Sanding the wood, the important preparation to make high quality product

Sanding is an important step in the woodworking process, especially for making good quality wood products. Sanding is the process of leveling and smoothing the surface of wood according to the desired standard. Sanding is the final process carried out on wood products that are sold and used without a finishing layer. In finished wood products, sanding is the first step to prepare the wood surface before the application of the finishing material. To produce the best finishing results, all wooden surfaces must be sanded well to get the even and smooth surface. 

Sanding is sometimes also needed to prepare panels that will be glued together to make larger panels. Sanding for the purpose of preparing laminate wood planks is of course not intended to produce a smooth surface, but to form a flat surface and remove wood fibers that would interfere the wood bond.

sanding the wood

The purpose  of sanding

In principle, sanding is purposed to produce a flat wood surface according to needs. The sanding process for wooden products that is used (marketed) without finishing material application is carried out to produce a smooth surface so that it can be used with smooth surface and good feel. Sanding in preparation for the application of finishing materials is purposed to prepare the wood to the finishing application. The sanding may be carried out differently according to the type of finishing material that will be applied on it. In general, sanding in preparation for modern finishing (NC, PU, ​​Water based), ends with sandpaper grade #180 or #240 (US Grade). Sanding process in preparation for a simple finishing process, oil : wax, requires a smoother surface, usually finished with #320 or #400 grade sandpaper.

Sanding for the purpose of preparing wood for gluing does not make the smooth surface but leveling the surface and cutting off the wood fibers. The coarser sandpaper is needed to this process

Wood sanding techniques

To produce a smooth and even surface, the sanding process must be done correctly. Here are the important things that must be considered when sanding wood.

• Do the sanding step by step

Sandpaper consists of various grit sizes, ranging from very coarse (low grit, around 40-60) to very fine (high grit, around 220-400). Sanding wood must be done starting with coarse sandpaper and followed by finer sandpaper until it reaches the desired standard of smoothness

Coarse sandpaper with grade 80 or 100) is used to level the surface and even out very rough surfaces after the components come out of the wood machine.

Finer sandpaper is used to remove scratches from previous sanding. The grade of sandpaper used should not jump too high from the previous grade. Sanding with grade 100 must be continued using grade # 120, then continue with grade # 150 and so on. Sanding with sandpaper that is too fine on a surface that is still rough will make the sanding process ineffective and result in waste and make the sanding results imperfect.

• Maximize the sanding machine 

The human power, has limitations. Humans can be tired emotionally and physically that will tend to inconsistent in results. It is highly recommended that the sanding process be carried out using sanding machines as much as possible. There are many wood sanding machine are created to do sanding according to the shape and model of wood. For the flat boards, a large sanding machine such as a wide belt sander or long belt can do sanding with excellent result. For curved and uneven shapes, there are several sanding machines can be used, such as : drum sanders, spindles sanders, brush sanders, etc. 

The machines are replacing the human power to make the sanding process to be done quickly with consistent results. 

For small components, a hand sander can be used which still uses electricity or air pressured power but with manual control. This tool can handle the complex shape product with high flexibility according to the shape and model of the item. For shapes that really cannot use a machine, sanding by hand is the only option, with some abrasive types option. 

• Replace the sandpaper when it becomes dull

Sandpaper has a rough surface which is the main tool for the sanding process. After being used use, this rough surface will be dulled and left the backing that cannot do the sanding anymore. When the rough part of the sandpaper is gone, the sandpaper is no longer functional and therefore should not be used again. Sanding with dull sandpaper is a waste of time and will not produce the desired results.

• Sanding movement

When do sanding, manually or with machine, it always need to be done correctly. First the sanding must be in direction with the wood grain. For the manually sanding, then the sandpaper movement must be along with the grain direction. Same thing with the machine sanding, the sandpaper movement or the machine movement must be according with the grain direction. Sanding across the grain of the wood can cause scratches that are difficult to be removed. 

The second rule is the sanding must be with even pressure and smooth movements to whole surface. Use the sandpaper grade according to the step of sanding, use the coarse sandpaper to leveling the surface and clean the big deep mark and followed by the finer sandpaper to clean the scratches mark from the previous process. Avoid too strong pressure to sand the wood especially when it done manually, since it tends to create uneven surface for the wood.

Sanding problem

• The surface is too rough

A rough surface on a product sold in an unfinished state will reduce the quality of the product and may not be accepted by buyers. While for finishing preparation, the rough surface will bring finishing problems. A rough surface can cause too much material absorption, affecting the color and smoothness of the resulting finish. Rough surfaces also tend to make the finishing to be ineffective. To get the good finishing result, more sealer and coating application is needed that mean wasting material and time.

• The surface is too smooth 

A wood surface that is too smooth occurs when sanding is done with too fine abrasive. As a result, the sanding process does work to cut the wood hairs on the surface but makes the wood hairs sleep and stick to the wood surface. This becomes a problem when the surface will be applied by finishing material. It will interfere the absorption of the finishing material applied on and resulted to the uneven color or blotchy or appearance in the resulting finish.

• Swirl mark, sanding mark or chatter mark

Swirl marks, sanding marks, scratches or chatter marks are the result of an imperfect sanding process. It happened when the scratches and marks cannot be removed by the sanding process. This is the common problem when the sanding process not be carried out properly

• Over sanding

Over sanding problem often occurs for the veneer sanding. When the sanding is done too aggressively, then it is eroding the surface too much and removed the veneer layer on the surface. it will damage the panel layer and make problem on the panel quality. Sanding that is too aggressive can also damage solid wood components and change the shape of the wood, making the wood product imprecise.

• Wavy surface (uneven, wavy)

Uneven surface or way is one of the results of sanding that is too forced in one particular place so that it erodes the surface too deeply at some points and disrupt the shape and flatness of the surface.

How to solve sanding problems

Even though there are many problems about sanding, these problems are actually rooted in one cause, the incorrect sanding process. These problems can be overcome in one way, : carrying out the correct sanding process. To minimize all the sanding problem, the solution is just : doing the sanding process correctly, step by step, and make sure each step is done correctly before continue with the next step.