You cannot see the neutral axis in SolidWorks. He shows it by manually drawing a sketch (the one shown with centerlines) at a specific "offset" from the inside of the bend. The amount of the offset is related to the K-factor set in the property manager and the thickness of the sheet metal part. So, when he changes the K-factor manually, the amount of the "offset" changes as well. The bend allowance is the arc length measured on the "neutral axis sketch". It can be measured either by measuring the arc length on the "neutral axis sketc", or by flattening the sheet metal part and measuring the distance between the bendlines of the corresponding bend.

In a word, K Factor depends on everything....it depends on inside radius, material thickness, material type, bend angle, tooling selection, grain direction, etc... a change to any variable of the bend will change the K factor even if its slight. It's always best to create samples bends with each one of the these variables controlled to get bend deduction/K factors specific to your own processes. If your company does the designing but not manufacturing, i would suggest just using a .4 or .45 K factor across the board and leaving the flat size development up to your suppliers. See these links... www.thefabricator.com/article/bending/analyzing-the-k-factor-in-sheet-metal-bending www.thefabricator.com/article/bending/analyzing-the-k-factor-in-sheet-metal-bending-part-ii

@Jeffrey Joey no we dont care

See these links... www.thefabricator.com/article/bending/analyzing-the-k-factor-in-sheet-metal-bending www.thefabricator.com/article/bending/analyzing-the-k-factor-in-sheet-metal-bending-part-ii While this is a good video for explaining how to use the variables in SolidWorks, it doesn't do the best job of explaining what these variables are, where they comes from, or how to apply them outside of SolidWorks.