I liked very much the CR-10 Dual Z axis by Caster, also the Frame Braces from TomExplorador. So I decided to unite them, and I made some adjustements for the Tevo Tornado. To get the idea of the construction please read the original things, especially look at caster's page https://myfordboy.blogspot.de/p/the-cr10-has-single-z-axis-leadscrew.html .
You need following additional parts:
600mm leadscrew and nut https://goo.gl/fM8znL
GT2 852mm Timing Belt: https://goo.gl/iXa4sv
3 Bearings: https://goo.gl/HnzTqr (1 x idler, 2x right lead screw)
2 x M8 threaded rods
6 x M8 nuts
7 x M5 x 20 screws (idler and lower holder)
7 x M5 x 35 screws (upper holder and geanty plate)
11 x M5 Tee nuts
2 x M3 x 20 screws and nuts (bearing cover left)
4 x M3 x 15 screws and nuts (lead screw nut)
6 x M3 x 10 screws (pulleys)
1 x M2,5 x 10 screw and nut (cuff (manschette8mm.stl))
A few washers.
Following parts you need to print more than once:
6 x BallNutM8
2 x 516_Nut (alternative 2 additional BalNutM8)
2 x pulley-64
3 x Spacer8-7mm (for mounting the gantry plate)
2 x Washer8 (right lead screw: between 64 tooth pulley and upper bearing and between cuff and lower ball-bearing)
2 x Z-RHL-75 (right side upper & lower holder)
For the left side you should use the 100mm holder, on the right side both 100mm and 75mm holder are possible, but the 75mm parts are more rigid.
For the gantry plate I used PETG, because it sees the most heat.
If you don't like to dismount the right Z wagon off the X axis, do it without the inner gantry plate screw, the gantry plate mounting with the 2 remaining screws should be strong enough.
The extruder of the Tevo tornado is higher than the one of the CR-10. If you don't like to loose some mm Z room, install the Tevo extruder turned 90° with the Titan_mount.
I'm new in 3d printing an my cad skills are limited. Please tell me any flaws, may I can improve this thing.