Well it looks like Demented Chihuahua and I had similar ideas about the same time with the extruder. He posted on the builders blog on Wednesday on the extruder topic. I don't have a ton of time to explain this current revision, but I hope it will spur some discussion.As you can see the basic design is very similar to the one Demented Chihuahua made. However, there are a few main differences. First, the filament guide must extend almost to the heater to prevent buckling in the filament. Also, the heater is insulated with drywall, or fire cement or some other insulating board. I choose drywall because it is dirt cheap and easy to work. Also in my machine I'm going to be using cartridge heater driven at mains voltage, switched by a SSR (time proportioning control).
There has been some question as to whether or not the filament can be pushed directly into the heater body without the molten plastic squirting back up the filament entrance in the heater. I did some experiments back a year ago, but never got around to documenting any of it. I repeated the experiment last night and had no troubles. I used a 0.095" filament pushed through a 0.103" hole. If a generous chamfer is added to the heater entrance, then filaments slightly larger than the hole in the heater could be used. This would prevent ANY mushrooming of plastic and the heater entrance. However, this still needs to be tested. I really am confident that this is how the Dimension FDM machines work.
Let me know what you all think :) Please let me see the holes in my logic and ideas.