"Hey, Brian now drills the 1.75mm heads to 1.8mm, and the melt chamber actually turns out to be a bit longer I believe."

"I will get several made with a smaller melt diameter to suit a 1.75mm and test them,"

"You can get a J-head for 1.75 with a smaller bore. PTFE liner. I am not sure if the hole in the brass block is any smaller.(that is what I would consider the melt chamber), I suspect not."

"the current j head the bore is 3.5mm, surely if you using a 1.75mm filament the the bore should be smaller, say 2.3mm , you could loose the ptfer liner and machine the bore to either filament size?"

"I didn't design the gear, it is from a RepRapPro Huxley. I used to print them for them.

I might be wrong, but I think the only difference in a J-head would be bore of the PTFE liner."