How to Grind Metal

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Grinding metal is a necessary process if you don’t want any sharp edges along a weld line or if you want to polish your piece. As long as you have experience with power tools and a shop to work in, you can grind metal yourself. With an angle grinder and a few different discs, you can smooth your edges and make the metal shine!

Best Way to Grind Metal

  • Tighten a C-clamp over a piece of sheet metal and the edge of your work surface so it doesn’t move.
  • Attach an 80-grit flap disc onto your grinder, then keep the disc parallel to the metal so it smoothes out the edges of the weld.
  • Apply light, even pressure when grinding along the length of the weld, and avoid staying in one spot for too long. Repeat this motion until the weld is completely smooth.
Method 1
Method 1 of 4:

Choosing the Right Grinder

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  1. Electric grinders easily cut and grind through metal. These types of grinders work best on large jobs or making straight cuts since they are bigger and cannot easily move with finesse. [1]
    • Electric grinders do not work well in tight spaces or curves.
  2. Air, or pneumatic, grinders use pressurized air to power the machine. Use an air grinder if you have a smaller, delicate piece of metal that you need to work on. [2]
    • Air grinders need an air compressor to run.
    • Air grinders do not have as much torque so they can’t cut through metal easily.
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  3. Grinding wheels are thick pieces of compressed composites that quickly grind through thick metals and remove big problems, like rust or tarnish. [3]
    • Grinding wheels generate a lot of heat, which could cause thinner pieces of metal to warp.
    • If a grinding wheel cracks from the heat, it could break and throw shrapnel.
  4. Dremel tools are small, handheld rotary tools used to shave away material. For work like sharpening blades, removing rust, or smoothing out short welds, use your Dremel. [4]
    • There are many different styles of Dremel heads that you can attach to get smooth or rough finishes.
  5. A flap disc is made of layers of sandpaper fit onto a hard backing piece. When you need to do finishing work or smooth out sheet metal without generating a lot of heat, attach the flap disc to your grinder. [5]
    • Flap discs don’t last as long as grinding wheels and cost between $4-$10 USD per disc.
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Method 2
Method 2 of 4:

Smoothing Welds on Sheet Metal

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  1. Set one end of a C-clamp on the piece of sheet metal and open its jaws wide enough to clamp to your work surface. Once it fits around the edge of your table, tighten the clamp so it doesn’t move. [6]
    • If your metal still moves around easily, put another C-clamp on the other end of your sheet.
  2. Fit the center of the disc onto the end of your angle grinder. Screw on the plate that holds the disc in place until it doesn’t turn anymore. [7]
    • Flap discs and angle grinders can be purchased at your local hardware store.
    • Wear work gloves while handling the flap disc so you don’t scrape yourself on the sandpaper.
  3. Welds tend to have dips up and down, so holding the grinder at an angle could cause it to gouge into the metal. Keep your grinding disc nearly parallel to the metal so the grinder smoothes out the edges of your weld even to the sheet metal. [8]
    • Some grinding discs have a slight angle to them. Try to use a disc with a flat edge.
  4. Wear safety glasses or a full face mask so sparks don’t fly into your eyes while you’re working. Turn on the angle grinder and touch the top edge of the disc to the weld. Pull the grinder down your weld line in one long stroke so the weld doesn’t turn blue. Repeat the motion until the weld is completely smooth. [9]
    • The sparks will shoot in the direction the disc is turning. Stand on the opposite side to ensure sparks don’t shoot towards you.

    Paying Attention to Your Grinder

    The spark flow from your grinder should consistently shoot out 3–4 feet (0.91–1.22 m) away from your piece for effective grinding.

    The noise your grinder makes should be consistent. If it lowers in pitch , you're applying to much pressure to the grinder. If the noise gets higher , you're not applying enough pressure.

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Method 3
Method 3 of 4:

Grinding Metal Corners

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  1. An 80-grit flap grinder will smooth out your surface without leaving deep scratches that lower grit disc would leave. Look at your local hardware store for your flap disc and screw it onto your angle grinder. [10]
  2. Look for an arrow on top of your grinder to see which way the disc spins. If you want a rounded-off corner, hold the grinder to the metal at a 5 or 10-degree angle so the sparks fly away from the corner. [11] If you want to maintain a sharp, 90-degree angle, place the edge spinning towards the corner onto your piece. Work in short back and forth movements along the side of the metal near the corner. [12]
    • Since the grinding disc spins in a circle, either the top or bottom of the grinder will go in the direction you need.
    • Wear safety glasses and work gloves while working with your angle grinder.
    • If you want more protection, wear a full-face welding mask.
  3. Attach a stiff, metal grinding disc to your angle grinder to work in tight interior corners. Hold the grinder so the edge of the disc is at an angle to the corner weld. Work in short movements to smooth the weld. [13]
    • Make sure to use a disc that’s specifically made for grinding metal.
    • Metal grinding discs produce more sparks than flap discs. Make sure to wear gloves, a full-face welding mask, and long sleeves.
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Method 4
Method 4 of 4:

Polishing Your Surfaces

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  1. Set the disc on the end of the angle grinder so the sandpaper side is facing out. A 120-grit disc uses finer pieces of sandpaper and will smooth out your surface without leaving scratches. [14]
    • Look for flap discs at your local hardware store or order them online.

    Tip: If your metal is covered in rust, try using a 40-grit flap disc first to remove it. The disc will leave scratch marks, but it will be easier to smooth out later on.

  2. Grinding metal produces sparks that could burn if you come into contact with them. Put on long sleeves and pants to cover as much skin as you can. Make sure to protect your face as well as your hands while you’re working with a grinder. [15]
    • If you want to protect yourself more, wear a full-faced welding mask.
  3. Hold the flap disc at a 5 or 10-degree angle to the surface of your metal and turn it on. Work in small strip sections at a time until you’re happy with the texture of your metal. Completely grind the surface of your metal before moving on. [16]
    • If your metal has nicks or rough edges, start with an 80-grit disc before moving to a finer grit. This helps preserve your discs for a longer amount of time.
    • If your metal moves around easily, clamp it to your work surface.
  4. Work in strips perpendicular to the last direction you used your grinder. Start on one end of the piece of metal and work your way across the surface. This helps smooth out any texture left on your piece. Continue alternating grind directions until you’re happy with the shine of your piece. [17]
    • Move clamps or turn your metal to make it easier to work on.
    • Try different discs if you want a different texture pattern. Discs with a lower grit will make distinctive marks on your surface and create a different design.
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Expert Q&A

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  • Question
    What angle do you grind metal?
    Christopher Thomas
    Metallurgist
    Christopher Thomas is a Metallurgist based in Birmingham, Alabama. With 16 years of experience working for Commercial Metals Company, Christopher specializes in designing modern infrastructure, metal recycling, fabrication, performance steel, and construction services. His company is responsible for creating high-end structures, from the AT&T Stadium in Dallas to the Pentagon. Christopher holds a BS in Metallurgical Engineering from the University of Alabama.
    Christopher Thomas
    Metallurgist
    Expert Answer
    The can be different preferred angles based on the function, purpose, and type of disc. For example, when using a fiber disc, a 10-degree angle is generally considered optimal, while a 30-degree angle is considered optimal for a grinding wheel.
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      Warnings

      • Wear thick work gloves and safety glasses when working with a grinder so sparks don’t fly up into your face.
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      Things You’ll Need

      Smoothing Welds on Sheet Metal

      • C-clamps
      • Angle grinder
      • 80-grit flap disc

      Grinding Metal Corners

      • 80-grit flap disc
      • Angle grinder
      • C-clamps
      • Metal grinding disc

      Texturing Your Surfaces

      • 120-grit flap disc
      • Angle grinder
      • C-clamps

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      Expert Interview

      Thanks for reading our article! If you’d like to learn more about grinding metal, check out our in-depth interview with Christopher Thomas .

      References

      1. ↑ http://knowhow.napaonline.com/know-how-notes-cutting-and-grinding-metal/
      2. ↑ http://knowhow.napaonline.com/know-how-notes-cutting-and-grinding-metal/
      3. ↑ http://knowhow.napaonline.com/know-how-notes-cutting-and-grinding-metal/
      4. ↑ https://youtu.be/C9jK3hwBFtU?t=3
      5. ↑ http://knowhow.napaonline.com/know-how-notes-cutting-and-grinding-metal/
      6. ↑ https://youtu.be/QitWDNB_qSM?t=1m38s
      7. ↑ https://youtu.be/QitWDNB_qSM?t=1m5s
      8. ↑ https://youtu.be/XhOp91r3Ed4?t=17s
      9. ↑ https://youtu.be/XhOp91r3Ed4?t=31s
      1. ↑ https://youtu.be/W2su6wsInwY?t=3m31s
      2. ↑ https://www.thefabricator.com/article/finishing/eight-tips-for-effective-grinding
      3. ↑ https://youtu.be/tRuuvJguRSc?t=32s
      4. ↑ https://youtu.be/dh5X-fFN4_4?t=20s
      5. ↑ https://youtu.be/UXXM6i3FJ5s?t=4m21s
      6. ↑ https://youtu.be/EMJGJ9gAJig?t=2m24s
      7. ↑ https://youtu.be/EMJGJ9gAJig?t=2m24s
      8. ↑ https://youtu.be/EMJGJ9gAJig?t=3m15s

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