Exploring the spin finish process

Rich Smylie, GMN
By Richard Smylie | Aug 2, 2018
A drag spin finish nameplate manufactured by GMN

A spin finish, also known as spotting or engine turning, is a mechanical metal decoration technique that creates visually-striking and repetitive circular patterns. The unique interplay of light as it reflects off the finished metal surface adds movement and enhances the aesthetic appeal of the part. Rising to popularity in the 1920s and 1930s, spin finish was frequently seen in the automotive industry, especially on dashboards and instrumentation panels. However, in recent times, this decorative finish has expanded its reach to include a broad range of industries such as aerospace, appliance, electronics, and more.

Our video below provides a look into the spin finish process accomplished at GM Nameplate’s (GMN) Monroe, NC Division. Primarily performed on aluminum or stainless steel, a mechanical spin finish is always applied on a flat sheet of raw metal. The metal sheet is first lubricated with oil to facilitate uniform spinning and prevent burning of the metal when the abrasive pad is applied. The abrasive pads are mounted on single or multiple spindles that descend on the flat surface to skin the metal in a circular, overlapping pattern. The extent to which the patterns overlap each other can be easily adjusted and altered. There are two types of spin finishes that can be applied:

  • Drag spin - Once the spindle(s) descends on the metal, it literally drags across the surface while continuously blading the metal and creating overlapping swirls.
  • Spot spin - Once the spindle(s) descends, it blades the metal from a targeted spot, ascends, and then descends again on a spot next to it, creating overlapping or isolated patterns.

The computer numerical control (CNC) spin finish machines at GMN can hold up to seven spindles at a time, and the diameter of each spindle can vary from a minimum of 0.5” to a maximum of 20”. The distance between each spindle and the speed at which they travel across the metal surface can be tailored to achieve different looks. Depending on the design intent, the swirling pattern can range from fine, to heavy, to coarse. Spin finishes can also be applied overall or selectively. For selective finishes, a resin is screen-printed on the metal, which protects the desired areas from the abrasive pad, thus creating contrasting looks within the design. Offering a range of sizes, depths, and pattern intensities, the cosmetic variations that spin finish can produce is truly vast.

Once the spin finish is applied, the metal sheet is run through a washing line to remove the oil from its surface. The sheet is cleaned, dried, and a clear or tinted coating is applied to the surface of the metal. As a subtractive process, spin finish takes away the inherent protective layer from the surface of the metal and hence adding a top coat is extremely crucial to seal the exposed metal for performance considerations. The sheets are visually inspected and then are ready to be formed into the desired shape. Decorative accents such as lithographic, screen, digital, and/or pad printing, along with embossed or debossed graphics, are often added to spin finished parts to further accentuate their beauty and allure.

With decades of custom manufacturing experience and printing capabilities under its belt, GMN has worked with several leading companies including Dell, Ford, Callaway, General Motors, Keurig, Fiat Chrysler Automobiles (FCA), and Vaio to create stunning spin-finished nameplates and components. Watch the video below to see the spin finish process in action.