How to Prevent Wood from Splitting When Drilling (and How to Choose the Right Pilot Hole Size)

One of the most frustrating moments in woodworking is when a board suddenly cracks right as you’re drilling or driving a screw. Splits can ruin visible surfaces, weaken joints, and waste good timber. Fortunately, most splitting can be prevented with proper prep work, the right pilot hole size, and a few simple drilling techniques.

Why Wood Splits When Drilling or Screwing

Wood fibers run along the grain like long threads. When you drive a screw directly into the wood without a guiding hole, the screw acts like a wedge and forces those fibers apart. This is especially common when:

• Working close to the edge of a board
  
  

• Using hardwoods like oak, beech, or maple
  
  

• Driving long or thick screws
  
  

• Drilling too fast or with too much pressure
  
  

Without a pilot hole, the wood simply has nowhere to expand — causing it to crack.

The Importance of a Proper Pilot Hole

A pilot hole creates a pathway for the screw. It gives the core of the screw space to sit while allowing the threads to bite into the surrounding wood. This reduces pressure on the fibers and prevents splitting. Pilot holes are essential for hardwoods, edge drilling, and projects where clean results matter.

How to Choose the Correct Pilot Hole Size

A good rule is:
The pilot hole should be the same size as the screw’s core (the smooth part beneath the threads), not the threads themselves.

If you hold the drill bit in front of the screw, you should still see the screw’s threads sticking out on either side of the bit.

Here’s a simple guideline:

• Softwood (pine, spruce, cedar): Pilot hole = 70–80% of the screw’s core diameter
  
  

• Hardwood (oak, maple, walnut): Pilot hole = 85–100% of the screw’s core diameter
  
  

Because hardwood doesn’t compress as easily as softwood, it needs a larger pilot hole to relieve pressure.

Depth Matters Too

Your pilot hole should be at least as deep as the screw you’re using. Mark the drill bit with tape to keep drilling consistent. Too shallow a hole increases friction and pressure, which can still split the wood.

Drilling Techniques to Reduce Splitting

• Start slow: Begin drilling at a low speed to prevent wandering and reduce stress on the wood.
  
  

• Pull back to clear chips: Let the bit clear sawdust as you drill. Packed chips increase heat and pressure.
  
  

• Clamp your boards: Clamping adds stability and keeps the fibers supported.
  
  

• Use a backing board: When drilling through a piece, place scrap wood underneath to prevent blowout on the exit side.
  
  

• Drive screws at a steady pace: Too much torque or high drill speed can split wood even with a pilot hole.
  
  

Better Results, Stronger Joints

Taking a little extra time to choose the right pilot hole and drill it correctly will give you cleaner work, longer-lasting joints, and far fewer ruined boards. Whether you're installing shelves, building furniture, or doing weekend DIY projects, mastering this simple technique dramatically improves the quality of your woodworking.