DC drop diameter?

[doug barr]

Planning on 6" mains and need to drop to tablesaw with 4" duct in cabinet and 4" over table guard. Should the drop be 6" and then a 6" to 4" y off in two different places for the cabinet and guard or should the drop be 4" right from the main. I don't want to choke off the air but I am concerned that the velocity of the air in the 6" drop may not be able to carry all particles up to main. Any thoughts on this? thanks Doug

[Jeff Monson]

Doug, I'm far from a dust collection expert, but most I see will run the 6" right to the tablesaw if possible, then either necking it down to 4" or preferably putting in a larger adaptor at the tablesaw cabinet to improve chip collection.

[David Hostetler]

Not sure if this will help you or not, but...

My table saw setup has 3 ports, a 4" belly pan, a 2.5" blade shroud (NOT the guard, the shroud under the table), and a 4" on the guard. The table saw is the first tool in line with the DC. I am not done hooking it up yet, but my plan is to come out of the DC with 5", to my Thien Separator, then out to the 5x4x4 Wye that is presently on the DC, one of the 4" goes down to the blade shroud and belly pan, the other goes overhead and to the Shark Guard.

Presently I do something similar, but the wye is at the DC, so the blade guard does not go through the Thien separator. A minor annoyance, but an annoyance no less... It works pretty well... I would imagine that you could do something similar, go to your branch with 6" then split your 4" lines off of that...

[Chris Friesen]

How much airflow does your collector give? Typically a "big enough" system would run 6" as close as possible to the tool, then split into 4/4 using a wye rather than a tee fitting.

[glenn bradley]

I run a 2HP Grizzly cyclone and take a 4" off the 6" main in two places; one for below the table and one for the overarm. Works well. Rule of thumb states to get as close as possible before reducing. I have applied real world requirements to this and some are 6" to within a couple feet while I have a 10 foot run of 4" hose in one location. All seem to work well at this point.

[Chris Padilla]

Doug,

Seriously consider increasing the cabinet opening to receive a full 6" DC pipe. The 4" to the overhead should be fine. Just use a 6:6:4 wye.

[Chris Friesen]

Seriously consider increasing the cabinet opening to receive a full 6" DC pipe.

Just curious...why?

The opening in the cabinet needs an equivalently-sized opening for make-up air to enter the cabinet. I suspect that most saws don't have the equivalent of a 6" duct worth of openings.

Given that he's got 4" both above and below the blade, that works out pretty close to the equivalent of a single 6" duct. From what I've read the ideal scenario is 3" above the blade and 5" to the cabinet, but that's splitting hairs and would probably require cabinet modifications to allow sufficient make-up air.

[Clint Olver]

Given that he's got 4" both above and below the blade, that works out pretty close to the equivalent of a single 6" duct. From what I've read the ideal scenario is 3" above the blade and 5" to the cabinet, but that's splitting hairs and would probably require cabinet modifications to allow sufficient make-up air.

Agreed,

C

[Anthony Whitesell]

Just curious...why?

The opening in the cabinet needs an equivalently-sized opening for make-up air to enter the cabinet. I suspect that most saws don't have the equivalent of a 6" duct worth of openings.

Given that he's got 4" both above and below the blade, that works out pretty close to the equivalent of a single 6" duct. From what I've read the ideal scenario is 3" above the blade and 5" to the cabinet, but that's splitting hairs and would probably require cabinet modifications to allow sufficient make-up air.

You are correct. The reason is quite simple, the total square inches of all open ports cannot (actually it can but not by too much) exceed the square inches of the drop. A 6" drop with a 6" and a 4" port at the same time would bad idea. The 6" drop cannot keep up with the combined surface area of the openings. Either stick with the 6x4x4 or the 6x5x3. A) I have seen this discussed here numerous times; and B) I did it and ended up removing it and dropping to a 6x4x4. I think I should have gone with a 6x5x3 through. I think I could use more cabinet draw and less from the guard.

[Alan Schaffter]

The issue is not quite as simple as it seems. You certainly don't want the total cross-section of the inputs to a wye to be less than the output, but they can actually be the same or larger. You need to know what CFM and SP are available at the start of a wye. See Bill Pentz's site for machine CFM requirements. If you have excess CFM or SP you can trade for CFM, you may in fact be able to use a 6 X 6 X 4 wye or even a 6 X 6 X 6 wye (it would be like running two tools at the same time)- it really depends on your DC and ducting. You must still maintain the minimum accepted velocity in the duct to the DC (approx 4000 fpm) to keep dust entrained in the air stream.

Also, to collect as much of the fine, dangerous dust generated by a tablesaw as possible and contrary to what is commonly thought, it is better to have the best over-blade shroud you can buy or make and collect as much CFM from it as possible, even more than from the cabinet. Dust captured in the blade gullets is not dislodge easily by below table suction so much of it is hurled into the air by centrifugal force when the blade is above the stock, while dust that is dumped into the cabinet stays there. (Tablesaws need to be re-designed so incoming take-up air blasts at the side of the blade to help dislodge dust from the gullets). With minimal suction on the cabinet, dust thrown there will stay there and won't escape from gaps. So, you do not need CFM or velocity from the cabinet you might think. You need just enough to get the dust into the ducting and main air stream. One caveat- you need a properly designed cabinet with a steeply sloped floor that directs dust to the port so it can't settle elsewhere and a below-table blade shroud that does the same. As Chris mentioned, you must have openings in the cabinet for take-up air- their cross-sectional area must equal or be greater than that of the cabinet outlet.