Caliper Radius Gauge Set – Four Versions for Precise Measurement – Up to 400 mm Diameter and easy math

I needed a radius gauge, which unexpectedly turned into a small math project.

Many gauges use a 90-degree angle , which results in a factor of 2.4142 … that the measured value must be multiplied by. Reducing the angle to 60 degrees naturally brings this factor down to 1 , but limits the maximum object size.

To cover more use cases, I designed two additional gauges with angles that correspond to factors of 2 and 3.

With the largest gauge, you can measure objects up to 400 mm in diameter.

The gauges have a 16 mm slot, so standard calipers fit perfectly. The edges clamp the caliper lightly, so it sits snugly. I created four different versions — let me know which one works best for you.

Model file

F

α

L (mm)

Rmax (mm)

Radius_Gauge_V3_1x.stl

1

60°

202

~116

Radius_Gauge_V3_2x.stl

2

83.62063°

178

~160

Radius_Gauge_V3_2k4142x.stl

2.41421

90°

180

~180

Radius_Gauge_V3_3x.stl

3

97.18076°

177

~200

F is the multiplication factor (Radius: R = m x F; m measured value); alpha is the opening angle; F: leg length; Rmax the largest radius that can be mearsured (probably in reality we cannot fully go to that limit, as we want the tool to make a tangent to the circle.

For the math please check the corresponding picture.

Printing

- PETG or PLA

- 0.2 mm layer height

- 3 perimeters

- 5 top & bottom layers

- 25% infill

- Print bed: at least 22 cm × 25 cm (e.g., Core One)

Let me know what you think about it an whether it works for you.