K factor not referencing A-Side

[william]

Hello All

I have the below scenario.
I have a curved solid body, I select the face I want as the true shape, by defining it as the A-Side. 

With the K Factor set to zero, I reasoned that the flat pattern would be the true shape of the selected face.

Because the shape is a conic, in theory the top and bottom arc lengths should remain constant from the curved face to the flattened true shape.

However, in practise, I have found that this works for one of the faces but not the other?? 

I have 2 parts. Both contain the same solid body. On one I defined the A-Side to the inside face, the other the outer face. Both parts have K factor set to 0. 

However, the flattened result remains the same?!

Therefore, on one of the parts the flattened shape is calculating correctly with the k factor referencing the A-Side. The other seems to be ignoring it. 

However, on the part that isn't behaving as I would expect, if I change the k factor from 0 to 1, it gives me the true shape of the selected A-Side. 

What is going on here? 

It would seem that the A-Side is ignored entirely when flattening the solid. Which is surely incorrect!

Screen recording attached for clarity, and ipt files for testing. 

@johnsonshiue 

[YannickEnrico · Accepted solution]

K factor never referenced the A-side. It references the inside of the bend. So if you want the outside, choose K=1,00, as you correctly found works.

Clarification: The inside of the bend is the smallest radius

[YannickEnrico]

Referencing the A-Side on a shape like this would lead to the wrong unfold as well, since you have bends in both directions. Hence K=0 is always inside, and K=1 is always outside

[pcrawley]

This is a good conversation, but for all practical applications, you wouldn't have a k-factor > 0.5.

There's a good (if a bit long!) article here if you're interested that explains where the k-factor comes from, how it is calculated - and why it is unrelated to "A-Side":  https://www.thefabricator.com/thefabricator/article/bending/analyzing-the-k-factor-in-sheet-metal-be... 

[kacper.suchomski]

And I join in. If everyone’s in, I’m in. 😁

[YannickEnrico]

That depends entirely on what you want to achieve.

I've had complicated end treatments that were cut with an angle grinder and a paper overlay as a guide - That requires K=1

Also, since the unfold depends on both K factor and Bend Radius, if one is not ideal, you have to adjust the other. In practicality I have countless experience compensating on the K-factor to achieve an appropriate laser cut flat, because customers didn't necessarily know or understand that bend radius had to be equal to thickness for our bend tables to apply

[william]

Thanks Peter!