Vent
Vent
Gary,
There are two "styles". If your filters are in the same enclosure as the rest of the cyclone, you need to provide a way to return the air to the shop. The second is if you build your closet around the cyclone, blower and motor only, and the filters are in another location outside the closet, then all you need to supply is some way for heat from the blower and motor to escape.
In the first "style", the size of the opening, and some sort of baffle is probably best, is determined by the airflow through the system, you'll want over pi * 3^^2 for outlet area, though that'll still yield rather fast velocity through the outlet. So maybe pi * 4^^2 would be better. Location of the outlet shouldn't matter all that much in this style as there'll probably be plenty of air and heat exchange within the closet to keep the motor cool.
There are several examples of this in the gallery, I think. Perhaps the easiest to visualize from the photos is
Jameel's.
For the second, probably two holes but smaller, an inlet and outlet. Seem to recall at least one person also incorporating a 4" or so computer type fan to ensure flow, either blowing directly on the motor from the inlet or sucking air out near the motor, can't recall which. Either should work just fine, and there is thermal overload protection on the motor. Were it me in this scenario, think I'd put the inlet low, and baffled so noise doesn't have a direct path out, and outlet, also baffled, above the motor. And were I using a fan, I'd probably put it blowing out.
Regards,
DWD