Jim, I built Gary's vac box and put 4 motors in it. They are divided into two chambers inside the box. Each chamber has two motors. Two motors are used to hold 90% of what I cut. The additional two motors can be turned on to increase the CFM to more securely hold the parts when necessary.
I've opted to run mine without input filtration. I have set mine up where I have a simple little desk fan to blow clean fresh air in to the intake part of the box so the motors are always getting clean fresh air. I check the motors regularly to see if there is any dust or debris build up and so far, after about 4 months of running daily, I've had no problems.
Gary did a fantastic job on the design for this box. It works great and my hold down capabilities on my sliding-valve controlled 7-zone table could not be working better. I am extremely pleased with the performance. Even at an altitude of 2500' ASL I still get 7"-8" of vacuum.
