The main purpose of using sandpaper is to obtain the "shape" of the surface we want.


First of all, let's choose what sandpaper is.


It is estimated that many people will make the wrong choice. To deepen our understanding, let's first talk about the characteristics of these different things:


The first step is to cut things. The process of cutting is to break the material and separate different parts of the material. For example, the scissors we use are a very important tool for cutting things.


The second step is to cut things, which involves shaping the material, removing protrusions beyond the required shape, and ensuring that the material's appearance meets our shape requirements. Cutting things such as our pencil sharpener, file, and push knife are all typical cutting tools.


Both of these things will remove certain things from the material.


Going forward, polishing is a common practice. Many people believe that sandpaper is a polishing tool, and using high mesh sandpaper will create a shiny effect on the surface of the material. But note that polishing is not done in this way, it is actually the process of adding something to the material. In general, wax is used during polishing, which is pressed into the gaps on the surface of the material. Perhaps we should simply press the fine particles on the surface of the material from the beginning into the gaps on the surface of the material. This is called polishing.


Is that grinding something? A typical grinding process involves no addition or reduction, using pressure to deform the surface of the material to achieve the desired surface smoothness.


Is that polishing something? Polishing is actually just a process of deburring. Basically, we rarely use it in models.


In principle, sandpaper is the same thing as a file. This is a cutting tool. If we look at micrographs, we can see that the surface of sandpaper is the same as that of a file, consisting of sharp particles with sharp edges.


These particles are fixed on the base paper by glue, and with each sliding of the sandpaper on the surface of the object, these hard particles will cut some material off the surface of the object. In fact, this is a micro and efficient cutting process.


Although common sandpaper has various fineness from 12 mesh to 20000 mesh, it should be noted that the cutting characteristics of sandpaper itself do not change with the increase of mesh size and the decrease of particles. It still cuts the material from the surface of the object and does not cause any changes in the material properties of the object.


Why is it emphasized that "it will not cause changes in the material properties of the object"? Many people find that no matter how high the intention of sandpaper is used to treat the seamless part, it can still be vaguely seen that the seamless part is different from other places. Perhaps after cutting the nozzle, they will find that the white part of the nozzle cannot be ground off no matter how hard it is ground. This principle is very simple, as the dissolution of seamless glue or the pulling of scissors have changed the characteristics of plastic, this change cannot be changed by cutting, unless your cutting depth completely removes the denatured material. Of course, improper pulling of the scissors may cause whitening at a depth of 1-2 millimeters below the surface of the material, and the amount of cutting required at this time can be imagined.


To summarize, the job that sandpaper can do is to change the shape of an object's surface through cutting. This shape change may be to make the surface smoother or to remove unnecessary protrusions from the material's surface. The job that sandpaper cannot do is to change the characteristics of the object.


How to use sandpaper? Gradually apply from coarse to detailed. In general, using 100-200 grit sandpaper for large cutting amounts allows you to directly cut the surface of the model to a depth of nearly 1 millimeter in just a few seconds.


This process is an effective process for repairing and organizing the appearance.


What is the next sandpaper to use? Actually, this is an arithmetic problem:


The approximate calculation is as follows: the mesh size of the previous sandpaper is X1.5. For example:


After using No. 100 sandpaper, the next sandpaper to continue polishing should have a mesh size of 150 instead of 200. After you polish it with 150 grit sandpaper, you will have a tangle point before continuing with X1.5. 150X1.5=225, so should we use 200 grit sandpaper or 250 grit sandpaper? In fact, the mesh size of sandpaper is approximate to the aperture of the camera.


There is a 220 grit sandpaper, and usually the 200 grit sandpaper we refer to is just a relatively easy to say and remember term. The regular sandpaper mesh size is intended to be 220 (P220) mesh and 240 (P240) mesh. Which one to choose between 220 and 240? Downward proximity principle, choose 220 intentions—— Note that sandpaper is cutting, and the larger the mesh size, the smaller the cutting force. Excessive differences in mesh size cannot remove the marks left by the previous sandpaper.


In fact, the increase in the strict sense should be multiplied by the Cube root of 1.5, but to save energy, it is directly X1.5 and then the mesh size under the orientation.


The previous calculation of mesh size actually gave us a very simple example of 100, and the actual model manufacturing actually starts with polishing with 220 mesh or 300 mesh. After all, the model parts are relatively precise and there is no need to cut from scratch.


When we often use a file, we will find that the gaps between the file teeth are filled with debris. This phenomenon is called file blockage. In general, we need to use a copper wire brush to brush off the burrs between the file teeth, otherwise these burrs will change the mesh size of the file and carry the fine particles that have been filed and scratch the surface of the parts.


Sandpaper is also the same, and it also has the problem of "paper blockage". The higher the mesh size of sandpaper, the more serious the phenomenon of paper blockage becomes. Therefore, it is necessary to frequently investigate the sandpaper during polishing. The fact that the sandpaper turns white and clumps on it does not mean that the mesh size of the sandpaper has increased, but rather that it needs to be cleaned. Thanks to the invention of 3M water sandpaper, most sandpaper can now be soaked and flushed. After washing, it can be reused once or twice, but only once or twice. And it should be noted that sandpaper with different mesh sizes should not be washed in a glass of water. There is a possibility that particles falling from coarse grit sandpaper may stick to fine grit sandpaper. It's very likely that just a single grain of sand will ruin half an hour of your homework.


It is necessary to use sandpaper with a mesh size of over 800 with water. Otherwise, the accumulated debris between the sandpaper and the parts will also severely peel off the flat surface that you originally lubricated.


After polishing with sandpaper with a mesh size of over 2000 and turning white, simply throw it away. There is no value in secondary use at all. This may seem like a waste to many people, but the characteristic of sandpaper is that sandpaper that loses cutting force is actually no different from waste paper.


Finally, when using sandpaper, the whole process needs to wear personal protective equipment such as masks or Gas mask. This is actually quite fun, as many people choose not to use airbrushes for the respiratory health of their families and instead choose to use pen painting to create models. But it should be noted that the dust generated by polishing causes much more harm to the body than the paint sprayed by the fountain pen. It is necessary to use sandpaper with a mesh size of over 1000, and it is necessary to wear a PM level mask.