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Tips For Drilling Holes

Many DIY hobbies and home projects require drilling holes.  I recently wrote an article on a home wiring project, which required drill many holes. These holes did not need sharp, clean edges, or have to look nice, they just needed to allow a wire to pass through a stud wall. However, there are many home projects and hobbies that require holes that are both functional and that look good. In this article, I’d like to share a few tricks I’ve learned over the years to do just that.

I am going to focus mainly on drilling holes in mild steel and wood. I do have some experience with using core borers and rotary hammers for concrete work and drilling holes in tiles, so if you have specific questions leave a comment and I will do my best to answer your questions. But for 75% of home projects working with metal and wood is most prevalent. When it comes to holes in any materials you obviously start by simply using a drill bit of the appropriate size. Drill bits are made specifically for different materials. Having the correct drill bit is paramount when starting out.

Safety First

I have to stress the importance of using eye protection anytime you are drilling any material. You will also find that hearing protection is also very important as you progress to different materials, making larger holes, and using the different equipment needed to make these holes. Please consider reading my articles on personal protective equipment (PPE). It covers safety when working on home projects.

The second safety “must do” is always secure your material in a vise or securely clamp it to a bench or work table. Never hold the piece you are drilling in your hand! Many bits used for drilling holes, especially larger holes, have a tendency to “grab” the piece that’s being drilled. If it’s not securely fastened down, or you’re holding it in your hand, this can cause serious cuts or injuries.

With that said, if you are using a hand drill, and the drill bit should grab the material, be aware that the drill will twist in your hands. If you are not prepared and do not have a firm grip on the hand drill, this can cause injuries to your hands and wrist. This becomes more of a risk when drilling larger holes and using bigger, more powerful hand drills. The key is to be aware and always be prepared!

Working with Metal

As mentioned above, for small holes you simply put the proper sized drill bit in your hand drill, or drill press, and drill away. If a larger hole is needed, you can start with a small hole, frequently called a pilot hole, and then increase the size of the drill bit and make the first hole bigger. It sounds simple and relatively is that simple. However, there are a few things you can do to make the process a little easier.

Tips For Drilling Holes in Metal

  • First and foremost is to make sure you have drill bits designed for drilling steel. For steel, you will need bits made of high-speed steel (HSS) or cobalt. “Carbon steel” bits should only be used on softer materials like wood or plastic. If you try using the carbon steel bits on steel, it will only ruin the bits and cause you lots of frustration. Good drill bits cost more, but it’s for a reason.
  • Secondly, you should use a little lubricant on the drill bit during drilling. The lubricant helps keep the bit cool and will prolong its life. They make special cutting fluids, but at a minimum use a little WD-40 or motor oil. As mentioned earlier, good quality bits cost a little more, so why not protect your investment for future projects.
  • Another good rule of thumb is that as the size of the hole gets larger, you should slow the speed (rpm’s) of your drill down. Remember the old childhood game of “crack the whip”? Well, the same principle applies. The further out from the center of the hole you get, the faster the bit is traveling. That additional speed will generate more heat and potentially damage the bit. Here’s where a lubricant is very important, especially when using hole saws. Also by reducing the speed, it helps in those situations when the drill bit “grabs” the material. It makes it easier for you to maintain control of the hand drill.

Types of Steel Bits

Step Bit

I’ve already discussed the need for high-speed steel (HSS) bits for drilling metal. But for larger holes, there are a few more options. The first is called the “step bit”. Click on the blue text to see an example of these bits that are available on Amazon. Because each of the steps on the bits range from 1/8” to 1/4”, these bits are normally used on thinner steel or sheet metal. These are great bits because you can drill a variety of hole sizes, without having to change bits.

Reduced Shank Drill Bits

Another option is the “reduced shank drill bit“. These are normally larger diameter drill bits, with the shank turned down to fit into a normal hand drill or smaller drill press. For hand drills, or drill presses with a 3/8” chuck, the 3/8” reduced shank drill bits normally go up to a 1/2” diameter. With the 1/2” reduced shank bits, the drill bits typically go up to 1” in diameter. The 1/2” diameter shank requires you to use a hand drill or drill press with a 1/2” chuck.

These bits are good for drilling through thicker steel. When drilling thicker steel, be sure to use multiple step pilot holes, with increased size each step (1/8”, 1/4”, 1/2”, 3/4”, etc…). Remember, these larger diameter holes are the ones that the drill bits can “grab” the material, so use lots of lubricant, hold on tight, and be prepared.

Mandrel Hole Saw

The last option I will be talking about is called a mandrel holes saw. When cutting metal you need to use the “bi-metal” hole saw. They are designed for cutting metal. You can probably get away with cutting up to 1/4” thick mild steel without to much trouble. Just remember to watch your speed and I would make sure to use plenty of the appropriate cutting lubricant.

Working with Wood

The good news is many of the same principles apply when drilling holes in wood. All the same safety rules apply! You still need to secure your material in a vise or clamp it to a workbench. And you still need to take care when drilling large diameter holes.

Types of Wood Bits

Working with wood doesn’t require the use of HSS bits, but if you need to buy bits anyways, why not by the better bits. You’ll have them for future projects, whether it’s for metal or wood. The above-mentioned bit options will work with wood, as well.  These are the three main options that I use and work well for most home products.

  • The first one is the spade/paddle bit. This is the type I use most of the time for holes up to 1”. The shank size is 1/4”, so it fits in most hand drills.
  • The second option is the auger bit. This is a good bit and seems to be a bit hardier than the paddle bit. They normally have the 1/4” shank, so they work in most hand drills, as well.
  • The third option is the mandrel hole saw.  The teeth on the mandrel hole saws do plug up with sawdust, so you do have to stop frequently and clean them out. But other than that, they cut nice holes.

Tips For Drilling Holes in Wood

The first tip I have to offer applies to drilling holes in both metal and wood. When clamping your material to the top of a workbench, lay a scrap piece of wood down first. This will allow the drill bit to completely go through your material without damaging your work surface or the drill bit.

Also be sure to use a hand drill that can handle the job. For one or two smaller holes, a cordless drill will work fine. If you are drilling several holes, or a few larger holes, be sure to use a heavier duty drill with some horsepower. You can easily over-heat and ruin a lighter duty drill.

#1 issue: One thing you’ll likely encounter when using hole saws on wood, is the starting (front) side looks good, but the back side will be a mess. It will be jagged or have big chunks break out. If the back side is out of sight, it may not be a big deal, but for many projects, that just will not do.

Hole Examples
Hole Examples

The cure: To prevent this from happening, begin drilling the hole normally, but watch for the center bit, of the hole saw, to just start coming through on the back side. Stop immediately! Then either flip the piece over or move to the back side. Now place the center bit of the hole saw into the small hole it just made, when coming from the other side, and begin drilling in the opposite direction. It should make a nice clean cut on the back surface, and then just continue drilling until the hole is complete. You should have a nice clean hole that will only require some light sanding.

#2 issue: What if you’ve cut a hole and decide it needs to be bigger. All of these hole saws have center bits that drill through the wood as it guides the cutting edge/teeth straight through the wood. Before you throw the piece away and start over, try one of these remedies. Both of these methods require the use of a mandrel hole saw to cut the new hole.

Round Stock with Spacer
Round Stock with Spacer
Round Stock and Spacer Installed In Mandrel Hole Saw
Round Stock and Spacer Installed In Mandrel Hole Saw

 

 

Cure #1: The simplest remedy is to find a piece of round stock that fits snuggle into the original hole. Even if you have to put a couple wraps of tape around it. In these photos, I used the plug I originally drilled out. It worked very well! The mandrel cutter’s center drill had something to start in. Once started, it drilled out nicely. Don’t forget to flip it over and drill from the back to prevent those jagged edges.  See the results below.

Hole Enlarged with Mandrel Hole Saw
Hole Enlarged with Mandrel Hole Saw

Cure #2: Another option is to create an adapter to replace the drill bit in the mandrel hole saw. Several years ago I had access to a lathe and made several adapters for different hole sizes. After putting the new desired size hole saw on the mandrel, remove the drill bit and install the adapter, for the appropriate size hole that exists. The adapter should guide the new saw through the wood nicely. These work well for enlarging holes in metal too.

Mandrel Holes Saw with Homemade Adapters
Mandrel Holes Saw with Homemade Adapters

I hope this information helps you when you need to drill some holes for a project. If you use the right equipment, have patience, and work safely, you can drill perfect holes every time! Good luck on your next project.

Squirrel Feeder
Squirrel Feeder


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