cutting metal ductwork

[mike mcilroy]

I used a short cut off piece of pipe that is "unconnected" to slip over the snapped together pipe, slide the uncut edge to the mark and then use a marker or felt tipped pen to trace around the pipe to be cut.

[Charles Lent]

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

You have no concept how much force you are dealing with. Atmospheric pressure is 14.7 PSI. That's just under 15 pounds of force pushing in on every square inch of your duct surface. Without the vacuum turned on, it's pushing that same amount from both the inside and the outside. Now remove just half of that force from the inside of the duct and you have over 7 pounds of force for every square inch of duck outside surface trying to squash that duct. For every 1 square foot of duct surface you will have over 1/2 ton of force trying to collapse it, and that's with a vacuum that is only 50 % efficient.

Go with the 26 ga metal ducting, or PVC. If not, you will be throwing your money away.


Charley

[Roger Feeley]

+1 on the double cutter.

I'm also a fan of the air powered nibbler. http://www.harborfreight.com/16-gauge-air-nibbler-96661.html

Hook that up to your air compressor, drill a quarter inch hole to start and just go. $25. I've had one for years and when you need it you need it.

[Ole Anderson]

You have no concept how much force you are dealing with. Atmospheric pressure is 14.7 PSI. That's just under 15 pounds of force pushing in on every square inch of your duct surface. Without the vacuum turned on, it's pushing that same amount from both the inside and the outside. Now remove just half of that force from the inside of the duct and you have over 7 pounds of force for every square inch of duck outside surface trying to squash that duct. For every 1 square foot of duct surface you will have over 1/2 ton of force trying to collapse it, and that's with a vacuum that is only 50 % efficient.

Go with the 26 ga metal ducting, or PVC. If not, you will be throwing your money away.


Charley

A typical DC will generate about 10 inches of suction (water column or wc) with all gates closed. 14.7 psi is equivalent to 407 inches of suction. 10 inches of suction is equivalent to 0.36 psi.

[Jim Finn]

26 gauge ells and 24 gauge pipe is what I used with success.

[Randall J Cox]

+1 on the double cutter.

I'm also a fan of the air powered nibbler. http://www.harborfreight.com/16-gauge-air-nibbler-96661.html

Hook that up to your air compressor, drill a quarter inch hole to start and just go. $25. I've had one for years and when you need it you need it.

Roger, great tip. I don't like dealing with sheet metal in my DIY projects over the years. Looks like just what I need, its cheap at $25 and it gets great reviews too. Thanks! Randy

[Bruce Wrenn]

HF sells both electric and pneumatic shears. Electrics are about $50, less the usual 20% off coupon. I have a set of Milwaukee ones that are over 30 years old. Old timers called them Keets, as that's who made them first

[Joe Jensen]

I bought an air nibbler for some sheet metal work and boy is that fun to use. But it throws small crescent moon shaped pieces everywhere

[Ken Grant]

Go with the 26 ga metal ducting, or PVC. If not, you will be throwing your money away.


Charley

I guess I must have thrown away my money when I set up my DC system I am running all 30 ga 6 inch snap lock with a 3 hp blower. The fittings on my setup are rigid enough to keep the pipe in the round shape on sections less then 5 ft long. If you have long runs you will probably need something to keep it from collapsing, which is not a big deal since you need some kind of hanger/support for long runs anyway. I just cut a 6 inch circle out of some scrap plywood and slip the pipe through. It has been working fine for the last couple years. I think PVC is a good option but I did not want to fight the insurance fire inspector on the PVC so I just went with metal.

Good luck!

[Mike Heidrick]

I bought an air nibbler for some sheet metal work and boy is that fun to use. But it throws small crescent moon shaped pieces everywhere

I keep a couple of welding magnets in the spray area of the crescent moon pieces. Really helps collect them for this steel swarf/chaff lol.

[Randall J Cox]

ok, another Q on ductwork. Have some metal ductwork that a friend gave me, just bought another bunch on CL. Trying to get them to join, seems like the crimped end is the same size as the non crimped end of other pieces. None is high end stuff, no spiral, etc. All 5 and 6". Now what? I have seen some couplers that slip over both ends of pipe and you tighten down a couple of bolts. Anybody use these? Do they work? At least it looks like they are cheap and would fit over both ends, hard to seal for leaks? Randy

[Andy Giddings]

Randy, am assuming that cutting off the pre-crimped end would not allow one connection to slide into another? Even if you use hand crimps to get a smaller end? If none of that works and you only have a few joints, I would try something like a flexible rubber coupling that you can clamp down as that will at least give you a good seal. Fernco make a wide range.

[Jim Finn]

ok, another Q on ductwork. Have some metal ductwork that a friend gave me, just bought another bunch on CL. Trying to get them to join, seems like the crimped end is the same size as the non crimped end of other pieces. None is high end stuff, no spiral, etc. All 5 and 6". Now what? I have seen some couplers that slip over both ends of pipe and you tighten down a couple of bolts. Anybody use these? Do they work? At least it looks like they are cheap and would fit over both ends, hard to seal for leaks? Randy

What you described here is called a draw-band. It will work ok and will seal like any other metal to metal duct connection. You should either caulk this and all seams or better still use a brush on duct sealer. (Kinda' like very thick paint)

[Randall J Cox]

I bought a double cut air tool from HF the other day on sale for $25 and it really cuts nicely. Only thing is you need to start from flat panel. Also it won't cut through seams, they are to thick to fit into the shearing jaws. I figured for that price what do I have to lose. Perfect for flat panels. As I'm only cutting through 26 gauge metal, like a hot knife through butter. Will keep it well oiled as all have recommended. Also says if not kept oiled daily, will void warranty. Most oil every hour if using a it lot. Randy