Thread: Improving machine cabinet dust ports

Re air inlet/entry ports. Should they be equal to or larger than the machine outlet ports or doesn't it matter if they are oversize?
Just doing some calcs. now my 150mm outlet port is connected to my saw table.

Originally Posted by Lappa

Re air inlet/entry ports. Should they be equal to or larger than the machine outlet ports or doesn't it matter if they are oversize?
Just doing some calcs. now my 150mm outlet port is connected to my saw table.

If by an "air inlet/entry port" you mean the air inlet port into a machine cabinet then the area should be greater.
As important is location and shape.
Location wise the ideal placement is in the cabinet opposite the outlet
An inward facing rounded lip will help reduce resistance especially if the size of the inlet is constrained by the machine itself.

Originally Posted by BobL

As important is location and shape.

An aspect of shape and location that Bob did not mention that is probably self-evident to most, but probably not all of us is that the location that produces the ideal airflow will not always be the best location to use. Maintaining the structural strength and functionality of the machinery is also extremely important.

While making the air entry opposite the DC port might create good airflow you may wish to consider another option if you find yourself cutting through metal thicker than 2mm.

Also, look at how the collection is working inside the cabinet to see if dust is accumulating in any corners. Even a 3/4" hole in a corner can greatly reduce manual intervention to keep the cabinet clear of dust buildup.

Cheers

Doug

Originally Posted by BobL

As important is location and shape.
Location wise the ideal placement is in the cabinet opposite the outlet
An inward facing rounded lip will help reduce resistance especially if the size of the inlet is constrained by the machine itself.

I'm planning on fitting a 6" outlet on my jointer when it's restored but I measured the dust chute opening and it's only 230mm x 190mm. I know this is smaller than the largest diameter of the 6" bell mouth hoods you recommend. Would I be okay making a box slightly larger than the hood and attaching it in between the chute and the hood? Or will this be pretty pointless?

Originally Posted by doug3030

An aspect of shape and location that Bob did not mention that is probably self-evident to most, but probably not all of us is that the location that produces the ideal airflow will not always be the best location to use. Maintaining the structural strength and functionality of the machinery is also extremely important.

While making the air entry opposite the DC port might create good airflow you may wish to consider another option if you find yourself cutting through metal thicker than 3mm.

Also, look at how the collection is working inside the cabinet to see if dust is accumulating in any corners. Even a 3/4" hole in a corner can greatly reduce manual intervention to keep the cabinet clear of dust buildup.

Both good points Doug,

If we want to get really nerdy about the ideal way, the dust collecting air should flow inside a TS cabinet then the the thing to consider is the direction of the blade and resulting spray of sawdust from the blade. The air collection stream should then be directed so that it flows as much as possible along with the initial dust spray so that it adds usefully to the initial moment of that spray .

A TS blade effectively sprays dust down under the table from the front of the blade so the best place to collect the dust is immediately underneath the front of the blade. to help carry the dust it would be useful if the air could come in from the top of the table but the gaps in throat plates around blades will only permit a few CFM to pass through them plus the wood itself often totally blocks this pathway.

The next question is where is the rest of the dust going? and can the incoming air flow be used to minimise dust escape along this path.

Most of the dust inside the cabinet that has not being grabbed is likely to be sprayed by the blade in an arc heading towards the back of the cabinet.
Hence the best place to have the air coming is likely to beat the back of the cabinet. The question is how much of a gap should be allowed - a completely open back will result in the most air being available but the speed of the air might be too slow to prevent dust escaping. You can generate higher speed incoming air by restricting the gap but while this will prevent dust escaping it will also restrict the flow. One way to do this is to try a few different size openings - maybe even install a sliding door mechanism of some kind to determine an optimum opening area

My unit is a home built table saw. It's just a 6mm ply box 600x800x450mm under the table top. I can cut a hole or holes anywhere
The saw is a Makita N5900B 2000W circular saw I bought in the 80s. One thing I have done is point the dust chute from the saw directly at the cabinet outlet - its about 200mm away in a direct line. The saw still has the rotating blade guard.

Before I connected the dusty, I had a 50mm connection directly into the cabinet side at the base, at 90 degrees from the open side of the blade, from one VC, and a 35mm connection directly to the dust chute from another VC. Probably 75% of all the chips etc came out the chute but there was definately dust and chips in the cabinet base but there definately was some in the VC.
I'll add a diagram to this post later to show locations of item.

table saw layout.JPG

Originally Posted by bueller

I'm planning on fitting a 6" outlet on my jointer when it's restored but I measured the dust chute opening and it's only 230mm x 190mm. I know this is smaller than the largest diameter of the 6" bell mouth hoods you recommend. Would I be okay making a box slightly larger than the hood and attaching it in between the chute and the hood? Or will this be pretty pointless?

Is the size of the opening in some sheet metal or something more serious like cast iron?

If it's the former then I would cut the sheet metal.
If its cast iron an forms a critical part of the structure - I wouldn't even bother with a box as it will add probably add at least the same amount of turbulence as my suggestion below

The diameter of a BMH for a 6" duct is 150 + 75 = 225 mm.
So the opening is easily big enough in one direction and close to big enough in the other.
This will give you 64% coverage of the opening under BMH conditions - this makes it really worth doing,
I would just make a normal BMH and trim it to fit the opening. There will be a small gap along the cut edge that can be filled with a bit of gap filler and smoothed over.

BHWbox.jpg

The other way to do it would be with a "round to rectangular flared" transition.
While better than a hard connect that would probably be worse than my modified BMH suggestion.

Some photos of the opening - inside and outside would be good.
If you want some help cutting the sheet metal opening I am happy to help.
It could be cut with a template and a plasma cutter or if it's not too thick a nibbler which I could probably borrow from someone.

Here's what were looking at.

Thanks for the pics Bueller. It is a bit of a different setup to what I was visualizing, not greatly different but there are some ways that it differs from mine that would certainly impact on the design.

I was expecting there to be a ramp involved but I was thinking more along the "open ramp" design in my carbatec 8" jointer. On mine the sides are open so the airflow space under the wheels would allow plenty of air into the cabinet a dn be sucked easily around the ramp and out through the DC port.

I am assuming that there will be only a thin space between the top of the ramp enclosure and the top of the tables when fitted. My initial thought would be to cut some of the metal away from the sides at the top of the ramp so that air can be sucked in from outside the ramp and pull the fine dust and chips down the ramp and out.

The presence of such a solid ramp meeting with the end of the machine right at the bottom of the rectangular port also makes me wonder if a rectangular-circle transition might be the way to go, maybe making the port on an angle to maintain the slope of the ramp into the port before making the transition to round.

I would like to hear BobL's opinion on this

Cheers

Doug

** WARNING ** - SUPER GEEKY AIR FLOW IDEAS discussed in this POST

Originally Posted by doug3030

I am assuming that there will be only a thin space between the top of the ramp enclosure and the top of the tables when fitted. My initial thought would be to cut some of the metal away from the sides at the top of the ramp so that air can be sucked in from outside the ramp and pull the fine dust and chips down the ramp and out

Yep - spot on - see below

The presence of such a solid ramp meeting with the end of the machine right at the bottom of the rectangular port also makes me wonder if a rectangular-circle transition might be the way to go, maybe making the port on an angle to maintain the slope of the ramp into the port before making the transition to round.

I would like to hear BobL's opinion on this

Lots of options here.

1) Just make make up a 250 x 250 mm plate with a short piece of 150 mm PVC ducting and attach to the existing 190 x 230 opening. There will be very little flow exactly because of what Doug says so it matters little that the exit post is sub-optimal because it's not the flow limiting step. Likewise adding a cut down BMH as per my previous post will do little to improve the flow

2) See option A below
Open up the vertical from 190 to 225 mm and attach a full size BMH as show at S1.
Then add a flow path as shown by the blue arrow, I would use some really coarse reo-mesh just small enough to stop toddlers hands getting in there.
Just use double the area of 150 mm duct to make the mesh intakes. One drawback to this method way of getting air to the flow path is if you don't have the DC on, sawdust will fall down through the mesh into the rest of the cabinet.

The problem now is Doug's second point that the exit air flow path is sloped relative to the BMH an so is effectively not full width. To get around this go to option B;

3) Further open up the vertical as shown at B so that the BMH exit is now sloped as per Doug's suggestion.
Of course an air intake like A has to be added to provide max flow.

planer.jpg

4) If you wanted to get super fancy you could do this.
This has a BMH into and out of the dust generation chamber.
Ideally you would need a 3rd BMH on the outside of the air inlet (these double BMHs are use in loudspeakers) BUT because the inlet is sloped it has more surface area so may not be needed - but it would be dead easy to put a 3rd BMH on at this point
planer2.jpg


Its interesting that I have two machines at the mens shed that have a very similar situation.
One is a 6" planer and the other is a 10" TS - To start with they are going to get option 1) above - they need something right away and I won't have time to finesse these until later this year.

Now you can see why I am interested in being able to turn out BMHs by the dozen.

Thanks for that detailed list of options Bob, I've got a lot to consider! I still haven't looked at the innards of the cabinet so I'll take a look and try and figure out a plan of attack.

Originally Posted by BobL

Open up the vertical from 190 to 225 mm and attach a full size BMH as show at S1.
Then add a flow path as shown by the blue arrow, I would use some really coarse reo-mesh just small enough to stop toddlers hands getting in there.

Just use double the area of 150 mm duct to make the mesh intakes. One drawback to this method way of getting air to the flow path is if you don't have the DC on, sawdust will fall down through the mesh into the rest of the cabinet.

Bob, I think you will find that the ramp is fully enclosed within the cabinet from what I saw in the photos so the mesh may not be necessary from a safety point of view but I do like the idea for some reason.

I am not sure whether I explained it well enough but I was suggesting cutting out the vertical sides of the ramp to create the additional air flow - for the reason that without a DC on (and lets be honest, many of us have passed a small piece of timber over the jointer without the DC on or even attached for expedience) the chips would fall on the ramp and get disposed of the next time the dusty is turned on.

Cheers

Doug

Originally Posted by doug3030

Bob, I think you will find that the ramp is fully enclosed within the cabinet from what I saw in the photos so the mesh may not be necessary from a safety point of view but I do like the idea for some reason.

that's right however the sides of the ramp also don't have direct access to the outside of the cabinet.

From the other photos of the planer it appears the base also extends right down to the floor so the back and side of the ramp is sealed which restrict flow. Either another opening would need to be made in the side(s) of the cabinet or the cabinet would have to be lifted off the floor by at least about 50 mm to allow air to get into the about. All these will add some restriction to flow which is why I suggested a double air entry

Putting holes in the sides also means the air has to do a 90º bend to get into the main airflow path

I am not sure whether I explained it well enough but I was suggesting cutting out the vertical sides of the ramp to create the additional air flow - for the reason that without a DC on (and lets be honest, many of us have passed a small piece of timber over the jointer without the DC on or even attached for expedience) the chips would fall on the ramp and get disposed of the next time the dusty is turned on.

Most chips may indeed far onto the ramp but the spinning blade will cause a fair bit of turbulence inside the ramp so I reckon finer chips and dust will go all over the place including down into the rest of the cabinet.

Originally Posted by BobL

From the other photos of the planer it appears the base also extends right down to the floor so the back and side of the ramp is sealed which restrict flow. Either another opening would need to be made in the side(s) of the cabinet or the cabinet would have to be lifted off the floor by at least about 50 mm to allow air to get into the about. All these will add some restriction to flow which is why I suggested a double air entry

Putting holes in the sides also means the air has to do a 90º bend to get into the main airflow path

Maybe so, maybe not. The jointer is obviously a WIP and we are both forming our own conclusions about what the end result will be. Right or wrong I see it as ultimately being raised up on some sort of mobile base so air getting in would not be a problem. I might be right or I may be wrong. Only Beuller can answer that so hopefully he can give us some fedback on how he sees the project. not much point in commenting further until we know more about it.