I really liked having a mouse platform attached to the arms of my old computer chair, but after breaking two MOBO mouse trays, I decided I could build a better one myself. When I bought a new DXRacer chair, I knew the time had arrived. I like the adjustable arms on this chair, but figured they wouldn't be the best mounting point for a mouse tray.
Step 1: The Mounting Point
I decided to attach a 3/16" thick steel plate to the bottom of the arm. There is a 3/16" bar attached to the bottom of the chair holding the arm, so I thought this was the way to go. I got a 6"x12" plate from Amazon for about $15 and used these tools to cut it through the center at 45 degrees. The Diablo Steel Demon blade is expensive, but cut through the steel plate like butter. I sued a flap disk in my angle grinder and a bench grinder to dress the edges. The measurements on the resulting pieces were 3", 6", 9" and the diagonal which I didn't measure (but should be 6*sqrt(2)").
Step 2: A Novel Use for a VESA Mount
I had recently mounted my computer monitor to the wall behind my desk, and really like the mounting arm. At only $12.99 on Amazon, it's a steal. A drill press made it easy to drill the mounting holes in the steel plate, but a hand drill would work.
Step 3: Making the Trays
I bought 2 mouse pads and traced them onto some 1/2" plywood I had laying around. After cutting them out, I spray painted them black.
Step 4: The Trim
Next, I attached some 3/4" T-molding to the outside of the trays. I cut 1 1/2" of the "T" off at intervals so the molding would bend around the corners, then I put a bead of caulk on the T that remained and stapled it on from the top. A little of the plywood edge is not covered by the molding, but the black caulk covered that up.
Step 5: Attaching the Plate
I carefully drilled mounting holes to match the holes in the bar holding the arm, then put the plate under that bar and reattached the arm to the chair. There was some plastic molding at the bottom that I am not using now.
I used a razor knife to split some 1/4" ID fuel line and ran it around the exposed edge of the mounting plate. My wife really appreciated that when she bumped her shin on it the next morning!
Step 6: It Works!
I now have a platform on each side. The right one is for my mouse, and I use the left one to hold my Logitech G13 gameboard when I'm gaming. The trays are very sturdy, fully adjustable and easily fold out of the way when not in use.