How to Measure a Corner's Radius Using a 3D Printed Tool





Introduction: How to Measure a Corner's Radius Using a 3D Printed Tool

About: We bring hardware products to life, specializing in engineering, prototyping, and mass manufacturing. We've worked with over 20 Kickstarter projects.

The world is filled with millions of different objects all with different shapes, angles, lengths, heights, widths, surfaces, depths, volumes, geometries, etc… You get the point. There are many different ways of measuring all of these different objects. Here we will focus on measuring rounded corners on physical objects. This can be a difficult task without the right tools.

Our Mechanical Engineering Team at Jaycon Systems creates, reverse engineers, and tests hundreds of hardware projects every year, so in order to make our lives easier, we came up with a simple 3D printed tool to help measure the various radii (believe it or not that is the plural of radius) of the things we work on. We hope we make your life easier as well by making these files available to the public.

Step 1: Step 1: Understand How Measuring Radius Works

Measuring rounded edges or corners of an object can be a difficult task. Most people approximate by using a ruler or caliper to measure where the curve starts and where it ends as seen in the first picture with distance A.

Corners located inside a physical object — a small container for example — as seen in the second picture can be even more difficult to measure and estimate. If someone is designing an item to fit up to these measurements, it can become a tedious trial and error game.

Step 2: Step 2: Understand How the 3D Printed Tool Works

We have used some of the measuring tools available out there, but we have found that most of them aren't suitable for tight spaces since they have a long handle that doesn't fit inside the piece we are trying to measure.

So in order to fix that problem, we created a set of plastic slivers that look similar to crescent moons. Each piece has the same radius on the inside and outside of the part, so you can measure both the inside or the outside corner radius of a part using the same piece.

The pieces are as small as 5mm all the way up to 40mm. If you need bigger sizes, you are welcome to make them your own as they are pretty easy to create with a 3D software. We believe that these will get a much closer if not exact radius measurement compared to using a caliper to guesstimate.

Step 3: Step 3: Download the STL File and 3D Print Your Tool

The STL files are set up as a group and also individually — in case you lose one, you can reprint it separately.

Download the STL files here.

Step 4: Step 4: Using Your Tool and Working With Corners That Are Only Partial Matches

Take a moment to check the next steps and see how these measurement tools work to measure radius. You will notice that at times an exact measurement cannot be taken as seen in some of the images below — it may be one size too large or one size too small, so the true size will lie somewhere in between.

In the first picture, you will see that there is a slight gap in the middle of the 14mm tool as we push it on the corner we are trying to measure, telling us this size tool is slightly too small.

As we use the 16mm tool instead, we still see a gap on the right side of the tool, which tells us that this tool is slightly too big. We would then feel safe to say that the correct size is an average of the slightly larger and slightly smaller tool at 15mm.

In the last picture, you see that the 38mm tool is a perfect match to what we are measuring, so we are happy to write down the exact reading of this tool as the radius.

We hope you enjoyed this tutorial and found the tool helpful. If you 3D print your own tool, please snap a picture and hashtag us at #jayconsystems so we can see how useful it was for you!

Who is Jaycon Systems?

We specialize in bringing products to life by offering a complete service line that takes product concepts to mass production. Our offerings range from product and electronics design to prototyping and manufacturing. We apply our knowledge of technology to most markets, among them consumer electronics, computer hardware, marketing/multimedia, and environment. With our entrepreneurial spirit and as a rapid-prototyping firm, we believe in building products right the first time and introducing them quickly to market. For more, visit



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    12 Discussions

    did send my mail adres, did not get the STL.....


    11 months ago

    - With such small variations - it seems a '3-point' version would be more accurate and easier to use - versus the 'full' corner. Point at each end of the radius and then one point in the middle - when all contact - correct - with the full 'corner' one can easily mistake one curve for another. Maybe cut these on the curve - to leave - only the three points (tiny posts if you will).


    11 months ago

    These have been around for years. I bought a set in the early 90's.

    2 replies

    Please make a copy of your set and send it to me!

    I really like this set of Radii Gauges, it's the most professional one I've seen made on a 3D Printer, although, I don't think I've ever seen a set that wasn't Printed although I haven't actually looked, I'm sure I'd find a heap of them available online, there's just not where I live...

    I'm sure I'd lose them all if I didn't have a way of keeping them all together; how on earth do you keep all the pieces organised!? I'd reckon a little box would be the simplest approach but that's not all that cool and I think there'd be other possible methods that are more space efficient and convenient than that, especially if it's a square box. Can you think of any other ways you could use to do this and it might even be worth while making another instructable if it involves 3D Printing or can't be summed up in a few sentences?

    Anyhow, thanks for the awesome instructable and I hope you'll reply soon.


    I could have used this, about a week ago. I making some Led tsil lights for a 67 firebird and wanted to make a circuit board with rounded corners to fit the contours of the light. I spent hours in eagle cad trying to get just right. Finally, i just said screw it and cut the corners off. This would have helped so much. I may just print this to see if I get make the pcb with the corners.

    1 reply

    Sorry for my spelling mistakes, lol. No spell correct and fat fingers

    Great post. Cool tool.


    11 months ago

    Very clever and useful!


    11 months ago


    Useful! I will try it