Also please make sure you are using bolts and not screws to attach the projector to the plate. Screws may do okay into wood but they are not designed to handle loads that consist of taking them in and out multiple times. They just wont hold their strength.
Look on the bottom of the projectors for the screw mounting inserts, these are likely metric size. you can tape a large sheet of paper to the bottom then mark the layout of the mounting holes on the paper, you now have a template to use as a guide for drilling the holes.
