My old keyboard tray hung too low and slid back and forth too easily, so I removed it and placed my keyboard and mouse on the desktop in front of my docking station.  This left little room for papers to be placed in front of me.

So, I converted my hanging keyboard tray into an adjustable keyboard platform / desk extension.

Features: 
Tilts forward and backward.
Slides out quite far
Buts up, flush with the desktop
Holds position well, is quite sturdy
Cost less than $20 in materials.

Materials:
2 - Orbit Watermaster  1/2 In. X 36 In. Pvc Riser
1 - Orbit Watermaster  1/2 In. X 18 In. Pvc Riser
2 - NIBCO  1/2 In. PVC Schedule 40 Tee (threaded 3 ways)

6 - 1/2" U-Clamps
10 - small screws
10 - small washers

1 - 2" x 10" plywood riser

1 - 12" x 26" plank 
(Keyboard tray that came with desk, a generic shelf would substitute)


Tools:
Screw driver or Cordless Drill
Drill bit for pilot holes
Square and Pencil
Hack Saw


Steps, Tasks: 

Attach Pivot Support to Underside of keyboard platform.

1) Attach Tee's to ends of 18" PVC Pipe.

2) On a workbench, center 18" PVC pipe on underside of plank. Mark it's corner position

3) Center plywood riser under PVC pipe. Mark corners with pencil

4) Place U clamps over PVC pipe onto plywood. Mark holes with pencil

5) Drill pilot holes through plywood halfway into plank.

6) Line up U clamps, pipe and riser based on your pencil marks and screw together


Attach Rails to Desk

1) Sit in front of your desk holding the plank and decide on desired position.

2) Place plank on top of desk, with Pivot Support hanging down. Mark center of Tee on desk edge.

   Measure and check that desk mark width equal pivot support, from center of Tee to center of Tee.  

3) Lie under desk and use square to draw a center line from desk front to desk back. 

4) Hold rail and U clamp along center line and mark U clamp holes 1" and 12" from front of desk edge.

5) Drill pilot holes, and attach U clamps to under side of desk. 

6) Repeat steps 4 - 5 for other rail

6) Slide PVC rails into U clamps, and test sliding ability. Remove rails for further testing


Setup Rails and Platform

1) Screw rails into Pivot support on under side of plank.

2) Slide the rails into the U clamps on the desk. 

3) Slide platform until rails come out other side, or but up against the wall.

4) Measure the excess rail length. 

5) Remove plank from desk and remove rails from pivot support.

6) Cut excess rail length off with hacksaw. Reserve these pieces


Reassemble and Enjoy

1) Reattach rails to pivot support, and slide platform into your desk.

2) Optional. Screw pieces cut from rails into front of Pivot Support Tees. Trim to your preference. They will limit backwards tilt, and provide handles to move the platform with.

3) Optional Lock. Wedge an old USB key between the option 2 tube pieces and the platform to lock it's position.