learndesignA parametric photo frame
Five user parameters drive a 3D-printable frame. Change the width and height and the frame rebuilds for a 4×6, an 8×10 or a 200 mm square without touching the sketch. Also a reference for fully defined sketches and the constraint tools that get you there.
I want one frame design that fits a 4×6, an 8×10, or anything else, without remaking it. Scaling the whole model would scale the frame thickness and the corner radius too. Parameters let each of those change on its own.
Chapters in the video: intro to 3:14, new sketch 3:14, set parameters 3:50, apply parameters 4:54, offset 5:28, extrusion 6:05, corner radius 7:15, test it 8:25, challenge 10:02.
Parameters
Press S, type para, Change Parameters. Add five user parameters:
| Name | Default | What it does |
|---|---|---|
width |
200 mm | outside width of the frame |
height |
150 mm | outside height |
frame_thickness |
20 mm | how wide the border is |
corner_radius |
6 mm | rounding on all eight corners |
material_thickness |
6 mm | how deep the frame is |
Photos come in imperial sizes, so when I am matching a print I type 4 in and 6 in. Fusion converts. Everything else is metric.
A parameter can also be an expression. width - 2 * frame_thickness is the opening width, and it stays right when either number changes. Names cannot have spaces or start with a digit, which is why these use underscores.
Sketch
New sketch on the ground plane. Centre rectangle on the origin, so the frame stays anchored when it changes size. Don’t type sizes while drawing; use Sketch Dimension afterwards and enter width for the top edge and height for the side. The little fx on the dimension means it references a parameter.
Offset the rectangle inwards by frame_thickness. The sketch is now fully constrained: nothing drags. Finish it. Keep sketches minimal; anything that is not needed is a future problem.
Fully defined, or not
Fusion colours sketch geometry by how pinned down it is. Blue lines and points can still move: drag one and it goes. Black geometry is fully defined, and a lock icon appears on the sketch in the browser once every line in it is black. Dimensions and constraints are the two things that turn blue into black. Position counts too: a rectangle with the right width and height is still blue if nothing ties it to the origin, which is why the centre rectangle snaps to the origin point first.
A sketch that is not fully defined will still extrude. The trouble comes later. Change a parameter and the loose geometry picks a new position on its own, usually not the one you wanted, and the feature downstream fails or moves. Every sketch in a parametric model should be black before you finish it. If a line stays blue, ask what it still needs: a size, a position, or a relationship to another line.
Quick check: press D, hover a blue line and see what dimension it offers. Or drag the line. If it moves, it needs something.
Extrude and fillet
E, click the border between the two rectangles, distance material_thickness. Read the dialog like a form: type, profile, start, direction, extent, distance, taper, operation. New Body.
Press Q (press/pull, which becomes Fillet when you pick an edge), select all eight vertical corner edges, radius corner_radius.
Test it
Change Parameters again. Try 4 in × 6 in portrait; the 20 mm border is too heavy at that size, so drop frame_thickness to 12 and the radius to something smaller. Try 200 × 200. Try material_thickness 40 and you have a shadow box.
Push corner_radius too far and the fillet fails: the feature goes red in the timeline. A red or yellow feature is a model that will break on someone else’s numbers, so fix it, don’t ignore it. The radius is limited by the frame thickness; five millimetres always works here.
The photo itself is a decal, placed by hand. That is an aesthetic decision, not a dimension, so it does not need a parameter.
Sketch tools and constraints
The tools that come up most, with the shortcut where one exists. All of them live on the Sketch tab of the toolbar once a sketch is active, and most are in the right-click marking menu.
| Tool | Key | Use it for |
|---|---|---|
| Line | L | Straight segments; click-drag from an endpoint for a tangent arc |
| Rectangle (2-point, 3-point, centre) | R | Centre rectangle on the origin for anything symmetric |
| Circle | C | Centre and diameter; type the size as you draw or dimension it after |
| Arc (3-point, centre, tangent) | Rounded profiles; tangent arc off the end of a line | |
| Polygon, Slot | Hex pockets, bolt slots | |
| Spline | Freeform curves, like the vase profile | |
| Sketch Dimension | D | Lengths, diameters, angles, distances between things. Type a number or a parameter name |
| Offset | O | A parallel copy of a chain of lines at a set distance, like the frame opening |
| Trim / Extend | T (Trim) | Cut back or stretch lines to where they meet |
| Fillet | Round a sharp sketch corner (do it in the solid instead when you can, so the radius can change) | |
| Mirror | Draw half, reflect across a centreline | |
| Rectangular / Circular Pattern | Repeat holes or slots at a spacing or around a centre | |
| Project | P | Bring edges of an existing body into the sketch as reference |
Constraints are the rules. Pick the constraint, then click the geometry it applies to. The glyph that appears next to the line is the constraint; click a glyph to delete it.
| Constraint | What it holds |
|---|---|
| Coincident | A point sits on a line, curve or another point |
| Horizontal / Vertical | A line stays level or plumb, or two points stay level or stacked |
| Parallel / Perpendicular | Two lines keep their angle to each other |
| Tangent | A line meets a curve, or two curves meet, with no kink |
| Equal | Two lines the same length, or two circles the same size. Dimension one and the other follows |
| Midpoint | A point sits at the centre of a line |
| Concentric | Two circles or arcs share a centre |
| Collinear | Two lines on the same infinite line |
| Symmetry | Two things mirror across a centreline |
| Fix / Unfix | Pins geometry where it is. Avoid it; a fixed line cannot change with a parameter |
| Curvature | Two splines or arcs blend smoothly |
Fusion adds many of these as you draw: a line drawn nearly flat gets Horizontal, an endpoint dropped on another gets Coincident. Watch the glyphs as you draw and correct the ones it guessed wrong, or it will fight the dimensions you add later. Turn constraint hints off and on with the Sketch Palette if they get in the way.
The habit that pays off: draw rough, constrain the shape, then dimension with parameters. Rough shapes with the right constraints snap into place the moment the last dimension goes on.