Big Radius Measurement Gauges

This is a set of radius gauges to measure both internal and external radius of any surface. 

Even when you dont have the full circle to measure diameter.

This set is designed for radius bigger than 20mm, up to 238mm.
Here's a list of the available radiuses:

Note: Bigger radius gauges have bigger steps, just because smaller steps wouldn't be noticeable on such small gauges. If you need sharper measurement you probably want to look into other techniques.

Printing/Assembly Instructions

• The box uses a quick-latch system of my creation, that you can see at this page.
  There are a couple of unsupported spots, that you should check out during slicing. Please refer to the quick-latch system page for more details.
   
• For assembly you will need four m3x20 bolts in total. Two for the hinge, and two for the latches.
   
• Since the quicklatch pin insertion could be tricky, i provide also a keytool which will make the process a bit easier.
   
• The box lid is provided with a groove meant to install 2mm EVA foam on the inside, in order to provide a firm cuscion for the gauges. The foam should stay in place if cutted at the right dimension, If it doesn't you can use some small m2 screws to secure it in place with the provided holes. Please do not use glue as it is evil.

Other tips:

If you really need a precise measurement, you might want to change your approach. 
Here is an analytical one. 
You will need a tape, a caliper, and some numerical calculus.

This nasty one can only be solved numerically (it's called a transcendental equation), so pick your method of choice.

Measure arc and chord with your tape and caliper, and then try to solve the equation for diameter.

If you are unexperienced with numerical solving algorythms you can just try to fit some guess diameter into the equation, and try to minimize the difference between the two parts. It shouldn't take too long even manually.