How to Select Grit, Diameter & Filament for Flexible Ball Hone in Hydraulic Fluid Power Machining

Flexible ball hones—also known as Flex Hones, ball hones, or cylinder hones—are essential tools for surface finishing and deburring in hydraulic fluid power applications. They remove burrs and improve surface finish at the same time, imparting an oil-retaining plateau finish that promotes lubrication and reduces friction and wear in hydraulic cylinders, valve bodies, pump housings, and other fluid power components.

Selecting the right flexible ball hone for your hydraulic application requires careful consideration of three key factors: bore diameter, abrasive type (filament), and grit size. This guide walks you through each selection criterion.

1. Selecting the Right Diameter

Flexible ball hones are always supplied and used in an oversized condition. This means a flexible hone for a given bore has a tool diameter that is slightly larger than the bore itself. The oversized condition ensures the abrasive globules maintain consistent contact with the bore wall, producing a soft cutting action.

If the bore size falls between two standard Flex Hone sizes, choose and use the larger-diameter tool.

Flexible ball hones are available in a wide range of standard diameters:

• Small Diameter (Standard Duty): 4 mm (0.157") to 76 mm (3")

• Medium Diameter (Standard Duty): 3-1/4" (83 mm) to 4-5/8" (117 mm)

• Medium Diameter (Heavy Duty): 3" to 8"

• Large Diameter (Heavy Duty, Wood Core): 8" to 18"

• Large Diameter (Extra Heavy Duty): 19" to 36"

For hydraulic cylinder applications, the hone should be 10-12% larger than the bore diameter.

Diamond Flex Hone tools are available in sizes from 4 mm to 19 mm (3/4").

2. Selecting the Right Abrasive Type (Filament)

Flexible ball hones feature abrasive globules that are permanently laminated to the ends of flexible, heat-resistant nylon filaments. The base material of the workpiece determines which abrasive type to select.

For fluid power applications, the most common abrasives are Silicon Carbide (SC) for steel and cast iron components, and Aluminum Oxide (AO) for aluminum valve bodies and softer metals.

Color coding helps identify abrasive types: black is for Aluminum Oxide, tan is for Boron Carbide, and yellow is for Diamond.

3. Selecting the Right Grit Size

Flexible ball hones are available in 11 different grit selections, ranging from coarse to super fine: 20, 40, 60, 80, 120, 180, 240, 320, 400, 600, and 800.

The amount of work to perform and the degree of surface improvement required determine the grit size. Lower grit numbers indicate coarser, more aggressive cutting action; higher grit numbers produce finer finishes.

Grit Selection Guidelines for Fluid Power Applications

180 grit has been the most popular grit size for automotive and hydraulic applications for years, used both as a deglazing hone and a secondary hone after rigid honing. 240 grit is particularly popular for hydraulic and brake cylinders.

For hydraulic cylinder applications, medium grits (180-320) are the industry standard. A 240 grit honing brush is typically used to create the perfect oil-retaining cross-hatch pattern in hydraulic components.

4. Progressive Grit Strategies

If the starting surface has a coarse finish, you may need to use a range of Flex Hones with progressively finer grits before achieving the desired finish.

• Coarse grit (120-180): Initial deburring and material removal

• Medium grit (240): General finishing and surface refinement

• Fine grit (320-400): Final finishing and plateau preparation

5. Summary: Complete Selection Checklist

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