Solid wood furniture production in China factories contains 4 major steps and a total of 44 small steps:
|1. Raw material preparation
|1.1. Board drying
|1.3. Material selection and matching
|1.4. Thickness setting
|1.5. Width setting
|1.6. Length setting
|1.7. Board matching
|1.8. Glue spreading
|1.9. Board splicing
|1.10. Glue Solidifying
|1.11. Planing and sanding
|1.12. Four-sided planing and shaping
|2.1. Thickness setting by broadband planing
|2.2. Fine Cutting
|2.5. Tenon making
|2.6. Sanded parts inspecting
|2.7. Components assembling
|2.8. Final substrates fully assembling.
|2.9. Sand inspection of the fully assembled white body(substrate).
|2.11. Sand inspection before painting
|2.12. Dust blowing off
|3.1. Color rubbing
|3.2. Background coloring
|3.3. First priming
|3.5. Light Sanding
|3.6. Second priming
|3.8. Light sanding
|3.9. Third priming
|3.11. Light sanding
|3.12. Color correcting
|3.13. Paint polishing
|3.14. Top coating
|4. Assembling and packaging
|4.2. Flaws repairing
|4.3. Dust blowing off
Yet panel furniture production is much simpler. It consists of only 3 steps: cutting, edge banding, and slotting/punching.
The five main steps of solid wood are even more complicated than panel furniture.
In terms of output, solid wood furniture in 5 workshops is not as high as panel furniture in 1 workshop.
Therefore, solid wood furniture is not cheap.
1. Raw material preparation
When preparing raw materials, we must select suitable wood. The standard solid wood square required for production is 3-6cm thick.
Yet these solid wood squares fail to meet production requirements. We need to splice them.
Some may ask: “Why don’t you buy a large piece of solid wood? It’s too much trouble to buy small pieces of wood and splice them”.
It is because large pieces of wood are not easy to dry and probably deform. We will need to split them to drop the residual stress to avoid deforming.
The firmness of the splicing solid wood is far greater than the solid wood itself.
Now let’s take a closer look at the raw material preparation process.
1.1. Board drying
We usually control the moisture content of the wood at 8%-10%. The dried lumber at such moisture content will crack less and deform less.
The wood will absorb moisture during storage, increasing moisture content. So we put the solid wood squares in the oven to dry before use.
We need to leave a gap between each layer of solid wood strips to increase air circulation.
The water vapor from the boiler outside the oven heats the air in the oven, thereby heating the wood squares. The wooden squares release the water due to heating.
Fans in the oven make the airflow, exchange the air inside and outside, and increase the drying speed.
Wood drying is a uniform process. It needs strict control of steam pressure and room temperature. If steam pressure and room temperature increase fast, the dehydration will be rapid. In this case, the wood surface will crack.
After heating for 120 hours, natural cooling needs 48 hours. This process loops.
The drying time of all the wood in the oven is 7 days. During the cooling process, the water continues to evaporate.
We usually use a professional moisture meter to test the moisture content.
Store the dried wood for a few days for moisture and internal stress balancing.
The wood can not be put into production immediately after drying. They must be placed in a dry shed for further moisture balancing with the environment.
At the same time, the internal stress of the wood is reduced and balances all over the wood.
The balancing will make wood shrink and swell less.
The balancing time depends closely on wood species, thickness, hardness, and drying requirements.
The balancing period should not be rigidly specified. It should be at least 15 days.
1.3. Material selection and matching
The wooden furniture includes external, internal, and hidden materials.
The exterior materials are visible from the outside, i.e., the door fronts and visible sides. The wood for these sides must be perfect, without scars, etc. The textures should be consistent.
The interior materials are invisible, such as inner rails, bottom panels, etc.
Hidden materials, such as drawer rails, cannot be seen under regular use.
1.4. Thickness setting
Usually, the imported wood is 2-3mm thicker than the written one. And domestic wood is just right, or 1mm thicker, or with a tolerance of ± 3mm.
It is easy to achieve a certain length and width but not a certain thickness.
The planing machine is only workable for uniform thickness. Thicker boards can not be pushed into the device, and thinner panels will make the blades run idly.
So the thickness of wood should be uniform with a tolerance of ± 0.5mm.
In this step, we deliver the boards from one side and then pull them out from the other side.
Before planing, the colors and flaws are invisible.
After double-sided planing, we can see one is whitish, and the other is reddish.
This step will expose flaws and imperfections in the wood. It is easier for us to deal with them later.
1.5. Width setting
We need to set the width after setting the thickness. The lumber was about 4/4 inch thick when we purchased it. Yet the width is not specified.
In addition, the edges of many sawn timbers are not straight, with many dull edges and defects. Even at the FAS level, about 17% of the surface can’t be used.
We use a linear saw to set the width.
If the wood surface has no significant flaws, we will only remove the irregular edges.
A lot of thin edges are left after the width setting.
The laser red line is the cutting position.
The flaws on the surface needs to be cut off.
Cut off the internal fissures, end split, scars, dead parts, and blue discoloration.
Because the moisture and carbohydrate (starch and monosaccharide) content exceed the standard, Cocococcus bisporus proliferates in wood tracheids or conduits.
The color-changing fungus invades the interior of the wood. The hyphae of the blue-staining fungus secrete colorants to dye the cell wall. Thus the wood stains blue.
Blue-staining bacteria proliferate in a suitable environment. It can turn the entire board blue in 2-3 days. If the woods are attacked by wind and rain, color bacteria invade the wood to make discoloration.
Blue stain is a general term for the discoloration of sapwood. In addition to blue, black, pink, green, etc.
Blue-stained wood is more prone to decay and less rigid, bending-resistant, and compression-resistant.
If we don’t deal with it, the bacteria may multiply into the heartwood. Thus wood usage is significantly reduced.
Because of the long cutting distance, width-setting will consume many saw blades.
We will replace the saw blades every half day if we cut hardwood like oak.
1.6. Length setting
Length setting has higher requirements than thickness and width setting.
There are 3 methods for length setting.
Method 1: Manual setting.
Measure the size first, then manually cut with a saw.
It is slow. But it is suitable to do some particular shape of furniture. With manual participation in the whole process, we can find problems at first time.
Method 2: automatic cutting according to the mark
It is workable for a large number of sawn timber that needs to be screened out. We mark the cut line manually. The machine will identify the line and cut it automatically.
Method 3: Automatically cut to length
The CNC automatic optimization saw can cut according to the mark and length. It is suitable for a large number of sawn timber with no need for screening.
1.7. Board matching
Before splicing, we will match texture, color, and width between the woods. Generally, a straight pattern matches a flame pattern.
Some people may prefer flame textures on all the visible sides.
But the flame texture is from plain cutting. It has naturally uneven stress.
If we splice all flame-textured woods, they will deform easily.
The width should also be sufficient to avoid waste.
After the color, size, and texture matching is correct, we will make a mark.
1.8. Glue spreading
We use white latex to bond the solid wood.
The main component of white latex is polyvinyl acetate.
In theory, it is possible to achieve formaldehyde-free bonding.
But there is still much inferior white latex in the market at a low cost.
We usually add the curing agent to the glue to increase performance and production efficiency. Thus the glue looks darker, as shown below.
1.9. Board splicing
Not all sawn timber needs to be spliced. For example, the bed end rail is a whole piece of wood.
But in most cases, we splice the wood to make large surfaces such as tabletops, cabinet doors, etc.
The width of the planed board is generally 40-80mm. If it is smaller, the usage rate will drop. If it is bigger, the board will be unstable. The width indicates whether a factory’s craftsmanship is excellent.
When splicing, the wood textures on the same side should face one direction. The fine grains should be spliced together. The flame grains should be joined together.
It is good splicing if we can make people ignore the seams or make them invisible.
And we should splice the same color together.
It is good splicing if the colors are consistent or have a natural transition.
Usually, splicing needs one man and one woman to work together.
The woman has the patience to spread the glue.
The man has a lot of force to do the pressing and locking.
Each splicing and pressing needs at least 2 hours.
It takes 2 hours for a circle of 20 groups to make a circle.
1.10. Glue Solidifying
Place the glued wood for about 2 hours to allow the glue to solidify.
1.11. Planing and sanding
For a strong bond, the glue is applied in excess.
So we need to do 1 planing and 2 sandings after splicing.
The rough sandings are with sandpaper 80# first and then 120#.
There is no glue on the surface anymore after planing and sanding.
Question: Why splice flame (mountain) texture and straight texture together?
Answer: it is to avoid the board to crack and deform.
The texture types have a lot to do with the sawing method.
We can get straight texture from quarter-sawn and flame texture from plain sawn.
In plain sawn, the end side has a complete annual ring. The slabs have more straight grains on the middle surface and more flame textures on the end surface.
Plain-sawn is probably not better than quarter-sawn. The densities on the two faces of the plain-sawn board are different. So it will be curved when shrinking or expanding.
If the deformation is large, it will crack along the wood rays.
In contrast, quarter sawn is more troublesome.
And it wastes more wood than plain sawn. Quarter-sawn only produces a straight texture.
The grain at the end is also straight instead of arc-shaped.
The straight grain is not popular with some people. But it is more stable, cracks, and deforms less than the flame texture.
This difference between plain sawn and quarter sawn is especially noticeable on oak.
The oak table will tend to deform and crack if it is made of all flame texture.
So the flame texture is not the best.
China’s solid wood factory is not cutting corners if they don’t use all mountain textures.
1.12. Four-sided planing and shaping
The wood surface is not flat after the width setting. So it needs four-sided planing to achieve a smooth and delicate effect. At the same time, complex shapes are built.
Store the wood for about 24 hours.
The assembly glue will be dry and fully integrated into the wood during that period.
The wood moisture will balance with the surroundings.
The wood will crack less and have less Scalability.
Furniture made of such wood can become a fine product.
Woodworking turns wood into products such as cabinets, tables, chairs, etc.
To make the solid wood into the desired shape, we need to further finely work on it with many tools.
For example, we can make nonstandard parts at the required length with a double-headed saw. We can make cylindrical parts with a lathe.
After the smaller parts are made, we must assemble them into larger pieces.
2.1. Thickness setting by broadband planing
Broadband sanding the boards to the required thickness and then polishing. Rough sand 0.2mm once and polish 0.1mm once.
2.2. Fine Cutting
Set the wood length according to the drawing. Ensure there are no crumbles or blackening. Ensure the tolerance of the length/width is ≤ 0.2mm, the diagonal line ≤1m is ≤0.5mm, and the one ≥1m is ≤ 1mm.
Shape the wood according to the drawings.
Ensure no crumble, burr, knife jumping, or blackening.
Ensure the surface is smooth and flat.
Before shaping, ensure the screws and knives are tightened, and the template is assembled correctly. Ensure the parts size tolerance is ≤0.2mm.
Drill holes according to the drawings. Ensure no chipping or burr. The hole size tolerance should be ≤0.2mm.
We need frequent trial installations and inspections to ensure product quality is good.
Most furniture is flat pack. We assemble the panels with hinges, cam-locks, bolts, plastic fitting fasteners, and screws. We need to drill holes for all the hardware with a row drilling machine.
A computer controls the row drilling machine to achieve high precision. If there is deviation, the parts will not match well with each other.
The spacing between the middle points of each drill bit is fixed. But we can set the size of the hole. So the designer should specify the hole positions strictly based on this spacing.
2.5. Tenon making
2.6. Sanded parts inspecting
The sanded parts should be flat and without sanding marks. The edges and corners should be consistent.
Before the inspection, we must notice where the parts will be used and sand them before filling the putty.
We usually place the sandpaper or sand cloth on a machine to increase the sanding speed.
The commonly used sanding wheels are mainly for various extremely uneven parts. The sanding machines are for small flat pieces. Sand beds are for bigger flat parts.
If the above machines can’t sand the special-shaped parts, we will hand sand with sandpaper.
We need to fill PE putty into the small pits before sanding. After drying for 40mins, The parts will be first sanded with 180# sandpaper, then #240 and #320.
Sanding with 320# sandpaper will not leave marks. Thus the products will be very smooth after painting.
2.7. Components assembling
Assemble components that do not need to be disassembled.
Before assembly, we must prepare the parts and ensure the sizes are according to the drawing. Ensure no chipping, burrs, or blackening.
We can start bulk assembling only if the first assembled part is consistent with the drawing.
During the assembly, we should spread the glue evenly. The assembled components should be free of nails protruding or nail-missing. The combination should be tight, and the glue should be wiped off.
2.8. Final substrates fully assembling.
Fully assemble the assembled components into a piece of the white body(substrate). Also, we need to ensure the first assembled sample size is consistent with the one in the drawing.
2.9. Sand inspection of the fully assembled white body(substrate).
Sand the fully assembled white body(substrate). Ensure the surface, and the joints are flat and without sand marks. Ensure the edges and corners are consistent.
Leave the fully assembled white body(substrate) in the warehouse for a period. Thus the internal stress balances all over itself. Also, the moisture inside will balance with the surroundings.
2.11. Sand inspection before painting
Re-sand the surface of the fully assembled white body(substrate). Mainly sand the capillary fibers off from the surface. Ensure the poor putty-filling, poor sanding, cracking, or deformation are removed.
2.12. Dust blowing off
Blow the dust off the surface of the fully assembled white body(substrate).
After blowing the dust off, we need paint on the furniture.
Painting can protect and beautify the furniture.
The paints for solid wood furniture include oil-based and water-based paint.
The specific steps of painting are as follows.
3.1. Color rubbing
Before painting, the wood base color needs to be harmonious and beautiful.
Color rubbing can help to achieve a good color and texture.
Before the bulk rubbing, it is necessary to do a trial to ensure the rubbing agent is appropriate.
We need to stir the rubbing agent evenly until there is no sediment. The rubbing brush must be clean, and the rubbing cloth must be non-fading.
The primary colors of natural wood are white and light yellow(except for some unique woods). The wood grain is very light, and it is unclear if we stand far away.
To show the wood texture well, we will formulate different glazes for different wood.
The glaze is a kind of pigment colorant from translucent to transparent.
It is composed of resin dissolved in a greasy solvent. It dries slowly and can be rubbed and brushed to look shaded and layered. It makes the color look soft and natural. It is commonly used in NC paint.
There are red, yellow, black, red-brown, and black-brown glazes.
The wood has a lot of dry conduits. The more conduits the wood has, the more glazes will be absorbed. The glazes will make the texture more visible.
We will bleach the dark parts for solid wood parts of inconsistent color before rubbing.
3.2. Background coloring
Select the required background color to adjust the color difference on the wood.
3.3. First priming
Before the first priming, blow the dust off and ensure the color rubbing is good. The first primer thickness is one cross in 16 seconds.
The crisscross “spray” can be significant even without thick stacking.
The primer is clear and mainly acts as a filler. It is sprayed on the product by hand with a spray gun.
Without priming, the conduits and screens on the wood will absorb the paint coating. So we must seal them with primer to avoid paint dents in the future.
We need three primers to seal the conduits fully. Sufficient sanding is required after each primer.
Ensure the primers do not hide the wood texture.
If the primer number or the drying time is insufficient, the topcoat will wrinkle two months later.
After spraying, let it dry for 6-8 hours.
3.5. Light Sanding
Fill all the scratches with putty first. Then lightly sand it with 320# sandpaper to remove the burrs.
We have different sandpaper ranging from 80#, 100#, 180#, 240#, 320# to 2000#. The higher the number, the finer the sandpaper.
3.6. Second priming
Before spraying, blow the dust off first. The 2nd primer thickness is one cross in 18 seconds.
After spraying, let it dry for 6-8 hours.
3.8. Light sanding
First, fill the defective areas with putty. Then sand it with 320# sandpaper until the surface is smooth, flat, and without large bright spots.
3.9. Third priming
Before spraying, blow the dust off first. The primer thickness is one cross in 16 seconds.
After spraying, let it dry for 6-8 hours.
3.11. Light sanding
Sand it with 400# sandpaper until the surface is smooth, flat, and without large bright spots.
3.12. Color correcting
Before correcting the color, ensure the product is good. Ensure the dust and pollutants are cleaned up.
The technicians configure the color and then make a color sample. Bulk color corrections are only allowed after the supervisor accepts the sample.
The primary color of the furniture is achieved during the process of color correction.
In color correction, we not only need to show the primary color of the furniture but also keep the texture clear.
The furniture factory formulates its color essence based on the paint factories.
The color of the furniture depends on the color essence and the amount of spraying. The more you spray, the darker the paint.
The worker sprays the color of the furniture with the spray gun. So color correction has high technical requirements for the operator. The air pressure, the spray gun muzzle’s size, and the spraying’s speed will affect the spray amount.
And these factors are very uncertain. It depends on the operator’s experience and feelings.
This is also why many solid wood pieces of furniture have a color difference.
3.13. Paint polishing
After color correction:
- Leave the products dried for 4-6 hours.
- Polish the surface with 800# sandpaper.
- During the polishing, ensure no polishing through and scratching.
Polishing after the painting is called paint polishing.
After sanding, there will be many fine wood fibers on the surface. They are soft, and the sandpaper can never get rid of them.
After the first priming, the wood fibers are hardened by absorbing the priming. Thus they can be easily removed with sandpaper.
Paint polishing can make the surface very smooth. It also leaves tiny polishing marks to increase the adhesion of the paint.
Before the subsequent priming, we need to polish the last one to increase the adhesion. Or the subsequent priming will peel off.
The sandpaper ranges from 320# to 800#.
3.14. Top coating
Before the top coating, ensure the product is good, and the surface is smooth. Ensure the dust and attachments are cleaned up.
The thickness of the top coating is one cross in 11-22 seconds.
The top coating is protective and makes the furniture smooth and delicate.
We will do top coating twice; the last one is the most important.
All the top coatings are done in sealed workshops. Only filtered air is blown into the workshop to ensure no particles are inside.
Or the particle will fall on the fresh coating. And the paint around the particle will gather to be a small bump, and the surface is not smooth.
The top coating can be 10% to 100% bright. The furniture factory can order relative coating from the paint factory.
It is not that thick paint is good. Only thin paint showing clear texture is the best one.
Let it dry for 4 hours.
4. Assembling and packaging
First, fit embedded parts into the furniture parts. For example, fit the cam-locks or nuts into the wood panels, and glue the glass on the door frames.
Then assemble the furniture parts into complete furniture. For example, build drawer boxes, drawing rails, and panels into a nightstand.
Packaging is to protect and store the furniture.
Packaging materials include EPE, flat foam, edge foam, corner foam, cartons, and wooden frames.
EPE wraps the furniture directly to prevent it from being scratched.
The EPE and foam are somewhat thick and flexible and can cushion a considerable impact.
The cartons protect the wood furniture and can be printed with shipping marks.
Check if the overall color is consistent. Ensure there is no color difference.
Check if the coating is flat under natural light. Ensure there is no sagging, uneven coating, orange peeling, missing coating, and foggy white.
Hand touch to ensure the coating is smooth and there are no bumps.
4.2. Flaws repairing
Repair flaws in the furniture coating.
4.3. Dust blowing off
Blow off the dust on the surface of the furniture.
Ensure all the parts are complete and match each other before packaging.
Ensure the packagings look good. Ensure they can protect the wood furniture well to avoid damage in transportation.