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Discussion Starter · #1 ·
Any kind of flame or igniter in a wood shop could be hazardous so be prepared when attempting experiments like I discuss below. With that disclaimer, I will get to the meat of this post.

It has been suggested on routerfourms.com that since a router in a table only produces chips above the table, there should be no need to have "under the table" dust collection. I have conducted an experiment using a 1/4" radius roundover bit in a table mounted router to visualize the air flow induced by the spinning router bit. A base line test was first conducted using an incense stick (WalMart) with the router bit not spinning; the smoke clearly rises to confirm that the laws of physics are obeyed in my shop. In the next photo, the router motor was turned on and clearly the direction of the smoke flow is reversed. The router bit acts like an impeller on a blower and induces its own air flow. This explains to me why you will get chips beneath the router table.
 

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Long discussions on dust collection with routers. Stick nailed one aspect by suggesting setting up a "snorkly" to feed clean air into the bottom of the router, then both below the table and behind the fence DC to get the majority of all dust produced. A tight fitting insert can only help keep the dust above the table.
 

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It has been suggested on routerfourms.com that since a router in a table only produces chips above the table, there should be no need to have "under the table" dust collection
Never read anything like that, but for a few years now I've had to do most of my work sitting, because of my back. I use my router in my table, and I "always" end up with a lap full of sawdust. But I have opened my router several times, just to check, and each time it has been totally sawdust free inside.
 

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The router bit would be "slinging" air outward as it spins, much like the centrifugal pump on a washing machine works. That would create a vacuum both above and below the bit as air rushes in to replace the air the bit is pushing outward.
 

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@ Joat.A lap full of sawdust,I know what you're saying.I also sit while working for the same reason.& as my legs fit under the table I cover them with the same old bed sheet I use for the rt cover. My new table will have better sawdust control with my new shop vac. James.
 

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It has been suggested on routerfourms.com that since a router in a table only produces chips above the table, there should be no need to have "under the table" dust collection.
except when doing ploughs, groves, mortises, veining, some edge dressing and rabbets...
the saw dust has no other place to go but under the table...
UTDC is a must but not at the expense of the motor...
 

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It has been suggested on routerfourms.com that since a router in a table only produces chips above the table, there should be no need to have "under the table" dust collection.

I don't recall "routerforum.com" ever stating anything so categorically. Can you provide references and links...?
 
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I believe that the statements were that it didn't make much sense to try and suck all the sawdust down through a narrow hole in the table. There are many setups that try and do just that usually by enclosing the router in a box which can lead to other problems. Some members say they have solved all those problems but not every one has, probably because they don't understand all the processes going on when they do. Certainly above the table DC is the best bang for the buck, because as I stated before, 100% is getting created there. And it's the simplest and kindest to your router. Some debris makes it's way under the table but I'm pretty sure it's being slung down there, not sucked down there. The vacuum at the bit isn't strong enough to overcome the one at the bit created by a DC pickup. You need more force than that to get those particles to go downward. Having some dust control under the table to catch them is good, you just have to be careful how you go about it.
 

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First, my Freud came with dust collection. However, it's ONLY about a 2-1/2" line and throttling a 3hp, four bag collector to that doesn't sound like a good shop practice.

Second, even with that kind of collection backing the table, the shelf under the router always caught a lot of dust and chips. After all, chips deflect, when they hit something, and can go everywhere, except into the trashcan across the shop.

The solution was to box the router in, which poses a risk of interrupting the cooling processes. The air for the motor has to come from somewhere, so it'd pull from the area of the router bit. As such, I ran a second line to the box.

In the end, after several long runs, I end up with, maybe, a tablespoon of sawdust on the table top.

I suppose, if the "ain't now sawdust under the router" thing were true, the ideal would be a four inch hose on top and a two inch at the box, along with a small intake, so the lower hose was less likely to pull from the area of the bit.

SIDE NOTE: I have a sanding table, on which I installed sides, a back and a top. Before doing that, it was barely worth using. After, it's one of my most treasured tools in the shop. Since the upper sides, back and top are nylon, I can stick long things out the sides or back, if need be. Otherwise, it'll handle things a couple feet wide.

When I sand, you can see sawdust flowing off an item and being drawn into the table. Even sanding exotic woods that you can, easily, smell, don't. As such, I also use for carving and grinding too. When it's clear of acting as a horizontal storage area, it's my go to place for free-hand routing. ALL the fines are captured and, depending on how I handle a piece (control the direction the router is tossing stuff), only a small percent of what the bit kicks off makes it to the shop floor. Still, there is enough that I vacuum (4" hose and tube) when I'm done.

Clearly, even good collection can't stop every bazillion mile an hour chip from escaping.
 

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My first shop built router table was completely open on under the router with a small shelf under router. I can tell you dust and chips definitely collected under the router on that shelf. A few year ago I built a new router table, with dust collect both under the router and on the fence. I have found this setup does a decent job, and is hooked up to my 2HP HF Dust collector. The router for both tables is the same Bosch 1617. The box that contains the router has holes drilled in front for relief air, and the larger hole in back for the DC hook-up. I make sure the DC is running when running the router, and have not had an issue with over heating.
 

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@ Joat.A lap full of sawdust,I know what you're saying.I also sit while working for the same reason.& as my legs fit under the table I cover them with the same old bed sheet I use for the rt cover. My new table will have better sawdust control with my new shop vac. James.
Never thought of using an old sheet. But, as I use a nice old office chair, with castors, the back will tilt, has arms, and swivel around to use my scroll saw, likely one would be more bother than worth, to me anyway. Got a nice brush that works well to get it off me. I have thought about a vacuum hookup of some sort under the table, but never came up with anything I figured would keep the air flowing well enough. But, since I'm planning on a composting toilet in my "new" van, will be using sawdust in that. So, decided I'd just make a shield under the table, with a slanted bottom, so all (read most) of the sawdust "should" slide down to one side, and into a bucket. Hopefully, it will be a workable solution to two issues.

And that office chair is great. Sometimes while sitting my back will bother because I am leaning forward to work. Just tilt back in the chair, the back tilts back a bit, and in a few minutes read to go again. Wish I'd thought of a chair like that a lot sooner than I did. Got it for $7 on craigslist, and the only thing wrong with it was the fact that the previous owner wanted something that didn't look used - more money than sense.
 

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Discussion Starter · #13 ·
I believe that the statements were that it didn't make much sense to try and suck all the sawdust down through a narrow hole in the table.
I am unaware of a router dust collector manufacturer claiming that you ONLY need a "beneath the table" system to remove the dust. In order to remove a high percentage of the dust/chips generated by a router, you need both above and below collection. Since the spinning action of the router bit naturally sucks dust/chips beneath the router table, the function of the "beneath the table" dust collection is to remove the dust that is naturally sucked beneath the router table by the spinning action of the router.
 

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I am unaware of a router dust collector manufacturer claiming that you ONLY need a "beneath the table" system to remove the dust. In order to remove a high percentage of the dust/chips generated by a router, you need both above and below collection. Since the spinning action of the router bit naturally sucks dust/chips beneath the router table, the function of the "beneath the table" dust collection is to remove the dust that is naturally sucked beneath the router table by the spinning action of the router.
I don't recall ever seeing any DC manufacturer recommending any particular type of collection system for any tool. Lots of different parts are sold to satisfy market demands. Fence makers are a different story but same reason. They incorporate a DC pickup in their fences to satisfy market demand. I have seen lots of examples where the end user built boxes around their routers and tried doing that though. And I recently saw a box attachment being sold with just a connection for a DC and I don't think it had any other openings but I really didn't look very hard at it and don't remember who sold it. And just to clarify a point, unless you do have a DC pickup below the table then nothing is being "sucked" under the table. That dust is getting shot under the table by the centrifugal force of the bit with some percentage probably being caused by collisions between particles after they have been ejected.
 

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Fine sawdust is the stuff I want to capture, and most of that will be above the table. Chips and large particles aren't so bad for health. I think the 4 inch port belongs on the fence and a smaller one under in a well vented box. A snorkel to the bottom of the motor that pulls in air through a filter, handles cooling. A nice brush to sweep the escapee dust off the table between pieces.
 

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Discussion Starter · #17 ·
I don't recall ever seeing any DC manufacturer recommending any particular type of collection system for any tool.

... unless you do have a DC pickup below the table then nothing is being "sucked" under the table.
I used the term "DC manufacturer" to include any apparatus that aids in the collection of dust at it point of origin.

I think you are splitting hairs to argue about how the dust got under the table. The point is that its gets under the table and need to be removed.
 

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A fun experiment would be to put my shop vac on the box under the table, but in blow mode. With that running, kick on the fence collection and see what happens.

Meanwhile, over on my carver, when I put a 4" like just off my little Bosch, I get VERY little debris on the table. Of course, there is no "under."
 

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I used the term "DC manufacturer" to include any apparatus that aids in the collection of dust at it point of origin.

I think you are splitting hairs to argue about how the dust got under the table. The point is that its gets under the table and need to be removed.
I want to accurately describe the processes that are happening so that other members understand what is happening and therefore make the best choices of how to deal with the problem. By using the term "sucked under" the table it may cause wrong conclusions and lead to poor solutions to deal with the problem. For example if someone actually thought that the particles were being sucked naturally through the bit opening then they might conclude that by creating more suction they will improve on that. That could lead to other problems. Since all of the dust is being created above the table then it's obvious with that statement that the first and best line of defense is a fence pickup. With the statement that some particles are being thrown under the table then it becomes obvious that if you want to catch those as well then you need a pickup under the table too.
 

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I was given this router table a few years ago. I don't use it much except for doing the edge routing of signs. I use my shop vac on the top and my larger 4" collector on the end for the underside. I don't get any dust or chips to speak of but again I really don't use it like most of you would. Hopefully the pictures will show you what I have set up.
 

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