing time on the shark was about 3 hours, give or take. Below is a PDF of the (customized) setup sheet that comes out of BobCAD/CAM:

One thing that some don't realize: because of the small feature sizes requiring the 1/8" bit, the speeds of machine movement I make on this part are NO DIFFERENT from those made by the big machines. They might get better overall surface finish, but not that much when you add in a finish pass, given it's a 3-d part with sloped walls on those fins. The thing is, we are both limited by how much force you can apply at the end of that tiny bit of carbide as you move it through the metal. It does not take much to break those, and so it doesn't matter how much stepper/servo torque or spindle power you have, because the cutting parameters are set by the bit, the bit size and the material. Which means that there's this narrow range where you're both making proper cuts, but not overloading that overlong piece of spaghetti. Remember...we're talking somewhere between 24 and 30K RPM. So, it doesn't matter the machine, it's a delicate operation, and my 4hr run to get that part is the same 4hr run they have, just their machine time and maintenance and labor costs more :D.

That's why my friend in his shop with the 13000# CNC that can only handle 256K bytes (!) maximum program, could actually NOT make this part, since it took somewhere on the order of nearly 2MB of GCODE. Imagine hacking that up into bite-sized chunks! :ugeek:


Thom (Rando)
===================================================== Creative tools and photographic art
A proud member of the Pacific Northwest CNC Club (now on Facebook)
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Location: Hoquiam, WA

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