Romantic gestures come in many forms, and one of those is one of a kind items. 3D printing is excellent for this type of use case, but to be one of a kind, it requires your input.

This is an OpenSCAD model intended to be modified to suit your preferences. The erm, heart of the design is a math function on line 20, and a scaling factor on line 11 that do the heavy lifting of making a heart of any kind of shape. The value “u” fed into that function runs from 0 to 1, and the function itself is normalized to always run from 0 up to the vertical scaling factor (unless the start and end values are the same - then it breaks).

You can add, multiply, and subtract many monotonic (or not!) functions to accomplish many effects. Here are a few, just replace the k with some floating point number:

• u^k - with low values for k (roughly less than 0.8), this creates a top heavy heart, with a flattened bottom. With high values, it becomes sharp at the bottom, and barely adds anything to the top at all.
• k^u - similar to the above small values (less than 1.2?) make a relatively round heart, while high values (5+) become almost leaf shaped. 1.4~1.6 is nice in my book.
• Multiplying by sin(90*u) accentuates features lower in the heart for any term it is applied to.
• Adding sin(180*u^k) adds a “bulge” to the heart, with the angle from the center that appears at depending on the value of k. <1 for mostly the top, >1 for mostly the bottom.

Math has a huge variety of things to offer, and experimenting in the digital space is very cheap. Find what looks nice to you.

I recommend test renders with a small number of steps (18-36 is typically plenty to see what the shape will look like), then really rendering with a medium-high number, perhaps 90 to 180. If you do something wrong, and the terminal begins spamming errors, closing it will allow the render to finish quickly. Often reporting the errors is much slower than getting past them.

This model could also be made into a chocolates box, or really a holder for anything else by changing (primarily) the top to bottom distance inside the box (line 2), the height of the box (line 7) and the height of the lid (line 8). For significantly larger boxes, you'll also want to make the walls thicker (line 9).