Step 3: Building the wire guide.
We will be putting a hole in the center of the bit using the 1.5" (38mm or close) hole saw. A pair of scissors would probably work if you are using cardboard.
First, grab the bit of 2"x4" (50mm x 101mm) plastic/wood/cardboard/whatever. Using a pencil/marker/eyeliner; make a mark in the center of the piece. Precision is not really required; you can eyeball this. Measure ~2" (~50mm) from the mark you made and place a mark. Do this again in the opposite direction. You should now have three marks on the material. The center mark is where the 1.5" (38mm) diameter guide rod will eventually go. The two side marks will be where the wire will be threaded through.
With the 1.5" hole saw bit affixed to your drill; create a hole in the center of the material where you marked. Swap out the hole saw with the drill bit and drill a hole on each of the other marks. Your finished piece should look nothing like this. This was done with the above tools minus the drill.
On to the guide rod. We will want to mark out every half inch (12.7mm) on the guide rod to help us in spacing our turns. So, with a ruler, go through and do so.
Place the rod through the guide hole, and you are almost ready to create the double helix.