The aluminum X carriage is created as outlined in the Volume 1. Since they are simple holes, it just becomes a standard drilling operation.
I made a small change which you are free to do if you wish.
In the upgrade section I did an article adding a Z Axis Bearing Mount Brace.
I decided to just add the length of the brace to the X carriage and make it one solid piece.
The original X carriage plate is 7” wide by 12” tall. I made this one 7” wide by 15-1/2” to accommodate the brace.
The first step is to place a mark 3-1/2” from the top as shown here.
Tape the X carriage template to this mark as shown here.
Mark the location of the 10 5/16” holes with a punch.
Drill the 10, 5/16” holes. Be sure to deburr all the holes.
Test fit the X carriage. You will be removing it to install the Z rails.
Remove the X carriage plate and install the Y rails as detailed in Volume 1.
Note you will a couple more fasteners, as you will need to attach the top of the rail to the now extended section at the top.
Something else I wanted to note. The assembled extended X carriage and rails is very heavy and hard to hold in place while you insert the first truck screws.
I had to get a help to help me hold it in place while I added the first couple screws.