OpenSCAD Rubbermaid 21-cup container rim profile

This is an OpenSCAD module that generates a rim profile shape of a Rubbermaid 21-cup translucent food container, commonly used for filament dryboxes.

I needed a parametric model I could work with, not an STL or a parameter-less STEP file as provided in other Things (for example https://www.thingiverse.com/thing:3138757 and https://www.thingiverse.com/thing:3245554 ).

The rim is made up of three different arcs: a small-radius arc for the corners, a medium-radius arc for the short sides, and a large-radius arc for the long sides. Of course, combining different-sized arcs means that nothing joins at neat 90-degree angles, so I had to optimize the arc start and stop angles and center positions to fit within the constraints of the container rim.

This profile generates an entire surface with the lid profile. Use the 'offset' parameter to generate a surface larger or smaller, and use the OpenSCAD 'difference' function to cut the rim out from a larger profile to make a lid that wraps around the container's rim. The lid will be tight with no clearance; so I suggest your cutout is 0.1-0.2mm larger than default.

An example is given in the OpenSCAD file.

This object is about 240mm long. A Prusa i3 printer has a build surface large enough to print this.

Print Settings

Printer Brand: Prusa

Printer: I3 MK3S

Supports: No

Resolution: 0.4mm nozzle, 0.2mm layers

How I Designed This

The container itself is hard to measure with all of its curves, so I laid it upside-down on top of a copy machine and made a copy of the rim that I could measure.

The corner arcs were fairly easy to measure; they turned out to be 32mm radius. The side arcs were more challenging. After estimating the locations of the arc transitions and measuring the displacement of the sides from straight lines, I used this online 3-point circle calculator to get an idea of the radius of each arc. After several trial-and-error iterations it appeared that 300mm and 2250mm were the radii for the short and long sides, respectively.

Then I modeled the three arcs in in Microsoft Excel, using Excel's solver add-in, to optimize the start and stop angles of each arc for one quadrant of the rim, so that there is no slope discontinuity between arcs and the object fits within its overall dimensions.

After optimizing I transferred the numbers to my OpenSCAD model, printed 2 layers of a profile, overlaid it onto the Rubbermaid container, examined the edges with a 10x magnifier, made corrections, re-optimized, and repeated the process. It took three prints before it looked perfect, with no visible deviation from the rim of my container.

Category: 3D Printer Accessories