You design a sheet metal bracket in CAD with perfect 100 mm dimensions.

But when the factory folds it, the final part measures out to 102 mm.

Why did your metal magically grow? You guessed the K-Factor. 👇

When you bend sheet metal, it does not act like a piece of paper.

The inside surface of the bend compresses and gets shorter. The outside surface stretches and gets longer.

But somewhere deep inside the thickness of that metal, there is a microscopic layer that doesn't compress or stretch at all.

We call this the "Neutral Axis." Its length stays exactly the same before and after the bend.

To get your flat pattern DXF exactly right, your CAD software needs to know exactly where this Neutral Axis lives. That is the K-Factor.

K = t / T

• t = Distance from the inside face to the Neutral Axis
• T = Total material thickness

If you get this number wrong, your flat pattern will be too long or too short, and your assembly holes will never line up.

If you are designing sheet metal in SolidWorks or any 3D CAD, follow these 3 rules:

𝟭. 𝗜𝘁 𝗶𝘀 𝗔𝗹𝗺𝗼𝘀𝘁 𝗡𝗲𝘃𝗲𝗿 𝟬.𝟱

Freshers assume the neutral axis is perfectly in the center (K-Factor = 0.5). It isn't. The bending forces push the axis inward. For standard steel and aluminum, it usually lives between 0.33 and 0.44.

𝟮. 𝗧𝗵𝗲 𝗥𝗮𝗱𝗶𝘂𝘀 𝗖𝗵𝗮𝗻𝗴𝗲𝘀 𝗘𝘃𝗲𝗿𝘆𝘁𝗵𝗶𝗻𝗴

If you use a sharp tool to bend a tight radius, the neutral axis gets shoved hard toward the inside (lower K-factor). If you use a massive, sweeping bend, the axis relaxes back toward the middle (closer to 0.5).

𝟯. 𝗦𝘁𝗼𝗽 𝗚𝘂𝗲𝘀𝘀𝗶𝗻𝗴, 𝗦𝘁𝗮𝗿𝘁 𝗔𝘀𝗸𝗶𝗻𝗴

You cannot calculate a perfect K-Factor at your desk. The true value changes based on the specific V-die width and press brake the factory uses. Stop trusting standard CAD tables and simply ask your fabricator: "What bend deduction or K-Factor do you use for this specific thickness?"

Have you ever had a sheet metal part fail because the flat pattern was calculated wrong? Let me know below! 👇