A rasp is a file that’s specifically for wood. They’re often needed for initial shaping and sculpting operations. They are mostly used because they don’t tear out the material where the grain changes direction. This gives a smoother and softer finish even around the curves.
Much like other tools, however, rasps are subject to wear. This means that, when used far too often, they lose their capacity to create soft curves. Fortunately, you can revitalize your rasp through these maintenance techniques:
Cleaning
Rasps are cleaned using file cards, nylon brushes, or with a soft wire brush. The file cards are for the coarser rasps, while brushes are for finer-teeth varieties. To clean them easily, you can use chalk to make the brushing smoother. You can also use soapy water to remove tiny bits of wood or dust stuck between the teeth.
Soaking the tool in hot water for a few seconds also works. The wood chips that got stuck between the rasp’s teeth will quickly soak up the water. As a result, they soon pop out of the file’s pockets. After soaking, remove the tool from the water. Brush it using a soft wire brush. Soft wire brushes are recommended as they doesn’t dull the rasp’s teeth.
Let the tool dry. You can use a hairdryer to completely dry it off. This prevents it from developing rust, which is known to hurt the tool’s performance.
Sharpening
Rasps can be sharpened using a sharpening block. Make sure to follow the direction of the rasp’s teeth. Use a figure-eight motion using a smaller sharpening stone in rasps with criss-cross patterns. This helps sharpen all sides of the teeth.
Using an acid bath is also a good way of sharpening a rasp. This is actually best for rasps with finer teeth that are hard to sharpen. Here are the steps in using an acid bath:
First, cut a PVC pipe that’s longer than the longest rasp you will sharpen. Stick a cup on one side using PVC glue. This keeps it tight, preventing the acid solution from seeping out.
The second step is to make a small hanger for the rasp to hang on firmly while being soaked. The handle is not to be soaked inside the acid solution.
Third, fill the pipe half an inch from the top with acid. There are a variety of acids that can be used such as citric acid and muriatic acid. Vinegar can be used too. It can be white vinegar, red wine vinegar, or cider vinegar.
Put the rasp inside. Make sure that it’s strapped securely on the hanger. Let it suspend freely but ensure that it doesn’t touch the bottom. The soaking time depends on the acid used. For vinegar, it’s around 12 to 24 hours. If the acid used is stronger, you can soak it for just 4 to 6 hours.
After soaking, rinse it with a solution of water and baking soda. This neutralizes the acid and makes brushing off any surface rust easier.
Dry the tool thoroughly. You can use a hairdryer or heat gun. Finally brush the tool with a soft wire brush to remove any dust. Remember to keep rasps properly and never stack them on top of each other.
And that’s how to sharpen and clean a rasp to create excellent soft wood curves. Remember that through proper maintenance, your tools should last for a very long time.
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