How To Prevent Tearout When Drilling

How To Prevent Tearout When Drilling

Drilling holes in wood is going to be a regular part of your woodworking projects, and we want to be able to drill clean and neat holes that don’t rip the wood as the drill is coming through the other side.  This tear out, the ripping of wood fiber by the drill bit, either means you’ve got some filling to do or you’re starting over.  Wood and time get wasted, and we don’t like that.

An ounce of prevention being a pound of cure, there are a few things you can do to ensure a clean hole on both sides of the wood you are drilling.  We’ll run through them for you, offer a video to support our tips, and keep it short.

Understanding Your Drill

The chuck on your drill (the business end where drill bits are inserted) is likely to have numbers and dial settings on it.  These settings represent the clutch, the torque value of your drill.  This clutch value determines the limit of resistance the drill bit encounters that will stop it from spinning.

The drill will likely include a speed setting as well.  Of course, the pressure you apply to the trigger can determine the speed of the drill bit spinning, too.  The speed setting for drilling should be high, while the speed setting for driving a screw should be low.

PORTER-CABLE Forstner Bit Set, 14-Piece (PC1014)

With drill bits you have options, among them:

  • Helical – the common all-round bit that comes in various sizes and lengths
  • Spade – for drilling large diameter holes, with a point that keeps the bit centered
  • Forstner – for drilling flat bottom holes like for dowel use, although you can also drill through wood to the other side, too
  • Countersink – for drilling conical holes that allow a screw head to sit flush with the surface of the wood

For our purposes in this article, we’ll consider the helical and the spade drill bits, those that will drill holes all the way through wood.  The clutch will be left wide open, and the drill speed will be set to high spin.

Drilling a Clean Hole

With torque, speed, and drill bit established, let’s turn to drilling a clean hole.  Of course, you’ll want to measure and mark carefully before drilling and pick a safe spot in your workshop for the task.  Goggles are a smart idea, too – safety first and always with power tools.

Tear out, blow out, ragged exit hole, and other names, all refer to the wood fibers that get caught in the drill bit and pushed out of the wood as the drill exits the workpiece.  You’re more likely to encounter this when drilling through softwoods, although tearout can happen when working with hardwoods, too. As we said, you’ll either have some filling and sanding to do to repair the damage or start over.

Here are a few suggestions to help you avoid this ugly mishap:

Drilling a Hole
  1. Sacrificial Board.  Use a piece of scrap wood of greater or equal density beneath the workpiece.  This “zero clearance” approach gives the wood fibers no place to exit the workpiece and results in a clean hole.  

Clamp the workpiece tightly to the scrap piece.  Don’t push the drill through the workpiece hard – let the drill bit do the work – and keep drilling until you are certain you are through the workpiece.  Release the clamp(s) to see the clean hole you’ve created.  

While this can help eliminate tear out, it’s especially effective when using a helical, spade, or Forstner drill bit.  It’s likely you will have chosen a helical bit since these are the bits that came with your power drill (corded and cordless).

  1. Drilling Straight.  Drill a pilot hole using a smaller diameter drill bit to identify your mark on the workpiece.  You can use this pilot hole to line up the drill you’ve chosen for a truer hole exactly where you want it.

Then use a scrap board that is true 90 degrees to line up the drill bit before you begin to drill.  This will ensure you are drilling straight and true to your mark, and get the hole off to a good start.  Again, we are assuming the use of a helical drill bit for this task – it will line up nicely with the scrap board and make the hole straight.

Mark your drill bit with a piece of tape to identify the depth of the workpiece and into the sacrificial board.  This will keep you from overdrilling so you can continue to use the scrap board for future drilling.  Again, don’t push the drill through the workpiece too hard or fast – let the drill bit do the work for you, just like a chef lets the knife do the cutting work.

Hole Saw Drilling
  1. Drill from both sides.  Not at the same time, of course, but yes, you can drill from both sides easily when you use a spade drill bit.  

Know the depth of the workpiece, and stop drilling with the spade bit just as the point at the tip breaks through the bottom side of the workpiece.  Turn the workpiece over, line up the point with the breakthrough hole and drill until the hole is complete.  

This is a very effective way of avoiding fiber blowout as the drill bit exits the workpiece. As an aside, Forstner drill bits are actually more effective than spade bits in avoiding tear out, but are usually used with drill presses rather than with hand-held power drills.  

  1. Tape.  Masking tape can help control tearout, too.  Attaching a strip of tape on the bottom of the workpiece where the drill bit will be breaking through can hold the wood fiber in place and prevent tearout.  A piece of tape on the top of the workpiece where the drill bit first enters the wood can also help prevent the occasional tearout on entry.

Taping the wood is not as effective as sacrificing the backer board beneath the workpiece, but it does reduce the chances of tearout. Mark your spot on the tape if using it on the top of the workpiece, of course, and then begin.

There are opportunities to use more than one of these measures when drilling your holes, too.  Using a spade bit doesn’t mean you can’t use the sacrificial board beneath the workpiece; using a Forstner drill bits, too, doesn’t mean you shouldn’t or can’t use that board beneath the workpiece.  It never hurts to hedge your bet to avoid tearout.

Here’s a video, a 2-minute demonstration, that includes both a helical and a spade drill bit, and these steps above to eliminate tearout and give you a clean exit hole.  

Knowing your power drill settings, setting them correctly, understanding the wood you are working with, and taking a simple precaution, will eliminate the chance of tearout.  Take the simple steps, drill with confidence, and avoid wasted wood and wasted time on your project.