trouble keeping DC fittings together

[Tyler Davis]

I have a basic duct run of 26 gage snaplock ducting, which terminates into black plastic tee's and wye's which then transition to aluminum blast gates and plastic flex hoses. All the snaplock is well secured and stays together, since the crimped connections make one male side and one female side of each joint.

The problem is joining the transitions which are the exact same size. For example 4" snaplock into 4"plactic wye. I have tried using regular duct tape. I have tried using the heavy duty aluminum HVAC tape ($20/roll). I have tried rubber Ferno couplings (the kid you use to join sewer pipes). I can't use hose clamps because these are basically butt joints.

Every single one of them has failed at least three times. My garage gets well over 100 degrees every day, and I keep coming home to find sections of my ductwork laying on the ground. The tape adhesive turns into liquid and has no holding strength. How do I get these damn things to stay put?

[Dave Bender]

sheet metal screws or rivets.

[Doug Shepard]

If the plastic and snap-lock are the exact same size, I think you probably want to get some of the plastice couplings to slip across the ends of the butt joint. I'd glue the coupling on the wye side and use sheet metal screws and alum. foil tape to attach it to the metal duct.

[John Keeton]

My first question would be why the plastic tee's and wye's?? Why not bring the 26 ga. straight to the blastgates? Actually, on the fittings, 30 ga. will work fine. Then you can just tape them with the foil tape, silicon the seams on the fittings, screw to the blastgate, silicon the junction, and you are done.

[Jim Becker]

The black plastic fittings were not made to mate with the metal duct. And if you look inside of them, you'll note that they add a lot of constriction...these retail dust collection fittings were not designed by anyone who knows or understands dust collection or air flow. My suggestion would be to replace them with appropriate metal lateral wyes. (NEVER use tees for dust collection...) and seal with foil tape.

[Tyler Davis]

rivets are not an option - these are butt joints

the wye's I am using are 4 x 4 x 2.5, which is not made in metal snaplock

what plastic couplings are you thinking of? I have already tried the rubber Ferno couplings with two hose clamps

[jerry nazard]

Tyler,

Have you tried cutting off a short length of 4" hose and securing it with a couple hose clamps?

-Jerry

[Tyler Davis]

jerry - I have not tried using flex tube as the coupling, however I have tried rubber couplings with hose clamps, which I assumed would be "stickier". The issue is that the flange on the aluminum blastgate is so short (1") and tapered that there is nothing for a coupling to grab onto. Maybe I just need to cover it with Liquid Nails before attaching it...

[Nate Folco]

rivets are not an option - these are butt joints

the wye's I am using are 4 x 4 x 2.5, which is not made in metal snaplock

what plastic couplings are you thinking of? I have already tried the rubber Ferno couplings with two hose clamps


You could always make your own snap-lock wyes. It's really not that hard, you just need some tin snips and some screws or rivets. Here is a template you can print out and use to cut pipe to make a 4x4x2.5 wye:
http://harderwoods.com/pipetemplate.php?f=dn&units=in&paper=letterθ=45&rmd=4&rbd=2.5&rbt=.0179&offset=0&Submit=Submit (http://harderwoods.com/pipetemplate.php?f=dn&units=in&paper=letter&theta=45&rmd=4&rbd=2.5&rbt=.0179&offset=0&Submit=Submit)

Here is a 6x6x5 I made:
http://www.ncwoodworker.net/pp/data/500/thumbs/4DC.JPG

[Adam Slutsky]

Tyler:

In my shop I have made some 4" couplings out of 4" snap lock pipe. Just cut a short piece off (say 6") and then get a crimping tool and crip one end. You can then attach the hose (or plastic fitting) over the crimped end. The downstream end can be attached conventionally with sheet metal screws, silicon and/or foil tape. Yes, the crimping on the upstream end is going in the wrong direction but hey it works and it is fast and simple and damn cheap!

[Steve Kohn]

It will not be the best solution for dust collection but you might wish to go to the Borg and get the appropriate size of "flex connector". Then use screws and aluminum tape to finish sealing the joint between the plastic and the metal duct work.

[Jim Becker]

Tyler, you can get 4x4x2.5 from suppliers such as Oneida who cater to dust collection systems. You could also use a 4x4x4 and then a reducer. A typcial dust collection system isn't a great choice for really small dust hoods, however, because of the way dust collection systems work.

[Michael Panis]

jerry - I have not tried using flex tube as the coupling, however I have tried rubber couplings with hose clamps, which I assumed would be "stickier". The issue is that the flange on the aluminum blastgate is so short (1") and tapered that there is nothing for a coupling to grab onto. Maybe I just need to cover it with Liquid Nails before attaching it...

I think I've tried just about everything Lowe's sells to connect to the blastgates. The only thing I've found that works is the dust collection hose. Also, I only use the Spring Hose Clamps:
http://www.rockler.com/product.cfm?page=16963&filter=dust%20collection%20hose

The standard clamps can't be clamped tightly enough to hold onto the taper:
http://www.rockler.com/product.cfm?page=16962&filter=dust%20collection%20hose

[John Keeton]

Use silicon to seal and screws to attach the duct to the blastgate. There are some pics at this thread http://www.sawmillcreek.org/showthread.php?t=79131 I realize that you are using different size material, but some of this may be of help.