Increasing from 4" to 6".....

[Phil Winn]

woodworking dust port sizes; how difficult is it? My machines,
SawStop, Powermatic, MiniMax, and General International all have 4" dust ports, but as we all know so well after reading Bill Pentz' website, for fine dust collection, the 6" machine ports work so much better; so how difficult is it to increase them? How would you do it?
1. Would you cut out the 4" tube (cut a 6" hole) and weld a 6" tube in?
2. Buy some 8" x 8" squares with a 6" tube stuck in the middle; cut the old
ones out, and "attach" the new ones?
3. Other thoughts?

4. For you dust collection calc wiz' out there....my horizontal ceiling ducts
are 6"; the wyes & blast-gates are also 6"....
A. What is the difference in performance if one increases the size of the port
to 6" from 4" ?

Thanks,
Phil

[Allan Johanson]

Hey Phil,

I'm not afraid of metalwork so from my point of view I'd first try to make a new "bolt-on" solution. Make an entire new hood, etc. Mostly for asthetics, but it can also work better if the hood is tapered. I try to pick an HVAC piece close to the dimensions I'd like then modify it as required to make it work. I'll use extra metal or add on some plywood and fasten it to the tool.

There are a wide variety of HVAC pieces that are a great start for any hood. Check with your local HVAC parts supplier. The BORG has a smaller selection, but I've been lucky so far that they've had what I've needed for only a few dollars.

When cutting metal with power tools, always wear a full face shield. I use a jigsaw to cut metal and little pieces go flying. You must wear eye protection!

Here's a sample of what I've done on my jointer. I used an HVAC side boot takeoff with a rectangular opening that was close to the rectangular hole in my jointer and it has a 6" round inlet. Nice tapered shape for optimum airflow.

http://www.sawmillcreek.org/attachment.php?attachmentid=16726&stc=1

As far as what this will do for you performance-wise, it's hard to know for certain because it depends on the tool. But, I can give you a couple examples of a 4" drop (flex hose and hood) converted to a 6" drop (flex hose and hood) with my Bill Pentz cyclone:

This is with identical ductwork, including the 4" (or 6") flex hose drops. The only thing that changed was the machine that the flex hose was hooked to.

Delta 12.5" planer (very restrictive machine)
4" drop....660 cfm 6" drop....780cfm

Delta DJ-20 jointer (moderately restrictive)
4" drop....810 cfm 6" drop....1030cfm

Look at that variation, especially in the 6" drop. Guys who get too caught up in DC theory are way off base when you actually factor in the machine.

All this to say "I don't know" and that other folks aren't going to know either unless they've actually tested your machines to see how restrictive they are. :p

BTW, another option is instead of making a single larger hood is to instead add on a second hood. Taking your 6" run to the TS and splitting it to 4" to the cabinet and 4" to an overhead hood like the Excalibur will do a better overall job than a single 6" port in the cabinet.

Taking a single port on the bandsaw and instead having 4" in the lower door and 4" under the table would also probably do a better job than a 6" hole in the cabinet.

Food for thought.

Cheers,

Allan

[Allan Johanson]

To clarify:

My main duct is mostly 7" in diameter and after a bunch of feet I reach these two machines in question, my jointer and planer. Then I reduce to a small size pipe to hook up the the machines. Can't find 7" flex hose that easily in my area. ;)

******

By 4" drop I mean reducing my main duct down to 4" and running a short length of 4" flex to the 4" hood on the tool.

By 6" drop I mean reducing my main duct down to 6" and running a short length of 6" flex to the 6" hood on the tool.

******

If you run 6" flex down to the tool with a 4" port, the airflow numbers will be between the examples I posted in my message above.

Reposted numbers with 6" flex to 4" port combo added and clarified text:

Delta 12.5" planer (very restrictive machine)
4" flex hose to 4" port....660 cfm
6" flex hose to 4" port....725 cfm
6" flex hose to 6" port....780 cfm

Delta DJ-20 jointer (moderately restrictive)
4" flex hose to 4" port....810 cfm
6" flex hose to 4" port....970 cfm
6" flex hose to 6" port....1030 cfm

FYI, the Performax sander is extremely restrictive too. About on par with the Delta 12.5" planer. I'm going to have to get very creative when it comes to making a new hood design for that puppy.

Cheers,

Allan