Anyone who has ever had to cut plywood for a project, has run across the big problem of working with it; that it chips and splinters along the cut edge, especially when cutting across the face grain of the sheet. This damage is commonly grouped together under the name “tearout,” although woodworkers use other terms to describe it as well.
This problem of tearout isn’t just limited to plywood, as it can happen with literally any type of wood, when crosscutting or cutting a curve that goes across the grain. However, it tends to be worse in plywood, mostly because plywood is more susceptible to this sort of damage, due to having a thin surface veneer.
Tearout isn’t much of an issue if all that’s being built are some rough shelves for a garage or sheathing a roof. But if the project is any sort of furniture, cabinetry, article for use in the home or even a workbench, we all want to avoid that tearout, so that we can have a nicely finished project. The only question is, How?
What Causes Tearout?
Before talking about the various ways of preventing tearout, it would be good to understand the various elements in causing it. The old saw about the first step in solving a problem is understanding holds just as true here, as it does anywhere else.
Tearout only happens when the blade is moving away from the board. In other words, a blade tooth entering into a board to cut it won’t cause tearout. But when that same blade exists on the other side of the wood, it will. So, knowing the cut direction of the blade can be a real help in predetermining where tearout will occur and what needs to be done to avoid it.
A table saw, for example, cuts as the blade tooth is coming back down into the surface of the plywood being cut. Therefore, it won’t cause tearout in the top of the plywood, but rather in the bottom side. On the other hand, a jigsaw or scroll saw (both commonly used for cutting curves) has a blade that reciprocates up and down, so it can actually cause tearout in both directions. It is better to use a bandsaw for cutting the curve, if possible, as the blade only moves in one direction, downwards through the material being cut, so it can only cause tearout on the bottom side.
There are three basic things that work together to cause tearout when cutting plywood. They are:
- Face Veneer – The thin face veneer on the plywood tears out easily because of less structural strength. Plywood with a thicker face veneer tends to tear out less, as the wood fibers can support each other, although that doesn’t totally eliminate the possibility.
- Friction – Perhaps the biggest culprit, as the sides of the blade rubbing against the end grain at the edge of the cut is literally what breaks off the slivers. While most blades have offset teeth to lessen the friction, there is still the edge of the tooth, not the face of it, which rubs against the end grain. While carbide teeth do not have an offset, they have a flat side which can rub against the end grain. This is especially true of lower quality blades, where the teeth aren’t ground as carefully.
- Dull Blades – Blades begin to dull as soon as we start using them and continue to get duller until replaced. So it’s rare that we’re actually using a blade at its best. As the blade becomes duller, it loses its ability to sever wood fibers, causing it to put more pressure on the fibers, before they are severed. If the tension holding the fibers together is less than that caused by the pressure of the blade’s teeth across the fibers, tearout will occur.
Something which works in conjunction with all three of these, is the lack of support the wood grain of the face veneer has, in preventing it from moving (tearing out) rather than cutting. We don’t see tearout on the core veneers of plywood, because they are supported by the next layer of veneer. But the face veneer, the one we most would desire to protect, doesn’t have that support.
Another factor which adds confusion to this discussion is that while the same elements cause tearout with any sort of saw, the cutting action of those saws can be quite different. So, something that might not be so much of an issue on a circular saw can become a big issue on a jigsaw, or vice-versa.
Measures to Prevent Tearout
There are a number of different methods which can be used to help prevent tearout when cutting plywood. These are not generally necessary when ripping the sheet, cutting in the direction of the face grain. They are only necessary when crosscutting, or cutting across the direction of the face grain. Perhaps the only time when they would be even more necessary is when cutting curves, as the changing direction creates a greater chance for tearout and the types of blades used aren’t as easy to find in a carbide version.
In order to prevent tearout, it’s a good idea to be familiar with all these methods, as there is no single one that can be used effectively in all circumstances. Rather, the right technique or techniques will need to be selected for each cut. Using multiple techniques together can be extremely effective. While that may seem to be overkill, it protects the project; and isn’t that the goal?
Select the Right Saw
As mentioned above, some types of saws are more prone to causing tearout in plywood than others. Therefore, it only makes sense to avoid using those types of saws, whenever possible, is a good starting point. Before making any cut, it’s a good idea to mentally review the blade action and where that is likely to cause tearout. The question then becomes, is that a problem or not?
Tearout may not be a problem, if the cut edge is going to be hidden or if it is going to be routed to create a profiled edge. In those cases, it only makes sense to use whatever saw is going to be the easiest and most efficient to make the cut. But in cases where visible tearout can mark the finish of the project, careful selection of the saw and saw blade can make all the difference in the world.
Use the Right Blade
Selecting the right blade can make a big difference in how much tearout the saw creates. If we compare a rip blade to a crosscut one, the glaringly obvious difference is that the crosscut has more teeth. That’s so that each tooth takes a smaller “bite” out of the material, helping to reduce the chance of tearout.
The saw blades which come with any new saw are not the best in the world. Even if the manufacturer supplies a carbide toothed saw blade, it will probably be a low-end “combination blade, with a tooth count somewhere between that of a rip blade and a crosscut one. In other words, it’s not really going to be good at anything. Better to buy a quality blade right off the bat and save that one for when some rough cutting is needed.
Blades can dull faster than most of us realize. So it’s a good idea to replace the saw’s blade at the first sign of it getting dull. There are a number of companies which offer sharpening services, for a reasonable rate, rather than having to sharpen them yourself.
Cutting Through from the Back Side
With some saws, the cutting action of the blade is going to be from above and with others it will be from below, as noted above. To avoid tearout in the finish surface, it is best to have the saw blade tooth enter the wood from the face side and exit from the back side. On a table saw, this happens with the plywood face up; but with a circular saw, it’s best to flip the sheet of plywood over and cut through from the back side.
Likewise, it’s best to cut with the back side up for both scroll saws and jigsaws, although there might still be some tearout. However, since the cutting action is down in both these cases, the major tearout will be towards the bottom or back side of the board.
Cutting the Face Veneer First
In cases where plywood with a thin face veneer is being used, such as in the case with many types of hardwood plywood, it can be extremely helpful to cut through the face veneer and into the first core veneer with a utility knife, before making a cut. While this won’t help at all if the saw blade crosses over the line, it will ensure that any tearout stops when it reaches the cut line.
In the case of complex cuts, like curves, in plywood, cutting the face veneer may be the only thing that can prevent tearout. If that is being done, then it’s a good idea to make the cut a little outside the line (1/16”), and then either route the edge with a template and straight bit with a bearing or sand the edge with a belt or oscillating spindle sander to bring the edge right up to the line.
Taping the Cut Line
Taping over the cut line with blue painter’s masking tape can help hold wood fibers in place, reducing tearout. This is an imperfect method, because the wood fibers can still be torn and merely held in place by the tape; but it’s a good idea, when used in conjunction with other methods.
When applying the tape, be sure to apply it on the side where tearout is most likely to occur. When unsure, play it safe and tape both sides; then look at the results. Be sure to press the tape down firmly, so that it adheres well to the surface of the wood.
When removing tape applied for this purpose, be sure to pull it in a way that the tape breaks contact with the surface of the plywood, away from the cut edge, then works its way towards the cut. If it is pulled off in reverse, starting at the cut edge, it could help lift wood chips which are still in place.
Using a Backing Board or Zero Clearance Insert
Tearout can’t occur if there’s nowhere for the wood fibers to go when they pull out of the board. Providing solid support to those fibers can be all that’s needed to prevent tearout in many cases. Of course, that can’t be done with all saws. There are three different ways of providing that support:
- Using a Sacrificial Backing Board – This method can be used with any sort of saw. The idea is to sandwich the board being cut with another, which can be sacrificed. When the cut is made, the blade enters the finish piece first, then the sacrifice board. Because the sacrifice board provides full support to the cut line, the face veneer on the project bard won’t be able to splinter.
- Using a Zero Clearance Insert – While there are some zero clearance inserts on the market, most woodworkers cut their own. A zero clearance insert is essentially the same idea as using a sacrificial backing board. Since the insert is actually cut by the saw blade being used, there is no empty space for the sides of the blade to cause tearout. However, the insert will need to be replaced after some time.
- Using a Crosscut Sled – One of the additional advantages of using a crosscut sled on a table saw is that the slot in the sled for the blade is usually cut by the saw’s blade, making it effectively a zero clearance insert.
Cut in Two Passes
This is especially useful for cutting plywood with a handheld circular saw and won’t work with many other types of saws. The idea is to score the cut line first, cutting down into the material only about 1/8”. Since less force is required, there is less flexing of the blade and less chatter. So the cut line ends up cleaner. Once that cut is finished, then the blade can be brought up to normal height, so that the material can be cut all the way through.
Raise the Blade Height
What the manufacturers suggest as blade height for table saws and circular saws is based more on safety than anything else. They state that the blade should only come through the far side of the plywood 1/8” to ¼”. But in this setting, the blade’s teeth aren’t coming down onto the face of the plywood that is being cut, but rather come at the surface at more of an angle, almost horizontally. In this case, the teeth can push the grain sideways, before cutting it, increasing the chances for tearout.
Use a Saw Guide
Whenever possible, it’s a good idea to use some sort of saw guide when cutting with a circular saw. Much of the splintering that can happen with a circular saw happens when the blade gets twisted in the kerf and the side of the blade makes contact with the edge of the cut. A guide essentially turns the saw into a track saw, ensuring that the blade is held straight in relation to the line of cut.
Add Support for the Board
Cutting a full sheet of plywood on a table saw entails special challenges, especially for the woodworker who has a portable table saw. These saws, with their smaller tables, make supporting a full sheet of plywood and keeping it up against the fence extremely difficult.
The best solution is to have a much bigger saw table, whether that means spending a small fortune to buy a cabinet saw or it means building a cabinet to set the table saw into, effectively increasing the size of the table. For the home woodworker, who has a limited tool budget, this is the ideal way to go, as the motor and blade for that portable table saw is probably just as big and powerful as it is for a larger stationary saw.
If there isn’t room in the workshop for a larger saw base, then consider using portable support stands to hold the sheet while it is being fed through the saw. This allows the woodworker to concentrate on holding the plywood against the fence, rather than concentrating on holding the plywood. Another good idea is to weigh the saw’s base down with sandbags, so that the saw won’t tip or move while cutting.
Attaching a longer face board to the fence, effectively extending it, can help a lot in this regard as well. That longer fence makes it easier to hold the plywood square up against it. Even a temporary face, held in place with clamps, will make a big difference, if it is long enough.
Using a Spiral Cutting Saw
As an alternative to using more traditional saws, using a spiral cutting saw (first made by RotoSaw), is an excellent means of cutting curved lines in a sheet of plywood. The spiral cutting bit cuts a bit off parallel with the surface of the plywood, rather than perpendicular, pretty much eliminating any possibility of tearout. While it is challenging to cut a straight line with this sort of saw, it is ideal for cases when curved cuts are needed.
If you’ve ever used a machinist’s mill, there’s a lot of similarity to the way a spiral cutting saw blade works and how an end mill works. The spiral edge of the blade is there to clear the chips out of the saw kerf, as well as pushing the tool’s table flush up against the wood. There is very positive contact between the tool and the plywood, giving excellent control. It takes a bit of practice to be able to make curved cuts accurately, but then, the same can be said for any sort of saw.
Rather than buying a spiral cutting saw, I bought a small cordless router and the spiral cutting saw blades. while a bit heavier and more costly than the spiral cutting saw, this gives me more flexibility, as the same tool can be used for edge work and other typical routing work. In order to make this combination work, I had to buy a smaller collet for the router, so that it would fit snug on the 1/8” diameter spiral cutting saw bits.
A Final Word
What works best for one sort of project might not work well for others. There are many factors which come into play, most especially the type of saw being used and the type of cut desired. I would highly recommend trying each of these methods out, including combinations of methods; on some scrap material, before using any of them on a panel for a real project. From that, it’s possible for the woodworker to determine what they want to use in their own shop.