A Burr in Your Saddle

Burrs are seldom considered good things. The rough, prickly husk surrounding the seeds of some plants is called a burr (often spelled with just one “R”). Those are the kinds that stick to the fur of animals to spread themselves out into a wide area to reproduce. They are pesky when they get caught on clothes and can be a real irritant to horses when they get under a saddle. 

In metalworking, the term burr (usually spelled “bur”) is used as another name for a rotary file, a tiny cutting tool with a rough head that somewhat resembles the seed pods. Usually when a fabricator or machinist talks about burrs, however, they are referring to the tiny, rough deformations that stick out from the edge of a metal part following a metal shaping activity.

Just like a burr in a saddle, the burrs on metal are annoying and should be removed. To do so is to engage in the secondary finishing process known as deburring.

Need for Deburring

Burrs can be caused by virtually any metalworking process, whether it be casting, turning, or engraving. They need to be removed from metal for several reasons:

  • Burrs reduce the functionality of parts. If burrs are not removed, the part can’t be mounted flush and square in place when being assembled. They will also likely prevent the smooth operation of moving parts. Measurements of the part can also be thrown off by the presence of burrs.
  • Burrs can interfere with other finishing work. Finer finishing processes, such as polishing, can’t take place if burrs remain on the workpiece. Electroplating and powder coating won’t be able to have a uniform application if burrs aren’t removed, which can cause cracking and failure of the surface coating.
  • Burrs can shorten the part’s lifespan. The friction and pressure put on the sections of the part where burrs remain can create stresses that will eventually crack the part and cause material failure. The unevenness of the part can also lead to increased corrosion.
  • Burrs are a safety concern. Many a metalworker and end user alike have received everything from minor abrasions to serious cuts from sharp or rough burrs that remained on a metal part.
  • Burrs are unsightly. Unless the goal is to achieve a “rough-hewn” look, the presence of burrs on an otherwise finished piece of metal will violate the aesthetic of the product.

History of Deburring

Of all the types of finishing procedures in metalworking, deburring is the most basic—and the most ancient. Primitive humans determined that a harder object could be used to smooth down a softer object by being rubbed back and forth across it repeatedly, originating the process called filing. It was used with stone, wood, and eventually metal. Bronze rasps used for filing down materials have been discovered in Egypt that date to over 3000 years ago. By the Middle Ages, metal files were coming into common use among blacksmiths. While files were used for all sorts of shaping in metalworking over the centuries, the advent of grinders and milling machines have replaced the venerable file as the tools of choice in most operations, with one main exception: files are still used these days for deburring.

The introduction of “barreling,” or placing items such as jewelry or weapons inside a barrel with stones to serve as media to create smooth surfaces by rolling the barrel goes back to the ancient Chinese and Egyptians. It was in use in the Middle Ages to smooth chainmail armor for knights and was in widespread commercial use worldwide at the beginning of the 20th century in machines that came to be known as rotary tumblers. Vibrational tumblers were developed during the 20th century, drastically reducing the time it took to deburr a metal part.

Types of Deburring

Deburring can be accomplished through a variety of methods. Manual deburring is the everyday method of metalworkers scraping, filing, or buffing burrs off metal workpieces using handheld tools. Mechanical deburring uses appliances such as grinders or deburring machines to take the burrs off. Thermal deburring and electrochemical deburring use energy to remove burrs from metal (especially useful in deburring hard-to-reach places on a workpiece). Some of the names of deburring processes include:

  • Abrasive blasting
  • Abrasive flow deburring
  • Bonded abrasive finishing
  • Brushing
  • Buffing
  • Burnishing
  • Centrifugal disc/barrel deburring
  • Chemical-mechanical planarization (CMP)
  • Cryogenic deflashing
  • Drag finishing
  • Electrochemical deburring
  • Electropolishing
  • Flame polishing
  • Gas cluster ion beam deburring
  • Grinding
  • Honing
  • Industrial etching
  • Lapping
  • Laser ablation
  • Laser engraving
  • Laser peening
  • Linishing
  • Magnetic abrasive deburring
  • Magnetic field-assisted finishing
  • Mass finishing deburring
  • Mechanical finishing
  • Peening
  • Pickling
  • Polishing
  • Sandblasting
  • Shot peening
  • Spindle finishing
  • Superfinishing
  • Thermal-energy deburring
  • Tumble finishing
  • Vibratory finishing
  • Waterjet deburring

As long as parts are cut from metal, there will always be burrs that need to be removed. The technology will continue to improve over the coming years, but deburring processes, tools, and machines will remain a subset of metalworking culture long into the foreseeable future.