Best Practices for Improving Sanding Results
While much time is spent in the woodturning community teaching us how to more properly use our tools to improve our turnings, very little time is spent showing how to do a better job of sanding. Let's face it, for some of us a piece of sandpaper IS our favorite turning tool, and we could use a little help learning how to better use it. Let's take a look at how to better sand our turnings:
Start with high quality sandpaper -
Low quality sandpapers will not produce consistently good results. The sizes of the grit on these sheets can vary quite a bit from one piece to the next. This can make it very difficult to remove scratch marks made by lower grits as you move through the sanding process. The quality of the adhesives used in these papers (as well as the type of backing material) can also cause the paper to deteriorate quite rapidly and sometimes become clogged prematurely. Switching to better quality sandpaper will not only give you better results, it will also save you time and money in the long run.
Provide adequate lighting -
Poor lighting conditions make it very difficult to really see any flaws which have been missed during sanding. While overhead lighting works well, a good lamp which can be positioned directly beside your work is best. Position lights so that the wood's surface is clearly visible, but make sure to keep it far enough away so as not to begin heating up the wood.
Clean properly between sanding grits -
While sanding, small pieces of grit which were embedded in the sandpaper will become dislodged and mixed in with fine sawdust which remains on the turning. If this mixture is not cleared away between sanding grits, the leftover grit from the prior sanding will continue to cut into the wood, making it nearly impossible to remove some scratches from the turning. Always make sure to clean the surface between sanding with a microfiber cloth or with a blast of compressed air followed by a cleaning with a dry cloth.
Adjust lathe speeds properly -
Remember that lower grits require higher lathe speeds. Higher grits require lower lathe speeds. The speed of your lathe should be slowed progressively as sanding moves forward. Lathe speeds of 1200-1800 RPM are suitable when using lower grits. This moderate rate of speed helps to reduce the likelihood that an uneven surface will be produced, while not producing excessive heat. Lathe speeds of just a few hundred RPM are best for using higher grits. The fine grains in the higher grits will sand your piece more quickly at these lower speeds, as high speeds cause the small grits to bounce across the surface instead of providing the cutting action that they should.
Proper use of lower grits -
Lower grit sandpapers can be used for refining shapes, removing tool marks, and removing end grain tearout. 80 grit sandpaper is usually best for working with hardwoods, while 120 is sufficient for most softwoods and softer hardwoods. Keep in mind that this is the most important step in the sanding process! Any defects that are not addressed during the first sanding will be nearly impossible to remove later on. Take the time to visually inspect the process of your sanding until all defects have been fully removed.
Proper use of medium grits -
When using medium grits (120-320), there are two important things to remember: always sand away scratches from the prior grit, and never skip over grits. Fine scratches will be readily visible from the prior sanding step, and will usually be of fairly uniform size. If these scratches are not removed each time, they will likely not be removed when switching to the next finer grit of sandpaper. Additionally, skipping grits will usually not allow you to remove the scratches from your prior sanding steps without a lot of extra work.
Proper use of higher grits -
The sky is the limit when it comes to using sandpaper grits of 400 and beyond. One can sand to grits well beyond 1600, and use buffing compounds that are even finer than this. Typically, though, it is not necessary to sand most domestic woods beyond an 800 grit sandpaper. Only harder, denser, more slowly growing tropical hardwoods benefit from further sanding. Using higher grits on domestic woods will improve the wood's luster, but only very slightly. One should learn that a good surface is produced by proper sanding while using the lower grits, not by continually stepping up to higher ones.