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Assemble the metal ducting like a zipper

When assembling pipe, start at one end and work the seam together like a zipper. Use one hand to keep the two edges close and the other to apply downward pressure. Use your leg, a workbench or the ground to support the back side of the pipe. If you make a mistake and have to dismantle a pipe, slam it down flat on the ground, seam side up. It should pop right apart.

Dont peel off old tape of metal ducting

If you have to disassemble existing ductwork fittings, there’s no need to peel off the old foil tape first. Instead, just score the tape at the seam with a utility knife and remove the screws right through the tape. When it comes time to retape, just clean off the dust and apply new tape right over the old.

Step by Step Guide to Cutting The Ductwork

Now that we’ve gone over the basics it’s time to get into the details. Before even attempting to cut ductwork, we must make preparations.

So let’s get into the grimy details!

Step 1: Safety First!

Using an angle grinder generates a lot of sparks and debris. So, it’s essential for you to follow these safety tips when using power tools.

Always wear safety glasses and a face shield to protect your face and eyes. It’s wise to wear ear-muffs or earplugs to cushion the grinder’s deafening sound.

When using an angle grinder there is a potential fire hazard. This is why you should wear fire-resistant sleeves or jackets. Don’t forget to wear heat-resistant gloves too.

If you’re unsure about which gloves to invest in, take a look at our picks below:

Glove 1
Glove 2 

Now that you’ve put your gloves on, you can move onto the next step.

Step 2: Initiate Test Run on Angle Grinder

Inspecting your angle grinder is one of the steps you can’t ignore. Making sure your tool is fully functional will reduce the rate of accidents.

First, make sure the grinder is not connected to a power source. After unplugging it, make sure the cord does not have any frays.

Next, check the guard of the grinder along with its handle. Make sure the guard can move freely and the handle is sturdy.

Move on to checking the cutting disks. Watch out for any cracks or knicks as they may cause the disk to shatter.

After you’ve checked all the components, run the grinder at a distance. Run for at least 5-10 seconds to see if everything goes smoothly. Look for any wobbles in the disk and reinstall if it wobbles.

Now, we move to the next step, cutting the ductwork.

Step 3: Commence Cutting the Ductwork

The cutting wheel has a 4 and a half-inch diameter and is perfect for cutting thin metals. The maximum thickness this wheel can cut is ¼ of an inch thick.

For sheets thicker than this, use a plasma cutter. You can also use a Dremel to cut ductwork as it can cut through ½ inch thick bolts.

After you’ve secured the piece onto the work surface, you may begin cutting. Cut in straight lines as twisting and turning may cause the wheel to disintegrate.

When your wheel begins to jerk, turn off the power switch. Wait for the disk to stop rotating and pull it back. If your wheel gets jammed, twist and break the wheel to take it out.

Now, we move onto the final step which is the finishing touches.

Step 4: Sand and Polish the Ductwork

This is a step that is mostly overlooked. That is you must always sand out the rough edges.

For this, you have to install a velcro pad and sand-paper (220 Grit) to commence sanding. Finish off by installing the polishing disk for a shiny finish.

This is how you cut ductwork with an angle grinder. We hope this post was helpful in learning the know-hows about angle grinders.


For this process there is a need of few elements, among them first you will require a snap-lock pipe, this is the duct you want to trim, next you will require a tape measure, this will allow you to have a proper measurement while cutting, and after that, you will require a marker for marking the sizes. You will also need to have snips which will be used to reduce, and lastly, to crimp the duct, you will need a five-blade crimper.


Mark the cut line or area on sheet metal with a felt-tip marker. Punch a starter hole in the metal with the blade of a straight screwdriver and a hammer, large enough to fit the tip of the compound snips inside. Cut from the hole to the line, then cut the line around a round duct or along the circle or rectangle opening on a flat duct.


Cut flex duct with a utility knife or shears and tin snips. Slice the metallic outer layer and the insulation around the round flex duct with the knife or shears and lay it back to expose the coiled wires. Cut each wire with snips, taking care to make the cuts even so the cut end is straight.

Things You Will Need

  • Tin snips, multiple options

  • Felt-tip marker

  • Hack saw (optional)

  • Utility knife

  • Shears

Warning Wear gloves when cutting ducts, recommends Perfect Home HVAC Design. Sheet metal edges are sharp and will cut hands and fingers, and cut coil wires also can injure. Cut ducts on a flat, solid work surface. Don’t try to cut ducts that are fastened to walls or ceilings unless you are an expert metalworker.


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