so how would you mount the x-axis to the y-carriages?
I have L-profile bridge with X rail on it in my home made CoreXY
I did the Printrbot Big-E w extrusion, have to dig up the link, but it’s all flat waterjet parts. You could save yourself some time and look at what I did. It uses Delrin wheels tho. I’ll be posting my Prosthetic bot design soon, which started w rails on extrusion. I saved weight by just using linear rail for X instead of mounting it on extrusion. Depends on size. If you use L brackets, longer legs are better than shorter in my opinion. You could take a look at how used belt in a C loop instead of a jack shaft or two motors. It allowed a single linear carriage on each side and keeps the weight down.
Brook
This one or similar? Looks quite nice but I would like to avoid using wheels. However, will look at it closer. Thanks!
It has some L brackets. Wheels are ok for light duty but they come w maintenance. I’ve been transitioning to rails almost exclusively. Z axis is fine w rounds tho.
So how big are you building?
General volume is (LxWxH) 390x290x290 mm with aim on a build volume of 300x200x200mm. Also I am opting for high temps to print exotic materials which print about 350-400°C.
I’ll have the hotend you need soon 
planning for 430c! Firmware change (lookup table) and it’s a bolt on mod.
Sounds good. Which hotend are you modding? I have milled a custom heater block so it can carry a thermocouple and took the order inliner out of an e3d, but it’s a cheap knock off for testing.
At work we modded a CraftBot hotend to full metal. Works pretty fine.
Sweet! Go go for it! We are making an all metal Ubis13 HF … probably calling it the HT: High Temp.
Totally missed this. Well I am in for one!