While the final specifications, of the J-Head Mk IV will not be finalized until all test results are in, I have decided to limit the number of changes.
Specifically, I will not be changing the design of the nozzle/heater piece at this time. This is because the new design would not have a PTFE liner all the way to the tip and the current design is both compact, has been proven to work, and has been working successfully for at least 3 months. Therefore, I have decided that any changes should and will be more incremental in nature. If the vented nozzle holder design is successful, I will be implementing that change and that change only for the Mk IV.
By changing the nozzle holder, only the method of cooling will change slightly and not the filament path. In addition, if the new nozzle holder is successful, it will be possible to add cooling to the more compact 36.5mm long nozzle holders. (I have one made and will be posting a picture within a day or two.)
The smaller 13x13mm 6.8 ohm nozzle/heater will, however, be tested extensively as I believe that if it works the weight savings and size reduction will be a positive improvement. However, the number one priority above all else is reliability.