Making the funnel neck step 1 draw a wedge shape on the sheet metal making it 4 inches wide at the top and 2 inches wide at the bottom and 6 inches in length.
How to make a funnel shape out of sheet metal.
To make a large funnel use a standard sheet of printer paper.
For small funnels fold a sheet of printer paper twice so you end up with four rectangles and cut those apart and use separately that s what i m using here.
You can get three guards out of a 3x8 foot piece of metal see drawing below from zeleny s book then cut out circles.
You can find cone calculators online.
Here is one way to make a cone from flat stock.
Drill a few holes through the overlapping rectangular shape.
I used aluminum sheet coil but you could use paper or any flat material.
Once you have a rectangle of paper follow these steps.
Form into an elongated cone so that the opening at the thin end is about inch in diameter.
Roll the cone template into a cone shape starting at the wide end working toward the pivot point end.
The cone has a diameter at the top smaller than the diameter at the bottom and to accurately trace the shape onto sheet metal you need to make a template out of construction paper.
Your circle will be 18 from the center of the circle to the edge i e 36 in diameter when flat when formed into a cone the finished diameter will be.