A radius gauge

[MichaelMoore]

Something like this?



I've got those in both metric and inch versions and they are very handy, but they only cover smaller sizes of radii. I took a length of scrap AL round bar, about 1.75" or so diameter, and made as many different OD discs out of it as I could, with a hole in the middle of them to string them on a piece of soft wire. Those let me do some checking for radii a bit larger than the machinist sets cover.

The gauges like I made are commonly used for checking a radius on a body panel. If you are extremely serious (or a designer at an auto manufacturer) you might have a set of sweeps like this 85 part set for $3000 from Fay Butler

Fay Butler Metal Fabrication: Sweeps

That's a bit beyond my needs! If I have to, I can print off some different radii onto paper and cut them out to try and narrow down the dimension on the part I'm checking.

I also got a set of these inside/outside radius gauges

https://www.baileigh.com/rg-750-radius-gauge-set

That measure from 2.5-30" radii. There are larger ones to cover larger radii. I have to admit there was a definite "that's a cool mechanical device" thought at work nudging to make the purchase.

As with angle grinders and clamps, measuring instruments are another of those tools where "no one ever said they have too many".

cheers,
Michael