Why Did Wood Split When Drilling Into It? 5 Causes

For someone who works with wood, there’s nothing worse than having a piece of woodwork split when drilling into it; it seems like all the hard work that went into shaping and finishing it was for nothing. Unfortunately, wood splitting because of drilling happens often, and you need to know why it happens and how you can fix it so that you don’t have to abandon your work.

Wood can split when drilling into it because of cracks, air humidity, weak spots, or using the wrong drill parts or settings. You should consider these factors to prevent a split. To fix it, you can use wood glue and sawdust for small cracks and fillers like epoxy and wood putty for large splits.

In the rest of this article, I will explain all the possible reasons why wood splits, both wood-related and drill-related. I also offer ways to fix these issues and avoid them in the first place. Keep reading for more information. 

Why Did Wood Split When Drilling Into It

1. The Wood Is Already Cracked

Sometimes the reason why wood splits when you drill into it is very simple: the wood is already cracked. If the wood you’re working on is cracked somewhere, especially near the area where you’ll be drilling, it will split under the pressure of the drill. 

Existing cracks in the wood weaken the structure of the piece you’re working with. Meanwhile, the drill exerts a lot of pressure, which reaches the weaker points of the wood and forces them to give. Even the most minor, invisible cracks in the wood can cause major splits when you start drilling.

How To Fix

To prevent this mistake from happening, you need to make sure that the wood has no cracks anywhere that could give to the pressure of the drill. Inspect the piece of wood you’re working on for any signs of cracks; if you see any, think of replacing it with another one.

If you noticed the cracks when it was too late, you could always try to salvage the piece of wood. There are plenty of ways to fix a split in the wood. You can choose the method that seems more convenient for you and might suit your situation more. 

If the split is small, you can try using wood glue. Wood glue is a quick and cheap solution that can fill the split and salvage your work. To fix a split with wood glue:

  1. Clean any debris or splinters resulting from the crack.
  2. Use a toothpick to hold the tiny split open while you use the glue.
  3. Pour the glue, making sure it gets into every crevice.
  4. Use clamps to keep the split closed while the glue dries.
  5. Wait for the glue to dry for at least five hours or overnight, then remove the clamps.

2. The Atmosphere Is Too Humid

Moisture content in the environment plays a significant role in woodworking and, specifically, in the ability of wood to split. High moisture content in the air allows water to enter the wood fibers, expanding them. This expansion affects the joints, pulling them apart, making the piece of wood much more vulnerable.

It’s possible that even in the opposite of the above situation, when the atmosphere is too dry, wood can become more likely to split when drilling into it. If the moisture content in the air is too low, it will pull moisture from the wood, making the fibers shrink. As a result, the joints will still be forced apart, resulting in weaker wood.

How To Fix

You can help prevent this issue by keeping the piece of wood somewhere with a controlled atmosphere. If the moisture level stays the same, there’s little chance of wood absorbing or releasing moisture.

Understandably, this isn’t always possible, but you can still prevent splitting if you isolate the wood so its fibers can’t be affected too much by the moisture in the atmosphere. There are a few different products you can use to seal your work: 

Most of the above substances are applied the same way, using a paintbrush and wiping the excess.

If you can’t prevent the split, you can still salvage your work. If the crack is small, you can use the method I suggested above with wood glue. Otherwise, you need a wood filler. 

For instance, you can try wood glue and sawdust. All you need to do is mix the adhesive and the sawdust and then apply it to the crack, ensuring it fills the entire depth. Allow it to dry, and then stain the wood to mask it. 

Check out my article on how long you should keep the stain on wood and whether you can leave wood stain on overnight. [Is It a Good Idea to Leave Wood Stain on Overnight?]

3. Drilling in the Wrong Spots

How successful you are at drilling wood also depends on how you handle your drill and where you position it while drilling. You want to avoid all the weak spots that can cause the wood to give and split. It might seem like it’s more or less the same material all the way through, but wood has stronger and weaker points that you should know. 

If you unknowingly drill into one of the weaker points of the wood you’re working on, the wood is very likely to split. And you are more likely to make this mistake unless you learn all about the different weaknesses of a piece of wood. 

How To Fix

Naturally, looking for weak spots may not be the first thing that comes to mind when you’re looking for a piece of wood to work on, but keeping these spots in mind before drilling can make it much easier to prevent splitting.

The spots you need to avoid are:

  • Edges: The closer to the edge you place the drill, the more likely it is to split because there’s not enough surrounding wood for support.
  • Knots: Knots are spots where branches used to grow, so they are tougher to get through but also more fragile. 
  • Thick grain: More prominent and pronounced grain signals a weak spot, which splits easily if you drill into it.

If you can’t avoid a spot and the wood splits, you can still use one of the fixes I’ve recommended above, or another way, like using epoxy

4. Issues With the Drill

Your drilling instrument can also cause the wood to split. There are many things that can go wrong with the drilling process, including: 

  • Choosing the wrong type of bit 
  • Having a dull bit
  • Using a too-powerful drill

How To Fix

To ensure you don’t split the wood in the first place, you must choose the right drill with the right bit. Unless you’re drilling into a massive and tough piece of wood, you don’t need a powerful drill, so test the drill to see how it can work on a similar piece of wood.

Also, choose the correct bits, depending on what type of hole you want to drill. There are specific types of bits for small, medium, or large holes, and they may vary depending on the depth of the hole. Typically: 

5. Wrong Drill Speed

While choosing the right drill bit helps, you should know the drill speed that every type of bit requires. A too-low or too-high drill speed can cause the wood to split while drilling, even if everything else is done correctly. 

When talking about drilling speed, you may encounter RPM as a way of measuring it. RPM means revolutions per minute, and it is specific for every type of hole, drill bit, and type of wood. Using a too-high RPM could cause the wood to burn, but a too-low one can split the wood.

How To Fix

Before starting your work, learn about the RPM that your drill should have for your specific situation. If, for instance, you’re drilling a one-inch hole on hardwood using a hole saw bit, you need to have an RPM of about 350. The same situation on softwood would require 500 RPM.

If you missed the opportunity to learn about this before starting to drill into the wood and the wood split, you could always use one of the ways I mentioned above or a filler stick. Using a filler stick is straightforward:

  1. Purchase the stick, making sure to choose one that is shaped like a crayon to reach the parts that are difficult to reach.
  2. Put the filler into the split, making sure to get all the way to the end of it (use a putty knife to reach every depth better).
  3. Spread the filler well and let it dry.
  4. Once it’s dried completely, sand the area to get rid of any excess filler.

Final Thoughts 

Wood splitting while drilling into it is a common problem because it may happen for many reasons. The type of wood, the settings and parts of the drill, and the placement of the drill may be factors that cause the wood to split.

To prevent the split, you should consider all of these factors and choose the correct settings for the type of wood you wish to drill into. If the wood splits, you can still fix it using wood glue, sawdust, epoxy, filler stick, and more.

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