Originally Posted by
wmodavis
Will you please help this novice understand the high and low helix angle thing. Sounds important so I want to understand.
I thought it would be obvious from the context.
The helix angle is the angle of the sloped ramp to the horizontal if it were unwound. Picture a screw in your mind. A fine thread screw makes lots of turns in a short linear distance and has a lpw helix angle. A coarse thread screw advances farther with each turn and has a higher helix angle, and if you've ever seen those twisty masonary nails they turn only a few turns over their length and have a very high helix angle.
Translating that to cable housing, brake housing which is a compressed spring is low helix, while index housing where the strands run lengthwise with a slow twist have a high angle. If they ran lengthwise and didn't twist at all that would be a 90° helix angle.
It isn't the helix angle per se that's an issue, it's whether the strength is derived from direct metal on metal contact, vs linear strands that need to be buttressed by the outer coating to keep from buckling when compressed.