The seat frame of the sofa is the main bearing structure, and the back frame is the main comfort support structure, so for the sofa, it is necessary to deal with the craftsmanship of the seat frame and the back frame to ensure the quality.

This article provides the common process of sofa seat frame and back frame, and the relevant data is for learning and reference only.

01 What are the structures of the sofa seat frame and back frame

The wooden seat frame and back frame are enclosed by four wooden squares to form a rectangular and hollow shape. Since the geometric stability of the rectangle is not ideal, it is usually necessary to add a triangular wooden plug angle reinforcement on the inside of the four corners of the rectangle, and the plug angle is generally an isosceles right triangle, with a thickness of 30mm and a right angle side length of 60~100mm.

For multi-seat sofas, due to the large span of the two wooden timbers in front and behind the seat frame, in order to reduce the deflection and deformation variables of the wooden timber, it is usually necessary to add longitudinal wooden strips (or plywood slats) on the lower side of the seat frame to pull and reinforce.

Part of the seat frame

The wooden bar is usually located directly below the intersection of the adjacent two seats, which does not affect the sitting comfort, but also makes the overall structure of the wooden frame properly dense and the force relatively uniform. At the same time, the wooden strip is positioned about 150mm below the spring-bandage elastic surface of the seat frame to ensure the elastic movement space of auxiliary materials (sponge, bandage, bow spring, etc.) on the seat frame and improve the sitting comfort.

Chaise sofa wooden frame

02 The nails of the sofa seat frame and the back frame are combined

There are usually four ways to connect wood: mortise joint, hardware joint, glue joint and nail joint, each of which has its own characteristics, and these four connection methods are common in the production of solid wood furniture.

Panel furniture is mainly hardware jointing, glue jointing, and some parts are supplemented by nail jointing. Generally speaking, nail jointing is basically not used and used less in principle, and it is also as inconspicuous as possible to play the role of connection, reinforcement mortise joint and glue joint.

Nails of the sofa frame combined

Upholstered furniture (sofa) is usually nailed as the main connection method, that is, the end face of the wood wood is close to the plywood board surface and nailing. This is because the gun nails are connected internally, without considering aesthetic factors, and the joint strength is guaranteed, saving processing steps, high production efficiency, etc.

Of course, a single gun nail has limited nail power, and by increasing the number of nails, the frame can be secured. In general, due to the high efficiency, the comprehensive cost of labor, equipment and process of frame processing is reduced, and the economic benefits are obvious.

03 Use of auxiliary materials in the seat frame and back frame

The addition of auxiliary materials mainly refers to the process of installing bow springs, rubber bands, etc. on rectangular seat frames and back frames, and covering plastic mesh or cotton felt on the elastic surface of bow springs and rubber bands.

The seat frame is generally a bow spring, rubber band cross combination to form an elastic surface, some enterprises use bow spring, metal bar cross combination, and some are three materials combined together. In addition, the edge usually adds stiffeners to make the elastic surface more elastic.

Bow springs, bandages crossed

Bow springs, metal bars crossed

03-1 Common specifications of seat frame parts

The bow spring buckle that holds the bow spring is hit 3 mm away from the inside of the wooden square. Bow springs and rubber bands are generally vertically nailed to the top of the seat frame, and the bow springs are nailed along the front and rear of the seat. Usually nailed bow springs first, and then nailed bandages, each bow spring spacing is 130 ~ 150mm.

Every rubber band and spring. Up and down interspersed, conducive to mutual position not to move, seat rubber is 75mm wide, spacing is 110 ~ 130mm. Each rubber band must have a uniform tensile force, and the inner space is 500mm, and the elongation is 170mm as the standard (elongation rate ≥30%). Each rubber band is hit with two rows of gun nails at 45°, each row is 5~6 gun nails, and the excess rubber band is cut flat with a blade on the outside of the wooden frame.

Plastic mesh (or cotton felt) along the wood, the upper surface is fixed, every 60~70mm to hit a gun nail. The bow spring shape arch, like the stone arch bridge form, the middle bulge is 20~30mm, which is conducive to supporting the load (human body) when there is a better rebound space, and the force can be better distributed.

03-2 Common specifications of back frame parts

Because the force on the back frame is relatively small, it is mainly a rubber band cross structure, and the rubber band and bow spring cross are less. The backrest rubber band is 50mm wide, and the rubber spacing is also appropriately increased. The plastic mesh is not completely covered here to ensure good rebound space for the backrest and provide full comfort.

Back frame

04 Common quality issues with seat and back frames

04-1 Beam position

The picture below shows the seat frame of a two-seated sofa produced by a sofa company. This seat frame adds a wooden square (middle position) below the spring-bandage elastic surface and across the seat, but since the wooden square is close to the spring-bandage elastic surface, the elastic surface has no room to descend, reducing product comfort, and it is recommended to cancel the wooden square.

The beam is in the wrong position

04-2 Materials and density

The picture below is the effect of a sofa interior frame on the market. It can be said to be unsightly, but it does exist in life. For example, some sofas have a very poor sitting feeling, no very poor, no elasticity at all, mainly because the thickness of soft materials, rebound, etc. are not enough.

In addition to soft materials, the thin plywood, low density of wood in between, and weak elasticity of bandages are serious problems.

The material and density are not suitable

04-3 Wood treatment is not in place

Wood lumber containing bark, wood drying is not in place, wood defects are not avoided in place, etc., will affect the quality. The figure below shows that wood contains bark, which is prone to insects during use. As for some wood drying is not in place, even the touch of hands has a sticky feeling, it is easy to produce decay, pests and other defects; Wood defect avoidance is mainly to ensure mechanical strength requirements.

The wood contains bark