I’m puzzled by the heat sink on the MK8 extruder head. It’s only in contact with the metal (or plastic) part of the upper and lower guides of the feeder. Why not have the fan blow directly at the entire feeder assembly, without the heat sink in the way? The same parts that contact the heat sink would get cooled, as well as a lot more.
What do you mean when you say MK8 extruder head? A lot of different things are called mk8 extruders.
I guess MK8-style. What you see on a lot of Prusa i3’s (inlcuding my Anet A8). There’s the fan, mounted to the heat sink, which is mounted to the part of the extruder that feeds the filament into the hot end.
I wouldn’t put too much stock in the engineering know-how of the companies putting together those cheap knock-off printers. We see a lot of baffling, illogical design decisions.
For efficient cooling you need sufficiently large surface area where the thermal exchange is happening. The heatsinks shapes are designed to maximize their surface areas and their material to distribute the temperature from the cooled parts.
Yup, I understand the concept of heat sinks and their surface area, but with the current setup, all that’s being cooled is the face of the feed lever and the face of the guide that the throat is inserted to. So you have two small areas being cooled by induction and the rest of the components (The feed gear, guide pulley, tension spring, filament, etc) actually being insulated from the cooling. Take away the heat sink (but leave the fan, of course) and the entire assembly and every part can be cooled by convection.
I’m sure there’s a reason, but it baffles me.
The thing that NEEDS to be cooled is the mount that supports the heat break / thermal barrier tube. Otherwise, heat conducted up from the hot block will make everything too hot and you’ll get filament jams, melt down plastic components on the carriage, etc.
Does the heatsink make good thermal contact with whatever bar/plate/thing the heat break is mounted to?
Not as good as it should, because they only allow for the two top screws (on the fan and heat sink) to be used. Everything works though. It just looks counterproductive from a cooling point of view.
The heatsink is supposed to keep the cooling block (the one the heat break is mounted in) cool. Some cloners don’t understand this and put standoffs between them, making the fan and heatsink completely useless.
There are no standoffs… just not the best contact. I’m pretty sure I can modify it down the road – but it’s working fine, so I’m in no hurry.
You don’t want the fan blowing into the feed side you would get lint and dust blown in. The heat sync pulls any heat out of the block that the throat screws into. You want the heat sync in contact all the way across the face of that block.
Now it makes sense! 
ye mk8 right bad design
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