How to Choose Abrasives and Grits for Flexible Hones

The Flex-Hone® from Brush Research Manufacturing (BRM) is a flexible, resilient honing tool that’s used for deburring, edge blending, and improving the internal surface finish of bores and cylinders. Versatile and easy-to-operate, BRM cylinder hones mount in machine centers, lathes, drill presses, and handheld electric drills for applications which include burr removal from cross-drilled holes and slots as well as surface finishing.

Trusted by manufacturers and hobbyists alike, the Flex-Hone® tool uses a low-temperature abrading process to produce a long-wearing surface with a plateau finish. Sometimes referred to as ball hones or dingleberry hones, the Flex-Hone® feature balls of abrasive grit that are permanently laminated to the ends of flexible nylon filaments. When selecting flexible hones, abrasives and grits must be considered.

Abrasive Types and Base Materials

The Flex-Hone® is manufactured in 8 abrasive types and 11 grit options for use with a wide variety of base materials and surface finish requirements. For mild steel, stainless steel, and cast iron, use silicon carbide (SC) abrasive. For low carbon to medium carbon steels, choose zirconia alumina. Z-grain abrasive can also be used with stainless steel and cast iron – and when you’re looking for longer tool life than SC.

BRM recommends aluminum oxide (AO) abrasive for deburring, edge blending, and surface finishing aluminum, brass, bronze, and softer metals. For deglazing Nikisil cylinders, we suggest 240 AO. Boron carbide (BC) abrasive is suitable for medium to high carbon steels, heat-treated steels up to 50 Rc, and with titanium. 

Flexible honing tools with tungsten carbide (WC) abrasive are ideal for high carbon steel alloys and exotic space age alloys found in aerospace and defense applications. For carbide, ceramic, hardened tool steel, and heat treated steels, BRM recommends the Diamond Flex-Hone® for burr removal and surface finishing. For a final finish on many base materials, levigated alumina abrasive is often the right choice.

BRM ball hones that use cubic boron nitride (CBN) or ceramic abrasive are available by special request for use with harder materials. If you own a Flex-Hone® and aren’t sure of its abrasive type, look for a colored dot on the tool’s stem. For example, black is for AO, tan is for BC, and yellow is for the Diamond Flex-Hone®.  For a complete list of colors by abrasive type, download the Flex-Hone® Resource Guide. 

Grit Selection and Abrasive/Grit Options

Choosing the right grit for a BRM ball hone depends upon the amount of work to perform and the degree of improvement that’s required. Often, coarse finishes require progressively finer flexible honing tools to meet final surface finish requirements. The Grit Selection Chart in the Flex-Hone® Resource Guide provides a good starting point, but final grit selection may involve trying cylinder honing tools.

Silicon carbide, aluminum oxide, and boron carbide Flex-Hone® tools are available in the following grits: 20, 40, 60, 80, 120, 180, 240, 320, 400, 600, and 800. Tungsten carbide tools are available in all but 400, 600, and 800 grits. BRM diamond honing tools come in mesh 170/200, 800, and 2500 while levigated alumina ball hones are available in extra fine grit only.

Download the Flex-Hone® Resource Guide for more information, including available abrasive/grit options for flexible honing tools that use alumina zirconia No. 1525 and Z-Grain No. 1549 abrasives. BRM’s free, full-color technical resource even explains how you can determine grit type by the color of the dot at the tip of the flexible hone.