Yep, I’m going to spend just a few moments discussing the martial art of sanding. Change channels now if you like, I understand. Still here? Okay then, let’s talk about how to get better results and minimize the amount of elbow grease involved.
The most common error is over-sanding. To get a feel of how much is just right, practice on a piece of scrap by taking a pencil and making a serpentine pattern down the face. Then, for the chosen grit, sand the piece until the graphite is gone… that’s “just right”. You’ll get a feel for how long that particular grit takes to abrade the appropriate amount of the top surface of the wood away. Then repeat this practice session with each grit you regularly use.
Plywood and anything with a veneer on it is especially tricky. If you are new to woodworking, I highly suggest taking a bit of scrap plywood and sanding through the face veneer on a portion. Do this to learn, by feel, just how easy it is to ruin your work piece. When sanding on a veneer, or on a hardwood piece adjacent to a veneered piece, extra attention must be paid to not penetrating said veneer. In our production woodshop, we avoid sanding on plywood-thickness veneers with anything less than 180 grit. And even then, it’s just a light clean up pass on the veneer. Obviously, if you’ve veneered something with a much thicker material, you can be more aggressive with your sanding; use judgment.
Grit vs. Finish
Secondly, what grit you sand a work piece to is controlled by the type of finish you are going to use (again, most tend to sand more than necessary). For example, lacquers, paints and urethanes build up a surface on top of the surface of the wood. The wood grain will not be felt when touched because the paint or lacquer builds up a “plastic”-like film over the wood. Only large imperfections will pronounce through the covering. Therefore, sanding up to 120 grit is usually sufficient to knock down any big-enough imperfections to get a nice, smooth finish with paints, urethanes and lacquers (Oh My!).
Stains, oils and varnishes, however, actually ‘soak’ into the wood, and become part of the wood fibers themselves. The wood grain and texture will be felt, so, much more detailed sanding must be performed to remove smaller imperfects, including those that may not be visible but can be felt by the sensitive finger. Therefore, a sanding progression up through 220 grit (in most cases) and perhaps even 320 grit (in some special instances) will get you that fine finish you desire.
The Right Tool
Also, don’t forget that sometimes the best way to sand an imperfection out of a work piece is not to sand at all. Don’t overlook using a rasp, a file, a chisel, a scraper, a flush trim saw, a rotary tool, an eraser, a fingernail… you can almost always find a tool to remove an imperfection that is the right size and fit without having to sand an entire area just to get the thing that was mucking up your piece.
When using any kind of power sander, the speed at which you move the sander over the piece will affect its efficiency. The secret here is, “Let the sander do the work.” A good rule of thumb is about 1″ per second. You’ll see most people frantically whipping that sander around on the work piece; this technique is considerably slower, but it is not so slow as to make the work take absolutely forever. Steady movement is key to good results. Also, resist the urge to: 1) press harder than an ordinary arm resting (listen to the motor; if it’s bogging down at all, you are pressing too hard), and; 2) tilt the sander on a side or corner to “get that little spot right there.” Keep the sander fully flat on it’s entire sanding surface. Heat is the sandpaper’s worst enemy; cool paper sands much more efficiently and last much longer. Remember that when thinking about pressure, speed and tilt with your power sander.
Quality vs. Cost
Last thing I’ll bore you with is the quality of your sandpaper. Believe me, less is not more when it comes to the price of your sandpaper. Economy sandpaper seems like a better deal because you get more sheets and less cost… up front. But, cheap paper handles heat poorly, clogs more frequently and loses abrasiveness much more quickly… noticeably so over the long run. Premium paper last longer, often multiple times longer than the ‘inexpensive’ stuff, and abrades much cleaner, cooler and usually with better results. You will actually save money investing in premium sandpaper because you will use less sheets over time, and so much so that the premium paper is more economical. I know… its not intuitive.
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Mike @ Doobly-Do Wood Works