09/07/2026
The Bend That Knows Better
Dedicated to Craig Godfrey — PMF teacher, metal fabrication guru, and the man who taught us that the metal always keeps score.
A fabricator is handed a drawing for a precision Z-bracket made from 0.102 6061-T6 aluminum.
Material thickness:
T = 0.102 in
The finished outside dimensions are:
2.000 in fl**ge × 5.000 in web × 3.000 in fl**ge
Both bends are 90°, but they aren't identical.
Bend #1
- Inside radius: 0.125 in
- K-factor: 0.40
Bend #2
- Inside radius: 0.250 in
- K-factor: 0.44
The formulas written on the board are:
BA=\frac{\pi}{180}A(R+KT)
SB=(R+T)\tan(A/2)
BD=2SB-BA
The apprentice looks at the drawing and says:
«“Two plus five plus three. Cut the blank ten inches long.”»
Craig doesn't say anything.
He just raises an eyebrow.
The fabricator calculates the blank, walks to the brake, and notices one more problem:
The tooling allows a previously formed fl**ge of 2.250 inches maximum to pass beneath the ram while positioning the second bend.
Once the 3-inch fl**ge is formed, the other bend can no longer be made without colliding with the machine.
The challenge
You have one piece of material.
No trimming after forming.
No flattening a bend back out.
And Craig is watching.
Three questions:
1. What is the bend allowance for each bend?
2. What exact flat length should you cut?
3. Which bend must be formed first?
Answer
For Bend #1:
[
BA_1=\frac{\pi}{2}(0.125+(0.40)(0.102))
]
[
BA_1=\frac{\pi}{2}(0.1658)
]
[
\boxed{BA_1=0.2604"}
]
Setback:
[
SB_1=0.125+0.102
]
[
\boxed{SB_1=0.2270"}
]
Bend deduction:
[
BD_1=2(0.2270)-0.2604
]
[
\boxed{BD_1=0.1936"}
]
---
For Bend #2:
[
BA_2=\frac{\pi}{2}(0.250+(0.44)(0.102))
]
[
BA_2=\frac{\pi}{2}(0.29488)
]
[
\boxed{BA_2=0.4632"}
]
Setback:
[
SB_2=0.250+0.102
]
[
\boxed{SB_2=0.3520"}
]
Bend deduction:
[
BD_2=2(0.3520)-0.4632
]
[
\boxed{BD_2=0.2408"}
]
---
The finished outside dimensions total:
[
2.000+5.000+3.000=10.000"
]
Subtract both bend deductions:
[
Flat=10.000-0.1936-0.2408
]
[
\boxed{Flat=9.5656"}
]
So the blank should be approximately:
[
\boxed{9.566"}
]
Not 10 inches.
---
But the mathematics only gets you to the brake.
Now comes fabrication.
If you form the 3-inch fl**ge first, it exceeds the machine's 2.250-inch clearance and prevents the opposite bend from being positioned.
Therefore:
[
\boxed{\text{Form the 2-inch fl**ge first.}}
]
Then form the 3-inch fl**ge.
The apprentice had the drawing.
The fabricator had the formulas.
Craig had the answer before either of them touched the brake.
Because precision fabrication isn't just knowing where the bend goes.
It's knowing what the metal becomes after you put it there.
Measure the finished part.
Calculate the flat.
Know your tooling.
Plan the sequence.
Because sometimes you can make every bend perfectly…
…and still make the part wrong.
— Dedicated to Craig Godfrey,
PMF teacher and metal fabrication guru. 🔩📐
