A twybil is a hand tool used for
green woodworking
Green woodworking is a form of wood craft or in broad terms, carpentry
Carpentry is a skilled trade and a craft in which the primary work performed is the cutting, shaping and installation of building materials during the construction o ...
.
It is used for chopping out
mortises when
timber framing
Timber framing (german: Holzfachwerk) and "post-and-beam" construction are traditional methods of building with heavy timbers, creating structures using squared-off and carefully fitted and joined timbers with joints secured by large wooden ...
, or making smaller pieces such as
gates.
It combines chopping and levering functions in a single tool.
The appearance of a twybil is that of a T-shaped double-edged
axe
An axe ( sometimes ax in American English; see spelling differences) is an implement that has been used for millennia to shape, split and cut wood, to harvest timber, as a weapon, and as a ceremonial or heraldic symbol. The axe has ma ...
with unusually long blades and a very short handle. This appearance is deceptive, as they are actually derived from a large double-ended
chisel with a side handle added for better control. The geometry of a twybil, particularly the long straight blades, makes it unworkable as an axe. Unfortunately many old examples have been damaged by such misuse. The related
mortising axe is similar, but single-sided and is forged and tempered to survive the shock loads of swinging as an axe.
Twybils always have two working ends and these are always different. The first is an axe-like blade, with the edge arranged parallel to the handle. The second edge is crossways, as for an
adze
An adze (; alternative spelling: adz) is an ancient and versatile cutting tool similar to an axe but with the cutting edge perpendicular to the handle rather than parallel. Adzes have been used since the Stone Age. They are used for smoothing ...
. This is used for prying and levering rather than cutting.
Use
The correct use of a twybil is highly specialized, that of rapidly clearing out
mortises. Mortises are rectangular holes used to take a
tenon for several forms of
joint
A joint or articulation (or articular surface) is the connection made between bones, ossicles, or other hard structures in the body which link an animal's skeletal system into a functional whole.Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw- ...
, most obviously the common
mortise and tenon joint. Mortises are always cut so that their long axis is along the
grain of the wood. Traditionally these were first cut by drilling with a
brace and bit to mark out each end, then the twybil used to break out the wood between them. The axe edge is used to split the intervening timber away from the sides of the mortise, then the other end to lever out the split block.
Their short handle allows them to be easily flipped end-for-end, making for quick working as each blade is used alternately. This is quicker to use than swapping between a chisel and a separate lever, safer than using a carefully sharpened chisel edge for levering.
Naming
The twybil has a variety of spellings and is sometimes termed the twyvil,
twilbil.
twivil,
trybill,
two-bill
or even dader.
In French, piochon. In Flemish and French-speaking Northern countries, they are known as bisaiguë.
Their name may originate from a root of "twy-" for "two", indicating their double-ended nature, and "-bill", a common description for edged tools (e.g. "
billhook
A billhook or bill hook, also called a pruning knife or spar hook, is a versatile cutting tool used widely in agriculture and forestry for cutting woody material such as shrubs, small trees and branches. It is distinct from the sickle. It was ...
").
The Oxford Dictionaries, however, define the spelling as twibill, from the Old English, twibile. Sloane
distinguishes the two names with twibil as the larger straight-bladed form and twivel as the shorter, single-handed curved form.
Construction
Twybils are made in a range of sizes, depending on the size of the work they're intended for. The length of the side handle remains roughly constant at around a hand's span and so their proportions change. A small one intended for making
hurdle
A hurdle (UK English, limited US English) is a moveable section of light fence. In the United States, terms such as "panel", "pipe panel" or simply "fence section" are used to describe moveable sections of fencing intended for agricultural us ...
s
[ Abbott, Green woodwork, p. 188] may have three arms of approximately equal length, a large framing twybil may be three feet long and yet still have the same handle.
Diderot's ''
Encyclopédie
''Encyclopédie, ou dictionnaire raisonné des sciences, des arts et des métiers'' (English: ''Encyclopedia, or a Systematic Dictionary of the Sciences, Arts, and Crafts''), better known as ''Encyclopédie'', was a general encyclopedia publis ...
'' of the 18th century shows a bisaiguë in use for paring end grain of a large joint, much as a modern slick chisel, which is long enough to rest on the carpenter's shoulder.
The shape of the working edges varies with size and purpose. Large twybils have short straight edges for splitting, like an axe or
tomahawk
A tomahawk is a type of single-handed axe used by the many Indigenous peoples and nations of North America. It traditionally resembles a hatchet with a straight shaft. In pre-colonial times the head was made of stone, bone, or antler, and Eur ...
. Small ones have a more curved edge, curving back beneath to a shape that is more like a short knife or
oyster knife, another tool used with a similar splitting and prying action. Both styles are forged and sharpened symmetrically. The levering end is asymmetrical, with a single bevel as for a
chisel. Large framing twybils are straight, with this bevel on the outside. Small ones are curved or hooked,
with the bevel inside.
Most surviving examples are old enough that they are
forged
Forging is a manufacturing process involving the shaping of metal using localized compressive forces. The blows are delivered with a hammer (often a power hammer) or a die. Forging is often classified according to the temperature at which it ...
from
iron
Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...
rather than steel, with hard steel edges
welded
Welding is a fabrication process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool, causing fusion. Welding is distinct from lower temperature techniques such as braz ...
to them. Modern examples may be wholly of steel, frequently recycled truck
leaf spring
A leaf spring is a simple form of spring commonly used for the suspension in wheeled vehicles. Originally called a ''laminated'' or ''carriage spring'', and sometimes referred to as a semi-elliptical spring, elliptical spring, or cart spring, i ...
s. A socket is forged on the side for the handle, this being a short wooden handle, often made to the user's own preference. Twybils are rare today, even amongst the recreators of specialist
green woodworking tools
Green is the color between cyan and yellow on the visible spectrum. It is evoked by light which has a dominant wavelength of roughly 495570 nm. In subtractive color systems, used in painting and color printing, it is created by a combina ...
. As such, good usable examples may command high prices.
Ashley Iles is one of the few bulk production manufacturers to offer one.
Other related tools
The
mortise chisel, even in its heavyweight "pigsticker" form, is used differently from a twybill, although the two may be used together. The twybill cuts the ''sides'' of mortices, ''along'' the grain. Its action is a splitting and prying one, so only requires a handle for leverage and is never struck. Mortise chisels are used for heavy chopping ''across'' the grain, are nearly always struck, and are used to square up the ends of square-ended mortises. Both tools are used for levering out chunks when first clearing out a mortise and so have similarly shaped
bevels, often with a curved bevel surface for a better
fulcrum
A fulcrum is the support about which a lever pivots.
Fulcrum may also refer to:
Companies and organizations
* Fulcrum (Anglican think tank), a Church of England think tank
* Fulcrum Press, a British publisher of poetry
* Fulcrum Wheels, a bicy ...
action.
Slicks are other specialised chisels also used to work on the sides of mortises, but are used for final clean-up to make an accurate and smooth-sided mortise, ''after'' the rough chopping has been carried out.
In the heyday of the twybil, mortises in small work were often round-ended and so could be cut very quickly by brace and twybil alone, the tenon being rounded to fit.
[ Edlin, Woodland crafts, ''The curious break and tools used to form mortises in gate hurdles'', figures 99 & 100, facing p. 100] Only large, or high-quality work required the square ends and smoothed sides of a precise mortise, trimmed by this variety of chisels.
The apprentice will often use all three mortising tools interchangeably and randomly, making much effort of removing the waste as small chips. The skilled framer uses each appropriately in turn, working faster, with less effort and not bothering to tear a large block of waste into fragments. They are also less likely to damage a precise edge by levering with a sharp, brittle chisel edge.
References
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Green woodworking tools
Woodworking chisels
Woodworking hand tools
Axes