How to Drill Into Thick Metal When Making Vehicle Modifications
Ever tried to drill into thick steel—like the frame of your off-road rig—using an underpowered, well-loved drill that’s probably older than you are? Welcome to the club.
If you do much modifying and fabricating for overlanding or serious off-roading, sooner or later you’ll need to bust out the bits and punch some holes through your vehicle’s chassis, bumpers, or other metal parts. Here’s my not-so-secret system for drilling clean, accurate holes in thick metal without throwing out your back or completely destroying your drill bits. (Though no promises about your sanity.)
Why Drill Into Thick Metal?
Whether you’re adding rock sliders, custom racks, or new suspension components, drilling into the vehicle’s frame or other heavy steel parts is a necessary evil. But if you’re not careful—or if you just jam a giant bit into that steel out of sheer bravado—you’re likely to waste a ton of time, snap bits, or end up with crooked holes that don’t do you much good.
In the article below and video above, I share how how I’ve learned (the hard way) to drill into thick metal. Please wear appropriate protective equipment (gloves, arm and eye protection), which I’m not doing in the video above.
Step 1: Start Small (Pilot Hole)
Trying to jump straight to your monster bit is like skipping the warmup before a trail run. Instead, grab a small pilot bit first. For example, for a 7/16″ hole through my Jeep frame, I used a 13/64″ pilot bit.
This gives you better control and accuracy, and it also reduces the strain on you and your drill. Once the pilot hole is done, you’ll have a center mark and a path to follow.
Pro Tip:
- Use bits with a hex shank if you can. They lock into the drill more solidly than round shanks and won’t spin in the chuck.
Step 2: Size Up (Step Bit)
Next, use a step bit (also called a unibit) to incrementally open that hole. Each “step” on the bit is marked with a size, so it’s easy to track your progress. A step bit cuts smoothly and makes the transition to larger diameters much less painful. I bought a set from Milwaukee that I’ve been happy with.
One Catch: Some metal components are thicker than the width of a single “step.” Don’t worry if the bit doesn’t fully punch through at the size you want—you’ll finish the job with your final bit anyway.
Step 3: Finish the Hole (Final Large Bit)
Once you’ve got a pilot hole and a partially expanded hole from the step bit, it’s time to bring out the big guns—the actual full-size bit you need, whether that’s a 7/16″ or larger. With the hole nicely prepped, your big bit won’t have to work nearly as hard. You’ll get through that steel a lot faster, and your arms will thank you.
Cutting Fluid Is Your Friend: Drilling metal generates heat. Too much heat will burn out your bits (and maybe your skin if you’re not careful). A few drops of cutting fluid can drastically reduce heat and friction, saving both your bits and your nerves. I use Tap Cutting Fluid.
Mind the Molten Metal (Safety Tips)
- Cover Up: Hot metal chips love to land on your hands, arms, and anywhere else they can leave a souvenir. Gloves, long sleeves, or even a rag draped over your hand can help avoid those little scorched souvenirs.
- Watch Your Drill: An older or lower-power drill can struggle to grip large round shank bits. Make sure the chuck is as tight as you can manage, and if possible, upgrade to hex shanks. Use that cutting fluid to keep the bit cooler.
- Eye Protection: Let’s just say sizzling metal flakes in your eyes are never “an adventure.” Keep some decent goggles on. (I wore reading glasses in the video above, but really should have been using more protective safety glasses or goggles, or a face shield.
Tapping Threads (Optional but Handy)
Sometimes you’ll need threads in those holes, for example when installing rock sliders or other bolt-on parts. If so, you’ll also want to:
- Use Cutting Fluid: It helps ease the tap through and prevent binding.
- Go Slow: Keep the tap straight and back it out gently to clear chips.
- Check Your Angle: Being slightly off-axis can lead to misaligned threads—or snapped taps.
Wrap-Up
Drilling big holes in heavy steel can be a frustrating process – but it doesn’t have to be. By starting with a small pilot bit, stepping up to larger diameters, and finishing with your final big bit—plus a healthy dose of cutting fluid—you can make quick, clean holes in your vehicle’s frame, sliders, or any other tough metal project you’ve got.
Stay safe, cover up, and get out there to conquer the road … or lack thereof.
Got a better trick for drilling into steel?
Share your sage wisdom in the comments. And if you’re reading this while picking out metal splinters from your clothes and hair—welcome to the club. We’ve all been there.
