Small cracks, dents, nail holes and tiny knots all need to be filled for your wood projects. Normally, you would reach for an off-the-shelf commercial wood filler. However, ready-made fillers rarely take stain correctly and they crack over time from shrinking. Also, unless painted over, these fillers never quite blend in correctly. There's a better way to fill these imperfections using a simple mix of sawdust and shellac. You can make this filler anytime you need it, so you'll never have any leftover to waste.
Hold the hardwood scrap over the plastic cup and sand a corner on the long edge with the 220-grit sandpaper. Sanding the corner of the edge will produce more sawdust than sanding the flat face of the board. You want to collect as much dust as you can in the cup. Use the same wood species as your project to ensure a match if you have to stain it or finish it natural.
Pour a small amount of shellac into the plastic cup and mix it with the sawdust using the small wooden sliver. If necessary, keep adding more sawdust or shellac until it reaches a consistency similar to peanut butter.
Press the mixture into the area to be filled using the wooden sliver like a spatula. Press it in tight and overfill the area.
Wait about five minutes for the shellac and sawdust filler to dry. You can tell when it's dry by observing the color. It will turn from dark to light when dry. Sand the area smooth with 400-grit sandpaper. If it's not quite level or if some of the filler pulls out while sanding, simply press in some more filler and sand when dry. Repeat this process as many times as needed to fill the area.
If you sanded your piece with a palm sander, you can collect the sawdust either from its dust collection filter or from the surrounding surface you sanded on. This will save time if you need a large amount of sawdust.
When working with a power sander, it's always a good idea to wear a respirator to prevent inhalation of sawdust.