cutting into double-wall duct

[sethmarx]

Any one have a simple way of cutting the inner wall of double wall duct. Trying to cut in for flex collars after duct is installed. Malcos circle cutter is good for the outside layer. Hoping there is a faster way than what I've been doing it.

[MM#7]

Any one have a simple way of cutting the inner wall of double wall duct. Trying to cut in for flex collars after duct is installed. Malcos circle cutter is good for the outside layer. Hoping there is a faster way than what I've been doing it.

double wall duct? never saw double wall duct except on a type b vent, but then again, there's a lot i haven't seen!

[sethmarx]

Sorry not B vent. This is high pressure duct with 'duct-mate' flanges, 1" fiberglass insulated with a perforated galv. liner. A sawzall chatters too much and wont turn tight enough. Offset snips dont do it well either.

[MM#7]

Sorry not B vent. This is high pressure duct with 'duct-mate' flanges, 1" fiberglass insulated with a perforated galv. liner. A sawzall chatters too much and wont turn tight enough. Offset snips dont do it well either.

wow, i guess the perferated metal keeps the duct liner intact. interesting! it's almost like you need a robo cutter with a special bit, or a malco hole cutter with the metal bit extended! hopefully you're wearing eye protection as well as safety gloves,always work safely and good luck!

[Fabrk8r]

Parting wheel, or if the cut-out is large enough, just cut a big enough area out of the center and then you can put your snips on the "inside" and cut the inner hole that way. The second option may be tough on your wrists though.

We make a lot of rectangular double-wall duct for sound attenuation. It's amazing how much a 5' piece can cut the decibels down. We buy the round double-wall and make our own taps.

[MM#7]

Parting wheel, or if the cut-out is large enough, just cut a big enough area out of the center and then you can put your snips on the "inside" and cut the inner hole that way. The second option may be tough on your wrists though.

what the heck is a parting wheel?

[Lash]

We usually cut the inner smaller and then cut slices to make tabs. We then pound the tabs over to fill in the gap between the inner and outer walls to protect the insulation.

[Fabrk8r]

A parting wheel, also know as a cut-off disc, is a thin grinding wheel for a 4-1/2" grinder that is made specifically for cutting metal.

[MM#7]

Any one have a simple way of cutting the inner wall of double wall duct. Trying to cut in for flex collars after duct is installed. Malcos circle cutter is good for the outside layer. Hoping there is a faster way than what I've been doing it.

curious, what gauge is this metal?

[Lash]

We've also used a smaller plasma cutter.

[MM#7]

We've also used a smaller plasma cutter.

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$or borrow/rent!

[Lash]

You can get a pretty decent one for around $1000-1500, plus it's a write-off anyway.

[Fabrk8r]

I'm starting to wonder if this might be a DIY project from the questions we're getting back on our replies.

[wsykes]

Any one have a simple way of cutting the inner wall of double wall duct. Trying to cut in for flex collars after duct is installed. Malcos circle cutter is good for the outside layer. Hoping there is a faster way than what I've been doing it.

you should not be putting flex on a high pressure system

[Ohio-hvacr]

Any one have a simple way of cutting the inner wall of double wall duct. Trying to cut in for flex collars after duct is installed. Malcos circle cutter is good for the outside layer. Hoping there is a faster way than what I've been doing it.

I've only experienced duct like this twice. Both times it was for either sound attenuation or for vibration isolation. Either way, this type of duct is not meant to be cut into, at least not in the field. If it must be done, I would suggest double cutters (electric shears) for the outside layer and snips for the inside. Good luck.

[Lash]

you should not be putting flex on a high pressure system

Who said it was high pressure?

[Lash]

Either way, this type of duct is not meant to be cut into, at least not in the field.

It's cut into all the time.....field, shop, whatever. You just have to know how to do it right. You can either make tabs like I said before (prefered for a round opening) or put a 'C' channel of bent metal over the exposed edge of insulation after you cut into it.

[Ohio-hvacr]

Sorry not B vent. This is high pressure duct with 'duct-mate' flanges

He said it was high pressure. You would be compromising the integrity of it if it was in fact for sound or vibration purposes.

[Lash]

You're right, he did say high pressure. I wonder what pressure is being considered high pressure. Resi guys think 2" is high..lol :P