I have a contractor table saw that I want to seal up for better dust collection. I have a good idea for how to close in the back and other holes, but I'm not quite sure what to do about the area where the sides meet the top.
Source: me
The underside of the cast-iron top is fairly irregular here. Will this have much effect on dust collection? How can I seal this area to get better suction near the blade? I'll be using a 1.5 hp collector with 4" hose, with the port directly under the blade.
If you feel it must be sealed up, some nicely placed HVAC aluminum tape will do the trick. A careful application at the edge of the table and bring it to the sides with a little turn-down to seal it up.
I do agree with Rob that 4" round will give plenty draw.
I wouldn't worry about it unless you hook everything up and find that you aren't getting good enough suction. In fact, you don't want to completely seal up the saw, or else there won't be enough air intake to feed the dust collection port. Airflow in must equal the airflow out. If you starve the dust collector by sealing up the table saw too much, you'll only strain the dust collector motor as it tries (and fails) to pull the same volume of air through nothing but the space between your blade and throat plate.
For comparison, I have a cabinet saw with a 4" dust collection port and good dust collection, and just like yours it has gaps on the underside where the cast iron table meets the cabinet. Of course, it also has the big curved hole for the height adjustment crank which allows you to tilt the arbor.
As I mentioned earlier, I wouldn't worry about it for now, but if you do later find that you don't get very good dust collection, you can always try cutting some foam to fill the gaps. Even then, you might be better served by adding dust collection above your blade--for example, some blade guards have dust collection ports.
