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BRM's Flexible Honing, Surface Finishing, and Deburring Blog

BRM's Flexible Honing, Surface Finishing, and Deburring Blog is the place for conversation and discussion about how to solve difficult finishing problems. For over 50 years, Brush Research Manufacturing (BRM) has helped customers use brushing technology to clean, rebuild, and resurface components ranging from engine cylinders to brake rotors to flywheels to firearms. BRM's Blog on CR4 provides real-world examples of how flex hones and wire brushes work. It also evaluates related technologies and invites questions from the community.

Cylinder Honing: Tool Diameters and Operating Parameters

Posted April 22, 2014 4:19 PM by Brush Research

Brush Research Manufacturing (BRM) supplies flexible cylinder honing tools for bores with diameters as small as 4mm and as large as 36". A flexible, resilient honing tool, the Flex-Hone is self-centering, self-aligning to the bore, and self-compensating for wear. Flexible hones improve surface finish and remove burrs at the same time, and can be used in either handheld power tools or machine centers. Known also as ball hones, these brushing tools feature abrasive globules permanently laminated to flexible nylon filaments.

Cylinder Hone Diameter

To produce a soft cutting action, Flex-Hone tools are always used in an oversized condition. This means that a deburring tool for a 3" bore, although listed as a 3" tool, has a diameter that's slightly larger than 3". On the BRM website, cylinder hones are categorized as standard small-diameter (4mm to 3"), standard and heavy-duty (3" to 18"), and super heavy-duty large-diameter (19" to 36"). Diamond Flex-Hone® tools are available in 4mm to 1-1/2" diameters and Flex-Hone for chamfer blending tools come in 4mm to 7/8" diameters.

Rotational Speed

Diameter is an important specification to consider not just during brush tool selection, but also during Flex-Hone use. Ball hone size helps determine the recommended operating speed in revolutions per minute (RPM). The Flex-Hone Resource Guide provides some general ranges for rotational speeds, but users should perform machine trials to test their own equipment against these guidelines. In general, however, larger tools run at slower speeds and smaller tools run at faster speeds.

Stroke Rate

Tool diameter also drives another important operating parameter: stroke rate. This is the number of inches per minute (IPM) that are fed or stroked during flexible honing operations. Depending on how the Flex-Hone tool is configured, stroke rate is controlled either by machine parameters or by a human operator. Stroke rate is also related to the angle of the cross-hatching on cylinder walls, the tiny oil-retaining grooves that help optimize lubrication.

Cross-Hatch Angle

Flex-Hone tools improve cylinder wall surface quality by imparting a cross-hatch pattern and producing a plateau finish. The angle at which these cross-hatched lines intersect can vary, and is a function of both stroke rate and rotational speed. As the Flex-Hone Resource Guide advises, use a slower stroke rate to achieve a smaller cross-hatch angle (e.g., 20° to 23°). Use a faster stroke rate to achieve a larger cross-hatch angle (e.g., 45°).

Putting It All Together

Tool diameter helps determine the recommended speed, and is related both to stroke rate and cross-hatch angle. Remember, however, that smaller-diameter Flex-Hone tools require faster stroke rates to achieve the same cross-hatch angle as larger-diameter tools.

Author's Note:

This CR4 blog entry originally appeared in the BRM Flex-Hone Blog.

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Deburring and Edge Blending for Aerospace Parts

Posted April 14, 2014 4:22 PM by Brush Research

Burrs, sharp surface edges, and surface roughness can injure workers, cause mechanical and electrical problems, and reduce the service life of components. Surface irregularities can also increase friction and wear, reduce fatigue limits, create excessive stress concentrations, and produce unwanted build-ups of plating and paint. As a recent SME blog entry explains, burr removal and edge blending are especially important in the aerospace industry, where part failure can have catastrophic consequences.

Heat, Friction, Stress, and Strain - Burrs and Sharp Edges

In aircraft engines, the mating surfaces of moving parts must be surface-finished to minimize friction. Excessive heat can change the properties of metal surfaces, and excessive surface roughness can cause greater material wear. Rotating parts also require a surface finish that optimizes lubrication. When more of a part's surface comes into contact with a lubricant, there's more heat transfer from the lubricant to the moving part. That's why the automotive industry recommends surface finishes that retain engine oil.

In the aerospace industry, surface finishing challenges include hole polishing and chamfer blending. Sharp edges and burr holes can increase both stress and strain. If excessive strain occurs, material failure can happen because of cracking. To keep strain under the yield limit, aerospace companies need to radius edges, deburr holes, and improve surface finish. Parts manufacturers also round-off or radius sharp interior and exterior corners.

Flexible Honing for Burr Removal and Surface Finishing

Brush Research Manufacturing (BRM) supplies Flex-Hone technology to aerospace companies, aircraft manufacturers, jet engine builders, and aviation MROs. A resilient, flexible honing tool with a soft cutting action, the BRM Flex-Hone removes burrs, blends edges, and improves surface finish at the same time. Available in a variety of sizes and abrasive types, this cylinder honing tool is also used for chamfer blending and hole-polishing.

With their abrasive globules bonded to flexible nylon filaments, Flex-Hone tools have a distinctive appearance that's earned them nicknames such as ball hones and dingleberry hones. In the aerospace industry, however, BRM's flexible honing tools are best known for solving tough surface finishing challenges. From high-quality hole finishing at a U.S. Naval Air Station to heavy-duty scale cleaning at Sikorksy Helicopter, BRM flexible honing tools are a proven solution.

Solving Surface Finishing Challenges

For surface finishing hard materials, BRM recommends Diamond Flex-Hone tools. With their resin-bonded crystals, these diamond hones are ideal for aerospace materials and space age alloys such as type 302, 304, 416 and 17-4 stainless steels; Hasteloy®, Monel®, and Inconel® 718; Titanium 6AL-4V; and specialty aluminum alloys. Versatile and easy-to-use, Flex-Hone tools feature a double-wire metal stem that's suitable for mounting in most machine spindles. Aircraft mechanics can also use flexible hones with electric hand drills.

For aerospace applications that require optimum lubrication, Flex-Hone technology is also the right choice. The plateau finish that flexible honing imparts removes the peaks produced by prior and honing operations to create a flat, smooth, cross-hatched surface with oil-retaining grooves. By eliminating elevated surface areas, plateau hones remove burrs, smooth sharp surface edges, and eliminate surface roughness.

Author's Note: This CR4 blog entry originally appeared in the BRM Flex-Hone Blog.

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Firearms Maintenance: Flexible Honing and AR-15 Chamber Polishing

Posted April 07, 2014 3:28 PM by Brush Research

The AR-15 rifle is a lightweight, air-cooled, magazine-fed rifle that's actuated by gas piston technology or direct impingement. Designed originally for the U.S. military, this popular firearm features a bolt and carrier mechanism. As the carrier fills with high-pressure gas, the bolt unlocks and moves rearward to extract the empty cartridge case from the chamber. When the neck of the cartridge clears the barrel extension, a spring-loaded ejector forces the case through a port on upper receiver.

First built by ArmaLite during the 1950s, the AR-15 is now manufactured by many different firearms companies, including Colt, Bushmaster, and Stag Arms. Popular among hunters, shooters, and law enforcement agencies, this lightweight rifle is available in a variety of sizes and configurations, but made mainly of aluminum alloys. The AR-15's accuracy and weight contribute to its popularity, and gun owners often have questions about the best way to clean and polish components such as the chamber.

Gun Tools for AR-15 Maintenance

At the website for Guns Magazine, an on-line article called AR-15 Building Tools - Part II described what the author called "handy" items for firearms maintenance. The list included rear-sight spring tools, a bolt disassembly fixture, and a front takedown pin detent installer. The gunsmith also emphasized the importance of polishing AR-15 chambers to ensure that spent cartridge cases eject properly. The gun polishing tool he mentioned by name was the Flex-Hone from Brush Research Manufacturing (BRM).

Flex-Hone for Firearms tools are used to polish and surface finish rifles, shotguns, pistols, revolvers, and paint ball guns. Designed for smooth bores, BRM guns tools are ideal or any size or type chamber, cylinder, barrel, slide, or magazine tube. In the case of AR-15 chambers, the Flex-Hone for Rifles safely removes residues, machining marks, corrosion, oxidation, and surface imperfections while imparting a wear-resistant finish. BRM rifle brushes feature silicon carbide (SC) abrasive and come in overall lengths (OALs) of 6", 8" 12", and 14". The length of the abrasive part is 1-5/8".

Flexible Honing for AR-15 Rifle Chambers

Flex-Hone technology uses a low-temperature, low-pressure abrading process to produce a long wearing surface with a minimum of stock removal, ensuring that the bores of your firearms remain at the precise dimensions required. Built with a double-wire metal stem, Flex-Hone tools can be used with either handheld electric tools or machine centers. As this video shows, BRM gun tools are also easy-to-use. They're trusted by hobbyists, professional, gunsmiths, and the firearms industry alike.

Self-centering, self-aligning to the bore, and self-compensating for wear, flexible hones must be used with a good quality cutting oil or honing fluid. This helps to minimize heat, and prevents the tool from loading. In addition to removing oxidation and corrosion, flexible honing produces a plateau finish that optimizes lubrication. To impart this ideal surface finish, Flex-Hone technology also removes highly-stressed surface areas that can contribute to the formation of corrosion. Smoother surfaces also prevent plastic buildup, and support the performance of firearms such as the AR-15 rifle.

Author's Note: This CR4 blog entry originally appeared in the BRM Flex-Hone blog.

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Flexible Hones for Nikasil Liners and Engine Rebuilds

Posted April 02, 2014 11:47 AM by Brush Research

Nikasil is a nickel-plated, silica carbide coating that's sometimes applied to the inner walls of engine cylinders. Invented by MAHLE in 1967, Nikasil reduces friction and wear, especially in aluminum bores. Nikasil liners improve oil retention and are thinner, lighter, and harder than cast iron or carbon coatings; however, some engine builders avoid this high-performance plating material. Because Nikasil coatings are thin, rigid hones such as honing stones can remove too much of the lining.

Some hobbyists also claim you can't deglaze Nikasil cylinders, but ball hone users know better. Made by Brush Research Manufacturing (BRM), the Flex-Hone® is a flexible, resilient honing tool that features nylon filaments permanently laminated to ball-like abrasive globules. Self-centering, self-aligning to the bore, and self-compensating for wear, BRM ball hones aren't designed for heavy-duty material removal. Instead, these engine hones improve surface finish - even with very hard materials such as Nikasil.

Cylinder Deglazing and Surface Finishing

In gasoline or diesel engines, the reciprocating movement of the pistons can create a glaze on cylinder walls. If this finish is too smooth, the piston rings will skate along the surface and fail to seat and seal properly. Cylinder wall glazing can also prevent engine oil from adhering to surfaces. During engine rebuilds then, Flex-Hone® tools are used to break the glaze and impart a surface finish with oil-retaining valleys for optimum lubrication and reduced engine wear. Note, however, that Flex-Hone® tools are not recommended for ported Nikasil cylinders.

At on-line forums, engine mechanics have described their use of BRM glaze breaker hones. For example, a motorcycle mechanic explained using flexible honing tools to deglaze the Nikasil-plated cylinders in a Kawasaki ZRX 1200 engine. Other bikers have documented their use of BRM ball hones in engine rebuilds for BMW motorcycles. At Thumper Talk, an on-line forum for dirt bike enthusiasts, users discussed Flex-Hone® tools for Nikasil liner preparation and debated which type of abrasive to use.

Abrasive Types and Flexible Honing

Flex-Hone® tools are available in a wide variety of abrasive types and grits to meet a range of surface finishing challenges. For Nikasil cylinders, BRM recommends cylinder hones with aluminum oxide (AO) abrasive. Nikasil-coated bores are easier to over-hone than cast iron engine cylinders, for which silicon carbide (SC) is the right choice. The Flex-Hone® Resource Guide provides complete information about how to select the right abrasive types and grit sizes for different base materials.

As members of Thumper Talk learned from a peer, it's important to choose the right cylinder hone and then use it correctly. When one user incorrectly claimed that flexible honing would remove too much material and fail to impart a cross-hatch pattern, another mechanic posted before and after pictures of an engine cylinder. The Flex-Hone® tool that this user chose imparted a plateau finish with a cross-hatch pattern of oil-holding valleys. A picture, they say, is worth a thousand words.

About the Author

This CR4 blog entry originally appeared in the BRM Flex-Hone Blog.

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Ball Hones for Metering Valves in Muscle Cars

Posted March 24, 2014 3:55 PM by Brush Research

In automotive applications, metering valves promote balanced braking between a car's front and rear wheels. Typically, these hydraulic components are used in rear-wheel drive (RWD) vehicles with front disc and rear drum brakes. In classic cars such as the 1970 Chevrolet Camaro, a metering valve is located in the brake line between the master cylinder and the front discs. By regulating the flow rate and fluid pressure, this hydraulic valve keeps the front brakes from operating until the rear brakes start working.

Disc brakes are fast-acting. Drum brakes take longer to engage because of spring tension and linkage clearance. By delaying the application of the front disc brakes, hydraulic pressure can build in the rear drum brake wheel cylinders. In addition to brake line connections, metering valves have a main bore with a piston that closes. To ensure proper braking action then, metering valves in older vehicles may need to be replaced. With the right tools and parts, however, these hydraulic valves can also be rebuilt.

How to Surface Finish Hydraulic Valves

At Muscle Car Research, an on-line forum for a family-owned business that provides auto parts and repair services, hobbyists ask questions and get answers about restoring muscle cars. For one mechanic, rebuilding an old General Motors (GM) metering valve was a project worth documenting in detail. Step-by-step, the user explained how to rebuild the hydraulic valve by using a seal kit along with tools and cleaners.

For improving the surface finish of the valve bore, the mechanic used a 1" ball hone. The Flex-Hone tool from Brush Research Manufacturing (BRM) has its share of nicknames, but ball hone is actually a trademarked name for BRM's flexible honing tool. Built with a double-wire metal stem and flexible nylon abrasive filaments, the Flex-Hone features abrasive globules (balls) that give the cylinder hone its unique appearance. For ball hone users, however, it's the tool's performance that matters most.

When to Choose and How to Use Flexible Honing Tools

Flex-Hone tools aren't designed for use with bores that are out-of-round, or that require heavy-duty material removal. That's why the user advised hobbyists to inspect the bore first for problems such as pitting, which can cause leakage. The valve bore for the 1970 Chevrolet Camaro wasn't pitted, however, and a 1" ball hone from BRM imparted a surface finish that promoted proper sealing and seating.

After chucking the Flex-Hone in a handheld electric drill, the muscle car mechanic followed BRM's recommendations for revolutions per minute (RPM). As a rule, smaller ball hones require faster speeds. For a 1" cylinder hone, 800 RPM is a good guideline. The Flex-Hone Resource Guide provides general speed ranges, but machine trials may be needed to verify parameters. This free, downloadable resource also explains the importance of using ball hones with a high-quality lubricant such as Flex-Hone oil.

BRM cylinder hones are self-centering, self-aligning to the bore, and self-compensating for wear. Using a low-temperature, low-pressure abrading process, flexible honing tools impart a plateau finish with oil-retaining grooves for optimum lubrication. This cross-hatch pattern also reduces seepage in hydraulic and pneumatic applications while promoting longer seal life. In addition to metering valves, automotive applications for Flex-Hone tools include deglazing engine cylinders.

Author's Note: This CR4 blog entry originally appeared in the BRM Flex-Hone Blog

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Automated Deburring and Surface Finishing for Parts Manufacturing

Posted March 17, 2014 8:27 PM by Brush Research

Leading manufacturers are automating surface finishing and deburring operations to reduce labor costs and speed high-volume parts finishing. Instead of removing burrs off-line as a secondary process, part manufacturers are performing both tasks on-line at the same time. Automated deburring and surface finishing eliminates time-consuming manual operations, improves production efficiency, and ensures part consistency.

Case Study: Orange Vise

The March 2014 edition of Industrial Machinery Digest examines how one machine parts manufacturer is automating operations with NamPower brush tools from Brush Research Manufacturing (BRM). For Orange Vise, a California manufacturer of CNC machine vises and quick-fixturing components, BRM's NamPower abrasive disc brushes exceed expectations. "We started using NamPower brushes for deburring," says Orange Vise founder Eric Sun, "but quickly discovered they provided a really nice surface finish."

Before Orange Vise began using NamPower abrasive brushes, the CNC parts manufacturer needed an employee to inspect each part and remove burrs by hand. "It was time-intensive," Sun told Industrial Machinery Digest, "particularly for work that was purely cosmetic." The company's CNC machine vises are made of different metals, and required grinding on non-critical, unhardened surfaces to create a uniform appearance over the entire workpiece.

Today, Orange Vise is using NamPower technology to achieve a smooth, blended surface finish on machined components. The Orange County manufacturer mounts NamPower abrasive disc brushes in its Mori Seiki NHX4000 high-speed horizontal machining center. NamPower brushes can also be used with robotic arms and transfer lines. BRM's abrasive nylon brushes work well with non-ferrous metals, cast iron, mild steel and ductile iron, stainless and alloy steels, titanium, and high-nickel alloys.

There are two types of NamPower abrasive disc brushes: dot and turbine. The dot-style NamPower brushes that Orange Vise uses are ideal for general-purpose deburring, surface finishing, and edge blending. Turbine-style brush tools are recommended for medium and heavy deburring because they have a heavier fill density.

NamPower Technology

NamPower abrasive disc brushes consist of flexible nylon abrasive filaments that are bonded to a fiber-reinforced thermoplastic base. With their unique combination of ceramic and silicon carbide abrasives, these BRM industrial brushes are designed to remove burrs and improve surface finish at the same time. As Industrial Machinery Digest explains, "the silicon carbide acts as a buffer to the cutting action" of the coarser, but extremely durable ceramic abrasive.

The industrial brush tool's nylon abrasive filaments work like flexible files, wiping across edges and surfaces while conforming closely to part contours. NamPower nylon abrasive brushes are also long-lasting and "self-sharpening", as the magazine explains. With their linear construction, sharp new abrasive grains come into contact with the work surface. The result is a consistent deburring action throughout the length of the bristles, from the first part to the last. According to Industrial Digest, there are reports of the NamPower brushes lasting for over 100,000 parts.

BRM's NamPower technology also features lightweight tool holders that help to reduce vibration, improve performance, and extend brush life. Made with a carbon fiber reinforced thermoplastic material that's bonded to a hardened and ground steel shank, these NamPower accessories are both rigid and well-balanced. They're also designed especially for use with NamPower's unique flow-through coolant system.

Unlike other abrasive disc brushes, NamPower deburring tools allow fluid to flow from the brush center instead of supplying lubrication only from the outside. As BRM's How to Automate Deburring and Surface Finishing video explains, the result is better cutting action and longer tool life. BRM's flow-through coolant technology also allows NamPower brushes to run at greater cut depths while reducing heat generation and eliminating filament smearing.

Author's Note: This CR4 blog entry originally appeared in the BRM Flex-Hone Blog.

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