Prevent Tea rout of Plywood when Cutting

Anyone who has ever had to cut plywood for a project has encountered the big problem of working with it: 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 “tear out,” although woodworkers use other terms to describe it as well.

This tearout problem isn’t just limited to plywood; it can happen with any wood when crosscutting or cutting a curve that goes across the grain. However, it tends to be worse in plywood, mainly because it is more susceptible to this damage due to its thin surface veneer.

Tearout isn’t much of an issue if all that’s being built are 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 discussing the various ways of preventing tear out, it would be helpful to understand the various elements that cause it. The old saying that 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 a board to cut it won’t cause a tear out. But it will when that same blade exists on the other side of the wood. So, knowing the blade’s cut direction can help determine where tearout will occur and what needs to be done to avoid it.

A table saw, for example, cuts as the blade tooth comes 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 cause a tear out 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 a tear out on the bottom side.

Three basic things work together to cause tear out when cutting plywood. They are:

• Face Veneer—The thin face veneer on the plywood tears out quickly because it has 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 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 break off the slivers. While most blades have offset teeth to lessen the friction, there is still the edge of the tooth, not its face, which rubs against the end grain. While carbide teeth do not have an offset, they have a flat side that can rub against the end grain. This is especially true of lower-quality blades whose teeth aren’t ground as carefully. 
• Dull Blades – Blades begin to dull as soon as we use them and continue to get duller until replaced. So it’s rare that we’re using a blade at its best. As the blade becomes more tedious, 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 that 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 tearouts on the core veneers of plywood because they are supported by the next layer of veneer. But the face veneer, the one we most desire to protect, doesn’t have that support.

Another factor that adds confusion to this discussion is that while the same elements cause tear out 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

Several different methods can be used to help prevent tear-out when cutting plywood. These are not generally necessary when ripping the sheet or cutting in the direction of the face grain. They are only needed 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.

To prevent tearout, it’s a good idea to be familiar with all these methods, as no single one 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 saws whenever possible, which is a good starting point. Before making any cut, it’s a good idea to mentally review the blade action and where it will likely cause a tear out. 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 routed to create a profiled edge. In those cases, using whatever saw is the easiest and most efficient to cut only makes sense. However, in cases where visible tear-out can mark the project’s finish, 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 significantly affect how much tear out the saw creates. If we compare a rip blade to a crosscut, 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 tear-out.

The saw blades that 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. It’s 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 that offer sharpening services for a reasonable rate rather than having to sharpen them yourself.

Cutting Through from the Back Side

As noted above, the blade’s cutting action will be from above with some saws and from below with others. To avoid tearing out the finished surface, it is best to have the saw blade tooth enter the wood from the face side and exit from the backside. 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 backside.

Likewise, it’s best to cut with the back side up for both scroll saws and jigsaws, although there might still be some tear out. However, since the cutting action is down in both these cases, the major tearout will be towards the bottom or back of the board.

Cutting the Face Veneer First

When plywood with a thin face veneer is being used, such as 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 if the saw blade crosses over the line, it will ensure that any tear-out 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 way to prevent tear out. If that is being done, then it’s a good idea to 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 oscillate 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 method is imperfect 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, use it on the side where tear-out 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 so that the tape breaks contact with the surface of the plywood, away from the cut edge, and 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 that 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. In many cases, providing solid support to those fibers can be all that’s needed to prevent tear out. 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 saw. The idea is to sandwich the cut board with another, which can be sacrificed. When the cut is made, the blade enters the finished piece first, then the sacrifice board. Because the sacrifice board fully supports 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 space for the sides of the blade to cause a tear out. However, the insert will need to be replaced after some time. 
• Using a Crosscut Sled—One additional advantage 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, 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 being cut but rather arrive 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 tea rout.

Use a Saw Guide

Whenever possible, a saw guide should be used when cutting with a circular saw. Much of the splintering that can happen with a circular saw occurs when the blade gets twisted in the kerf and the side of the blade makes contact with the edge of the cut. A guide turns the saw into a track saw, ensuring that the blade is held straight about the cut line.

Add Support for the Board

Cutting a full sheet of plywood on a table saw entails particular challenges, especially for the woodworker with a portable table saw. With their smaller tables, these saws 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 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 are probably just as big and powerful as they are for a larger stationary saw.

If there isn’t room in the workshop for a larger saw base, 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 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 also help in this regard. 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, 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 tear out. While cutting a straight line with this sort of saw is challenging, it is ideal for cases when curved cuts are needed.

If you’ve ever used a machinist’s mill, there are a lot of similarities to how a spiral cutting saw blade and an end millwork. The spiral edge of the blade is there to clear the chips out of the saw kerf and push the tool’s table flush up against the wood. Very positive contact between the tool and the plywood gives excellent control. It takes some practice to make curved cuts accurately, but the same can be said for any saw.

Rather than buying a spiral-cutting saw, I bought a small cordless router and 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 routine work. To make this combination work, I had to buy a smaller collet for the router to fit snugly on the 1/8” diameter spiral-cutting saw bits.

A Final Word

What works best for one project might not work well for others. Many factors 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 techniques, on some scrap material before using any of them on a panel for an actual project. From that, the woodworker can determine what they want to use in their shop.