Making nozzle Holder for J-head extruder from Alum?

Hi, Im new here and to 3D printing but not to machining. I have a CNC router and mill that Ive built and a lathe, so I was hoping to make a majority of my parts myself for my first printer. Ive looked at many of the different hotend designs and like the J-head alot, but was wondering if there was a need for the nozzle holder to be make from PEEK or if I can make it from 7075 aluminum. ( I have that laying around) I was planning to make my nozzle from brass, and thread it into the aluminum and have the PTFE sleeve just like the rest of the J-head. Are there any problems with this idea?

The Peek is designed in these extruders to operate as a thermal barrier between the hot end and the extruder. If you use aluminium to replace this piece you will need to come up with a way to cool it to a temperature compatible with your extruder body. Trouble you have with this is that Alu conducts heat well. If you cool the Alu, heat will transfer from your heater.

Not impossible to get round the issue I am sure, but probably you will need to redesign the extruder to take into account the heat conducting powers of your replacement material

Im planning to use a Bowen cable and mount my extruder elsewhere so heat there shouldnt be an issue. But I do see what you mean about the aluminum possibly robbing heat from the heater block. Ill have to take a closer look, But maybe Ill just buy my first hot end...

You can use stainless steel with a very thin section instead of PEEK as thermal insulation. There are a few designs out there using this idea. You still need to use a PTFE liner inside to reduce friction on the feed.