The two scales are about equally linear in the 400-600 range. This chart shows (Grit number * Particle diameter) for both scales:Īs we can see, there is no clear conclusion - the ISO scale is more linear for grits below 400, while the CAMI scale is more linear for grits above 600. Some extra data - I wanted to see whether the ISO scale or the CAMI scale are more linear when comparing grit number and particle diameter. Here is the same data in tabular format: Grit No You can even mix and match sandpaper from the two scales without issue. The lower the grit number, the coarser the finish but quicker the material removal rate. Extra coarse sandpaper 24-36-grit: Used for sanding old floors and removing old paint and varnish. Coarse sandpaper 40-50-grit: Used to remove old finishes and shape wood. The higher the grit number, the finer the abrasive particles and the smoother the finish that can be achieved. Medium sandpaper 60-80-grit: Generally used to get rid of scratches and sand rough wood. In other words, for woodworking, it does not matter which scale you use until you get to grits 360 and above. The grit is a rating of the size of the abrasive particles embedded in the sandpaper. As you can see, the difference between the two scales is <25% up to 320 grit. The left axis indicates the grit diameter in um, and the right axis indicates the percentage ratio between CAMI and ISO grits. This grit level can also be used for taking off multiple coats of paint or any varnish that is difficult to remove. Here is a chart showing the grit size and the ration of grit sizes for numbers from 24 to 1000: The best sandpaper for opening the grain of wood to accept stain, polyurethane, or paint, or for sanding hard metal like steel and concrete. The tricky part is that the two grit numbers are not equivalent - for example, P360 is rougher than 360. As a final way of knowing that you took out every last scratch on a project, use 400 grit sandpaper with the grain. The 400 grit picks up where 320 leaves off. Though in reality you can stop at 220 in most cases. This will be as high as I would recommend going on the average project. “220”), while the ISO grit size is designated by the letter “P” followed by a number, e.g. The next and final step in the common sandpaper grit is 400 grit. The CAMI grit size is designated by a number (e.g. There are two main classifications of sandpaper: the American CAMI/ANSI standard, and the international ISO/FEPA standard that is replacing it.
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