What is the appropriate technique when using a file on metal?

Using a file on metal requires an understanding of the filing technique to achieve effective results while maintaining the integrity of both the file and the material being worked on. Applying pressure on the forward stroke is essential because this is when the teeth of the file engage with the metal to remove material. This technique is crucial for efficiently shaping and smoothing the metal surface.

In contrast, applying pressure on both the forward and return strokes can hinder the filing process, as it may lead to excessive wear on the file's teeth without significant material removal on the return stroke. This is especially important when dealing with harder metals, where controlled pressure helps prevent damaging the file. For very soft metals, while the filing technique may vary slightly, the best practice remains centered on applying pressure during the forward stroke to avoid clogging the file's teeth and ensure smooth cutting.

Thus, the technique of applying pressure only on the forward stroke, with the exception of very soft metals, is the most effective and efficient method for filing metal, leading to better results in sheet metal work.