Wood processing techniques

Swallowtail joint, typical of old wooden houses and churches

I have written several times about wood jointswith a focus on those in traditional Japanese carpentry which I admit I'm fascinated by. Each time, the comments appreciated those joints, but also recalled the craftsmanship of the Romanian folk craftsmen who built houses and churches out of wood using the dovetail joint, constructions that have resisted time and the passage of time, remaining standing. Being a beautiful and durable joint I will elaborate a little on the subject.

swallowtail
Stolniceni Prăjescu wooden church built in 1733

The dovetail joint is a corner joint that is not only used on houses. It has been used throughout history in furniture construction, for example in cabinet or drawer joints. It has very high tensile strength, which explains its preference for joining drawer fronts.

There are several ways to make the cuts and joints, and it is also a way to identify the period to which the piece of furniture belongs. In all these joints, the wood is cut at the ends in a trapezoidal shape, and the 'teeth' thus formed interlock to form a very durable joint.

Several such teeth are made at the ends of the pieces to be joined, cutting at various angles. The teeth may be joined with or without glue, but nails or screws are never used. The joint holds together very well without glue.

There are several types of swallowtail joints:

  • the actual splice - after the pieces of wood have been spliced the ends of the fibre are visible on both sides of the splice;
swallowtail
photo source: technologystudent.com
  • half swallowtail joint (half stock) - the cutting of the teeth is done in such a way that after the joint the fibre ends are only visible on one side of the joint;
swallowtail
photo source: technologystudent.com
  • groove joint (sliding) - a trapezoidal groove is cut in one piece of wood and the other piece has a trapezoidal tooth at the end. The joint is made by sliding (translating) the tooth from one end of the groove to the other.
swallowtail
photo source: wikipedia.org

Joining drawer fronts is often done using the second method to stay hidden.

swallowtail
photo source: popularmechanics.com

As the swallowtail is an aesthetic joint, which if done well adds value to the object, there are also craftsmen who choose to make the joint normal, visible on both sides.

swallowtail
photo source: byhyu.com

In the past, all these wood cuttings were done by hand, with great precision, so that the wood joints were perfect. After being drawn, the cut was made with a saw and the fine workings with a chisel.

swallowtail
photo source: craftsy.com

There are now milling cutters (routers) with which cuttings can be easily made, and at industrial level they are made with great precision using CNCs. However, classic craftsmen, who go for the traditional version, continue to make the joints by hand, and the objects are very much appreciated by the followers of traditional works.

Finger-jointing is the way logs/bark/wood joinery is done for wooden houses. Specific to our country are log houses with a rectangular or square section, as can be seen in the old houses of Maramures or wooden churches all over the country. Our older friends may remember church in Leleasca, which I wrote about after a visit to the area. I have seen such joints in wooden churches all over the country, so I can't say that they are specific to a certain area.

swallowtail
Church of Leleasca - corner joint

The combination of rectangular or square section cabinets is practically the most sturdy, the strongest option for wooden houses. It has tensile strength and is highly mobile in case of an earthquake. It is much safer than round logs. Basically, our ancestors found the most efficient system for making strong and safe houses.

The way it is done is the same as for furniture joints, except that it is done at macro level. The shape of the cut-out is also trapezoidal, imitating a swallowtail. In the past, the pattern was carved with an axe, so you can see how skilled craftsmen were at making perfect cabinet joints by making the cuts with an axe alone. Now they use chainsaws and templates to make the joints as accurately and quickly as possible. In the case of industrial machining, CNC is also used.

I didn't set out to write about making the dovetail joint. I'm certainly not the one to tell you about cutting angles and dimensions, as many of you are specialists with years of experience behind you. It is, however, a joint close to our hearts, a joint with which we have begun to identify. It is a calling card of the old craftsmen makers of houses and churches who have stood the test of time, bringing proof of their skill to the present day. It is a kind of gratitude to a long and ancient line of woodcarvers.

About the author

Mihaela Radu

Mihaela Radu is a chemical engineer but has a great passion for wood. She has been working in the field for more than 20 years, wood finishing being what defined her during this period. She gained experience working in a research institute, in her own company, as well as in a multinational. She wants to continuously share her experience with those who have the same passion - and more.

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  • There is a difference between the dovetail joint used in furniture and that used in houses. The furniture joint has tails on one side and pins on the other. It can only take traction in one direction, the other direction is used for joining. The houses have tails in both directions, thus resisting traction in both directions, but the joint is assembled by overlapping the beams alternately. Once overlapped, the joint cannot be untightened by pulling.
    Compare the corner of the house (teeth are trapezoid-shaped on both sides) with the corner of the drawer (teeth are trapezoid-shaped on one side and rectangular on the other).

  • We built a house made of wooden beams, shaped, treated, numbered and joined in circular rows one after the other in a dovetail system, ground floor and first floor on a foundation of 3.20 m with 22 pillars and three rows of 16mm reinforced concrete beams and 8mm braces, calculated according to engineers to withstand an earthquake of degree 9 on Rihter. We left it for 3 years in the initial phase, we treated it fireproof, antifungal inside and outside for three years, then we wrapped it outside with dense fireproof pilistiren of 10 cm, and inside with mineral wool and fireproof plasterboard. It has a great thermal, acoustic and electromagnetic insulation (we used autoclaved aluminium foil on the roof, and inside mineral wool with aluminium). I am at your disposal with details.

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