# Fabrication Formulas

## Formulas

### Bend Allowance (BA)

The amount of added to the sum of the two leg lengths to obtain the flat pattern length.

$BA = {\dfrac{\pi}{180} \cdot B< \cdot (IR + K \cdot MT)}$

### Bend Deduction (BD)

The amount removed from the sum of the two flange lengths to obtain a flat pattern.

$BD = {2*(\tan \left( \dfrac{B<}{2}\right) \cdot (IR + MT))-{\dfrac{\pi}{180} \cdot B< \cdot (IR + K \cdot MT)}}$

### Material Thickness (MT)

The gauge of the material in decimal form.

### Bend Angle (B<)

The inside angle between the two legs or flanges of a bend.

### K-Factor (K)

The ratio of the position of the Neutral Axis to the Material Thickness.

$K={\dfrac{180 \cdot BA}{\pi \cdot B< \cdot MT}-\dfrac{IR}{MT}}$

### Y-Factor (Y)

A constant based off of the K-Factor used by Pro-Engineer in place of a K-Factor.

The final formed inside radius after spring back has occurred.

The final formed outside radius after spring back has occurred.

### Outside Setback (OSSB)

Distance between the outside tangent points and the apex of the outside mold lines.

$OSSB = {\tan \left( \dfrac{B<}{2}\right) \cdot (IR + MT)}$

### Inside Setback (ISSB)

Distance between the inside tangent points and the apex of the inside mold lines.

$ISSB = {\tan \left( \dfrac{B<}{2}\right) \cdot IR }$

### Outside Mold Line (OML)

A line that runs parallel to the outside of the workpiece.

### Inside Mold Line (IML)

A line that runs parallel to the inside of the workpiece.

### Outside Offset (OSOS)

The measurement from the surface of the outside radius to the apex of the outside mold lines.  When calculating the outside offset use the included bend angle.

$OSOS={\dfrac{IR+MT}{\tan{\left( \dfrac{B<}{2} \right)}}-(IR+MT)}$

### Inside Offset (ISOS)

Distance between the inside mold lines and the bend line.

$ISOS={\sin\left(\dfrac{B<}{2}\right) \cdot \left(\sqrt{2 \cdot ISSB^2}-IR \right)}$

### Inside Through the Material (ISTM)

The distance between the outside and inside mold lines.

$ISTM={\tan{\left(\dfrac{B<}{2}\right)} \cdot MT}$

### Inside Shift (ISS)

Distance between the outside mold lines and the bend line.

$ISS={ISTM-ISOS}$

### Bend Line Shift (BLS)

The distance from the Outside Mold Line to the original bend line on the flat pattern.  This is used to calculate the back stop location when working off of a flat pattern.

### 5 thoughts on “Fabrication Formulas”

1. Rob McDonald says:

I would like to INCLUDE A LINK TO YOUR WEBSITE FROM SOME OF MY TRAINING MATERIALS i AM DEVELOPING FOR A CLASS AT OUR COLLEGE. iS THAT OK WITH YOU?

• Brian says:

Absolutely we are completely open with our material, the idea is to spread the knowledge as much as possible.

2. amin says:

thanks for your excellent information i want to know about the formula that are used when working with 3&4 roll bending machines i mean bend allowance bend deduction k factor etc please help me.

3. Nick pRIME says:

I’m lost! In one sentance THE ba IS DEDUCTED AND IN THE NEXT IT’S ADDED (TRYING TO BUILD A PART AND HAVE THE FLAT PATTERN CUT)

• Brian says:

Nick,

I’d love to help, which formula are you looking at?