Well, ive been working for the last month or so to get dual mk5 heater cores printing on my mendel with very limited success. My biggest issues are excessive loading of the filament through my bowden cable. I can get pla to run through it at REALY low speeds but if I try to extrude over about 10mm/s it jams and strips the filament in my wades extruder. Ive been wondering if the hobbed bolt i made was the cause so I ordered some from ebay about a month ago but have yet to recieve them.
One of the issues I have with the pla is probably filament swelling leading to excessive backpressure but so far I havent found a solution to that. The 1/8" stainless pipes I tried initialy as filament guides seemed to transfer heat too far up their length causing real bad back pressure and when I tried to shorten one of them I made it too short and the ptfe tubing swelled and deformed between it and the upper filament guide section. I currenty am trying a stock makerbot barrel and nozzel assembly and with it I can get the 10mm/s or so feed rate with some reliability though i had to add two heat sinks instead of the standard one. I beleve this is at least partly because the mendel carriage encloses and retains the heat better than a standard makerbot open air design.