Drawing revision traps that put the wrong part on the bench
Eight revision traps that survive an approved change: stale flat patterns, unmarked thickness edits, datum shifts and models that disagree with the PDF.
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Topic hub · 44 guides
Design and CAD
A drawing is a contract. These guides cover the design decisions that survive the shop floor: bend relief and corner relief, hole-to-edge distance, tab and slot, datum strategy, tolerance stack-up, STEP and DXF hand-off, drawing notes, revision control and design for coating, assembly and transport. Written for design engineers who would rather fix it in CAD than in a concession.
Guides in this topic, page 2
Design rules, CAD hand-off, bend allowances, tolerance stacks and the drawing notes that decide whether a part is made right first time.
Model-based definition for sheet metal: PMI over a 2D drawing
Model-based definition for sheet metal: what semantic PMI carries, where graphic-only annotations fail, and how bends, thickness and the flat pattern are handed over.
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Hole-to-edge distance for sheet metal: the rule by process
Hole-to-edge distance is set by the force behind the hole. Why punching needs 1.5–2t, laser cutting needs 1 mm, and a loaded bolt needs 2d from the centre.
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Minimum flange for sheet metal: the die opening decides it
Minimum flange for sheet metal is set by the die opening, not the drawing: how V decides flange, radius, force per metre and the bend length left at 200 T.
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GD&T for sheet metal: profile and position on formed parts
GD&T for sheet metal: why profile and position control a formed part where ±0.5 mm cannot, and the datum scheme a bent bracket needs to be inspectable.
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Weld access for sheet metal: designing joints the torch can reach
Weld access decides whether a 3 mm fillet is real or cosmetic. Torch clearances, joint geometry and the drawing note that keeps the bead where it was designed.
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Drawing numbering and revision blocks that survive 20 years
Drawing numbering and revision blocks that last: field structure, check digits, the interchangeability rule and a change note an operator can act on.
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Assembly tolerance for sheet metal: fixture, part and stack
Assembly tolerance is a stack of part, fixture, weld and coating error. How to add it worst-case or by root sum square, set datums, and size a clearance hole.
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Tolerance versus capability: setting a number the process holds
Tolerance versus capability with real spread figures: what Cp and Cpk mean on a formed part, the arithmetic for a 300 mm bracket, and how to set a number the shop can hold.
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