This question will usually raise a debate from shop to shop. Is skipping grits in the sanding sequence a good idea? If so, how many can I skip and still end up with a good finish?
To understand the finer points of this discussion, let’s begin with how sandpaper is manufactured, explore the technical meaning of the words ‘grit’ and ‘abrade’, and raise awareness of exactly what each grit level does to the material being sanded or abraded. Also worth considering is the effect that each grit will have on the material’s surface, and how that will impact the next grit in the sequence.
The term grit is defined as a small abrasive particle of sand or stone, while abrade means to scrape or wear away by friction or erosion. When you use an abrasive, you have thousands of little ‘teeth’ that are scraping, wearing away, or scratching the material being sanded or ground.
One interesting sidenote: When we see abrasion happening on wood, we generally refer to it as sanding. When the same procedure is done on metal or stone, it is called grinding or, in some cases, polishing. It is the same process. Material is being removed from the workpiece by the process of using abrasive grains or grit.
As the abrasion takes place, it leaves behind what we refer to as a scratch pattern, which contains a series of peaks (high points) and valleys (low points). It is a result of the abrasion that took place on the surface of the material being sanded or ground. The size of each abrasive particle has a direct correlation with the size of the peaks and valleys left behind. A larger abrasive grain will leave a deeper and wider valley, creating a taller and wider peak. So, an 80-grit abrasive particle will cut a deeper valley than a 150-grit particle.
The reason for this in-depth explanation is to qualify the statement that you should never skip more than one grit at a time in a sanding sequence.
If you are a craftsman who skips from 80 to 180 grit, I am not bringing this up to say that you’re doing it wrong. That’s not for me to point out. I’ll leave the conclusion up to you, but once I’ve finished painting the picture of how grit sequences work, you might just want to reexamine your process.
Let’s say we have used an 80-grit, aluminum-oxide sandpaper on a piece of maple. If you want the best finish possible with the least amount of work, the most prudent thing to do is use every grit in the sanding sequence (such as 100, 120, 150, and 180). This method slowly and thoroughly lowers the peaks we created with the 80 grit, while keeping the scratch pattern even across the entire surface of the workpiece. When we’re finished sanding, and are ready to apply some stain, we can be assured that the piece will take the stain evenly and give us a consistent color across the entire piece.
But say we go from 80 to 180 grit. With enough time and energy spent sanding, you can still end up with the same result. However, because we skipped so many grits, it is going to take much more time and effort to lower the 80-grit peaks and establish the 180-grit scratch pattern that we need for a high-level finish.
If we don’t spend the time with the 180 grit that we need to at this point, what kind of scratch pattern will we have?
We began with the deep valleys and the high peaks left by the larger grain of the 80-grit sandpaper. When we use the 180 grit on top of that, with the smaller grain size and less aggressive properties, we will have just slightly taken the very tips off the peaks. This still leaves the deep valleys that were there from the 80 grit.
Now, what happens when the stain is applied? It fills in the deep scratches left by the 80-grit sandpaper and leaves a dark, and most likely, uneven color across the surface of the workpiece. It will give a much darker appearance as a result of the stain that is collecting in the deep valleys left by the 80-grit sandpaper.
So, it comes down to how good of a finish do you really want? For the sake of spending a little less money and saving a little time sanding, will you skip from 80 grit to 180 or even 220? Does it really matter, or do you want the best finish possible on that piece that you’ve spent so much time building?
Me? I’ll use the correct grits in the sanding sequence because I want the best finish that I can possibly get. Following the grit sequence, or at the very least, never skipping more than one grit at a time, always yields that deep luxurious finish that we all envision when starting a project.
Another good question
Why is my sanding disc coming off the sander? There are several reasons, depending on the method of attachment. With hook and loop, the hooks could be worn out on the backing pad or there could be too much dirt and debris hampering proper attachment. A PSA backing pad can also build up a layer of dirt, dust, or possibly a thin layer of chemical leftovers from all the different glue attachments and re-attachments. Clean the backing pad regularly using a cleaner that will not leave an oily film.
When attaching a new disc, always make sure it is centered. Press the disc firmly and evenly into place.
Nick DeMars is a woodworking specialist at Klingspor Abrasives. He can be reached at firstname.lastname@example.org.
This article was originally published in the April 2022 issue.