I agree, the fillament path should be reducable from the hobbed section down to the melt chamber. The thermal break and the mounting arrangement are two of the limiting factors that really need to be addressed. I’ve experemented with shortening the lower path a bit, and i’m working on a solid fillament follow up to this extruder of mine: http://www.thingiverse.com/thing:1201229 but even that one could be lowered. The hotend itself should theoretically be able to be made shorter. The top of the hotend should be the hobbed bolt / gear / etc mounting location, countoured to fit the fillament chamber, still allowing for an idler for tension adjustment and cleaning, and with a much wider heat sink / integral mounting flange to attach to structure, possibly with integral gas or water cooling mini loop. The approach taken by the Toranado extruder is a good one http://www.thingiverse.com/thing:1246951 but the motor and gear setup doesn’t have enough horsepower to match the Wade extruder fully. That being said, I think the wade gear size could be reduced (or my preferred zero backlash belt option) by at least 1/4th without reducing print quality or speed. Possibly further.
I really like the drive option found on the Bondtech extruders. http://shop.bondtech.se/ec/extruders/bondtech-qr-175-universal.html as the dual hobbed gears make for much stronger and more consistant extrusion, while eliminating most causes of fillament stripping. I don’t necessarily like the planetary gear NEMA motors as I feel the additional gearset leaves a possibility for a bit of lash that you don’t get in a belted or a direct drive design. Possibly less than you would see with a Wade gear setup though.
The J head style mounting flange design is very popular, but it is really not ideal for what we are trying to do, which is attach as short of a metal hotend to structure as possible with as little possibility for deflection as possible and as little mass as possible. It’s too tall. If we took all of that metal and made it into a wider heat sink plate thing, probably threaded to fit 3 or 4 M5 bolts or maybe even a dovetail slide in mount, possibly adding in a ceramic heat break plate it should be possible to make a much shorter, somewhat wider hotend that is more stable, has a shorter run to the melt chamber to minimize PLA bore lock, but still heats and prints like a hexagon or an E3Dv6. I even have most of a design for such an extruder worked up. My mill isn’t up to cutting one yet though. I think there are also efficiencies that can be had at the heat block as well. A ceramic disk to eliminate the weak point between the heater and the upper barrel possibly, maybe a hollow cylendrical heater core that the fillament passes directly through instead of the side mounted units we use today to lower the mass and raise the efficiency somewhat? a pasta extrusion die style deop in from the top nozzle to eliminate threads and leaks there?
I think if you took the core of a bondtech extruder, coupled it with my theoretical shorter hotend, added something like the ducting from the Toranado design, possibly with a copper coil filled with argon wrapped around the barrel to a heat exchanger on the back somewhere, and then added either something similar to my belted powertrain or some other zero backlash powertrain option, you would have a very compact, very accurate extruder that would eliminate most of the corner blobbing and layer inconsistancy that we see with today’s best options on small items. I think even if I get the prototype for my theoretical hotend exactly right the first time, I’m still looking at a few $100 to make something workable. And even then it may end up too complex to manufactur efficiently, or may have a very low adoption rate.
Thats my $0.02 cents on the subject anyways.