Converting a J-Head from 3mm to 1.75

I have 3 j-head hot ends - the official ones from hotends.com. They are all made for 3mm filament, and that's obviously the filament size I've been using. I'd like to transition to 1.75 for a variety of reasons,and I'm wondering if it's possible to just replace the PTFE liner inside the hot end to convert to 1.75mm? Something I read somewhere - I can't remember exactly where - seemed to indicate that the melt chamber is smaller in a 1.75mm hot end, and one made for 3mm would be too big to be controllable with narrower filament, but I don't know if that's true or not.

All 3 J-heads have been purchased in the past year and a half. I believe they are all Mk V-B models.

Hotends.com sells a replacement tube - I just don't know if it's meant for a conversion. I know I could probably buy a larger length from mcmaster, but the hotends product also includes a "short piece of tubing that guides the filament through the hollow set-screw". Since I don't know what this is, I'd be inclined to purchase from hotends.com.

Any help would be appreciated.

I used PEEK 1.75mm j-head before, half year ago, I bought chinese made metal 3mm e3d and put the OD 3mm ID 2mm PTFE tube inside from the top of e3d down to the half heat block. It run without any problem for half year.

I have got two 1.75mm Mk Vb jheads from hotends.com. I have not run a 3mm version so cannot compare the two sizes.

The 1.75mm size has a PTFE tube inside and I have replaced this with my own after it was damaged.
I used a 1/4" PTFE rod cut to length and I drilled a 2mm hole down the middle, the Wiki says 1/8" I think. After screwing in the brass hot end (be careful or the peek will split, just do it hand tight) the 5/16" hollow lock set screw is tightened down on the tube.

There is a short PTFE tube that pushes into the inside of the hollow lock set screw. It is 4mm od/2mm id x 7mm long, same tubing I use for my Bowden tube.

Further thought .................. my brass nozzle is drilled out to accept 1.75mm filament, not sure what diameter the 3mm version is drilled out but I don't think it will be suitable.

Edited 4 time(s). Last edit at 01/10/2015 06:59AM by dave3d.