Dewalt scroll saw with a broken blade

Why Do Scroll Saw Blades Break?

When I was a new woodworker learning to use a scroll saw, I was frequently frustrated by the blade breaking right in the middle of a critical cut. You, too, may have experienced this and wondered: Why do scroll saw blades break?

The main reasons scroll saw blades break are:

  • The blade is dull.
  • The blade tension is either too high or too low.
  • The workpiece is moved into the blade too fast.
  • The blade is being twisted.
  • Cheap, lower-quality blades are being used. 
  • The wrong type or size of blade is being used for the material being cut.

Let’s take a look at each of these reasons and see what you can do to prevent your scroll saw blades from breaking so frequently.

Dull Blades

One of the most common reasons scroll saw blades break is because they have become too dull to effectively cut material. As the blade gets duller, the chances of it breaking increase significantly.

Here are some symptoms that can tell you if your blades are too dull and should be replaced:

  • It becomes harder to cut with the blade as resistance to the material increases.
  • The wood starts to burn from excessive heat caused by friction generated by the dull blade.
  • There is more noise when cutting materials.
  • The material begins to chip or splinter.
  • The scroll saw motor begins to bog down or stall as you have to increase the pressure to push the material into the blade.

Blade Tension Set Too High or Too Low

You generally want to tension the scroll saw blade enough so that it doesn’t drift in the cut.

Blade drift occurs when a blade that is not tensioned high enough moves off the pattern line or intended cutting path no matter how carefully you attempt to follow the line. The drift cut will often follow the grain of the wood.

Although you want the blade tension to be high enough to prevent drift, you can set it too high. When the tension is too high, especially when using more narrow, fine-toothed blades, the stresses on the metal are too great. This causes the blade to prematurely break, usually as you’re making a tight-radius or curved cut.

Likewise, if the blade tension is set too low, you not only run into blade drift but can also experience frequently breaking blades. This is because the blade flexes and gets caught in the workpiece, resulting in the failure.

There are two common methods you can use to set the appropriate blade tension:

In the first method, while the machine is turned off, use a piece of wood to push against the front of the blade. Gradually increase the tension until the blade deflects 1/8 inch or 3/16 inch with moderate pressure.

The second method of setting the blade tension involves having an ear for music. While the machine is turned off and unplugged (This is very important for safety reasons!), pluck the side of the blade like you would a guitar string while steadily increasing the tension. The tension is correct once a C musical note is heard.

I’m musically challenged and can’t tell a C note from a G note, so I always go with the first method.

Feeding the Material Too Fast 

Feeding material too quickly into the blade can cause it to break. This is especially true if the material is thick or the blade is thin or has very fine teeth.

The pressure exerted while scroll sawing too quickly applies additional tension on the blade, just as if the blade was installed with too much tension.

Pace your cutting speed to the size of the material being cut and the size of the blade. Thicker materials and thin or fine-toothed blades require slower feed rates.

The appropriate speed rate is determined by trial-and-error and is part of learning to use a scroll saw. After a few hours of using one, you’ll be able to quickly tell if you need to slow down.

Twisting the Blade

Twisting the blade too much during the cut can cause it to suddenly break.

Attempting to make a very tight radius cut with a blade that is too thin for the thickness of the workpiece can also cause it to twist.

Twisting can also occur when making tight cuts too quickly. The blade binds as it is pinched in the cut and twists to its breaking point as the material is rotated to follow the pattern line.

Selecting the appropriate blade size and feed rate will help to avoid twisting and blade breakage.

Broken scroll saw blade

Using Cheap Scroll Saw Blades

One reason your scroll saw blades may be breaking frequently is that they may be cheap, inferior blades.

Good scroll saw blades are relatively inexpensive, so buy the highest quality blades as you can afford. You’ll save money in the wrong run as you’ll have to buy fewer blades.

Standard scroll saw blades, which are the least expensive type, are stamped from steel and do not last as long as better quality ground and precision-milled blades.

Precision ground tooth blades have teeth that are milled from hardened steel, which allow them to cut straighter and smoother and last several times longer than standard blades. Olson’s PGT blades are an example of high-quality precision ground blades.

Precision-milled blades, like Olson’s Mach Speed Blades, are also higher quality than regular blades. These blades are engineered to be very fast, accurate, and durable.

Using the Wrong Size or Type of Blade

If the scroll saw blade is too small or has a high number of teeth per inch (TPI), it is more likely to break when cutting thick materials. Therefore, it’s important to use the right size and type of blade for the material being cut.

Scroll saw blade size refers to its width, length, thickness, number of teeth per inch, and type of tooth profile.

Scroll saw blades are classified by a numbering system ranging from 3/0 to 12. As the number gets larger, the blades increase in size.

Larger blades are more durable, so break less often. For that reason, select the largest blade that still provides the desired smoothness of cut needed.

Lower number blades, such as 3/0, 2/0, 1, 2, 3, and 4, have more teeth per inch, are thinner, more narrow, and sometimes shorter than higher-numbered blades. These blades are used for cutting thinner materials and for more detailed cuts, like veining.

Numbers 5, 7, 9, and 11 are the most commonly used blade sizes, as these blades will cut the majority of materials. These blades can cut materials ranging in thicknesses from 1/8 to 2 inches.

You will want to select blades in the 9, 10, 11, and 12 sizes for thicker materials up to 2 inches.

The chart below shows the recommended maximum material thickness and recommended types of cuts for each blade size.

Blade NumberMax. Material ThicknessType of Cut
3/0 & 2/01/16″ to 3/32″Very intricate; veining
01/16″ to 3/32″Very intricate; veining
11/16″ to 3/32″Very intricate; veining
23/32″ to 1/8″Tight radius cuts
33/32″ to 1/8″Tight radius cuts
43/32″ to 1/8″Tight radius cuts
51/8″ to 1″Fine details
61/8″ to 1″Fine details
73/16″ to 2″Moderate details
83/16″ to 2″Moderate details
93/16″ to 2″Moderate details
103/16″ to 2″Larger details
113/16″ to 2″Larger details
123/16″ to 2″Larger details

 

Types of Scroll Saw Blades

So, besides the size, what types of scroll saw blade should you consider?

Several types of scroll saw blades are available. The major differences between the various types are the shapes and configurations of the teeth.

Here’s a description of each of the major blade types:

  • Standard tooth blades have teeth that are the same size and distance apart from each other.
  • Skip-tooth blades are similar to standard tooth blades, but every other tooth is missing. The extra space allows the blade to stay cooler while cutting, which reduces the chance of metal fatigue causing the blade to break.
  • Double-tooth blades are skip-tooth blades with larger gaps between sets of two teeth.
  • Reverse skip-tooth blades have several teeth at the bottom of the blade that point upward to reduce tear-out on the bottom of the material being cut. This type of blade is recommended for cutting plywood.
  • Precision-ground blades are also skip-tooth blades with very sharp and aggressive (fast-cutting) teeth that have been ground to shape. These blades leave a very smooth cut.
  • Spiral-tooth blades are twisted, with teeth on all sides. This design allows you to cut in any direction without turning the material, but the cuts can be rougher than those made by the other blade types.
  • Crown-tooth blades have teeth that are shaped like a crown with spaces between each crown. These blades are good choices for cutting plastics and similar materials. While they cut slower than some other types of blades, they can be installed either end up in the scroll saw.