It would be unlikely that the cooling fan on the motor would draw sawdust INTO the motor. Rather it would be more likely that it's blowing the created dust in the cabinet through the motor into the airstream of the spinning blade causing all that dust to be blown out of the cabinet as well. I also have direct drive motors on my table saws, but there is no cloud of dust that emits from my saw cabinet. I do have the bottom seal off with the exception of the 4" port for the Jet dust collector. The back was factory made solid with no openings except for a shop vac which I sealed off. I did not seal off the 1/2" or 3/8" gap al around the table to the top of the saw cabinet. This gap allows air to enter and draw the dust down into the DC port. You do NOT want to seal off the entire cabinet or you will create a negative pressure space or vacuum inside the cabinet where there is NO air movement. You need air to move into and through the cabinet for any DC or shop vac to work. You can't seal off all the openings in the cabinet and then use a dust collector or shop vac.
The motor sits next to and partially into a box on the side of the saw, the bottom of that box is open to allow for airflow. The motor fan is drawing enough air that the bottom of that box to suck a piece of cardboard up and hold it there against that opening, and that's with the area around the table top open and the back of the saw open. It seems to be designed to draw air from outside the cabinet up into the box and over the motor, and then out the back. The fan outlet blows hard out the back of the saw. The outgoing air from the back of the saw with the back open is as strong as the exhaust on my 5hp Sears Shop Vac.
When I'm cutting, even with the back off the saw, I can see dust billowing out from under the edge of the table, falling down the sides and getting sucked up in a swirl into the bottom of the motor box. Dust is also coming out of the handwheel slot on the front of the saw and I get a rooster tail of sawdust upward out of the blade slot. The sawdust coming out of the blade slot is made worse by putting the back panel on the saw, (which I made and added). The saw originally had an open bottom, and open back. I closed off the bottom to try and contain the dust below as it would pile up and foul the casters on the cart I added. With the bottom added, it does catch the majority of the dust but I seem to get just as much on the floor as in the box. The bad part is that it spreads the dust all around, launching it airborne rather than just falling into the bin.
I assume you are using a 40 tooth all purpose table saw blade in this saw? Possibly a 60 tooth for crosscutting? The 40 tooth would have about a 15 degree tooth angle, not like the newer RAS blades with a negative or zero degree tooth angle.
I'm running a 28t all purpose blade on it right now, it gives me the fastest and cleanest cut ripping 2x4's down into slats. The blade doesn't matter much, I don't think its the blade causing the dust issue, it did the same thing with an 80t Freud blade as well.
I've been sort of careful as to which blades I use on this, this saw turns really fast, I think I read somewhere that it turns 7250 rpm, I think it was an old Montgomery Wards catalog online somewhere. They were making it a selling point that higher RPM makes for better and faster cutting. It sounds really fast when its running, it almost sounds like its running away as you take away any load. I tried using one of those reflective tape type tachometers on it but I got irratic readings anywhere from 6600 to 7780 RPM.
If the blower motor is causing this dust to get blown all over, I would suggest trying to wrap the motor with a thin metal tube like a furnace pipe, or even a cardboard tube like from an Oatmeal box, and see if you can draw clean air into the motor from outside the cabinet, but it will depend on which direction the blower is moving the air like I asked above? Typically, gravity is the most effective way the dust is "collected" as you pointed out from your early working experience. Having said that, a cabinet type industrial saw will have the motor and belts all contained inside the cabinet. A contractor type saw, like the early Craftsmans have the motor and drive belt pulley hanging outside the cabinet and a large rear opening for the belt to pass through as well as an open bottom for the dust to fall down to the ground or into a collection bag. There are some aftermarket bottom plates that have a sloped area with a dust port in the middle which is then attached to a shop vac:
It could be that this saw was only intended to be used outside and the dust was never a consideration it it's design?
The motor fan sucks air from the end, I can't tell in the cloud of dust whether its actually just being drawn in around the motor or through it. There's open ports around the brushes, and the fan is only open on one side toward the rear. The air blows straight out the back with a vengeance. But there still is air being forced upward out of the blade slot. The fan is blowing so much air that I have no doubt that its also picking up dust from the cabinet and moving it around, its even sucking it up from outside the cabinet and drawing it into the motor box opening.
I tried making a screen to try and stop some of the dust coming from the outside by making a small wood frame with three layers of window screen that fits snug into the bottom of the motor box, but it clogs that screen up in half a minute, and that was with the bottom door open and the rear of the saw wide open.
If this thing was made to be used outdoors, they sure didn't make it easy to move, the cabinet didn't have any means to mount wheels, it had 3/4 round legs on the bottom and its twice the weight of my Craftsman saw. Its why I built the heavy duty roller cart for it. To get it on the cart, I had to use a come-a-long and a pipe mounted through my floor joists overhead, two of us couldn't lift it long enough to center it on the cart. When I first brought it home, it sat in my enclosed trailer for about a year, I used it in the trailer a few times but it only had a flat plywood cart under it and the upper and lower back panels weren't there. It made a lot of dust on the table and the steam of dust out the back would blow 20ft in a straight line out the back door of my trailer. I ripped down 8 sheets of plywood for shelving one day and realized it had plastered the wooden fence behind my trailer with sawdust in a 4ft circle. I had to scrape and hose down the fence the next morning. The sawdust stuck to the fence was like fine powder and 4" thick.
I think because of the blade speed, the dust is a lot finer on this as well, which is adding to the problem of trying to contain it. Even with the 28t blade, the sawdust is like flour with a mix of strings here and there from rip cutting.
My old Craftsman model 100 saw on its open square stand with only a three sided cardboard box fitted into the lower stand makes almost no dust other than what falls off the table or spills out of the box. It never fills the air with dust to the point I can't breath.
With the Wards saw I have to wear a respirator and face shield, when I'm done I'm covered with dust, its in my hair, in my beard, in my pockets, and in my shoes. I feel like I rolled in a pile of sawdust. It covers everything in the basement.
I found that the dust collection unit does better if I leave it off the saw and just leave the vacuum port open, it then draws in the surrounding air and filters out the dust. It does little to nothing connected to the bottom of the cabinet or with the hose hanging behind or below the blade.
After ripping 18 2x4's into 3/8" thick strips, I have 1" of sawdust in the bottom of the box, and about a coffee can full in the dust collection bag. The rest is airborne and all over the place. I hung clear plastic around the corner of the basement where I was running the saw to try and contain the dust in one area.
I really had hoped that this saw would be similar to the Craftsman, but with a nicer fence and faster cut. If it would drop its sawdust downward, I don't mind cleaning out the box when I'm done and sweeping the floor around it. I was hoping to not have to run a dust collection unit with it. I don't on the Craftsman saws.
I have this and a slightly larger Delta dust collection unit, I don't have a pic handy of the Delta but its an early version of the 50-767.
This red unit has less capacity than the Delta but it moves double the amount of air. I generally run the Delta on the surface planer and larger miter saw, and this one on this and another table saw I have. The red unit is much quieter too.