cutting metal ductwork

[Randall J Cox]

I have been given 5" and 6" snaplock metal ductwork from a friend, left over from his cyclone installation. Five ft straights, 90 degrees curves, wyes and blastgates. Plus I am buying some used ductwork to add to it. My question is, how do I cut snaplock pipe after it has been snapped together? Can it be unsnapped? (It doesn't look like it to me.) I know they make left right and straight cutting tin snips, assume I only need straight? Any other tips for working with this stuff? Thanks. Randy

[Ben Rivel]

This is what I bought to cut mine: LINK I just got it all though so I havent tried it yet but from what I read online, saw in youtube videos and had a couple co-workers tell me they have used before thats what I gathered was the way to go.

[Hoang N Nguyen]

I used a jig saw with a metal cutting blade on it, cut metal duct pipes like butter. You'll need to drill a hole slightly bigger than the blade before you can start cutting though. Doesn't take much time at all to make a cut, I'd say in the neighborhood of about a minute for a cut.

[Brian W Smith]

"Technically" and it's a rule we break routinely,aviation snips(assuming that's what the OP meant by rightys and leftys) are not meant for center panel or sheet work.They were/are designed for taking off,or trimming,say around 1/4-1/2" max.Shears,saws,nibblers are what's used for center panel cuts.....cut oversize,then "finish" with av snips.Just sayin.

Edit;die grinder with cutoff wheel gets a hole started pretty durn quick....and then break the above rule.

[Lee Schierer]

I had to cut some duct work this past Thursday to shorten it an inch. I opened my workmate just wide enough to hold the tube. I rotated the piece so the seam was up and then used a hacksaw with a fine tooth blade to cut through the seam. As I cut through the metal I rotated the tube so that fresh material was move under the side of the blade closest to me while keeping the blade in the kerf. After cutting a couple of inches, I cut in from the end with a pair of regular snips and then used the snips to cut the rest of the way around the tube.

Be aware that most snap lock duct work is pretty thin gauge and is designed to be pressurized, not for vacuum applications. If you have a strong DC and operate the system with all inlets shut, you may collapse some or all of the duct work flat.

[Jebediah Eckert]

I'm doing my system right now. It seems the snap lock comes apart just when you don't want it to. If it's together solid I like Hoang's idea of the jigsaw, I may give that a shot. Those snips work fine for me in the past but it had to be flat, not snapped together. Make a bunch of measurements all around the pipe before cutting, it is really really easy to go off square.

I think Lee is right, there are plenty of videos of big machines collapsing 30 ga duct. Oneida sells 26 gauge snap lock and that will hold up past their 5 hp models with all the gates shut. That's at least what they recommend to use.

[Ole Anderson]

I used an angle grinder with a thin cutoff blade to pierce the duct, then a jigsaw with a very fine blade to make the actual cut.

[Charles Lent]

The double cutting tin snips (aviation style is better) removes about 1/4" of material as it cuts, leaving an easy path for this cutter to follow and maintain a straight cut. It is the "Tool Of Choice" for doing this by the professional sheet metal workers.

Charley

[Andy Giddings]

Also used a jigsaw with a fine blade for 24ga snap lock. Works ok but am going to try the double cutting snips next. Cutting the tube is fairly easy compared with getting 24ga to snap together :-)

[Bob Cooper]

Angle grinder works great

[mike mcilroy]

I used a jigsaw with a bi-metal blade and tipped the saw into the pipe with no hole drilled. Plunge cut? Works fine and is fast.

[Jim Finn]

The double cutting tin snips (aviation style is better) removes about 1/4" of material as it cuts, leaving an easy path for this cutter to follow and maintain a straight cut. It is the "Tool Of Choice" for doing this by the professional sheet metal workers.

Charley

I am that professional sheet metal worker (retired) and agree, double cuts work well for this. Light gauge snap lock pipe can be taken apart and cut with tin snips. To take the pipe apart you have to push in at the seam at one end and it will start to come apart and then you can work it apart all the way to the other end. Not easy but it can be done. As has been mentioned, mark a line all the way around the pipe, weather it is snapped yet or not and cut with tin snips. Sheet metal workers almost never use straight cutting aviation snips. We use Rights (red) or lefts (green) for these cuts.
I have also done plunge cuts with a Sawsall for heavy gauge duct. Pretty noisy though.
If you have trouble with the snap lock pipe coming apart just install a pop rivet or a screw through the seam.

[Tom M King]

Cut through the seam with a 4-1/2" angle grinder and thin metal cutting disk like Ole was talking about, and then finish with offset handle tin snips. The offset handle version keeps you hand above the cut so the only thing inside the tube is the lower jaw of the snips. Just cut enough with the disk to get the snips started. These are available in the box stores too:
http://www.amazon.com/M6R-MetalMaste...n+snips+offset

One of the pictures at that link show you how your hand stays out of the way of the metal, unlike "aviation" snips.

[Randall J Cox]

Lots of good ideas. Don't think I will collapse this pipe as I only have 1.75 HP motor. I know its easy to get off center when cutting something round, will mark around before cutting. Thanks for all tips. Randy

[Peter Kelly]

If the duct is already formed into "round" I mark the length with a sharpie then wrap the cut line with a piece of blue tape butting the edge up to the mark. Follow the edge of the tape with an angle grinder and you get a nice square cut.