Carpentry construction products and elements must be hygienic, beautiful and comfortable when using them; they can be divided into frame, plate, frame-plate with rectilinear and curvilinear shape.
Under the influence of temperature and humidity, wood can change its dimensions within quite large limits. For example, when drying from the limit of hygroscopicity (moisture) to a completely dry state, depending on the species, the wood changes its dimensions along the fibers by 0,1 to 0,3%, in the radial direction by 3 to 6% and in the tangential direction by 6 to 10%. Thus, during the year, the humidity of external beech doors changes from 10 to 26%. This means that each board in that door, which is 100 mm wide, increases its dimensions by 5,8 mm when it gets wet and shrinks by the same amount when it gets airy. In this case, cracks appear between the boards. This can be avoided if the carpentry products are constructed in such a way that the inevitable changes of individual parts of the product are carried out freely, without disturbing the form of strength. So, for example, when making a door with an insert, this insert, which is inserted into the grooves of the vertical friezes of the frame, should have a gap of 2 to 3 mm, but so that when it is completely dry, it still does not come out of the groove (fig. 1).
Figure 1: Cross-section of a door with an insert
Carpentry products should be made of narrow solid or glued slats (board door frames, carpentry boards, etc.).
Carpentry construction elements do not suffer from higher static or dynamic stresses during their exploitation. And yet, when constructing these products, care should be taken that the voltage direction coincides with the direction of the wood fibers, or that it slightly deviates from it. Otherwise, the strength of the element can be significantly reduced.
The elements of carpentry construction products in the direction or at an angle are connected to each other using plugs and notches - splines, using glue, screws, metal tape and externals.
Most often, the elements are connected using plugs and notches. The strength of the connection of the elements to the plug and mortise depends on the humidity of the material and the accuracy of the plug and mortise.
Most carpentry building elements are connected with a single or double plug that has a flat or round shape. However, when making doors, round wedges are widely used - dowels for connecting vertical and horizontal elements, door frames with inserts, etc. These connections do not reduce the strength of the product, and provide 17% wood savings compared to other methods.
When making doors, built-in room furniture, elevator cabins, etc. the fronts of the boards and billets are attached to a double plug, with a plug and a notch and with a plug and a notch with a tooth. In these cases, the boards and slats are connected with flat round plugs and notches or inserted wooden pegs (fig. 2, 3, 4)
Figure 2: Glued door elements covered with veneer
Figure 3: Details of plank connections
Figure 4: The connection of the vertical and horizontal parts of the door with inserted round pins
In order for the product to be solid and to have sufficient rigidity, there must be a certain relationship between the dimensions of the plug and the elements. The following dimension ratios are recommended: the width of the heart must be equal to half the width of the element in which the groove is; the length of the plug should be equal to the entire width of the billet or board minus the shoulders of the connection; the thickness of the real plug is made from 1/3 to 1/7. and the thickness of the double plug from 1/3 to 2/9 of the thickness of the element; shoulder size from 1/3 to 2/7 for the first plug and from 1/5 to 1/6 of the element thickness for the double plug; the width of the notch for the double plug should be equal to the thickness of the plug itself.
There are different types of connections. The most important of them are given in Figure 5.
Figure 5: Different types of carpentry connections
In practice, plates are mostly bonded with a drug on the contact sides, on the tongue and groove with the brain. When the joists are connected across the width with glue, the connecting sides of the joists must be smoothly drilled, quickly assembled into boards clamped with wedges. Glued boards should be planed on both sides on a double-sided planer, in order to remove unevenness created during gluing.
Tongue and groove can be rectangular, triangular, semi-circular, oval or dovetail. This method is most often applied when making door frames, parquet, vertical and horizontal elements for doors from waste on special machines - automatic joining machines and requires a large consumption of wood, and therefore should be applied only in case of extreme need.
The connection with the chipboard is used in the production of parquet floors. The brain is made of soft wood. Window and door elements, built-in home furniture, elevator cabins, etc. are fastened with screws. Before they are turned, the screws should be greased with stearin, graphite dissolved in vegetable oil, similar grease.
In the places where the screws will come, holes should be drilled, the depth of which is approximately equal to twice the depth of the thread. If, on the other hand, it is necessary to connect two elements of greater thickness, then a hole equal to the diameter of the screw is drilled.
Connections using iron fasteners (fig. 6) are not used much in practice, but they can be used for connecting vertical elements with horizontal ones, for filler doors and doors with infill.
Figure 6: Connections using iron fasteners
Connections using nails are not used for connecting carpentry elements. Wooden wedges are used in the manufacture of windows, doors and other carpentry construction products, then for additional binding of elements at the points of their connection and to prevent deformation of various frames during their exploitation.
A characteristic feature of carpentry connections using plugs is that they can only be made with the use of glue. These connections must not be made without gluing. Elements that are glued together must remain tight in the clamp for at least 6 hours under a pressure of 2 to 12 kg/cm2,
Massive elements of carpentry products can be assembled by gluing smaller elements from one type of wood, as well as by combining noble species and ordinary wood. Vertical and horizontal elements of windows, doors, boxes and other products can be made of glued coniferous wood, covered with oak planks 8 - 10 mm thick (fig. 7). It is preferable to glue the elements and cover them with wood using phenol-formaldehyde glues that are stable in water.
Figure 7: Glued window and door elements, covered with hardwood tiles
Assembling frame structures and frame structures with plates is done using mechanical, hydraulic or pneumatic clamps.
