Just my 2 cents
It's a 50/50 thing for me...
The good the bad and the ugly ..it's true it will suck out the dust from inside of the cabinet but I know that heat kills any motor..
The dust pickup on the fence will pickup most of the chips/dust and if you are not using the fence the chips are going over the edge of the router table the norm not going down a 1 1/4" hole in the table top..
The OP plate has a hole in it to help suck the chips down but it's very small at best and is not very big at that, most of the time so the chips still go over the edge and on the floor, just the nature of the beast...
As far as closing up the back side of the cabinet, it's not needed if the cabinet is made right from the get go...it will just block you from use the router table from the back side...some time you may want to use the table for the bigger/wider items and if you flip the fence around you will have a bigger table top the norm..
Most tools don't enclose the motor in a dusty cabinet they know it needs clean air to run cool and it should not suck up dust from the machine but on the other hand the ones that do use a enclose motor and the router is not, that's to say it will suck in air/dust and blow it over and inside of the motor...it's true the bearing are sealed but not the winding/Arm. inside the router..and a 4" hose vac.system may defeat the engineer of the router by doing so..pulling the saw dust backwards into the motor...
So you can see why I'm at a 50/50 thing on vac.systems on the router cabinet.
Originally Posted by deck99
I am just wrapping up the table top on my new router table. I am now going to start the cabinet the top will sit on. My new fence has a 2 1/2 inch dust collection on it. On my other tables I have built, I never built a box around my router. I see a lot of tables have a 4" dust port under the router box. Is this really necessary? Or should I say is it a big help?