The required finish of the surface is P220. You have two sanding machines with two units in each. Here is an example of how you might follow use this as a guide yourself. This is because, while you could start with a lower grit, it will not only create extra work to compensate, but also will be a less efficient sanding process. When determining your grit sequence, a good rule of thumb is to choose the finest starting grit possible to achieve your desired removal rate. These questions can give you a good sense of where to start. What material am I sanding, and is it hard or soft? Is it very resinous, like pine?.What tool(s) will I be using, or will it be hand sanding?.How many sanding units do I have available for the total sanding process (more applicable to wide belt sanding).How much material do I need to remove on one side of the work piece?.What stage am I at in the sanding process – calibration, leveling, shaping, preparation for finish, between coats of finish, scuff sanding, fine sanding or polishing – and what am I trying to accomplish?.When evaluating the application to determine your grit sequence, start by asking yourself the following questions: In the illustration, you can see the highest peaks are the lowest grit, say 80, and if you skipped to 180, it only cuts the top, leading to a very uneven scratch pattern, versus the pattern all the way to the right, which is very even, and happens when you progress through the grits without skipping. When you do follow the proper technique and Golden Rule of sanding, each successive grit will remove the proper amount, leading you to a more even scratch pattern on the final pass. Sanding Swirls in the wood from incorrect grit sequence or poor sanding technique. This will lead to over-sanding and swirls in the wood. Therefore, each abrasive must be able to remove the scratch from the previous grit, so, for example, if a P180 follows a P80, the P180 will not totally remove the scratch. If the valley of the scratch is invaded, the wood will close, causing pooling and a blotchy finish. The goal is, throughout your grit sequence, to even out the peaks and valleys so that the surface will become smoother, without “invading” the valley. When you use a coarse grit, you are creating a deeper scratch with higher peaks. When you are sanding, you are applying a sharp cutting tool to your surface and creating scratches made up of peaks and valleys – known as RA and RZ. Why You Should Follow The Golden Rule Of Sanding The only way to be sure is to test it out in your specific situation. We can, however, make no guarantees for products from other manufacturers. This sequence cuts out P100, P150 and P220.Ĭaveat: This rule can generally be applied with higher quality abrasives, and we have seen it hold true with our own products. The golden rule for choosing your sequence is to never skip more than 1 grit.įor example, if you start with P80, and need to finish at P240, rather than using every grit from P80 – P220, you can do P80 – P120 – P180 – P240. So, what to do if you need to rough sand all the way on through to the finer grits for finishing? If you don’t need to sand at every stage, you can limit what grits you need… but, even if you do need to sand course through fine, as long as you stick to the golden rule of sanding, you still can get by without keeping every grit available in the shop. For instance, if you’re only ever going to do rough sanding, vs if you plan on only using stain finish, or if you need to refinish cabinets or sand lacquer or other shiny finishes, will all influence what grits you should have on hand. What grits you’ll need, and in what format of product (belt, disc, sheet, etc.) will depend greatly on your sanding application. You might be wondering, “does that mean I need to stock all the grits, from 24-2500 at all times?” This is much more easily explained in the following graphic: Depending on the material, we offer products from P24 all the way to 10,000. P100), where coarser, or larger grains, have a lower number and finer, or smaller grains, have a higher number. There are different systems out there, and typically, Uneeda’s products follow the FEPA standard, in which grit is denoted by the letter P and then a number (e.g. With the sieve number, grain size is determined by the number of meshes per inch, whereas with micro grains, the size is determined by the sinking speed during sedimentation. The sizes are standardized and determined by two main methods: sieve number or micro grain. Coatings.)Ĭoated abrasives, such as sanding belts, discs or sheets, come with a variety of standard grain sizes, more commonly known as grit, or grit size. (You can learn more about these other elements in the linked articles. Sandpaper, or coated abrasives, as the broader category is known, are composed of abrasive grains, adhesive and a substrate backing.
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