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Half-baked tablesaw dust collection idea

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Forum topic by JeffP posted 02-19-2016 12:33 PM 977 views 0 times favorited 12 replies Add to Favorites Watch
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JeffP

573 posts in 965 days


02-19-2016 12:33 PM

Topic tags/keywords: question

Like many of you, I’m disappointed with the performance of my “under the table” dust collection on my saw.

It is a sawstop pcs saw, and it seems they built a sort of “shroud” around the blade area to attempt to create better suction…in reality, all it does is greatly reduce the airflow.

That said, a big part of the problem with under the saw collection on a TS just has to do with the basic geometry of what’s usually going on during use. Only some fraction of the waste and fine dust winds up anywhere near the hole in the insert where it could get sucked in.

Obviously, there are those above the table guard/DC-shroud things that are the intended solution for this. Somehow, those land squarely in my “just too much in the way to put up with it” zone.

So here’s the idea I had. As stated in the title, it is only partially baked:

It amounts to combining a blower and a sucker to move all the stuff away from above the table.

The “blower” would be compressed air being shot in the general direction of the blade from near the front of the fence and pointing towards the back of the saw. Could be a typical flexible coiled air hose coming from behind the table and mounted along the length of the fence with an air gun mounted near the front of the fence pointing backwards.

The “sucker” would be just an open “cowling” back behind the saw hooked to a DC. Not sure if this could work effectively with the cowling below the surface of the table and just creating a “suction zone” in that vicinity to suck down the debris and dust as it passes by.

My intent would be for this to be in addition to the (weak) under the table collection, not a replacement for it.

Ok, flame suit on. Help me bake the idea, or tell me why I should take it out of the oven and toss the remnants in the can.

-- Last week I finally got my $*i# together. Unfortunately, it was in my shop, so I will probably never find it again.


12 replies so far

View Fred Hargis's profile

Fred Hargis

4260 posts in 2066 days


#1 posted 02-19-2016 12:57 PM

No flaming, just a suggestion. I’ve read others have tried the compressed air idea, and no one reported to was effective…most guessed the speed of the blade is just too fast. But here’s what will work: more DC (I think, not knowing what exactly you have) and the seemingly dismissed overblade pick up. Believe me, the biggest complaint I have about the SS saws (I have an ICS) is that puny 4” dust pickup they use. The shroud is less of an issue (to me) than the inability to get enough air flow through the port. Even so, I can pull about 550 CFM through the port (large DC) and I put an Excalibur over the blade (from my previous saw). This set up gets probably 95+% of the dust, below and over the table.There is some chips (very little dust) on the bottom of the cabinet, mostly from when I forget to close that shroud “door” on blade changes. The thing about trying to invent something else is that it’s probably already been tried. I don’t think the idea is half baked at all, otherwise others wouldn’t have already tried it.

-- Our village hasn't lost it's idiot, he was elected to congress.

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ChrisK

1827 posts in 2655 days


#2 posted 02-19-2016 12:58 PM

Look at he nozzles offered by http://www.exair.com/en-US/Primary%20Navigation/Products/Air%20nozzles/Pages/Air%20Nozzles%20and%20Jets%20Home.aspx.

The key to dust collection is air movement. The sucker behind the blade needs to be able to pull enough to air to collect the dust coming from the blade. An air nozzle blowing air to the sucker will help. It needs to be more of a wide fan than a narrow jet.

-- Chris K

View bigblockyeti's profile

bigblockyeti

4007 posts in 1294 days


#3 posted 02-19-2016 01:59 PM

I’ve thought about using an air jet of some sort to drive the dust down into the cabinet where it will be sucked up. I find the biggest issue is when trimming up a piece where less than a full kerf is being cut, the exposed side of the blade tends to throw more sawdust at me than down into the cabinet. If I mounted a blow gun nozzle above the work piece and close to the blade I could drive the dust down but only if the air flow was substantial and the air speed was greater than the tangential speed of the blade trying to throw the dust at me. Ultimately this concept has the ability to get very complicated very quickly, for the time being I just rest in the fact that I have a bit of sweeping up to do after spending some time in the shop and that’s ok with me. Have you tried removing the dust shield from around the blade on your SS?

View clin's profile

clin

627 posts in 569 days


#4 posted 02-19-2016 06:14 PM



Like many of you, I m disappointed with the performance of my “under the table” dust collection on my saw.

It is a sawstop pcs saw, and it seems they built a sort of “shroud” around the blade area to attempt to create better suction…in reality, all it does is greatly reduce the airflow.

- JeffP

I disagree. The shroud ensures the fastest air speeds near where the dust is actually created to optimize dust collection.


Only some fraction of the waste and fine dust winds up anywhere near the hole in the insert where it could get sucked in.
- JeffP

I’m not sure this is true. The dust comes from the cut. The cut is at the front right where the blade goes down under the table top. So I think the best opportunity is to get the dust from underneath.

While I don’t know this to be true, I suspect that the dust that comes out the top is actually dust trapped in the teeth and going under and around with the spinning blade until some of it then gets flung of the top.

Regardless of the whys, obviously, there can be significant dust on top. But I don’t think expecting dust to be sucked paste the blade through a zero clearance insert is ever going to work well.

Again, I don’t know this to be the case, and I’d love to see some high speed video of exactly what does happen.


Obviously, there are those above the table guard/DC-shroud things that are the intended solution for this. Somehow, those land squarely in my “just too much in the way to put up with it” zone.
- JeffP

I also have a SS PCS and find the overarm dust collection to work extremely well. And I only have a shop vac connected to the whole saw. I can barely feel any air movement in the overarm hose, but in combination wioth the gaurd it works well. I also find that the SS guard is so easy to take on and off, and controls dust so well, I use it any chance I can.

Note: I do find that when the cutoff is thin (< 1/2” or so), then the guard doesn’t fit against the stock and then I get some significant dust out the top.

Regardless of how well a guard can work, there are always cuts where you just can’t use the guard.


So here s the idea I had. As stated in the title, it is only partially baked:

It amounts to combining a blower and a sucker to move all the stuff away from above the table.

- JeffP

Sounds plausible that it could work. But I think the compressed air would create a very turbulent airflow. More likely to scatter the dust than drive it. I think you’d need to get a rather wide column of air movement so that edges of the column (where there would be the most turbulence), would be away from where the dust is.

Maybe if you could blow a sheet of air along the top of the table. I think you’d have to experiment and see what helps.

In general, the problem with vacuums, is that the air gets sucked into the inlet from all directions. So as you move away form the inlet, the air speeds drop dramatically. That’s where shrouds come in. They help to control the airflow.

Blowing air does have the advantage that due to the momentum of the air, it tends to stay in a column. That’s why you can blow papers off a table from across the room with a fan, but can’t suck them in from across the room.

I’d look at the blowing air as a way to guide the dust. I’m not sure the theory behind it, but blowing air is used in some doorways to provide some sort of way to keep the inside air in and the outside air out. Like a wall of moving air. Maybe blowing air could work more to contain the dust than to actually propel it toward the vacuum.

-- Clin

View Dave's profile

Dave

145 posts in 2770 days


#5 posted 12-26-2016 11:56 PM

I’ve tinkered with the “air curtain” idea Clin mentioned. The key isn’t so much to blow the dust back into the collector. Instead, as he says, the idea is to create a “barrier of air” that traps the really tiny dust behind it (and away from your lungs).

Take a look at some fume hood designs too. Those air curtains are explicitly designed to keep sub-micron particles away from the user. From what little I’ve read the airflow can be too fast AND too slow – so there’s a range of air speeds that work best.

Let us know what you do!

-- "I'm not afraid of heights. I'm afraid of widths." - Steven Wright

View JBrow's profile

JBrow

1024 posts in 493 days


#6 posted 12-27-2016 01:54 AM

JeffP,

I too am contemplating the idea to achieve the probably un-achievable goal of perfect in-the-cabinet table saw dust collection. I have a PM66. There is no under the under-the-table dust shroud; just a 4” dust port. When I upgraded my dust collector to a 5 HP unit with impressive suction, I added a 4” dust port to the cabinet (two 4” dust ports).

I found that even with the dust collector upgrade (with near tornadic air speed) and two in the cabinet 4” dust ports and after sealing the cabinet for air leaks, I continue to get dust on the table. However, when I use the factory wider throat insert, dust collection is a little better than the zero clearance insert; but for me still unsatisfactory.

When I modified my zero clearance insert by drilling 1/2” holes at the front and back of the saw kerf in the zero clearance insert as well as a pair of 1/2” holes at midpoints in the kerf, zero celarance dust collection improved, but was still wanting.

I have also noted that much more dust is collected under the table than is thrown out onto the table, whether with a zero clearance insert or factory insert. All of these factors have combined to lead me to conclude as has clin, that the dust and debris thrown onto the table is dust and debris trapped in the gullets of the saw blade. Going one step further, I suspect that if the dust and debris trapped in the gullets while the teeth are under the table can be dislodged, near perfect under the table dust collection can be achieved.

Therefore, based on this analysis, if compressed air is introduced, the direction of the high velocity air must be such that it would dislodge the debris trapped in the gullets. I therefore doubt that compressed directed in the direction of blade travel would have any effect other than keeping debris trapped in the gullets. On the other hand if the high velocity air flow is directed at the proper angle to the blade against the direction of the blade, some of the debris may be dislodged from the gullets. I personally suspect high velocity air flow directed against the rotation at some unknown angle could be effective in dislodging at least some debris. The compressed air would be under the table. I am not sure how above the table compressed air, no matter the direction, would improve dust collection.

I also am wondering, in the case of thee PM66 with no dust shroud, whether a pair of angled baffles affixed to the zero clearance insert might combine with the air flow generated by the spinning blade to passively dislodge some debris by introducing localized turbulence near the gullets as the gullets pass from the in-feed side of the insert below the table. When I clear the deck of some pressing projects, this is the direction I will pursue to improve under the table dust collection.

View Redoak49's profile

Redoak49

2268 posts in 1562 days


#7 posted 12-27-2016 02:42 AM

I have the SawStop PCS and am satisfied with the dust collection. When using my Sawstop with the over blade dust collection it works great.

I am not a fan of blowing dust around the shop and putting fines in the air.

What might be of interest is what dust collector you are using and what your air flow and static pressure is when connected to the saw. These things make a lot of difference. With insufficient air flow, it just will not work.

View JAAune's profile

JAAune

1716 posts in 1890 days


#8 posted 12-27-2016 05:54 PM

Increasing airflow under the saw helps a lot. A 4” port is insufficient. Find a way to get a 6” hose connected to an appropriately-sized dust shroud and you’ll find collection efficiency improves dramatically. I’ve got my hose right under the blade and it gets almost everything as long as the blade is not exposed on one side during cutting operations. Some does escape above the table but not much.

-- See my work at http://remmertstudios.com and http://altaredesign.com

View JAAune's profile

JAAune

1716 posts in 1890 days


#9 posted 12-27-2016 06:03 PM

Regarding the PM66, the issue with that machine and most of its contemporaries is that a collection hose at the base of the cabinet is pretty worthless. It needs to be located as close as possible to the area where dust is naturally thrown off the blade. This seems to be to the rear and below the blade. I have a contractor saw so I settled for mounting the hose below. The motor blocks the rear.

You want to seal most air leaks in the cabinet but be sure to leave some at the right locations. The air leaks determine the direction of airflow and a 6” duct can pull far more air than a zero clearance insert will allow through.

-- See my work at http://remmertstudios.com and http://altaredesign.com

View Kelly's profile

Kelly

1366 posts in 2517 days


#10 posted 12-27-2016 07:14 PM

I have a three horse collector drawing from my cabinet and, some times, the overhead (an Excalibur).

The over-arm does especially well with flat stock. It does its worst when I’m out on the edge.

The idea of air pushing at the front isn’t bad, since I’ve blown air across the table to direct it to the blade guard-collector and, as long as the air pushed it toward the over-arm collector hood, it cleaned the table up.

As to the bottom side, and mindful of the size of collector I have drawing from it, the big cabinet under the blade is a good thing, since I think a shroud there would compromise its effectiveness by limiting the air it could pull at that point.

On the other hand, focusing the air draw at my sanding table by adding nylon sides and a top made a REMARKABLE change in whether it was worth having in the shop or not. Of course, that’s several square feet of draw area.

When I get the current three thousand two hundred fifty-five projects I have going out of the way, I want to make another collector hood that rides in the miter slot or is held down by switchable rare earth magnets (probably the better option) to see if it would better allow me to use push shoes, and better collect the tossings that are generated when you cut the edge of a board or flat stock.

This could be little more than a three sided box with another that drops over it and overlaps the bottom one. The front might have a notch out so it could ride a board and still rest on the table.

A clear plexi top “might” allow you to monitor the blade, but I try to watch the board on the fence anyway, so I could save the plexi and acrylic for other projects.

This actually could have a directed air valve on the front, if only for experimentation.

http://www.woodcraft.com/Product/161961/(H)-Magswitch-MagJig-60.aspx?gclid=CI_F7pCKldECFUlNfgoda90M9g

View Holbs's profile

Holbs

1468 posts in 1602 days


#11 posted 12-28-2016 02:27 AM

My right tilt Delta Unisaw has that fantastic sloped baffle for underneath table dust collection and it works 98% perfect (the smooth metal angled shelf directed to the 4” port). However, my PM66 has nothing underneath and the saw dust builds up. Was thinking of doing some cardboard/metal/plywood baffling under my PM66, which I’m sure many others have done successfully.

-- The Carpenter Bee is derived from the Ancient Greek word wood-cutter

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OSB

147 posts in 99 days


#12 posted 12-28-2016 07:19 AM

I like some of the ideas here.

Adding a little blow gun to dislodge the dust between the teeth sounds like it could keep a lot of dust from coming out of the ZCI at the back of the blade.

Thinking about this and the half kerf problem, I think you could make a custom ZCI with an opening on the non cutting side to increase the airflow there and use something like a half sled in the non cutting side miter slot to make a funnel so the suction isn’t lost at the surface of the table.

Maybe it could be a zero clearance feather board with a solid top to keep the suction from getting lost in the feather slots.

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