For engineers who already know the math—but still lose projects. For the last few years, I’ve been sharing technical guides here on Mechanical Design Handbook —how to size a motor, how to calculate fits, and (as you recently read) how to choose between timing belts and ball screws. But after 25 years in industrial automation, I realized something uncomfortable: Projects rarely fail because the math was wrong. They fail because: The client changed the scope three times in one week. A critical vendor lied about a shipping date (and no one verified it). The installation technician couldn’t fit a wrench into the gap we designed. University taught us the physics. It didn’t teach us the reality. That gap is why I wrote my new book, The Sheet Mechanic . This is not a textbook. It is a field manual for the messy, political, and chaotic space between the CAD model and the factory floor. It captures the systems I’ve used to survive industrial projec...
The Most Expensive Word on a Drawing Is "Standard"
The most dangerous words in an engineering specification are not complex formulas. They are adjectives.
- "Robust."
- "Standard."
- "High quality."
- "Fast."
These words feel safe. They feel aligned. They are not.
They are undefined variables.
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Vague words create expensive assumptions.
Why "Standard" Creates Downstream Cost
When a drawing calls for:
- Standard tolerance
- Standard surface finish
- Standard lead time
Each stakeholder interprets it differently. A machinist may assume ISO 2768-m. A designer may mean "what we used on the last job." A purchasing team may assume the lowest commercial grade.
These interpretations are not equivalent. The result is variation in:
- Manufacturing time
- Material selection
- Inspection criteria
- Rework risk
Ambiguity forces vendors to protect themselves. Protection costs money.
The Vendor's "Risk Premium"
When a machine shop receives a drawing with vague requirements, they face a dilemma. If they assume a loose tolerance, the part might be rejected by your QA department. If they assume a tight tolerance, they have to slow down their machines, use fresh tooling, and increase inspection time.
To protect their margins, experienced vendors automatically add a Risk Premium. You are literally paying extra for the vendor to guess what you want. Conversely, inexperienced vendors will quote the cheapest possible interpretation, virtually guaranteeing a dispute upon delivery.
The Exponential Cost of Precision
A common mistake among junior engineers is applying a blanket "tight" tolerance to avoid ambiguity. However, machining costs do not scale linearly with precision. Tightening a tolerance from +/- 0.25 mm to +/- 0.05 mm is not a 20% cost increase; it often requires a completely different manufacturing process, climate-controlled inspection, and higher scrap rates.
| Tolerance Band | Typical Process | Relative Cost Multiplier |
|---|---|---|
| +/- 0.25 mm (ISO 2768-m) | Standard CNC Milling | 1.0x (Baseline) |
| +/- 0.05 mm | Precision Milling / Boring | 2.0x - 3.0x |
| +/- 0.01 mm | Grinding / Honing | 5.0x - 8.0x |
Precision exactly where you need it is engineering. Precision everywhere is just expensive.
Engineering Is the Management of Variables
Engineering is not about feelings. It is about constraint definition. If a requirement cannot be expressed as:
- A numeric value
- A tolerance band
- A measurable performance target
- A recognized standard (ISO, ASME, DIN)
It is not a specification. It is a placeholder.
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The Practical Rule
Before releasing a drawing or issuing a PO, audit it. For every adjective, ask: "What number replaces this word?"
Don't trade feelings. Trade numbers.
Replace:
"Fast actuation" → 200 mm/s +/- 10%
"High strength" → Minimum yield 450 MPa
"Standard tolerance" → ISO 2768-mK
Clean specifications reduce negotiation later.
Closing
Many project overruns are not technical failures. They are definition failures. The math makes the machine work, but the definitions make the project work.
If you are tired of losing budgets to vague specifications, vendor disputes, and endless email chains, I've written more about these operational realities in The Sheet Mechanic. It is a field guide for engineers who need to manage constraints, budgets, and humans—not just CAD models.
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