Deep scratches and torn fibers characterize the sanded wood surface. Sanding tears fibers in the surface of wood, while scraping leaves behind fewer ragged fibers that tend to be longer.
FOX CHAPEL PUBLISHING
If you are a craftsman looking for the smoothest finish to your piece, reveal the true beauty of your wood’s grain and figure by sanding, scraping or using handplanes. Woodworker’s Guide to Handplanes (Fox Chapel Publishing, 2010) by Scott Wynn evaluates and compares handplanes for the best result in every woodworking situation. The following excerpt from Chapter 1, “Smooth: What to Use, When, and Why,” explores how to smooth wood using the best tools and techniques possible.
Understanding How to Smooth Wood Is Essential
To get to that level of finesse—of craftsmanship—the use, position, and intended finish of a piece, or parts of a piece, all will have to be considered when deciding on the best tools to use for a project. To make informed decisions, understanding the nature of the different surfaces different tools produce is essential.
The three ways to smooth wood—sanding, scraping, and planing—all leave a different kind of surface.
Sanding abrades the surface, leaving a series of irregular microscopic grooves with slightly fuzzy edges. Sandpaper, which consists of randomly distributed abrasive particles of irregular size, shape, and orientation, tears and scrapes the wood fibers. The points and edges of the particles project and wear unevenly, cutting to different depths. The result is most noticeable when starting with coarse sandpaper and then skipping grits, because coarser grits leave deep scratches finer grits will not reach (see Image Gallery).
Sanding also leaves a myriad of microscopic torn fibers hanging onto the surface. And even though you may be meticulous, sanding thoroughly through progressive grits, you still have to sand to a grit finer than 600 to get light to penetrate the torn fibers with enough clarity to bring out the grain of a figured wood.
Scraping, using the burr turned on the edge or a sharpened blade held at a high angle, tears the wood fibers as well, removing wood essentially by compression failure at the edge of the burr (see Image Gallery). The burr is a relatively blunt cutting edge that establishes a point where compression failure begins, rather than actually cutting or shearing the wood.
Hard tropical woods scrape cleanly, I suppose, because scoring the wood fibers with a blunt edge is more effective on hard, brittle wood. But the softer the species, the less cleanly the burr-edge pulls wood away, often causing the chip to collapse upon itself, while tearing the fibers from the surface being smoothed. The surface of pine, for instance, can be shaped with a scraper, but ends up fuzzy.
The big advantage the scraper has over sandpaper is that on most hardwoods, it removes wood as fast as 60-grit paper and leaves a finish like 400-grit, all with one tool that will probably last a lifetime and cost less than a single package of sandpaper.
Moreover, unlike a plane, it is virtually impossible to get any major tearout with a scraper, though on some woods the resulting fuzziness confirms surface tears. Nor is the scraper unidirectional, as some believe. It cuts better in one direction than the other, though cutting in the wrong direction does not usually result in the disastrous tearout you might get with a plane.
Both sanding and scraping leave the edges of the wood pores ragged, though technically the results are slightly different. With sanding, the last grit used determines the size of the ragged fibers. Whatever the grit, however, torn fibers are plentiful (see Image Gallery). With scraping, the ragged fibers are fewer and longer. In both cases, the fibers lie flat until finish is applied, and then stand up, swollen and stiffened with the finish.
A sharpened plane cuts by shearing the fibers off cleanly. The lower the angle of the cut, the cleaner the shear; the higher the angle, the more the blade scrapes. The shearing cut is clean—the surface is not torn by abrasion or compression failure—and light penetrates the surface structure, refracting through the changes in direction of the wood grain, and revealing the dazzling beauty of the wood’s figure (see Image Gallery).
The surface, however, deserves further consideration. Most woods display wonderful clarity with a little raggedness at the end of the pores (see Image Gallery). The residue rises when applying finish and stiffens when it dries, resulting in a rough surface. Removing the tails to achieve a smooth surface creates a conundrum: in order to get the smoothest surface you must risk compromising clarity by lightly roughing it up.
There are a couple of ways to approach the issue. The first is to consider the planned finish. Penetrating finishes, such as oil, raise the grain less and bring out the figure of the grain more than surface finishes.
On some woods, vigorous application and removal of the oil eliminates the tails, especially if the last step is buffing with a wool rag.
Some woods require rubbing with steel wool after the first or second coat of oil. Steel wool hooks the hanging fibers and pulls them off. Polish some surfaces by rubbing them hard with shavings before applying oil.
I go over broad and/or horizontal surfaces, after planing to a fine finish and applying the first coat of oil, with 1000-grit or finer sandpaper, working either wet or dry for the second coat. The grade of sandpaper I use may vary according to the type of oil I am using and other factors.
Surface finishes, such as varnish or lacquer, do not bring out the figure as well as oil for two reasons: (1) the finish does not penetrate as deeply and (2) light must travel through a thickness of film before striking the wood and bouncing back through again. The clean shear you get from planing is muted, and, therefore, probably less critical. I have also had feedback from finishers that (in one case anyway) the plane left the surface too smooth without enough tooth for the finish to adhere.
To prepare for a heavy surface finish, such as brushed varnish, catalyzed varnish and lacquer, or nitrocellulose lacquer, my general procedure is to remove the machining marks, snipe, and such with a plane. If the plane leaves minor tearout, I remove it with a card scraper. If the project or parts of it (such as shelving) are less sensitive—and especially if the wood is difficult—I may remove the mill marks with a handled scraper, such as the Stanley 80, followed by the card scraper.
A handled scraper is faster than sanding through three or four grits of sandpaper. I follow the planing (or scraping) with a quick, light pass with 220-grit sandpaper to even out any minor irregularities or any traces of the plane or scraper. If the finish is to be shellac, I will follow the planing (and scraping if necessary) with 320- or 400-grit sandpaper. (Follow that procedure for shellac applications except for French polishing, which has its own set of procedures.)
Shellac does not seem to flow out as well as lacquer, even when applied thickly or repeatedly. Shellac seems to benefit from extra sanding. The catalyzed finishes flow out wonderfully and cover a multitude of sins. Unfortunately, catalyzed finishes can also make a closed-pore wood like cherry look like plastic laminate.
Flat and Smooth
On broad horizontal surfaces, take special care to prepare the surface, no matter what the finish. Once the light glances across the surface, variations in flatness will literally be glaring. Sanding a horizontal surface flat will not yield satisfactory results. Belt sanders and orbital sanders used directly after power planing will result in a surface that looks like a calm pond in a slight breeze when the light reflects across it. I have found most stationary thickness sanders do not give satisfactory results, either. Only the top-end industrial sanders used to finish plywood sheets give anything close to acceptable results.
Hand planing yields flat surfaces, especially if the handplanes used are the correct size for the work. Unfortunately, large surface handplaning is one of the hardest skills to master, though the results can be quite rewarding. Using the tools, techniques, and information presented in this book can accelerate your efforts to acquire these skills. Flattening and smoothing a horizontal surface requires a series of handplanes. If tearout or minor imperfections remain, follow with one or two scrapers. Use a handled scraper, such as a scraping plane (not the Stanley 80) to maintain flatness if tearout is extensive. Use a card scraper over the whole surface for minor tearout. Usually this leaves the surface sufficiently flat and smooth so that, depending on the finish, a light sanding with 220-grit or finer is all that is needed. Often I can even skip this step and have to sand only lightly after the sealer coat of finish.
If I am not satisfied the surface is flat, I may sand using 220-grit or finer with a half-sheet sanding block to remove any slight ridges or any minor unevenness left between the cuts of the plane or scraper. The ridges or unevenness will not telegraph through visually upon completion of the finish, or physically while sanding between coats.
That is particularly important with a brushed-on varnish finish. The coats do not blend, so cutting through a coat will leave a ring, necessitating removing the finish and starting over. (You can usually avoid cutting through to minor high spots, by either hand sanding without a block, or using a soft block, after the first coat of finish.)
Handling Edges After Using Handplanes
There is another often-underestimated subtle difference more than one client has pointed out to me. While the handplane leaves a surface whose visual and tactile quality is usually unsurpassed, the surface it leaves on an arris (a corner where two faces come together) usually can be improved.
If you watch clients study pieces of furniture, they will always—consciously or not—run their hand along the edges, making the edges of a piece among its most important features. The edges can clinch the deal—or break it. Knocking the edges off with a handplane will leave a somewhat harsh, unfriendly quality to the piece, even if done with a round-blade chamfer plane. Follow the final touches of a plane with a light sanding to soften the edges, usually with 220-grit sandpaper (or finer if the chamfer was well cut). This will make the all-important edges satisfying to the touch.
So smooth is both visual and tactile, looking and feeling differently in different places, with different results from different tools, and sometimes different results with the same tools—in different woods. How do we use that information effectively?
I have come to a number of conclusions through my experience working with planes. For one, removing a lot of wood by sanding is, in most situations, a poor and inefficient choice. Bring wood as closely as possible to its final shape and finish with a cutting edge—a plane, scraper, or power tool.
After grinding the work with abrasives, sanding with succeeding grits to eliminate the deep scratches from the coarse shaping grit is expensive and time-consuming, and raises excessive fine dust. Sandpaper’s first use was as a final step in polishing the work, and at its most aggressive, removing minor tool marks. I think that remains its best use.
Another important point: Wood shaped by abrasives, rather than by a cutting edge, results in both the shape and surface being different. The differences are subtle, but important. The cut pieces reflect the crispness of the edge used to shape them, and the sweep of the stroke the artisan used to make the cut. Sanded pieces feel and look ground down, reflecting the back-and-forth scrubbing or rotary movement of the abrasives used. The artisan must be aware of the differences and how they will affect the final product.
In summary, on a piece where you want to bring out the figure and texture (grain) of the wood—a piece that is to have no finish or only a light finish such as linseed, lemon, or tung oil, wax, or shellac—smoothing with a clean-cutting plane gives spectacular results and brings out the beauty of the wood.
With some difficult-to-plane woods, however, taking the surface all the way down to a polish with a plane can be demanding and not necessarily efficient. On some special pieces, the extra effort may be worth it. That is an individual decision.
For most work, however, leveling with a plane, smoothing (if required) with a scraper, and a final polishing with sandpaper will be the most efficient procedure. This technique is especially applicable if a heavy surface finish, such as lacquer, brushed varnish, or a catalyzed finish, is to be applied.
The Challenge of Sandpaper Grit
The grit size on sandpaper refers to the maximum size contained. On most papers, up to 65% of the abrasive is smaller than the listed grit size, some quite a bit smaller. This means the scratch pattern will be inconsistent, with the listed grit size making deeper scratches than the remaining abrasive. This inconsistent scratch pattern will then have to be reduced by the inconsistent scratch pattern of the next finer grit, and so forth, until the scratch pattern is fine enough not to be easily discerned by the eye or hand. That is why you should not skip grades when sanding. Some of the new premium papers have a more consistent grit size with as much as 95% of the abrasive being of the listed size, so attaining good results should be easier.
This excerpt has been reprinted with permission from Woodworker’s Guide to Handplanes: How to Choose, Set Up, and Master the Most Useful Planes for Today’s Workshop, published by Fox Chapel Publishing, 2010.