Another router table question

[Anna]

Mine is based on the NYW plans. I have a switch/plug from a BT for power with the plug in the router cavity. The door has holes in the bottom to allow air flow in. Collection is fair but I have some jigs stored in there, as well as the router cord, and my DC port is only 1 1/2".

Pappy, how are the individual bit drawers working out instead of one big drawer on each side with multiple levels of bit holders in it like in this picture?

I know how to build the latter because I have the DVD, but I wonder if it's more practical to have the bit holders in their own individual drawers like the NYW version instead.

[Anna]

Right now, I was planning on getting some rubber grommets, or using a piece of rubber from a gasket kit, to seal around the cord. I don't figure it will be airtight, because you do need some air inflow for full effect.

Then the router will be permanently inside the box?

[LarryG]

the same mass of air will have to move but through a smaller area.

That's exactly the problem. The mass of air will be smaller because the inlet will restrict how much air can move. The amount of air that is moving through a DC system is controlled by how much can get in, not by how much can get out. That's the whole point of all the discussions about minimizing resistance in the system by using larger ducting and larger ports: the more wide open everything is, the less resistance there is, the larger the volume of air that is moved. And the larger the volume of air moving, the more dust is collected. It is air quantity, not air speed, that does the work.

Of course, I've already been wrong about one dust collection question, this morning ...

[RodKirby]

ALL my powered tools on bases (mobile and not), have

• Power in (from a wall socket), wired to:
• A (very) short extension lead for the tool inside the base, and an exterior socket for the Shopvac.

I run the wires thru a connection box, either at the "back" of the base or inside...

[Anna]

The mass of air will be smaller because the inlet will restrict how much air can move. The amount of air that is moving through a DC system is controlled by how much can get in, not by how much can get out. That's the whole point of all the discussions about minimizing resistance in the system by using larger ducting and larger ports: the more wide open everything is, the less resistance there is, the larger the volume of air that is moved. And the larger the volume of air moving, the more dust is collected. It is air quantity, not air speed, that does the work.

Of course, I've already been wrong about one dust collection question, this morning ...

I'll have to disagree on the first statement, just to be pedantic. The mass of air flowing in has to be the same as that flowing out, if no air accumulates or is depleted inside the cabinet, which is the case for a router table.

For clean up, as in a router table, it is the air speed that matters, rather than just the total air flow. When a debris settles, you need higher air speed to move it. It's sort of like leaves falling off the tree. With a light breeze, you'll spend the rest of autumn raking leaves off your yard. If there's a brisk wind flow, then your neighbor gets the exercise.

I'm all theory right now because I don't have a DC. And fluid mechanics wasn't exactly my strongest suit. But maybe you can try this:

- Put a coin, nut, piece of wood cutting, whatever, in one end of a pipe with the same diameter as the DC hose and see how fast/well the DC cleans it up.

- Then attach the DC hose to a smaller diameter pipe with the same debris in it, with the same distance from the outlet, and see if you can observe any difference in the effect.

I'm just writing this off the top of my head. I don't know if it's going to make a difference, but I'd like to know if it does or not.

Oh, just to be clear: If your DC is good, you'll of course have good suction to begin with, and maybe you don't have to worry about air flow so much. But you'll get better performance with higher speed of air flow in the table cabinet (and that becomes significant for us who have dinky shop vacs). Until someone tells me otherwise, anyway.

[LarryG]

I'll have to disagree on the first statement, just to be pedantic. The mass of air flowing in has to be the same as that flowing out, if no air accumulates or is depleted inside the cabinet, which is the case for a router table.

I perhaps wasn't as careful with my writing as I should have been. I don't disagree that the mass/volume/amount of air flowing in will equal the mass/volume/amount of air flowing out. What I was saying is that whatever quantity is flowing in and out will be smaller than it might otherwise be because it will be controlled by the inlet, not by the outlet.

Or at least that would be the case with a low-velocity, high-CFM dust collector. Are you saying that you're going to use a shop vac? I thought you were saying you had no dust collector yet, but were designing this router table with a view to getting one. If you're going to use a shop vac, I think you will need to make the bottom of the box funnel-shaped and put your vac outlet at the very bottom of the funnel, pointing up, so gravity will work in your favor. I don't think a shop vac is going to do a very good job of scouring a router box otherwise. A shop vac does a great job of whisking away debris that's right at the inlet, because of precisely the reason you say: the air is moving at such a high speed. But it does a poor job of gathering up debris from a wider area, because the volume of air being moved is low. This is the whole reason people invest in expensive dust collection systems, rather than just use a shop vac.

[cabinetman]

I'll have to disagree on the first statement, just to be pedantic. The mass of air flowing in has to be the same as that flowing out, if no air accumulates or is depleted inside the cabinet, which is the case for a router table.

For clean up, as in a router table, it is the air speed that matters, rather than just the total air flow. When a debris settles, you need higher air speed to move it. It's sort of like leaves falling off the tree. With a light breeze, you'll spend the rest of autumn raking leaves off your yard. If there's a brisk wind flow, then your neighbor gets the exercise.

That's a pretty good example, and I agree with you. You can only move a certain volume of air through a certain size tube. I've had different types and sizes of DC systems, and the faster you can move the air the more efficiency you can expect, just like the force of the wind.

On a two bag 1.5 hp system I have a 4" hose. If I hook that same hose to my 7hp cyclone, the difference is night and day. What goes in must be able to get out.

[Anna]

I perhaps wasn't as careful with my writing as I should have been. I don't disagree that the mass/volume/amount of air flowing in will equal the mass/volume/amount of air flowing out. What I was saying is that whatever quantity is flowing in and out will be smaller than it might otherwise be because it will be controlled by the inlet, not by the outlet.

Or at least that would be the case with a low-velocity, high-CFM dust collector. Are you saying that you're going to use a shop vac? I thought you were saying you had no dust collector yet, but were designing this router table with a view to getting one. If you're going to use a shop vac, I think you will need to make the bottom of the box funnel-shaped and put your vac outlet at the very bottom of the funnel, pointing up, so gravity will work in your favor. I don't think a shop vac is going to do a very good job of scouring a router box otherwise.

I think I see why we had a disagreement. I just read the DC thread. I think the DC works differently from a shop vac (I honestly didn't know! ). From what I understand now, the DC adjusts its air flow based on the inlet, so that it practically shuts down when there is no air flowing in. The shop vac runs at the same speed no matter what. With the DC, it makes sense to increase the inlet size to get optimum performance. For the shop vac, I still think it makes sense to take advantage of the Venturi effect (smaller inlet to increase speed).

I'm still debating about using the funnel thingy inside the cabinet. If my theory is correct, I probably won't need the funnel. I'll have a slit in the bottom front of the router cavity which, ideally, should sweep air in to the other slit (I have two back walls, probably spaced about 4 inches apart) before it gets to the vacuum port. If it doesn't pan out, I'll have to manually vacuum the inside of the cavity every time I use the table.

[RodKirby]

Anna - I think you have an idea about how "funny" I am with dust

In my experience - a Shopvac hose on the fence - if routing an edge; or on the side of the router table - if the workpiece covers the router bit; will give you 90% DC. Cleaning out the router table of the "leftover" dust is not a big deal.

I guess what I'm trying to say is: relax - don't get hung up trying to get the last 10%

[Anna]

Anna - I think you have an idea about how "funny" I am with dust

In my experience - a Shopvac hose on the fence - if routing an edge; or on the side of the router table - if the workpiece covers the router bit; will give you 90% DC. Cleaning out the router table of the "leftover" dust is not a big deal.

I guess what I'm trying to say is: relax - don't get hung up trying to get the last 10%

Thanks for the advice, Rod. I believe you are right.

So... having seen pictures of your shop, how do you get the last 10%?

[Anna]

That's a pretty good example, and I agree with you. You can only move a certain volume of air through a certain size tube. I've had different types and sizes of DC systems, and the faster you can move the air the more efficiency you can expect, just like the force of the wind.

On a two bag 1.5 hp system I have a 4" hose. If I hook that same hose to my 7hp cyclone, the difference is night and day. What goes in must be able to get out.

CMan, I think it will really help solve my problem if you give that "inadequate" 1.5 hp dust collection system to me.

[cabinetman]

CMan, I think it will really help solve my problem if you give that "inadequate" 1.5 hp dust collection system to me.

Nothing to get all excited about, it's just a mobile station pick up. The cyclone has real suction,

[RodKirby]

So... having seen pictures of your shop, how do you get the last 10%?

An occasional (depending on the amount/type of use) "wave around" of the Shopvac hose
I get to see how much dust is in the router table enclosure each time I change the bit height.

[Stan]

Great thread and information, in the process of a router table here also. As for the excess cord inside the cabinet that may trap dust -- I'm going to cut the cord to just reach to the 'inside the cabinet' power receptacle. Figure that will take care of that issue.

[LinuxRandal]

Then the router will be permanently inside the box?

I am not gonna say permanent, because I can and do see my father and I sharing the router for a while (he really doesn't see the need for a 3+ HP router, just upgraded to a 2+ last Christmas via me).

I did by a Milwaukee 5625 from HDT last black friday for this project (just finally getting to it).

As for the tip, if it was the one I saw, they used a gate on the inflow side of the equation. Made sense, adjustable, and you can close the gate before shutting off the dust collector for a little vac effect.