Jig for removing crimps on crimped HVAC duct...

[dbhost]

So while I am aware the HVAC duct CAN be used, but with the direction of the flow / smooth side / crimped side, the duct and fittings are effectively reversed. .

I want to be able to easily flatten out our the crimped side.

So I have a plan, right or wrong, I am thinking taking a couple of cutoff pieces of 2x6, and gluing them so I have a piece of 4x6, using the duct as a drawing template and trace an arch in the glueup.

Once dried and secure, set it on end and cut the curve on the bandsaw.

Using this, with a couple of clamps to basically smoosh the crimps out...

Now the fun part.

[LCHIEN]

Pictures would help. You talking about taking the corrugation off the end? Won't it then not mate to the next piece?

[dbhost]

The idea is to smooth the crimped outlet ends and turn them into inlets, and crimp the inlet and and turn it into outlets.

That way the air rushing by doesn't smash into the open side of the crimped ends causing drag.

Basically in order to most efficiently use HVAC ducting, since dust collection flows effectively in reverse, I want to reverse the fittings to keep from causing drag, the pipes can simple by turned around obviously...

The problem is wyes made for dust collection ducting are stupid expensive and just not reasonably achievable price wise. A bit of DIY, which is no small part of woodworking anyway, and I can adapt much less expensive standard HVAC fittings and still get good airflow. I think... Honestly, if I could find one that was cheap enough, and easy enough to use, a muffler expander tool would make quick work of this, but I don't think they go this big... Unless they made one to work on Fart can equipped Hondas...

[woodturner]

It seems like the small amount of "drag" (static pressure) added by the "opposite" facing joints would be insignificant. Do you have experience or knowledge to believe otherwise?

FWIW I use HVAC ducting for my dust collector and have not been able to measure a reduction in static pressure at the tool pickups. Dust collector is rated for 1150 cfm at 11" SP and I measure within 5% of that at the tool pickups.

[LCHIEN]

Ah, I didn't think about wyes. I was just thinking about parts with one innie and one outie.
I'll bet the press that puts those crinkles in uses a big ass hydraulic press!

[d_meister]

crimping new ends is easy and there are many hand tools and methods available for that, but smoothing existing crimps would likely require something like a sheet metal roller;

https://www.amazon.com/%E3%80%90Upgrade-version%E3%80%91Manual-Rolling-Mill-Machine/dp/B089XVCFJF/ref=sr_1_5?keywords=Sheet+Metal+Roller&qid=1639240639&sr=8-5

Wouldn't it maybe work well enough to simply join pieces with short pipe sections like a F/F pipe coupling? And, don't you really only need to effect a "sex change" at the absolute ends, assuming the wrong direction of the exposed crimps in the airstream is negligible?

[dbhost]

crimping new ends is easy and there are many hand tools and methods available for that, but smoothing existing crimps would likely require something like a sheet metal roller;

https://www.amazon.com/%E3%80%90Upgrade-version%E3%80%91Manual-Rolling-Mill-Machine/dp/B089XVCFJF/ref=sr_1_5?keywords=Sheet+Metal+Roller&qid=1639240639&sr=8-5

Wouldn't it maybe work well enough to simply join pieces with short pipe sections like a F/F pipe coupling? And, don't you really only need to effect a "sex change" at the absolute ends, assuming the wrong direction of the exposed crimps in the airstream is negligible?

I have a pair of crimpers, no problem. The issue is the Wyes...Pipes and elbows can be turned around easily...

[capncarl]

I recommend cutting off the crimped end with a pair of aviation tin snips and but joining the 2 pieces of duct and wrapping the joint with aluminum foil tape. Even a close pulled up joint like this will be better than a reversed ac duct joint. If it is not rigid enough you can wrap a piece of thin flashing metal around it and fasten it with a couple of pop rivets.

[Carlos]

With the thinner material, I've done fine just using narrow pliers to stretch the crimp outward, and make it an outside connection instead of inside. This works with what I think is 26 gauge--the really flimsy stuff. It does not work with the more solid material. Then attach as normal and cover with foil tape.

[dbhost]

With the thinner material, I've done fine just using narrow pliers to stretch the crimp outward, and make it an outside connection instead of inside. This works with what I think is 26 gauge--the really flimsy stuff. It does not work with the more solid material. Then attach as normal and cover with foil tape.

I I tried using a couple of 2x2 cutoff pieces as anvils, and vice grips as the press, and sure enough, smoosh, smooshed away the pressed parts to smooth them out...

Just FWIW, I am not going to 6" yet, I have a single 5" into dual 4" runs still, and will likely stay that way for a while. Maybe stay that way. It works. Don't fix what ain't broke as it were... Is 4" ideal? Hardly, But aside from the miter saw, it picks up fine from everything I own, my biggest issue really is most of my stuff has 2.5" ports...