For this tool focus, we’ll look at the parts of traditional bevel-down bench planes and how they are adjusted. In the photo above, you can see the most obvious parts: the rear handle, or tote; the front knob; the cutter or iron and cap iron; and the iron body of the plane.
For bench planes used to flatten, true, and smooth lumber, the bottom or sole of the plane needs to be as flat as possible and square relative to the sides. Planes used only for removing stock and making a board roughly flat don’t have to be quite as flat. The reason is that to flatten a surface, a plane depends on the front – or toe – and the back – or heel – of the plane to help limit the depth of cut. If a plane’s sole bows out in a convex curve, the results would be very unpredictable because they would vary with the pressure placed on either the toe or heel of the plane. If it is bowed inward in a concave curve, the toe and heel would make contact with the surface, but the iron would not cut the wood. A plane can only create a surface as flat as its sole.
The iron assembly is made up of two parts, the iron itself and a chip breaker. The iron is the part that actually cut the wood. A plane iron actually pries a chip of wood from the surface as much as it shaves of a layer. The sole of the plane in front of the mouth (the opening the iron sticks through to meet the wood) helps to keep the wood from splitting uncontrollably. The chip breaker helps to control this splitting by breaking the fibers of the wood so the wood already cut is not strong enough to pry up even more material. The chip breaker attaches to the iron using a screw that passes through a slot in the iron and into the chip breaker.
The cap iron holds the iron securely to the body of the plane.
The part of the plane body that holds the iron is called the frog. The top surface, or bed should be as flat as possible and make full contact with the iron to reduce chatter when the plane is being used. The frog includes the lateral adjustment lever (the part that looks like a tail sticking up in the photo above) and the iron depth adjustment knob (the brass knob that can be seen at the lower rear portion of the frog. The screw on the top of the frog is used to adjust the pressure the cap iron places on blade.
The lateral adjuster is used to adjust the amount of the iron that is exposed on the left and right side of the plane. It is used to make sure that neither side of the plane iron extends further than the other. The depth adjustment knob is used to control the depth of cut. It makes more or less of the iron extend through the mouth of the plane.
On most planes, the opening of the mouth of the plane can be adjusted by using the frog adjustment screw (the brass screw shown in the photo above.) To adjust the position of the frog, two screws (which fit into the two empty holes in the photo above) are loosened and then the frog adjustment screw is used to move the frog forward or backward. Once it is in the desired position, the two screws are re-tightened.
That covers the components of a traditional bevel-down plane. Now let’s move on to how the adjustments are made in use.
When using a plane for rough stock removal, the chip breaker is set so that a significant portion of the iron extends past the chip breaker (between 1/8″ and 1/4″), the frog is moved backward to allow larger chips of wood pass through the mouth, and the depth of cut is adjusted for a deeper cut.
For flattening, truing a surface, the chip breaker should be about 1/8″ from the cutting edge of the iron, the frog should be adjusted so that about half the mouth of the plane is open for chips, and the depth of cut should be adjusted to take a progressively finer cut. The depth of cut starts out fairly aggressive and as the surface becomes flatter, the depth of cut is set finer and finer until the surface is as flat as desired (or as flat as the sole of the plane).
For smoothing the surface of board, the chip breaker is set with around a hundredth of an inch or so of the iron exposed, the frog is moved forward so the plane can only take a very thin shaving, and the depth of cut is adjusted to only a few thousandths of an inch. This fine setting makes the chips as week as possible which helps to prevent tear-out.
This post has been a long one. Next time, I will look at the components and use of bevel-up or low-angle bench planes. Until then…