Flexible Hones vs. Rigid Hones for Surface Finishing

The Flex-Hone® tool from Brush Research Manufacturing (BRM) is a resilient, flexible honing tool that removes burrs from bores, deglazes cylinder walls, and imparts a superior surface finish. Rigid hones are also used for surface finishing, but are recommended for different tasks. Learning which type of hone to use is an important lesson for manufacturers, machinists, metalworkers, and hobbyists. Sometimes, the Flex-Hone® is the right tool for the job. At other times, a rigid hone is recommended.

Which Type of Honing Tool Do You Need?

BRM’s cylinder honing tools are flexible because they feature abrasive globules permanently laminated to nylon filaments. Rigid hones are rigid because they use honing stones instead. This distinction is easy enough to understand, but there’s more to the story than just product descriptions. Flexible honing tools have many advantages over rigid hones. Yet honing stones are still recommended for the following tasks: initial cylinder honing, cylinder resizing, geometry correction, and heavy-duty material removal.

What are Flex-Hone® tools used for then? In addition to deglazing the walls of cylinders that are not out-of-round, flexible honing tools are used to surface finish bores that have been honed to size with honing stones. Flexible cylinder hones are also right for removing burrs from cross-drilled holes, breaking edges on internal features such as cross-holes and keyways, and imparting a final surface finish with a uniform series of peaks and valleys.

Soft Cutting and Uniform Surface Finishing

Rigid hones are right for some applications, but flexible hones offer numerous advantages. For starters, Flex-Hone® tools have hundreds of cutting points for a full 360° of cutting action. By contrast, rigid hones have only two or three stones. Flexible hones also impart a uniform surface finish along the length of the entire cylinder. Honing stones can impart an uneven or unidirectional crosshatch, and require operators to reduce pressure on the tool when surface finishing the top of the cylinder.  

Self-centering, self-aligning to the bore, and self-centering for wear, Flex-Hone® tools don’t require special training, expensive equipment, or complex setups or cleanups. Because a flexible hone puts little pressure on a cylinder wall, the tool won’t gouge out the metal or cause torn or folded-over edges. Plus, since pressure against the cylinder wall is equalized, operators don’t have to worry about making cuts in both directions. Flex-Hone® tools also remove burrs and improve surface finish at the same time.

From Rough Surfaces to Plateau Finishes

Honing stones are necessary for some applications, but rigid hones can produce a rough surface finish with high, sharp peaks. By smoothing these raised areas, flexible honing allows piston rings to seat and seal without damaging their edges. The substantially flat surface that a flexible engine hone imparts also promotes longer seal life, increases bearing area, and reduces wear. By creating a series of uniformly-spaced, oil-retaining grooves, flexible hones also help to reduce seepage in hydraulic applications. 

As BRM’s Gold Booklet explains, Flex-Hone® tools are also the surface finishing solution of choice because they’re long-lasting. By contrast, honing stones can wear out quickly. When even one stone in a rigid hone breaks or cracks, the tool must be removed from service and the damaged stone replaced. The abrasive globules in a Flex-Hone® tool are practically unbreakable, however. Plus, they’re self-wearing so that the abrasive is always on the outermost edge of the tool.