Radius Gages Explained

July 17, 2020 10:42 am

Radius gages are fairly self-explanatory and simple to use. These measurement tools are used on a number of different objects like hinges, tools, taps, and dies. They are used to measure existing radii, which is a critical operation when it comes to applications such as pattern making, precision machining, layout creation, and part inspection. In this article, we’ll explore the main applications in which a machinist would need a radius gage set and break down how to accurately use the tool. As always, we will wrap up with our top model recommendations.

Radius Gage Anatomy

It is probable that when you hear the term “radius gage” you will also here the term “fillet gage”. The different names are often used interchangeably. It just depends on who are you talking to. They are both used to take measurements, however their purposes are a bit different. Fillet gages are designed to measure the interior radius of a part while radius gages are designed to measure the exterior radius. This simple difference is depicted in the image below.

Image Credit: https://extrudesign.com/radius-gauges-fillet-gauges/

Because of this fundamental difference, the term “fillet gage” is used more frequently in relation to welding and “radius gage” is most frequently associated with machining projects.

Using a Radius Gage

The most common use for a radius gage set in machining is for checking imperfections like bumpy surfaces or offcuts of metal debris. For example, it can determine if the curvature of a part is the correct shape.

An easy trick to ensure your measurement is accurate: shine a light on the opposite side (from behind) of the object, any light passing through informs that the curves of the gage and the part have not contacted correctly.  This gage type is also great for drawing specific radius measurements directly onto workpieces as it helps attain accurate cuts and desired curves when machining.

Radius gages are particularly useful when it comes to inspecting tool and die cast molds. They are used to identify any set up issues by ensuring die casts have been assembled with the correct radius measurement. This is crucial because the rounded edges of metal molds must be at optimal precision in order to achieve the structural strength they need.

Radius Gage Set Models

Starrett SD167GHZ Radius Gauge Set

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Each gage is clearly marked with its associated radius and has 5 different gaging surfaces for both convex and concave radii. This set features a satin stainless steel finish and is stain resistant. All of the gages have precision radii for smooth and accurate readings.

Accusize Industrial Tools 26 Pc Radius Gauge Set

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Take a look at this option if affordability is your priority. This gage set covers a measuring range of 0.010″ – 0.500″ and features a satin chrome finish. Each gage is individually marked with associated measurements and is resistant to rust.

INSIZE 4804-26E Radius Gage Set

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This specific set has a range of 0.10″– 5″, however INSIZE offers gage sets with other measurement ranges. This option is also on the more affordable side and includes a green plastic casing.

Mitutoyo 186-901, Radius Gage Set

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This set includes 25 different “leaves” (each individual gage). Each gage includes 5 different radii. The measurement range is 1/64″ to 17/64″ by 64ths and 9/32″ to 1/2″ by 32nds. A 4″ long holder makes this model great for checking radii in hard-to-reach locations.

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