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Essential Hand Tool Techniques
By David Tilson
The Geometry of a Cutter
The sharpness angle is the factor most easily controlled by the woodworker. It affects the durability of the cutting edge and influences the rake angle. A small sharpness angle, say 15°, will result in a blade that easily wedges apart the wood fibers, but dulls quickly. A large sharpness angle, about 60°, would result in a very durable edge, but the cutting action would tend to crush the wood fibers and would yield more cutting friction. A sharpness angle of 90° would give a scraping cut due to the 0° rake angle, acting like a snowplow pushing the wood out of its way.
The rake angle determines whether the blade acts like a wedge or a snowplow. A wedge-like cutting action (large rake angle) can produce very smooth cuts on end grain or when cutting with the grain, but tends to produce severe tearout when cutting against the grain. A smaller rake angle greatly reduces tearout while not greatly affecting cutting performance with the grain, but it severely impairs cutting performance on end or cross grain. A zero or negative rake angle crushes the wood fibers and pushes them out of the way, producing no tearout on difficult grain such as birdseye or curly maple, but the surface left on the wood is not quite as good as that left by a blade with a larger rake angle, due to the crushed fibers.
The clearance angle of the blade allows the heel of the bevel to clear the wood surface without rubbing or crushing the wood.
As a blade dulls, the rounded-over cutting edge produces a negative clearance angle immediately behind the (dull) point and a small or negative rake angle at the cutting edge. This greatly increases cutting friction as the blade is crushing the wood in front of it as it cuts, and crushing the wood it leaves behind as well.
For more information on sharpening, see How to Sharpen Stuff.
Cutting Action of a Smoothing Plane
As the wood fibers are wedged apart by the blade, they may have a tendency to split apart slightly ahead of the blade. If the grain runs parallel to or up out of the surface of the board, this is not a problem, as the splits will run up into the waste wood and be removed. If the grain runs down into the board, then the plane is cutting against the grain and large chips of wood will be split off leaving pockets of torn grain on the surface of the board. This is most easily avoided by always planing with the grain, however this is not always possible.
In order to minimize tearout when planing against the grain, modern smoothing planes have several features designed to break off the wood chips before the splits extend far into the board and leave a torn surface. The first of these is the chip breaker, which is clamped to the back of the blade about 1/32" to 1/16" behind the cutting edge. The second feature is the front of the throat opening. The frog of the plane is adjusted to make the throat as small as possible without causing chips to clog the opening. This way, the largest chip that can be torn out must be smaller than the throat opening.
With a sharp blade and properly set frog and chip breaker, a plane can take a shaving as thin as 2/1,000", about the thickness of a human hair, and leave only microscopic tearout.
An additional way to reduce tearout on difficult grain is to use a plane with a steeper bedding angle (angle between the blade and sole of the plane). This produces a smaller rake angle and its associated benefits as described in the cutter geometry section above. Some planes are available with 50° to 60° bedding angles for use on difficult hardwoods like curly maple and mahogany.
Tuning Up a Hand Plane
First, in order for a plane to truly flatten a board, the plane's sole must be absolutely flat. There are a few ways to be certain of this, the simplest one being to tape a sheet of sandpaper to a thick piece of plate glass, then lap the sole of the plane until the scratch pattern left by the sandpaper covers the entire surface of the sole. It is important to note that the plane must be configured as if it were planing wood, except with the blade retracted into the sole, in order to allow for any warping of the plane body that may occur when the blade is locked into position. 280 or 320 grit sandpaper used with a cutting lubricant such as oil or water (if the sandpaper is waterproof) gives the best balance between fast cutting and a smooth surface, finishing up with 400 grit.
Next, the back of the blade and the bevel of the chip breaker must be dead flat to prevent chips from lodging between them. Note that the chip breaker flexes when it is clamped to the blade, so the bevel must be lapped near the edge of the glass with the body of the chip breaker overhanging the edge, and tilted below the surface. This allows the heel of the chip breaker's bevel to clear the back of the blade, keeping the front edge tightly pressed against the blade. Finally, the blade must be sharpened and polished, to give a razor sharp edge. Plane irons are usually sharpened with a 30° to 40° bevel.
The chip breaker is mounted to the back of the blade, with its edge 1/16" to 1/32" behind the cutting edge. Be careful not to let it slip over the cutting edge of the blade, as this would dull the blade. The distance between the chip breaker and the edge of the blade is related to the maximum thickness of shaving to be taken, with a closer setting being used for very fine work, especially on difficult grain.
Unless you are using a plane with from-the-rear frog adjustment, loosen the frog screws now so they are just slightly snug, but will still allow the frog to move if lightly tapped with a small hammer. Clamp the blade into the plane body, and use the frog adjustment screw or a small hammer to adjust the frog until the throat opening is 1/32" to 3/32". Once again, a closer setting is used for finer work. Firmly tighten the frog screws.
Now it is time to make the lateral adjustment to the blade. Advance the blade until it is just barely visible as a dark line when sighting down the sole of the plane. Move the lateral adjustment lever or tap the side near the top of the blade lightly with a hammer to square it to the sole. The blade should produce an even thickness shaving across its width. Retract the blade just inside the body of the plane.
Last, take "dry run" passes across a fairly flat board, advancing the blade slightly after each pass, until the shavings are the desired thickness. Your hand plane is now ready to flatten and smooth most any board out there. A similar procedure can be used to tune up a block plane.
Also, see Bench Planes for additional info. and tips on use.
Sharpening Chisels and Marking Tools
The purpose of this class is to teach the proper care and use of hand tools, so this discussion of sharpening will be limited to the techniques specific to the tools to be sharpened.
Chisels are usually sharpened at an angle between 20° and 30°. A 20° angle is used when cutting softer woods, such as pine, basswood, or poplar. A 30° bevel is best for hard or abrasive woods like rosewood and teak, or hard pieces of oak or maple. It is important when sharpening chisels to hone the back of the blade absolutely flat, and not bevel it. If the back of the chisel is not flat, it will be very difficult to cut joinery accurately. One additional item, which can make your chisels more convenient, is to put flats on any round handles, so the tool won't roll off the bench.
Marking knives are sharpened to 25°, and the back is honed flat. The blade for a standard marking gauge is sharpened in the same manner.
Cutting Action of a Scraper
If a smoothing plane were set with its chip breaker about 5/1,000" from the cutting edge, its cutting action would be roughly similar to that of a scraper. In fact, shavings from a sharp scraper look like plane shavings, only the wood is crushed.
A scraper is simply a piece of steel with one edge mushroomed over to form a sharp hook or burr. As the burr cuts the wood, the shaving is crushed and any chips are broken by the body of the scraper, preventing chips from being wedged out of the wood surface.
How to Sharpen a Scraper
The tools for producing a sharp scraper are few and simple: a mill smooth file, a burnisher, and of course, a scraper blade. A burnisher is a piece of steel much harder than the scraper that has a smooth surface without sharp corners. A scraper in its simplest form is a piece of saw steel with one edge filed flat. Thus, a scraper can be made from old saw blades or putty knives, and a burnisher from an old file or drill bit; however, commercially available scrapers and burnishers have the advantages of better quality and consistency of steel, and are designed for greater comfort in use.
To sharpen a scraper, first any remnants of the old burr must be removed. The faces of the scraper are lapped on a fine sharpening stone or file (I use the file because it's quicker, but the stone produces a smoother surface). Next, the scraper is held edge up in a vise, and its edges are filed at 90° to the faces (they could be touched up on the stone after filing for an extra smooth surface). The final step in sharpening a scraper is burnishing. The burnisher is rubbed along the edge initially at 90° to the face of the scraper, then at a gradually increasing angle until it is about 2° to 15° from horizontal.
What angle to burnish to is up to the user. Burnishing to 15° gives a very aggressive scraper that cuts best when held at a low angle to the wood. Burnishing to 2° yields a scraper that cuts less aggressively, but can be held nearly perpendicular to the wood.
For more about different types of scraping tools and their different uses, see Scraping Tools.
Tips on Building a Small Bench with Hand Tools
Remember when planing the boards to plane diagonally to the grain in order to ensure that any cup or twist is removed, then take a few smoothing passes to leave a smooth, even surface. After planing, it is a good idea to take one pass down the corners of the board to knock off the sharp edges, thus preventing cuts.
When making the saw cuts for the joints, remember that it is much easier to saw just outside the line, then trim to the line with a chisel than it is to put wood back on the board after over-cutting with the saw.
The shoulder cuts on C must be the first joint cut, as they determine the spacing of the legs. The dados for the legs are laid out from C, and the rabbet on B is trimmed to fit its dado. The notches for C are marked on the outside face of B; otherwise, it is difficult to accurately mark their depth.
The half-dovetails are laid out after all other joints have been cut. First cut the half-tail on one end of both stretchers (part D), and use them to mark their mating notches. After cutting the notches for one end of both stretchers, assemble the bench, set the ends of D into their notches and pull the legs towards each other and mark the length of D to the inside of B. This marks for the shoulder cuts on D and ensures that when D are installed, they will lock all the joints firmly and prevent the bench from wobbling.
When doing the final smoothing, try not to change the wood's thickness around the joints significantly as this would result in loose joints.
Don't forget to chamfer the top and feet, and knock off all sharp corners after the bench is assembled.
Your newly finished bench can be finished with oil or shellac for a natural look. The bench in the photos was finished with a thinned coat of golden oak stain, then oiled and finally waxed with a paste mixture of linseed oil and beeswax. This gives a low luster, aged look to the bench.
©2001 David J Tilson