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The Flexible Hone Hits the Road

Sept. 8, 2011
Commonly used in production machining, a flexible hone is a portable, powerful tool that also meets exacting surface finishing requirements in the field
Vektek advised Chinese technicians to use the Flex-Hone to surface-finish the cylinder cavities, in order to eliminate a sealing problem. The Flex-Hone can be used in any rotating spindle, including a hand drill.
Vektek’s customer, a heavy-equipment manufacturer in China, had a problem with cylinders not sealing properly.
The left cavity was finished with the Flex-Hone tool. Finishing with the ball-style hone in the field gives cylinder cavities a superior finish that is virtually unattainable using standard cutting tools, like reamers or drills.
Frequently a customer’s milling processes won’t achieve an acceptable finish, so Vektek recommends using a Flex-Hone tool to improve that finish, as part of a cylinder installation project.

Most metal finishing tools are specialized devices: the designs used in factory production setups generally are not available or applicable in situations where precision secondary finishing is required in the field. Yet, there are instances when deburring, edge blending, cross hatching or other forms of honing surface finishes are required in the field, for installation or emergency repair services.

For example, when Vektek Inc., a supplier of hydraulic and pneumatic clamping systems for metalworking, tool-and-die, and mold industries sells cylinder products, the customer must ensure that the device into which the cylinder is installed has a properly finished cylinder cavity, or it will not seal and function properly.

Finishing on the fly
“One of our customers, a heavy-equipment manufacturer in China, had a major problem with their fixture cavities that caused our cylinders not to seal properly. These fixtures were supplied for mass produced parts,” said Rod Nelson, v.p. of International Sales for Vektek. “The trouble was that the customer’s cavities were not machined suitably for installation. A flaw in their finishing process was missed. As a result, it appeared that the Vektek seals were leaking; a problem that was not a shortcoming in the cylinder design or quality, but nevertheless had to be solved at the customer’s site or these very expensive fixtures would not be useable.

“Because many times the customer’s milling processes won’t give them a good enough finish, we recommend that they use a Flex-Hone® tool to improve that finish as part of the cylinder installation process,” Nelson added.

Gordon King, Vektek’s Shanghai office general manager, explained that the finishing with the flex-honing tool in the field gives the cylinder cavities a superior finish that is virtually unattainable by using standard cutting tools, such as reamers or drills.

“There are two holes that are perpendicular to the cylinder cavity wall,” King explained. “Oil flows through these holes to different sides of the cylinder, but it must never leak past the body seals between them. The oil flows at high pressure (approximately 3,000 psi) through the lower hole, to extend the cylinder. To return the cylinder, the oil flows into the hole toward the outside of the cavity. Because the required hole size and roundness are within 0.0005 in. and the required surface finish is better than 32 roughness, imperfections such as minute scratches will create oil leaks if the holes aren’t finished correctly prior to cylinder installation.”

King added that the consequence of a leaking cylinder could be very serious because these Vektek devices hold workpieces stationary on machining fixtures. If the oil pressure in the cylinders drops due to leakage, the grip on a workpiece would fail, requiring the machine to be shut down and production to halt.

Highly flexible finishing
A Flex-Hone tool is a flexible, ball-style hone made by Brush Research Manufacturing for surface finishing, deburring, and edge blending of products, including hydraulic cylinders, where tight tolerances and smooth surface finishes are essential for sealing purposes. This tool can be used in any rotating spindle, ranging from the machining centers of high-volume production environments to hand drill motors for secondary finishing, custom field finishing, or even DIY applications.

Vektek advised technicians at the manufacturing plant in China on using the flexible hone to surface finish the cylinder cavities properly, so that the sealing problem would be eliminated.

“They were leaking because the insides of the cavities were too rough,” Nelson explained. “In all, 300 cavities were Flex-Honed, and 299 of the 300 cavities were saved and polished exactly to specification. One cavity was slightly out of spec, but it also provided an adequate seal. So, in the end, we saved 300 very expensive holes.”

Nelson said the flexible hone is so useful to his customers in properly preparing cavities for his company’s products that Vektek has for many years specifically recommended the Brush Research tool in its product catalog and data sheets.

For this operation the Flex-Hone was mounted on a standard drill motor. King said that because this tool can be used in such portable equipment it is all the more useful for highly polished field finishing operations.

“These cylinders require a very good seal, very accurate, very round, and with a high-quality finish,” he said. “Because the flexible hone is self-centering, it is easy to get a uniform hole finish because it is always exerting the same sort of pressure on all sides. This is a true finishing operation done in the field.”

Powerful field operations
The Flex-Hone has been used successfully in many types of field operations over the years. Some examples include finishing automotive brake cylinders, drums, and disc brake rotors. The tool is used for resurfacing firearm barrels and cylinders. In a more dramatic instance, it is a method of deglazing and resurfacing the cylinder bores of large and small engines installed in cargo ships, which could be stuck at sea if were not for this versatile and easy-to-use device.

Immediately recognizable by the cluster of ball-shaped abrasive globules that are attached to flexible filaments extending from a central shaft, the versatile Flex-Hone is sometimes referred to as the “ball hone.”

Available in sizes ranging from very small diameter hones (4 mm) to those up to 36 inches or more in diameter (a size appropriate for large engine cylinder bores), these tools can be custom designed by Brush Research to the size, shape, and abrasive grit to fit an application’s needs.

In the case of Vektek cylinders, Nelson said, the Flex-Hone is recommended for use on a range of cartridge-mount cavity sizes installed in customer specified materials, so the supplier does not recommend hone sizes or specifications.

“Manifold mount cylinder models have a required cavity finishing operation,” he said. “They range in size from 1-1/16 in. to 1-7/8 in. We recommend that our customers consult with Brush Research to determine which specific Flex-Hone size and grit type is best for their material and application.”

The “grit” to which Nelson refers is the material that composes the ball-shaped globules on the tool, which accomplish the surface finishing work. A wide variety of grit types are available, depending on the material and application of the item to be surface finished.

While all of the flexible hones from Brush Research produce a soft-cutting, abrading action, some applications require a non-directional micro-finish, while others, such as diesel engine cylinder walls, require a cross-hatched pattern (cross hatching the surface provides better lube oil distribution and retention.)

In all cases the Flex-Hone Tool provides “plateau” finishing, the removal of burrs as well as torn and folded metal peaks that remain on metal surfaces after previous finishing operations. At the same time, plateau finishing retains the microscopic valleys in metal finishes in order to enhance lubrication properties.

The Flex-Hone tool is recommended for applications like the installation of Vektek cylinders because it is self-aligning and self-compensating for wear, which means that even after some abrasive globules are worn, the finishing action on metal surfaces will remain even. These features save the machining center or service shop on flexible hone replacement and eliminate the need for elaborate setups, and make it an effective and highly versatile field for use in the field.

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