Parametric design for makers: why every dimension should be a variable

Fixed geometry vs parametric geometry

A downloaded STL is fixed: to change the width you scale it and everything else scales too, including the holes that had to stay 4 mm. A parametric model says "width = 80; hole = 4;" and rebuilds itself. Change the width, the holes stay 4 mm and stay 5 mm from the edge because that is how they were defined.

Why makers benefit most

Makers print for specific objects: this phone, that shelf, my pegboard. A parametric model designed for one size adapts to the next with a number. It also survives the reality of printers: your machine prints holes 0.3 mm small, so you bump the clearance parameter once and every hole follows.

What "parametric" looks like in SpeakCAD

Every model is an OpenSCAD program where the AI puts the important dimensions at the top:

javascript
// Phone stand
phone_width  = 78;   // mm, with case
phone_thick  = 10;
angle        = 60;   // degrees
cable_slot   = 12;
wall         = 3;

You never need to read it, because editing is a sentence: "angle 65 degrees" changes one line. But the code is there, and if you want to take it further in OpenSCAD desktop, you can.

Stable parameters across edits

The AI is instructed to keep parameter names between edits, so the design history stays coherent and edits are surgical. That is also what lets SpeakCAD compare versions fairly for the free re-download rule.

Parametric habits worth adopting

• Ask for the dimensions you might change as parameters.
• Describe relationships ("the lip is always 2 mm taller than the phone thickness") rather than results.
• Keep one model per part so parameters do not tangle.