Open the power shears and slide the bottom blade under the metal siding.
Cut hole through wall with aluminum siding.
Sometimes called a spiral saw or rotary cutting tool.
Measure from the edges of the sheet metal to the point at which you wish to place the hole.
5 cut along one of the vertical lines with the power sheers.
Hold your drill firmly with two hands photo 4 and brace it against your leg if possible.
Apply a thick bead of silicone adhesive.
Line the blade up with the drawn line.
Create a paper pattern of the size and shape of hole you wish to cut.
Use a scrap of plywood as a backer for the hole saw s pilot bit and to protect your work surface.
Here s one that claims to come with a circle cutting attachment for 15.
It s basically a smallish router and used all the time for cutting holes in drywall shower walls etc.
If you notice that the saw binds pull the hole saw away from the siding tilt the hole saw in a different direction and restart drilling the hole.
A bimetal hole saw is easiest to use because it ll chew through an occasional nail without dulling and cut cleanly through vinyl or aluminum siding.
6 pull the wall cap and duct out of the wall.
Like twist bits hole saws chuck right into your drill and will cut through thin gauge sheet metals like aluminum and steel.
When using a hole saw to drill the hole in aluminum siding keep the saw slightly tilted to one side to reduce the chances that the hole saw will bind while cutting the hole.
Tons of companies make similar tools.
Assuming you ve got access from below to the joist space you can use tin snips also called aviation snips to cut the siding and a hole saw or reciprocating saw sabre saw or sawzall to cut.
Hole saws cut bigger holes for large holes a hole saw gets the job done cleanly and quickly.
Position the pattern on the sheet metal where the hole needs to go and draw a line around it using a permanent marker.
I have an ancient dewalt 660 with a circle cutting attachment.