Originally, this Y carriage design was meant for the plasma build.  After building it, I decided it would work well as a starting point for all builds with only slight modifications.

 

Y Carriage Plate Adapter

The Y Carriage Adapter Plate, is the key behind the Y carriage. It is designed be be milled out of 1/2" aluminum, but I will be starting with 1/2" Corian. 

The Y carriage plate has to be at least 1/2" thick so that the bearing truck bolts heads can be recessed below the top surface.

Eight 6mm screws are used to attach the Y carriage plate adapter to the two extended 20 mm trucks.

I used two extended trucks in stead of the standard trucks for more rigidity. This gets twice the bearings against the rails.

I found it easyer to just place the trucks on one of the Y rails and install the plate in place.

 

Y Carriage Riser Block

Next, I added the 8 T-nuts for the Y carriage Riser block as shown here.

I'm using 1/4-20 bolts and T-nuts.

With the carriage in place the T-nuts are placed on the inside edge of the carriage.

A 14" long piece of 2040 series 1 extrusion is slipped over the T-nuts.

I make sure the extrusion is flush with the outside edge of the Y carriage adapter. The end should be flush with the end of the Y carriage adapter. 

With the extrusion flush with the front edge of the carriage, it will be overhanging 2" on the back, as shown here.

 

I created two carriages, one is a mirror of the other.  They will be placed on the Y rails in this orentation.

 

Conclusion

The finished carriage blocks look like this.

From this point I will start to add components for the X axis.