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Metal Fabrication

The Nitty-Gritty of Sanding

A breakdown of sanding equipment and techniques

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    Sand spans thousands of miles of sun-baked beaches and desert the world over, with an ever-growing presence overtaking many parched landscapes. It outlived the statue and legacy of the narcissistic namesake figure of Percy Bysshe Shelley’s Ozymandias (my favorite poem). The expression "having the sand" refers to one’s wherewithal to withstand adversity.
   
    Consequently, sand-related products, such as sandpaper, handheld sanders and industrial-grade finishing machines, play integral roles in fashioning smooth, finished, dimensional signs. Whether it’s a 50-grit, belt sander designed to dig deeply into a surface or 180-grit sandpaper intended to delicately abrade final fabrication stages, these materials are as integral to a signmaker’s repertoire of tools as design software, vinyl or lettering enamels.

    I’ve compiled a summary of some sanding equipment available to signshops. Plus, an independent signmaker and mass-production sign company will explain how they attain ideal smoothness.
   
    The tools

    Signmakers’ sanding tools range from the low-tech that rely heavily on elbow grease to heavy-duty CAD systems. The most basic item is, of course, sandpaper. Sandpaper, which comprises scores of small, sharp edges, is available in open or closed coats. "Open-coated" means the backing sheet isn’t entirely covered with abrasive, whereas a "closed-coat" fully covers the sheet. Open-coat is the only acceptable type for sanding wood or HDU, because the shavings, or swarf, cling to the paper and quickly cause it to clog.
   
    Two sandpaper grades exist: commercial and industrial. Commercial grade denotes the garden-variety products purchased in hardware or home-improvement stores, whereas industrial products comprise denser materials and are less readily available. 3M (St. Paul, MN) is a well-known manufacturer of both varieties. Aluminum oxide is the most common sandpaper abrasive, whereas ceramic materials are much tougher and more expensive. Further, commercial-grade sandpaper typically comprises kraft paper; cotton or polyester backs premium-grade sandpaper. Sandpaper’s abrasiveness is measured in grit — the number of abrasive particles per inch on the paper. A lower grit number represents a denser abrasive content (Fig. 1).

    Standard sanding of a wood or HDU sign typically begins with 60- or 80-grit sandpaper to rough the surface, followed by 100- to 120-grit to smooth the surface before staining, and 150- to 180-grit to smooth a surface between coats of stain or sealant.
    
    Fig. 1: Sandpaper Grit Scale
    Grit
    Name
    Use
    60-80
    Coarse
    Early-stage roughing, stripping
    100-120
    Medium
    Smooths, removes small marks
    150-180
    Fine
    Final sanding before applying stain or sealant
    220-240
    Very fine
    Sands to smooth between finishing coats
    280-320
    Extra fine
    Removes blemishes between final coats
    360-600
    Super fine
    Removes luster or minute surface scars

    Sanding blocks and sponges are also common implements. Generally made from rubber, commercial blocks are available in many styles: soft or hard (as well as with contrasting sides); rectangular, rounded or wedge-shaped; with sanding belts or pre-adhered slabs of industrial-grade sandpaper.

    Blocks, which offer a substantial mechanical advantage over hand sanding, make it easier to apply necessary pressure with a tool. However, those who make their own blocks know the appropriate weight and pressure. For many shops, electric tools are necessary. A common finishing tool, a belt sander, comprises a continuous loop of sandpaper wrapped around its front and rear rollers. When the user switches on the sander, the rear drive — which is generally connected to the motor — spins and spurs the belt forward.
   
    Depending upon the model, sanding belts are typically 3 to 4 in. wide and 18 to 24 in. long; for certain specialty applications, belts approximately 1 in. wide are available. Belt grits, ranging from 24- to 320-grit, are available in paper or cloth. As with hand-applied sandpaper, cloth-backed products outlast paper.

    Also, ceramic abrasives outperform, and cost more than, aluminum oxide. Other commonly used products are orbital and palm sanders. Orbital sanders, which move in a circular motion, incorporate pads attached to an offset bearing, which provides random patterns and operator mobility without scarring the work surface. Holes in the pads expel sanding dust during operation.
   
    Palm sanders use 1/4 or 1/3 sheets of sandpaper and vibrate in a slight circular pattern that, like all sanders, must move with the wood grain to avoid scratching the substrate. Both are more compact than a belt sander.

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John Deaton, who has operated his shop, Deaton Designs (Harlan, KY), for 10 years, has been fabricating signs since 1986. Most of his signs use MDO plywood, though he increasingly selects HDU. Deaton sands manually with pieces of sandpaper and sanding sponges, as well as with a palm sander that’s "worth its weight in gold." In the early stages of smoothing the surface, he sands with 100-grit by hand.
   
    Before priming, he breaks out his palm sander, with 150-grit sheets, and then repeats the process after having applied two coats. Before sanding edges, he’ll finish them with exterior wood filler, which Deaton said dries in two hours and withstands unlimited sanding. All told, he spends approximately 30 minutes sanding MDO signs to ensure the edges are completely smooth and sealed to prevent water seepage.

As a less costly alternative to an entire HDU sign, Deaton often produces an MDO face, for which he creates 11/2-in.-thick letters using 15-lb. Sign*Foam®. To smooth the letters, he’ll often attach a small strip of fine sandpaper to a Dremel® tool.
   
    "For an HDU sign, I charge about $90 per square foot," Deaton said. "An MDO sign will cost about half that, but the letters provide dimensional appeal."

    Sanding urethane requires substantially more work. On average, Deaton devotes two to three hours sanding HDU, particularly when he gilds the primary letters, which he does on roughly eight of 10 such signs.
   
    "If you gild on a surface that’s less than perfectly smooth, the result will look terrible," Deaton explained. "Any grit on the surface will cause your gild to not look right."

    Contrastingly, Hanson Sign (Falconer, NY) — a 55-year-old, high-volume, full-service company that maintains 38 full-time employees and two production plants — uses a 54-in.-wide, Italian-made SCMI Sandya 30 to sand the scores of redwood, cedar and HDU signs the company fabricates on a subcontract basis.
   
    After Hanson planes its 6-in.-wide planks, joins them with biscuits and adheres them with two-part epoxy, the Sandya performs its job.

    According to Hanson General Manager and Vice President Brett Aversa, the machine simultaneously performs two functions. As the board enters the machine, several belt-sanding heads equipped with 80-grit paper aggressively smooth the surface. As the sign progresses through the Sandya, another set of heads abrades the surface with 120-grit belts to complete the process.
   
    Having finished this procedure, Hanson primes and paints the sign, applies rubber masking and crafts the sign using its two MultiCam routers. After sanding, HDU often requires an extra coat of primer, Aversa said, because its cellular structure somewhat precludes smooth surfaces.

    Hanson has owned this machine for three years, after having traded in its 36-in.-wide sander. Having spent four years fabricating signs in the shop, Aversa vouches for the time Hanson’s machine saves.
   
    "Sanding one side of a 4 x 8-ft. sign by hand would take about an hour," he said. "With this machine, we can do it in 10 minutes."
   

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