The main question in how do we prepare wood for finishing comes down to sanding versus planing. Which is the best way to achieve a smooth surface without blemishes. As some of us saw with Garrett Hack’s presentation, he was skilled at doing the final preparation of the wood using a hand plane to achieve a super smooth glass-like finish. Unless you are good with setting up a hand plane and skilled at using it, you may not get the same results as Garrett Hack. It is harder to plane figured woods. You need a sharp blade. As a result, must of us resort to sanding. However, unless you are careful you can sand away fine details or round over edges.
A scraper might be able to be used, but it does not leave a smooth surface. Can you achieve a smooth surface without sandpaper? It may be possible, but can be difficult to achieve. So sanding is the next best way the smooth wood. David found that sanding without a downdraft table led to he and his wife finding dust infiltrating all of their house.
Sandpaper may go back in history since the time of the Egyptians who used sharkskin to prepare wood. It wasn’t until the 1600’s that small shards of glass was attached to a paper backing and used as glasspaper to sand wood. It was around the 1830’s that sand was used on a paper substrate to smooth wood.
Today we have all kinds and grades of sandpaper with different particles used as the abrasive agent. There is stearated and non-stearated paper. Stearated sandpaper is also known as self-lubricating sandpaper. It is used primarily for sanding wood and paint finishes as well as metal. The applied lubricant or soap prevents clogging and extends the life of the sandpaper. Garnet and Aluminum oxide can be used as the abrasive substrates on the paper. Garnet paper is inexpensive and fine for sanding bare wood but open coat stearated paper are cheaper in the long run because they cut faster and last longer.
Not all sandpapers are equal, and you tend to get what you pay for. Experience has shown that it is cheaper to buy a more expensive sandpaper because it cuts faster and lasts longer. Yes sandpaper is a cutting tool: a great number of small cutting tools actually. These cutting tools are the abrasive particles and better sandpaper has stronger, sharper particles that are arranged better.
Sandpaper made in North America is graded under the Coated Abrasives Manufacturers Institute (CAMI) while European papers are rated under the P scale dictated by the Federation of European Producers Association (FEPA). The later always has a P in front of the grit number so it is easy to tell. A grit size in one system does not exactly equal a grit size in the other, so you may want to be careful to pay attention to what system you are using.
The most important first step is to start with coarse enough paper. This is the biggest mistake beginners make. If there are major imperfections in the wood surface or the surface needs to be leveled a bit, as when a rail meets a rail on a face frame, then start with 60-grit. Sand longer than you think you need to in order to remove all of the surface imperfections. If hand sanding, using a padded block for your paper gives better results as does making the final strokes with the grain as much as possible.
The second important factor is to make small jumps in abrasive coarseness. If we take 60, 80, 100, 120, 150, 180 and 220 as being grits that are readily available, make no more than a two grit jump as you move to finer grits. Under this rule you would move from 60 to 100, 150 and 220. If you started with 80, you can go to 120, 180 and 220 grits. For power sanding you can use hook and loop backed paper because it can save partially expended sheets for later use. When using a random orbital sander, you may find it helpful to use a padded glove to prevent too much vibration being transferred to your hand.
The third important factor is sanding to a grit that is appropriate to the finish you are using. For most film forming finishes, shellac included, sanding finer than 180-grit can be counterproductive. Some like to sand to 320 or higher with some woods and if you are using an oil finish. John Kennedy will sand to 400 or 600 grit with his oil/varnish/mineral spirits finish and you cannot argue with his results. Sanding with 220 and finer between coats is helpful if you want a glossy finish. Stearated paper is much superior for sanding finishes and using waterproof paper with some soapy water or mineral spirits is a great time- and money-saving trick.
David’s downdraft table is constructed with an angled bottom with the vacuum port at the wide end. The top has chamfered holes in the pegboard to facilitate dust extraction. The downdraft table works well and really cuts down on sanding dust being spread all over your shop.
