I've been thinking about extruders and their problems concerning the nozzle/barrel design. Nophead had mentioned the idea of a water jacket for an extruder and I thought that was an idea worth considering. The goal is to have a short melt zone for the filament without having a large heat sink mounted to the extruder/Z axis to remove heat from the upper barrel.
I welded this extruder from stainless steel tubing. The diagram (not to scale) shows how it's constructed- the inner barrel is tapered at the tip and then has a short thin wall transition section to the upper barrel section to minimize heat transfer to the upper barrel. The upper barrel has a water jacket around it for cooling. This assembly will be mounted to the Z axis by a block that clamps around the water jacket.
This particular extruder has a one piece barrel/nozzle. The next version will probably have a removable nozzle/heater so I can easily change nozzle size without removing the entire extruder or having to take apart the entire assembly. The machined groove at the top of the barrel is for a plastic guide for the filament to reduce friction as it enters the barrel.
I'll use a small aquarium pump with a PC radiator and cooling fan to complete the system.
I still have to make the heating element- more than likely it will be an aluminum or brass piece with a resistor mounted to it. No idea how well the water cooling will work but it'll be a fun experiment! I can easily modify the shape/size of the water jacket if needed.
I've been out in the garage cutting aluminum extrusion for the chassis so I should have another good update before the weekend is over...