Ok guys. This is how I VESA mounted my ACER H236HL monitors on a PLANAR 3 monitor stand ($200).
First you will need just a few tools and hardware:
jig saw with metal cutting blade
5/32 drill bit
Phillips head screw driver
plastic pry tool (similar to tool used to take apart a cell phone - thin flat blade, guitar pick, last resort, flat blade screw driver)
12 - 1/8" x 1" flat washer (homedepot/lowes)
12 - M4-.7 hex nuts (homedepot/lowes)
red/blue lock tight (optional)
Now you want to pop off the back cover to your monitors. I found this site that shows you how to do it:http://www.manualslib.com/manual/455818/Acer-H236hl.html?page=29#manual
Now take the vesa mounting bracket that comes with the and place it up to the back of the monitor cover. You need to mark out two places to allow for the power and DVI plug clearance. Also, take the hinge cover off (one screw from underneath). you can set it on later when your done. See pic:
I notched out the bracket with a jigsaw. I made two inward cuts then used vise grips and bent the metal tab I just cut back and forth until it broke off. Notice how I lined up the top of the bracket with flat spot on monitor back and edge is lined up with HDMI port. Do this the exact same on each one. I know, it is NOT the center of the monitor. Don't worry, the stand allows for adjustment. G
Go ahead and drill your 4 holes while you are marking for the bracket mods. These need to be pretty precise. I dropped in a bolt after drilling each hole to make sure I didn't shift the bracket.
Now we need to modify 6 of the flat washers. These are the top ones. The mod is to adjust for the bend in the monitor backing. See pic:
I used vise grips to hold one edge of the washer. I held it on an angle on my garage floor and wacked the top of the vise grips with a hammer to get the bend seen in the picture. Im sure there are 100 ways to do this.
Now mount the bracket with the hardware that came with the stand plus the hardware I mentioned above. Locktite can be used. I had some blue laying around so I used it. This is optional. Just snug them up PDT (Pretty Darn Tight - im from GA). If you see the monitor backing distorting when you tight the bracket down, then something isn't right. Check your hole alignment and/or washer bends.
Now pop your cover back on gently but firmly. Make sure all snaps are pressed in then replace the two screws. Repeat for each monitor.
You're ready to assemble your stand now.
One more note on "centering". I had to offset the center monitor a good bit to center it from the front. See my pic:
This is my first write up. Let me know if you have any questions.