Over the blade dust collection

[John K Jordan]

JKJ, Not sure how it would affect your problem (Too much suction? A totally foreign concept, to me.) but I've wondered about drilling some holes in my ZCI, left and right of the blade slot. I've seen a picture of that somewhere, but no explanation of how well it worked. Don't see how it could hurt, but I'm open to anyone's thoughts.

I've read several discussions about holes in inserts and the consensus has been that if the insert is covered by a wide piece of wood or a sled the holes are blocked and do nothing. That would go for the wide opening in the non-zero clearance insert too.

My experience with making my own bandsaw inserts is holes with suction behind them do help for at least one case, skimming cuts on the edge of a block where 1/2 of the holes are not covered by the wood. Even then, a lot of sawdust gets thrown sideways to I use a 4" auxiliary pickup on the top of the bandsaw table, held with a strong magnet in a position which seems to catch the most.

As for plenty of suction, I have one DC pickup just behind my lathe and it works better than I imagined. It pulls in so much air that I've watched fine sanding dust travel a couple of feet horizontally to be sucked up. I lose sandpaper and paper towels when I'm not careful. There is never sawdust in the bandsaw cabinet and after drum sanding with a 22-44 the particulate monitor doesn't show an increase 10' from the sander. The table saw is the worst.

I joke that you don't want to let your cat get too close. A video from ClearVue shows a vertical 6" duct snatching a 25' measuring tape, carrying it through the horizontal duct, and dumping it in the bin.



JKJ

[Jim Becker]

Brian, the design of the cabinet makes a difference relative to good collection with ZCI. Most cabinet saws have enough holes to provide makeup air to keep things moving efficiently. Some sliders that use a shroud design make for a more closed system and ZCI can affect collection negatively. But the benefit that a ZCI provides can be made up for with a scoring blade to keep the bottom of the cut clean.

[Brian Behrens]

Brian, the design of the cabinet makes a difference relative to good collection with ZCI. Most cabinet saws have enough holes to provide makeup air to keep things moving efficiently. Some sliders that use a shroud design make for a more closed system and ZCI can affect collection negatively. But the benefit that a ZCI provides can be made up for with a scoring blade to keep the bottom of the cut clean.

Thanks Jim. I didn't know that. I will run some experiments by leaving the motor cover open a bit to let some more air in.

I've done a lot of reading (online only) and right now I think I am going to get the Grizzly unit. It appears the Excalibur is no longer available, the PSI has poor feedback, and the sawstop unit is $100 more with no advantage I can see. But I haven't seen a lot of info on how the actual guard mechanism functions on the sawstop unit. It may be the superior unit but I would have to drive a few hours down to Atlanta to see it in person.

[Mike Kees]

Brian the Excalibur guards are now called a different name. I believe the one in Rod's post is the same one (pictured). Mike.

[Tom M King]

On my Unisaw, I covered up every hole, and stuffed the gap between the top and base. I built a wooden box to go over the motor, that accepts a slide in 12x12 furnace filter as the air intake. The filter is to keep dust in, rather than to filter anything out. This setup uses the Exaktor overarm assembly. I use ZCI's, and a 3hp DC keeps any dust out of houses I work in.

[Matthew Curtis]

If every hole is closed up how do you get airflow? To get dust being sucked out don't you need air flow. Where is the air coming from if the saw is sealed up?

[Jim Becker]

If every hole is closed up how do you get airflow? To get dust being sucked out don't you need air flow. Where is the air coming from if the saw is sealed up?

This is correct...there must be air source equivalent of the area of the port/duct minimum and where that air source or sources is/are located can affect efficiency in clearing a "box" of debris.

[Tom M King]

If every hole is closed up how do you get airflow? To get dust being sucked out don't you need air flow. Where is the air coming from if the saw is sealed up?

Since this came right after my post, I'm not sure if it was directed at me or not. If it was, air comes in through the 12x12 filter, as I stated. There is a big opening where the end of the motor sticks out on cabinet saws, which is typically covered by a plastic, or sheetmetal cover. My wooden cover with the filter replaces that stock motor cover. It works great with a 6" main duct, and 4" to the overarm assembly.

Edited to add: If any hole is left open, some sawdust will find its way out through inertia. You still need to move enough air to get past the point of wishful thinking.

[Derek Cohen]

Some time back I asked a woodworker friend - who specialises in dust control - about drilling a ZCI to increase airflow to the main dust collector (I have a Hammer K3 with a ZCI from Felder). He said "don't do it". Apparently, after much research, any holes drilled actually restrict air flow. I thought this illogical, but he showed me the studies, and it required very careful placement of holes, and of a certain size to make any positive difference. Simply drilling holes at random makes the airflow worse!

Well this information came back to me today after I tested out my over-the-blade collector. I am still shaking my head at the results.

My dust collection is a 2 hp Carbatec with 5" hose. I would prefer 6", however all my machines are by Hammer - the tablesaw is a K3 - and they have 5" outlets. I plan to add 6" ports when I upgrade the DC. The suction from the DC is adequate for all the machines I have. It is not as though there is inadequate suction. It is not enough, however, to suck up via both the main outlet of the tablesaw and the blade guard .. (or so I thought - now I am having second thoughts ... the plot thickens ). The outlet from the blade guard is (from memory) 2".

So a few months ago I added a hose via my Festool CT26E to the blade guard ....



It seemed to work, but I must admit it was more work and I got lazy, and so did not use it much.

Today I was fitting some dividers to an apothecary chest I am building (see here for the build), and decided to use the overhead dust collector. I was curious (with this thread in mind) to see how well it collected the dust ...



On went the CT26E, and this is the result ...



Dust!

I then had a lightbulb moment and decided to switch off the CT26E, and tried with a second divider ...



No dust!

hmmmm ... so I decided to use the CT26E again, and cut half way through the third (and last) divider ...



No dust, again!

I then tried the dust collector on the remaining half ...



Dust!!

I think even blind Freddy can see the pattern that has emerged.

One last trial. This time I disconnected the hose to the blade guard and capped it. Tried again ...



And that is the way it will remain now.

Summary: overhead dust collection is overrated.

Regards from Perth

Derek

[Nick Decker]

Interesting, Derek. Maybe the suction from above is just nullifying the suction from below and you've succeeded in creating "dust limbo"?

Or, could this be akin to that Down Under thing where water rotates the wrong way around a drain?

[John K Jordan]

... I tested out my over-the-blade collector. I am still shaking my head at the results....

Curious as to the location and size of the air intake to that saw. Some table saws apparently rely on only what room air leaks in around the height/tilt controls and through the insert around the blade. A 5" DC port is about 20 square inches.

JKJ

[Tom M King]

It doesn't work like that with mine. Without the overhead suction, there will be dust, not only on top of the saw, but also in the air, regardless of how much air gets moved through the saw. It should be noted that my setup is completely different than Derek's, in every respect, so don't think it's fair to state, one way or another, how any different setup will work.

[Rod Sheridan]

Some time back I asked a woodworker friend - who specialises in dust control - about drilling a ZCI to increase airflow to the main dust collector (I have a Hammer K3 with a ZCI from Felder). He said "don't do it". Apparently, after much research, any holes drilled actually restrict air flow. I thought this illogical, but he showed me the studies, and it required very careful placement of holes, and of a certain size to make any positive difference. Simply drilling holes at random makes the airflow worse!

Well this information came back to me today after I tested out my over-the-blade collector. I am still shaking my head at the results.

My dust collection is a 2 hp Carbatec with 5" hose. I would prefer 6", however all my machines are by Hammer - the tablesaw is a K3 - and they have 5" outlets. I plan to add 6" ports when I upgrade the DC. The suction from the DC is adequate for all the machines I have. It is not as though there is inadequate suction. It is not enough, however, to suck up via both the main outlet of the tablesaw and the blade guard .. (or so I thought - now I am having second thoughts ... the plot thickens ). The outlet from the blade guard is (from memory) 2".

So a few months ago I added a hose via my Festool CT26E to the blade guard ....



It seemed to work, but I must admit it was more work and I got lazy, and so did not use it much.

Today I was fitting some dividers to an apothecary chest I am building (see here for the build), and decided to use the overhead dust collector. I was curious (with this thread in mind) to see how well it collected the dust ...



On went the CT26E, and this is the result ...



Dust!

I then had a lightbulb moment and decided to switch off the CT26E, and tried with a second divider ...



No dust!

hmmmm ... so I decided to use the CT26E again, and cut half way through the third (and last) divider ...



No dust, again!

I then tried the dust collector on the remaining half ...



Dust!!

I think even blind Freddy can see the pattern that has emerged.

One last trial. This time I disconnected the hose to the blade guard and capped it. Tried again ...



And that is the way it will remain now.

Summary: overhead dust collection is overrated.

Regards from Perth

Derek

That's not my experience with cabinet saws and sliders.

No overhead collection results in a shirt pocket full of dust, and the particle counter off scale.

Regards, Rod.

[Josh Kocher]

I'd echo that too.

I've been using a Felder guard fitted on the splitter of my contractor saw and it's far better collection than before. I use 3" to the guard and 5" below from my 2hp cyclone.

There are always going to be some cuts that end up with dust on the table. But overhead DC improves the collection overall.

I like the Felder guard because it's not bulky, it's effective, and it's cheaper than all the other overhead DC options I could find: sharkguard, sawstop, excalibur, etc... I guess Don's is cheaper though.

[Dominik Dudkiewicz]

My experience with overhead collection on my Table saw has been very positive. Without it, despite having a CV1800 and 6" bell-mouth cabinet port I still get a lot of dust firing off the blade, whereas with the overhead port I get virtually zero dust or chips depending on the cut. Worst case I get some small amount of chips but no dust.

I made my own out of perspex and scrap aluminium. I have a 4" hose / port to the overhead. I think reducing the 6" in the cabinet to a 5" would provide a better balance as the overhead is far more effective than the cabinet port so more flow to that results in better overall performance.

The guard is easily moved up or down and left to right so that I can use the crosscut mitre gauge closer to the blade or move the fence closer to the blade for narrow rips.

20161010_070716.jpg

20171012_122919.jpg

20171012_123449.jpg

Cheers, Dom