5 Tips to Avoid Over-Grinding with Your File Belt

August 19, 2021 3M Canada

File Belt Tool on bench


3M first introduced the U.S. collision repair industry to File Belt Sanders and Belts in 2013 with a focus on improving the spot weld removal and part replacement process. These tools have since become a go-to solution for body technicians to remove parts faster, more affordably, and with less impact on original parts.

In this article, we’ll go through some tips, tricks, and techniques to solve one of the most common issues with using a file belt tool for spot weld removal: over-grinding.

The Risks of Over-Grinding

Over-grinding is a common and understandable issue when removing spot welds—you want to ensure that the weld is thoroughly removed so you don’t have to go back and re-grind later. However, because the goal is to remove the damaged panel without causing unnecessary harm to the undamaged panel, over-grinding should be avoided.

Over-grinding can help reduce the thickness of the original part, making it difficult to predict how the part would perform in a subsequent collision. It can also create air gaps between parts, making the strength of a replacement spot-weld uncertain if one happens to be placed in that exact spot during a repair.

To avoid these safety issues and other complications caused by over-grinding, let’s look at some techniques that can help minimize the impact of spot weld removal on original parts and ensure sound, long-lasting repairs.

Tip #1: Use the bottom of the contact wheel.

To avoid over-grinding, it’s important to use your file belt sander in a controlled, uniform manner. The best way to have maximum control is to use the bottom of your file belt as pictured in the left image, holding the sander at a shallow angle as opposed to using just the tip and a steep angle. When using only the tip of the sander, as seen in the right image, you’ll have a hard time telling how deeply you’re cutting into the damaged parts. The small radius of the tip contributes to over-grinding and will cause unnecessary damage, while the bottom of the belt will offer a smooth, even grind.

Correct angle.

Correct angle.

Incorrect angle.

Incorrect angle.

Tip #2: Use the belt to measure cut depth.

Another way to avoid cutting too deeply is to use the belt as a visual guide to the depth of your cut. Watch the belt from the side as it grinds through the metal. Once the belt backing sinks below the surface of the damaged panel, you’ve likely cut through the top layer and don’t need to grind further.

Check your work, and adjust the following cuts adding or subtracting depth as needed. If done correctly, you’ll only scuff the undamaged panel, preserving its depth and strength.

Use the belt to measure cut depth

Tip #3: You don’t have to grind off the entire weld nugget before separating panels.

Attempting to remove the entire weld nugget before the parts are separated can lead to over-grinding. Ideally, you’ll grind away enough of the damaged panel to separate the parts, leaving a small portion of the weld nugget on the undamaged part. This remaining portion will be removed in the surface prep step, so don’t worry about grinding so deeply that the panel below gets damaged.

Here, the grinding has gone too deep and has damaged the panel underneath.

Here, the grinding has gone too deep and has damaged the panel underneath.

Here, the spot-weld has been ground just enough to remove the top layer of the nugget and not damage the bottom panel.

Here, the spot-weld has been ground just enough to remove the top layer of the nugget and not damage the bottom panel.

Tip #4: Use larger, sweeping strokes to remove the spot weld.

We often see users focusing their work on the spot weld itself by positioning the tool directly over the weld, pulling the trigger, and pushing down until they feel the weld is removed. This typically results in over-grinding the centre of the spot weld and leaving the edges unremoved. Instead, we recommend moving the belt in forward-backward strokes over the weld to remove the material evenly. This will limit over-grinding and cause less damage to the panel below.

Tip #5: Repair Technique: Utilize file belt in sectioning applications.

While your file belt sander is perfect for removing spot welds, it can also be used in other applications. One technique we recommend is to use your file belt tool in addition to your cutting wheel to section off hard-to-reach areas.

Sail panel and rocker panel areas are difficult to section because of complex door jamb edges and geometries. By using your file belt tool, you can complete plunge cuts that would otherwise be too difficult to perform using only a cutting wheel. Start by taping off and marking your sectioning line as usual, then complete your open area cuts using a cut-off wheel. Next, in the hard-to-reach corners of the jamb, use the file belt to grind away the area of the damaged panel next to your sectioning point. This is a fast and easy way to help remove the material in a controlled manner without cutting too deeply with your cutting wheel.

Use your grinding wheel first to cut away the easy-to-reach areas.

Use your grinding wheel first to cut away the easy-to-reach areas.

Finish cutting in hard-to-reach areas using your file belt sander.

Finish cutting in hard-to-reach areas using your file belt sander.

Please contact your local 3M Collision Repair Specialist or visit 3M.ca/CollisionRepair for additional information regarding 3M abrasives, power tools, best practices, or Standard Operating Procedures.

About the Author

3M Canada

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