Thread: Improving machine cabinet dust ports

Unfortunately they are not true bell mouth hoods as far as efficient dust collection is concerned.
A BMH has a radius of curvature of the bell at around 1/2 the radius (1/2R) of the pipe. The ones from Rainbow you link to look like about a 1/4R.

A crude way to tell is to measure the width of the Bell (X) and then the width of the pipe (Y) and divide X by Y.
RainbowBMH.jpg
The resulting number for a true 1/2R BMH wshouldill be at least 1.5 wheres I get 1.27 for the Rainbow ones.
The Rainbow ones are actually a bit worse than this because they have quite a bit of flat on the edge of bell whereas there should be no flat until the 1.5R
While they will be better than nothing they won't be as efficient as the 1/2R version.

I'm still making BMHs for sale from time to time - PM me for details etc.

Just checked,
Y=160mm
X=235mm
Not perfect, but getting close?
IMG_1605.jpgIMG_1606.jpgIMG_1607.jpg

Originally Posted by Moo73

Just checked,
Y=160mm
X=235mm
Not perfect, but getting close?

Unfortunately I t’s not 235 mm because a substantial portion (looks like about half) of that is flat. Can only count the curved section of the mouth.

I think I know where I went wrong, I was taking the diagrams a bit too literally, and forgot the flat part of the bell actually isnt flat... played around in sketchup:
BMH, 150mm installed.jpgBMH, 150mm cross sctn.png
So, using 76mm hole saw - created a template and using epoxy filler, modified to the min. requisite 150mm duct, 225mm opening with r37.5mm:
IMG_1611.jpg
Sawstop ICS external view BMH outlet:
IMG_1615.jpg
BMH inlet side, before sanding
IMG_1609.jpg
First time powering up cyclone, and dusting out the sawstop with bmh insitu

Good effort and nice Vid. It would be good to get the inside of the BMH as smooth as you can.

Having that saw the only criticism I see is that you can't tilt the saw blade now. The motor will swing towards the port. The access door you were reaching through in the video is an option if you choose not to cut into the saw's cabinet at the existing 4" port.

Pete

Must admit, I was trying this work out why the bulging door under the table extension
But not really a problem. The final version will either be cut into the door (big gulp, pucker moment), or will build a replacement door with the profile to match the bulge.
Decided I’d rather pull across the cabinet via the side doors rather than front to rear.
means I get a better air intake, cross flow from the belt door without having to cut more holes. A mesh guard will be next, just trying to avoid blocking it up too much.

Originally Posted by Moo73

A mesh guard will be next, just trying to avoid blocking it up too much.

Not sure why you need a mesh guard?

Are you concerned by something getting through to the impeller?
Anything small enough to get through a throat plate will be easily dealt with by an impeller.
My TS has had an open 6" duct directly underneath the blade for 7 years without any problems.

If you are worried about something jamming in the ducting then you have to weigh that up against the many more times it will block up against any sort of mesh.

If you decide to use mesh, my limited testing shows that air flow losses due to using a mesh are low provided the mesh uses a spacing that is larger than 25mm, any less than this and the flow losses escalate rapidly.

No, on the SS ICS, the door I have open for the air to come into the cabinet is right where the motor belts run. I’m thinking some small vermin mesh in a frame might work

Make up air into the cabinet. The SawStop has a door on the left to access the belts and an electronics box just below it and the big boxy door over the motor on the right. Both have a few louvers but not enough to let in enough air for the 6" port of the DC.

Pete

I have a Powermatic 66 table saw with a 4" dust port. I don't want to cut up the cabinet to allow for a larger port. would adding a bellmouth to the port inside the cabinet increase performance?

Originally Posted by t3steve

I have a Powermatic 66 table saw with a 4" dust port. I don't want to cut up the cabinet to allow for a larger port. would adding a bellmouth to the port inside the cabinet increase performance?

The short answer is "yes" but the overall improvement depends on the total flow
The size of your DC - a 3HP DC should result in a slightly better performance than a 2HP etc
The ducting used to connect the TS to the DC - if you are using 6" ducting the improvement will be greater than if you are using 4" and greater still if you are using mostly flex.
How many holes there are in the cabinet to allow air into the cabinet - most TS have too few and too small air inlets into the cabinet. This means cutting more holes into the cabinet preferably.

Bob,
Thank you for your advise, the only air inlets are the arc cutout openings that the blade raise/lower and tilt hand cranks move though.

Steve, I felt the same way about my General 650 cabinet saw. After following this forum for a few years, I finally bit the bullet, bought a Clear-Vue and installed a 150mm (6") port in my saw.
Should have done it long ago. What a difference!!