Yeah, getting the one of the surfaces to conform to the other is a big concern. The E3D cyclops/chimera heatsink uses setscrews to mount a smooth barrel, and apparently doesn’t work for pla unless you use heatsink thermal compound between it and the barrels. At Deezmaker, we experimented with plating the barrels and settled on gold plating. Diego had a different hypothesis as to why it worked, but mine was that the gold, as a relatively soft metal, was deforming enough to provide better thermal contact with the cooling block.
Are there any dis-advantages to extruding the aluminum heatsinks rather than completely CNC'ing them
Gold plate? Nice 
I suspect there’s probably a simple way to make a nice collet or taper grip interface that has high contact stress over a large surface area, but it’s arguable whether the need for more alternative hot end formats is really present anymore. Several existing all-metal designs work well enough that I don’t see much value in trying to reinvent things (except for the pure intellectual pursuit of it, which isn’t what Shai is going for here.)
@Ryan_Carlyle I’d like to see an easily-replaceable nozzle component that only cost a few cents to produce, so that users wouldn’t need to know how to clean them out if they clog (which most people are doing wrong anyway, leading to further problems down the road) and they could instead afford to throw them away and use a new one if they so chose. Of course, it would still be possible to clean them out for those who have more money than time, but I don’t think the current situation is serving the people who just want to print and don’t want to learn about how the printer works. Of course, there are the cube3 cartridges that come with a whole new filament path, up to and including the nozzle, but you shouldn’t need to clean-out/replace your nozzle as often as you change spools (especially with thier sub-1kg cartridges), and their system still means that if a nozzle clogs, the rest of the spool is wasted.
Nozzles aren’t expensive in China. A nozzle such as an E3D 0.4mm would probably cost $0.10 to make for 500 pieces. I’m basing this off quotes we got for similar nozzles.
That’s cheap! Mine cost me two bucks, but are hard coated
Yeah, but not what I’m talking about. What I have in mind needs to continue well into the cold zone and be replaceable cold, with no chance of leaking or shearing-off the threaded portion of a nozzle when it seizes up (I’ve seen this too many times). It also has to require no more than one tool to do the replacement (no counter-tightened joints to lock things together).
Yeah I hate counter-tightened joints as well. That’s why we designed our new mini hotend to have a single nozzle the spans from middle of the heatsink to bottom.
On another note, would it be possible to create a fan with a center hole so it sits on top of the heatsink and points down? This way it can act both as a heatsink cooler and a print cooler.
Would it be possible? Of course. Is there an existing part that can be used for the purpose, rather than you needing to design them and get them manufactured? Almost certainly not.
What about a squirrel cage or two down a tube?