topic Re: K factor not referencing A-Side in Inventor Forum

K factor not referencing A-Side

william — Wed, 02 Apr 2025 02:18:55 GMT

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

Re: K factor not referencing A-Side

YannickEnrico — Wed, 02 Apr 2025 04:31:11 GMT

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

Re: K factor not referencing A-Side

YannickEnrico — Wed, 02 Apr 2025 04:26:11 GMT

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

Re: K factor not referencing A-Side

pcrawley — Wed, 02 Apr 2025 09:16:52 GMT

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-bending

Re: K factor not referencing A-Side

kacper.suchomski — Wed, 02 Apr 2025 09:23:41 GMT

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

Re: K factor not referencing A-Side

YannickEnrico — Wed, 02 Apr 2025 09:36:59 GMT

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

Re: K factor not referencing A-Side

william — Wed, 02 Apr 2025 19:08:31 GMT

Thanks Peter!