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I am in the process of starting to build a new router table. I want to enclose the router and lift in a box so I can use dust collection for what falls through from the router. It occurred to me that if I build the box then the router will be sucking in a lot of dust into the motor because of the box. Am I just over thinking this or is this a problem I need to address in the build? I will be using a 4" pipe for dust collection located in the back and bottom of the box with a slanted board inside the box to feed the dust down to the connection. How did you keep the dust out of the motor intake? Thanks guys.

Chuck
 

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Dunno, but I sit to rout, and have a fairly large hole for the bit, so lots of sawdust goes thru the hole. I know this because most of it seems to end up in my lap. I was told by an 'expert' that my router would pack in a lot of sawdust, and fail sooner than it should. Well, I opened up my router to check, and lo and behold, not a speck of sawdust in there. Apparently the fan inside the router is more than enough to keep it clear of sawdust. Can't say what would happen in your case tho, as my router just sits in the open, not in a box.
 

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Different schools of thought here Chuck. Mine is enclosed on 3 sides and yes, it makes a mess but it works for me. Certainly NOT the only way of course.

If you enclose it, you will have to leave enough openings to allow the dust collection to work. If you close it tight, your dust collection will not work properly because it can't draw enough air to move the dust. And, it's been discussed here in the past, your router might overheat due to the enclosure. Use the search function to find it, and lots of other hints and tips on dust collection for the router table.
 

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Hi chuck, you are the first one I have seen concerned about this. There are two things involved in this, one is makeup air for the dust collector and running dust and chips through the router, not good. here are some pictures of how I solved the problem.

Cut a hole in the bottom of the box larger than the lift to allow air to flow into the box and the router motor to extend down below so it breathes fresh air.

Also a good idea to wye off the DC hose to the top back of the fence.

I also incorporated an adjustable opening in the side of the box to adjust air flow to keep the box clean.
Herb
 

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Unlike Herb and others I am deeply concerned about the effects of trying to draw air against the direction that the router wants to pull it. The router is trying to draw air from it's bottom and push it past the bit. The motor in the router and the bit are both generating quite a bit of heat so I don't want to add the heat from the bit to the heat of the motor plus defeating the draft through the router. The suction in the box lowers the possible flow through the router since it is going contra to it and the air flow going past where the air is supposed to exit the router causes turbulence as the two air flows try to pass each other which doesn't do either one of them any good.

In my opinion the best arrangement is to keep the area around the router open and try to gather the dust at the bit or just above and around it. Some of the manufacturers have incorporated dust collection in the area between the router and the bit as part of the base and this actually enhances the flow of cooling air. Air moves from areas of high pressure to areas of low pressure (the principle in physics is that energy always moves from higher potential to lower potential regardless of what type of energy we are talking about.) Any time a fan starts pushing air it will build a high pressure in front of it. This principle is what allows a helicopter to hover. So if you remove the air as the router fan pushes it the more air will flow through.
 

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I feel that sucking dust into the router is not good. I solved it on my enclosed table by making two seperate systems in the same box. The 4" dust collection hole is at the back of the machine enclosure, with infeed air holes on the front panel (4 x 2"), allowing the air to be drawn across the bottom to the exit. Then I used a piece of flexible hose big enough to fit over the bottom of the router (in my case that was 4" ducting hose), and cut a similar sized hole in the floor of the box. The router then has its own air tunnel sucking clean air through it.
 

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It would need to be well below the air intake for the router Bob otherwise you have a Venturi Effect across the intake opening which still pulls air the wrong way. This is a pretty good explanation of what is happening by Matthias Wandell who I would not have expected to be that knowledgeable about physics.
Air blowing across the opening of the router causes a pressure drop. Since the air at the other end is at full atmospheric pressure and the fact that energy always travels from higher potential to lower potential that means the air at the other end wants to move backwards against the flow. The fan in the router should be capable of still moving air in the intended direction but the potentials have to be added together for the net result and since one is positive and one is negative you have a deduction from full flow. A vacuum at the other end by the bit has the opposite effect. Since both potentials are in the same direction the net result is increased flow.
 
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Discussion Starter #9
Chuck thank you for the tutorial that made things very clear for me. It raises the question that Herb addressed by using the air suction to pass his router to the collection hose thus allowing the router to blow air into its motor. Are you saying by the Venturi Effect that the router motor would fail to blow enough air into the motor to cool it? Since it is grabbing air from the same source (the hole around the router) wouldn't the air flow not be affected by the dust? Herb's idea looks promising I just want to know why you disagree.
 

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You lost me Chuck, all I know is that it was designed by an engineer and it works great. This is not a system that Bench Dog has, which to me describes exactly what you are talking about. The system I use draws air from around the router housing at the hole in the bottom of the box and through the air vent in the side of the box for the DC, not from the end of the motor sticking through the box where the router gets its air. Seems to me this would cool the router not cause it to heat up.
I have yet to see any top of the table dust collection system that works to get all of the chips.

Herb
 

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Herb...
the top of the router is vented through the bottom of the router box???
 

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i dont think youve caught my meaning.

With NO dust extraction, the router is pulling air from the ROOM, through a tube which enters the box from below, through the router, and exiting at the bit. If the router were used in this fashion, the dust would be blown into your face by the router fan.

The dust extraction is completely separate, and when on, pulls air through the box containing the router (helping it to keep cool) and then exiting at the rear of the box.

At the same time I have a 2 1/2" hole in the table top just to the rear of the router plate, directly into the box. The fence has a tunnel which covers this hole even when the fence is moved back or forwards. This actually helps the router flow as it is sucking at the top of the router while the fan blade is pushing.
 

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Bob unless you have a tube from outside the box that attaches to the suction end of the router then the router will be negatively affected by sucking air out of the box around it. How much is a question I can't answer without doing experiments, altering the variables, and recording and comparing the results.

A vacuum does not actually suck anything into the hose, that's a misconception. That's like trying to push a string. It just doesn't work. What is happening is that the vacuum impeller pushes air away from the hose and the higher atmospheric pressure at the other end rushes in to take its place. Higher potential always moves in the direction of lower potential energy. The air molecules that strike objects on the way to the hose push those objects to the hose and down it. That means that when you turn on the vac, the pressure inside that box has to drop or the vac doesn't work. This pressure drop works to defeat some of the flow through the router. Like I said I don't know exactly how much as that requires experimentation. As I said earlier, the only way the router cannot be affected is if there is a tube from outside the box that attaches to the suction end of the router. It would then be unaffected by the pressure drop in the box since it would be totally isolated from it. Then sucking air down from the table top area would improve the flow.
 

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Charles, youre not getting it. The router takes air from outside the sealed box via the tube attached to the bottom of it. The flexible tube allows the router to rise and fall and still keep fresh air supplied to the router cooling fan on the bottom of the machine. The dust inside the box is extracted from the rear.
 

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Herb...
the top of the router is vented through the bottom of the router box???
Not that I am aware, I think the router is exhausting into the box towards the underside of the table towards the hole around the bit.
It is sucking air from below the box,where the bottom of the router extends below the box. The DC system is sucking air from around the router opening in the bottom of the box and from inside the box,the adjustable air vent tin the side of the box is to supply makeup air for the DC system as it is drawing more air than is available in the box as I understand it.
Herb
 

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Ok Bob, I guess I didn't read it carefully enough. That is the one case where the router will not be affected by being in a box with suction applied to the box is when the air supply to the router is separate from the air in the box.
 
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Cherryville Chuck,

Thanks for the video on the Venturi Effect. Is Matthias Wandell an amazing person or what?

By the way, are you related to CVP? Just curious.

Rob
 
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