What is a circular saw?

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The circular saw is a woodworking and do-it-yourself power tool used to cut wood by the cutting action of a toothed blade rotating at high speed. And although there are other circular saws, or special cutting discs that we can install on our woodworking machine, which are used to cut other materials, in this blog, as you know, I focus mainly on carpentry work. So I’m going to focus on circular saws for wood.

The circular saw is a tool that uses a toothed blade to cut wood. For this reason they are also often referred to as disc saws. And although some people sometimes refer to table saws as disc saws, in this blog when I talk about disc saws or circular saws I always refer to the portable handheld power tool that I talk about in this post.

As for the wood cuts we can make with this woodworking and DIY tool, these can be: straight cuts in the direction of the grain (flush); cross cuts at 90 degrees to the grain, or at an angle, or mitered with respect to the grain of the wood; or cuts with the inclined cut-off wheel. With the circular saw we can only make straight cuts (well, except for some special techniques that we are not going to go into), but with the advantage that we can cut faster and even get cleaner and more precise cuts than with other machines such as the jigsaw.

We are going to see the different parts of a circular saw, and the different systems they have to adjust them to the cuts we have to make in each of our carpentry projects.

On the motor side of the saw blade we have the plastic housing that protects the electrical parts, prevents us from touching the electrical parts, and has the necessary elements to operate the electric saw during the cutting of wood or other materials.

1. Ignition trigger
2. Handle or knob
3. Unlock button
4. Disc saw motor
5. Access to change brushes

The trigger is the button we press to turn on the saw blade. It is usually located at the bottom of the handle.

The handle is used to hold the circular saw with one hand while pressing the trigger. And next to the handle we usually have the knob, which is used to hold this power tool also with the other hand. While cutting, we must always hold the saw with both hands, firmly and always alert to any unforeseen event such as a possible kickback.

The unlock button is used to unlock the trigger to operate it. In this way we avoid accidentally turning on the saw blade. Unlike with the jigsaw, this button is not used to keep the trigger activated.

The circular saw motor can be connected directly to the saw blade or by means of an endless screw. The nameplate gives the power in watts and the rotational speed. As for the rotational revolutions, it is important to take them into account when installing a new cut-off wheel, since cut-off wheels usually have a limitation as to the maximum revolutions at which they can rotate.

Over time, the brushes that carry the electric current to the saw motor wear out and may need to be replaced. To avoid having to open the entire motor housing, saws today often come with easy-to-open plugs that provide access to easily change the brushes.

On the saw blade side of the circular saw we have the parts directly involved in cutting and some protection systems.

The circular saw blade has a hole in the center so that it can be installed in the machine with the help of a screw, and has teeth on the outer edge to cut the wood. As for the central hole, it should have a diameter equal to the raised edge around which it should sit on our saw. Although sometimes when buying a cut-off wheel for a circular saw we will also find adapter rings for different diameters. As for the teeth, they can be made of different materials harder than the metal of the disc itself. And we will find cutting discs with different number of teeth. In addition, the teeth can have different shapes, even on the same disc. Thus, the shape and number of teeth will influence the cutting speed and the cleanliness of the cut.

In some circular saws we see behind the cutting blade a metal plate that surrounds a small portion of the blade, staying a few millimeters away from it and following its curved shape but without reaching the full cutting depth of the blade. Thus, it maintains its position with respect to the blade even if we change the cutting depth. This is the riving knife, and it must have the same thickness as the blade and is used to prevent the cut we make in the wood from closing against the blade, thus reducing the possibility of kickback.

It is the screw that keeps the circular saw blade fixed in its position. It can be Allen type or hexagonal head. In the case of an Allen type, the circular saw usually comes with the necessary wrench to loosen and tighten the screw. And to prevent the cut-off wheel from moving while loosening or tightening the screw, it is necessary to block the wheel either with a piece of wood or by using the cut-off wheel locking button provided with some of these power tools.

When we want to change the cutting blade of the circular saw, it is necessary to lock the cutting blade to tighten or loosen the screw that holds it in place. To do this we can use a piece of wood to block the disc, or in some circular saws we will find a button that when held down blocks it. It is also important to know which way to turn the tightening screw, because if the screw does not loosen even when the locking button is pressed, it may be necessary to turn it the other way. In direct shaft saws (see below in types of saws) the screw is usually tightened clockwise (normal for all screws), but in a mini saw I have with a worm screw (see below), the tightening screw is tightened counterclockwise.

To install the cut-off wheel on our circular saw, we must place it between two washers that are fitted on the turning shaft. The end of the pivot shaft we will see that it ends in a more or less rectangular shape, so that the washer that goes over the disc fits in that shape. Thus the clamping screw presses on the upper washer when it is inserted into the hole in the pivot shaft. As for the other washer, the lower washer, it is very important when buying a new disc, since the central hole of the cutting disc must fit perfectly in the circular flange that we have in that washer. However, some discs come with rings that allow the disc to be adjusted to different washer sizes. And even on some circular saws that lower washer has a flange on one side and a flange with a different size on the other side.

We can also have a washer for when the cut-off wheel hole is larger than the seat diameter in the tool-holder. So many times, when we buy a new cut-off wheel, we see that it comes with simple washers that serve to adapt it to different models or brands of circular saws.

It is the guard that protects the lower part of the cutting disc, and protects us from cutting ourselves in the case of turning on this power tool when we are not cutting with it. What is not clear to me is whether this guard will close fast enough in case of kickback of the circular saw.

So, when we want to cut a piece of wood, as we bring the blade close to the edge of the wood the guard will start to open to allow the blade to make contact with the wood. This guard includes a tab to open it if necessary if for any reason it does not open by itself. For example, when cutting with the blade at 45 degrees, the movable guard often has difficulty opening, so we must use the flange carefully while starting the cut.

The fixed guard is the rigid housing that surrounds the top of the cut-off wheel. It serves as an anti-cut protection and also to guide the sawdust produced towards the suction inlet located on the fixed guard itself.

The suction port is a small tube (or sometimes a simple opening) protruding outward or to the rear of the fixed housing. It serves to evacuate a large part of the sawdust produced when cutting wood. It can also be used to attach a suction tube, although sometimes connecting a suction tube here can make working with the disc saw uncomfortable and even dangerous. I talk a bit about this later in the section on the dangers of the circular saw.

The metal base is the base that we rest on the wood to be cut (or on a cutting guide in some cases), and slides on it while we proceed to cut the wood.

The depth of cut adjustment system, on the back of the saw blade or on the side, is usually a knob or a lever that can be loosened to raise the cutting blade with respect to the metal base. We only need to loosen or tighten in one place, because at the front there is a hinge that allows the rest of the saw blade to be tilted forward with respect to the metal base.

Similar to the cutting depth adjustment system, we have a system for adjusting the inclination of the cutting disc. But in this case we have two knobs that we can loosen to tilt the saw laterally with respect to the metal base.

When changing the cutting inclination we can be guided by a scale that tells us the degrees that we are inclining the disc, but it is not a very reliable scale and it is advisable to have another system that allows us to verify or adjust the angle. I usually use a plastic technical drawing square, or architect’s square, to check the angle of inclination at 45 degrees.

In the metal base we also usually have a couple of notches in which to fit a lateral guide, usually metal, which we fix in the desired position. This allows us to make parallel cuts, generally rip cuts, although it is not usually a high quality cutting guide.

These guides are indentations in the front of the metal base that are aligned with the cut-off wheel. These help us to follow the cutting line when cutting with the blade at 90 degrees or with the blade at 45 degrees.

These are saws with a blade connected directly to the motor shaft or by means of a spur gear system. Thus the cut-off wheel rotates in a plane at 90 degrees to the motor shaft. The rotational speed of the cut-off wheel can be the same as that of the electric motor or as determined by the transmission ratio of the spur gears, if any. These are the most commonly used circular saws and are the ones that we usually find in hardware stores in the largest variety of brands and models.

They are lighter than worm saws and are more maneuverable.

Worm drive saws are disc saws in which the motor shaft drives a worm gear that rotates a pinion. And this pinion rotates the shaft to which the cut-off wheel is connected.

In these saws the cutting disc rotates at 90 degrees to the axis of the electric motor. Because the motor is in a position parallel to the cut-off wheel, these circular saws are usually longer and narrower. As they are narrower and longer, they are useful in wood construction as they can fit into narrower holes and also allow reaching a few more centimeters when stretching the arm while cutting.

A worm gear system is used to transmit the power from the motor to the disc. The worm gear is a spiral gear aligned with the motor shaft, or parallel to it, which rotates a flat gear connected to the cut-off wheel: the motor moves a worm that rotates a pinion. And this pinion rotates the shaft to which the cut-off wheel is connected.

The worm gear configuration causes the blade to rotate slower than direct-shaft saws (the cut-off wheel rotates slower than the motor), but in return these circular saws have more torque. On the other hand, they are somewhat more difficult to handle.

I don’t have a “normal” worm saw, but I do have one of those mini saws that are becoming a bit trendy lately (I don’t really see the point of them). And these mini saws work with a worm gear. The truth is that the one I have only used it once, and in spite of its small size, I found it very uncomfortable to handle. In addition to being a cheap circular saw, it comes with a pretty bad cutting blade that splinters a lot of wood. But, from the picture, you will surely get an idea of how the worm gear system works.

The traditional circular saws, with their power cord. These are the ones I use in my small home woodworking shop, since it is very rare that I have to use the circular saw outside the shop or in areas where I can’t plug it into an electrical outlet. They have the advantage that the battery does not run out, and also being used to unplug it after working with it, there is not so much danger of accidentally turning it on if I am not going to work with it.

Safety aside, which we will see later, let’s see how to use the electric circular saw:

To cut wood strips or boards with the circular saw, it is advisable to clamp one side of the wood to be cut with clamps (generally we clamp the part of the wood that we put on the side of the saw motor).

First we mark the cutting line, and adjust the depth of cut of the circular saw so that no more than one tooth protrudes through the bottom of the wood to be cut. This will achieve a cleaner cut and also reduce the effect of kickback. And proceed to cut with the saw, holding the circular saw with both hands whenever possible.

A trick for clean cuts is to make sure that the good side of the wood to be cut is facing down. Because of the way the circular saw cuts, it makes a cleaner cut on the underside of the wood, while causing more chipping on the upper side.

Another trick for clean cuts is to put painter’s tape on the wood and paint the cut line on top, as the painter’s tape will help contain the splinters that are produced when the blade, in its cutting action, pushes the wood upward. But don’t expect this to achieve a perfectly clean cut either.

My best trick for clean cuts in wood is to use a good quality cut-off wheel with the circular saw.

Now we rest the front of the metal base on the wood to be cut, turn on the saw before the blade touches the wood, bring the blade close to the wood and start cutting. Slide the metal base over the wood, making a straight cut until the cut is complete. Thus, in miter cuts (e.g. 45°) or 90° cuts in narrow timbers, it may be sufficient to cut by hand, but in wide timbers and boards it is necessary to use joinery guides that allow a straight cut to be made. These will also help to cut more accurately.

Now, if we are going to cut a board with the circular saw it is necessary to use a guide to make a straight cut. And we also need a large surface on which to rest the board. Let’s look at two ways to do this:

a.- I usually cut them on my shop table. I adjust my homemade fence to cut straight with the circular saw, I adjust the cutting depth so that only one tooth of the blade protrudes from under the board and, holding the saw firmly with both hands, I cut the board. The problem is that this way I have the blade facing me and the motor facing the inside of the board, and although I have experience doing this, if you are a beginner in these tasks it may not be the safest way to cut a board. If the piece of board left on the motor side of the saw is small then I don’t have this problem, as I can cut on one edge of the table while staying on the motor side.

b.- Another option is to cut the board on the floor. Not directly on the floor, but on top of a rigid foam insulation board, for example, and with the height adjustment of the disc as in the previous case. We adjust the guide and we can cut the board. The advantage is that now we can climb on top of our board so that we are on the motor side.

We must not forget that we must always be aware of the dangers of these carpentry tools and never trust, since the disc saw is one of the most dangerous carpentry machines with which we will work and we must always keep in mind that a kickback can occur.

Coming soon.

According to what I find on the Internet:

The bottom of the cut-off wheel should be about 5mm lower than the bottom of the riving knife.
The space between the teeth of the cut-off wheel and the edge of the separating knife should be about 5mm.

But I will try to look for more information about it.

The main advantage of the circular saw I would say is the speed with which it cuts the wood, but also, with good carpentry guides and a good quality cutting disc suitable for the type of work we want to do, we can make perfectly straight cuts, and cut the wood very accurately and very cleanly.

This carpentry tool will help us to pre-dimension the wood, to give it the final dimensions, and even to make precise cuts when cutting, for example, some mortises to make some woodworking joints.

The main disadvantage of the disc saw is that it is more dangerous than other power saws such as the jigsaw or a saber saw.

Another disadvantage is that the disc saw is only good for making straight cuts, so it is not as versatile as a jigsaw.

Good quality cut-off wheels for the disc saw are expensive, and we will find many cheap cut-off wheels on the market that give the impression of being of good quality but make mediocre cuts in the wood. Keep in mind that a tool of a good brand always comes with a cut-off wheel of that brand. It’s not going to be the best blade of the brand in question, and it’s not going to be a blade with a multitude of teeth for super clean cuts from the brand itself, but it will still be a quality cutting blade that will make better cuts than the cheap blades.

I guess we have already read the manual of this power tool and its recommendations, haven’t we :)? And is that whatever I say on this page or anywhere else, it should not be accepted as valid if it goes against what the manual of the saw in question says, or what its manufacturer says in that manual or anywhere else. That said, let’s take a look at some of the hazards I’ve encountered myself when using this electric DIY and woodworking machine. While there are many things I’m leaving out of the computer that you can find elsewhere, here I’ll focus more on my experience(s).

The main danger of the circular saw is kickback. However, we will avoid it to a great extent if we cut dry, straight and flat wood, if we keep the saw blade clean, if we adjust the cutting height according to the thickness of the wood, if the saw has a separating blade behind the blade, if we hold the saw safely with both hands, keeping the cut straight with the help of a guide and if we are attentive to any strange movement of the saw.

Note that a rip cut (parallel to the grain of the wood) is more likely to cause kickback.

Don’t use a circular saw for gardening or felling, and do not cut boards that are green or have resinous knots.

We must also keep in mind where the cable is before bringing the saw to the position where we are going to start cutting.

For some tasks it may be a good idea to connect the shop vac to the area of the housing that covers the saw blade where the chips come out, but for some cuts the shop vac tube may make it difficult to handle the saw, and it is better to use a mask. And goggles, better with goggles, although this woodworking tool does not eject shavings as dangerously as the wood router.

Also, circular saws are noisy, so it is best to wear hearing protection.

As you can see, disc saws can be dangerous power tools for beginners and even not so beginners.

As you may have noticed if you follow this woodworking and do-it-yourself website and my YouTube channel, I have bought several circular saws over the years. I have been able to work with several brands and the best recommendation I have is to buy a model that has a riving knife behind the cutting blade. Although it does not prevent counter-attacking 100%, it does help to avoid it to some extent. And also in this case I would bet, if we can afford it, for a good brand saw.

If we are going to look for a cheap circular saw we have to think that surely we are not going to be able to give it a more or less intensive use, but it will be for sporadic uses. And remember that a cheap saw comes with a cheap cut-off wheel, which is likely to make a bad cut. My experience is that good quality cutting tools (discs, blades, knives …) make the difference in making a clean, good quality cut.

That said, I remind you that a good quality saw always comes with a good quality blade. Okay, it won’t be the best in the range, but it’s good for a lot of the cutting we’re going to do.

And a cheap saw will probably not have gone through a good quality control, so it is easier to get a defective one.

We should also consider what we are going to cut with our circular saw. And often a mini-saw is enough. But I don’t find worm gear type mini saws comfortable to handle. I would go with a mini saw that is a smaller version of the typical direct spindle saw with the blade rotating directly with the electric motor shaft.

With battery or corded? My first opinion is that with cable, since normally (in my case 95% of the times) we are going to use the disk saw in the workshop, and it is very annoying to run out of battery or that something breaks down in the battery or the connections of these and have to leave a project half done. If we opt for a battery-powered disk saw, again we must think that we need a good quality battery.

Yes, I know I’m putting a lot of focus on buying a good quality brand name disc saw, but nowadays we can buy affordable models for about 100€. And a disc saw is a tool that we will use for many years to come.