Tunneling with twin needle, on home sewing machine. 

Doing a basic straight stitch with a twin needle on 2 layers of medium weight cotton, thin lightweight fabric tunneling is more pronounced.
Starting at 0.25 neele tenison, going all the way up to 9, to compare the tunneling of the twin needle stitching.
I never set the tension all the way down to 0. Always bumped up to 0.25, lessons the chance of a thread nest forming.
At 0.25, you can barely see any tunneling, and it gets more pronounced at needle tension goes up. At 9 you get a very pronounced tunnel, which you can use to add texture to a fabric panel if you want some extra styling at a garment.
I used regular serger cone thread for both the needle and bobbin, to lesson the tunneling you can also use bulky nylon thread in the bobbin. Will do a video later to compare them.