Continuous Curvature Radius Gauges

What is Continuous Curvature

If you know, you know. I didn't know until 12 years into designing. So here's some help for the rest of the uninitiated following along.

Ever wonder why the curves on Apple's devices just feel different than on most products? Turns out there's a reason, and it's called continuous curvature. Those of us with a mechanical engineering background are used to circular radii used in standard fillets. For a given profile, a circle is inscribed so that it is tangent to both lines being “filleted.” This gives us an easy-to-machine profile that provides internal stress relief. However, there is another method of filleting a surface. Instead of an inscribed tangential circle, this method uses the mathematical definition of curvature. Don't get it yet? Me either. Here's some resources that I've found to at least kind of describe what it is and how to implement it.

https://hawkridgesys.com/blog/solidworks-continuity-curvature

Constant Curvature Gauges

I couldn't find any on here so I made my own set, from 1-50mm. Each gauge has the internal and external radius for the given size. I made them thin so they'll print fast. Personally, I don't use these enough to constantly keep a set on hand. If you do, great! Maybe throw a design up in the Remix section for a cover and pin for the different size sets. Otherwise pick the couple sizes you need and print them off.

For Users

I made these while trying to reverse engineer the mac mini/mac studio dimensions for a mac studio cooling fan project (to be posted later). For reference, my finding was that a mac mini m1/mac studio has an external continuous curvature radius of 40 mm. If you dimension your project with these, post your results in the makes! You might save someone else quite a bit of time.

Since we're using step files, make sure your slicer is set up to import the files at high resolution. This is an automatic pop up in the latest PrusaSlicer, but if you're not using that either follow your slicer's instructions or import the step into your favorite 3D modeling program and export as a high resolution 3mf or STL.

Remixers -  Please Read!

Step and original SolidWorks files are provided. The gauges are run as a series of configurations, with the gauge label tied to a configured Label custom property. I found the length of the side of the tool had to be about 5mm larger than the measuring radius for the tool to build. I think it's due to the corner radius I put by the retainer hole. If you do expand the selection beyond the 50mm set, please upload your work to the remixes. I used 20mm length intervals every 20mm of added radius. Please keep that interval going if you can, for usability for others. The next step should be a side length of 90mm for a 61mm-80mm radius.