Practical Mechanical Design
& Manufacturing

Some problems show up repeatedly in design reviews. A deep pocket with a narrow opening looks elegant — but a cutting tool long enough to reach that depth will chatter, deflect, or break. None of these are obvious in CAD. All of them are obvious when you ask how it gets made.

Three factors determine whether your design succeeds or fails: material choice, manufacturing process, and design features. They're inseparable. Material determines possible processes. Process determines design constraints. Design requirements dictate material and process.

Machining is subtractive manufacturing — you start with raw material and remove material until you have the shape you need. Every feature is a cutting operation that requires time and tooling. When you design for machining, you're always thinking: every feature requires a tool to reach it, every surface must be accessible.

A colleague sent me a sheet metal file to modify. I added two holes, sent it to the shop. Two days later, the machinist came: "Did you check the K-factor?" K-factor was 0.5 — the software default — wrong for 2mm stainless steel. Twenty parts would have been scrap.

Welding shows up on almost every mechanical design project — structural frames, sheet metal enclosures, tube assemblies. Compound-angle tube cuts needing extra setups, continuous welds on thin sheets that warp badly, or joints that welders simply cannot reach. These issues happen often and add real cost.

Casting creates geometries impossible with other processes — internal cooling passages in turbine blades, engine blocks with integrated water jackets. All formed in one piece during solidification. The practical workflow is catalogue first, custom last. Search industrial catalogues, pick options that might work, then adapt.

The economics are compelling — complex geometry with integrated features, produced consistently at high volume, at a fraction of what machining would cost. But plastic manufacturing has its own rules. Wall thickness, draft angles, shrinkage, flow paths — these aren't optional. They're built into the physics.

"We can just 3D print it" has become the modern equivalent of "we'll fix it in software." AM gives you geometric freedom that no other process can match. It does not give you free parts, fast parts, or parts with properties identical to conventionally manufactured components.

You've spent the previous chapters learning how things are actually made. Now comes the real engineering challenge: choosing. This chapter gives you universal DFM principles — design decisions that reduce cost and improve manufacturability regardless of process — and a systematic method for selecting between processes.

You've designed a beautiful part. Every dimension correct, every tolerance rational. Then someone has to put them all together, and everything falls apart. Assembly typically accounts for 40 to 60 percent of total product cost. Not material. Not machining. The labor, the fixtures, the rework.

Glass, adhesives, seals, rubber profiles, fastener types, gas springs, sliders, locks, latches, levelling feet, handles. Components you'll specify in almost every design. This chapter covers how to find them, select them, and design around them. These components drive your geometry.