Lucky for me, the first time I ever tried to fit a 1/2″ drill bit into a 3/8″ drill, my dad was around to help. As I stood there, panicking that I wasn’t going to be able to drill a large enough hole, my Dad calmly mentioned three different solutions for dealing with a drill bit that was too big for the drill.
If your drill bit is too large for your drill, the easiest thing to do is use a different type of drill bit. Spade bits, Forstner bits, and hole saws are all designed to drill large holes using a normal-sized drill.
I’ll dive into each of these options in more detail, as well investigate a few other options as well, so keep reading!
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Use a Spade Bit to Drill Large Holes in Wood
Spade bits are easy to use, given you’re trying to drill a hole in wood. They come in a wide variety of sizes, and are accessible and affordable. A set of 5-6 spade bits typically costs around $10.
The center point embeds itself in the wood, acting as a pilot point for the rest of the bit. The two sharp edges then spin around, carving a circle around the pilot point.
Spade bits drill holes in wood quickly, however the “back” end of the hole tends to be a bit messy, since the bit flies through and blows out the back of the hole. This is the biggest downside of using a spade bit.
To avoid this problem, clamp your piece of wood to a scrap piece of wood before you start. Then your drill bit will simply drill through the back and straight into the next board, preventing blowout.
Another solution is to drill the hole until the point just pokes through the other side of the wood. Then flip the board over, and drill from the other side.
Spade bits come in a variety of sizes, and can be used with a corded drill, cordless drill/driver, or drill press. They are drill bits intended for wood only; metal or masonry can’t be carved the same way wood can be, and therefore spade bits are ineffective.
It’s also worth noting that spade bits struggle to enlarge already drilled holes, since they require a pivot point to work. To get around this, I’ve sometimes clamped plywood to the back of the hole, and used that to be my pivot point. However, this tip only works if your main piece of wood is relatively thin.
Forstner Bits Drill Large, Clean Holes in Wood
If you’re looking for something a little bit neater than a spade bit, a Forstner bit is a great choice. They’re precise tools that, when used with a drill press, create a perfect diameter hole with a flat bottom.
While Forstner bits can be used with a portable drill, they’re harder to use and won’t be as precise.
Because they create a flat bottom, they’re the ideal drill bit if you’re drilling a hole that won’t go through the entire thickness of the wood. This is especially true if the depth of the hole matters, since with a drill press, it is easy to repeatedly drill identical holes. You can see an example of this in action in my Pikler Triangle build.
Forstner bits are also significantly more expensive than spade bits, making spade bits my go-to recommendation for beginners. As a quick comparison, a mid-level set of Spade bits typically costs around $10 for a set of 8. This mid-level set of Forstner bits costs $25.
Once again, Forster bits are a wood-only drill bit.
Hole Saws Drill Large Holes in a Variety of Materials
Hole saws are a circular drill bit with teeth at the edge of the circle. The teeth drill through the circumference of the circle, ultimate drilling a hole through the material. While Spade bits and Forstner bits drill holes up to 2 1/2″ in diameter, hole saws can drill holes much larger than this.
As an example, I first purchased a hole saw to drill a 3″ diameter circle in butcherblock for a kitchen faucet installation. That’s the type of circle hole saws are best for.
Because hole saws only cut the circumference of the circle, they can only be used to drill holes that go entirely through the material. They’re slow-going saws, but crucial for drilling large holes. Like Spade bits, hole saws do a poor job of expanding an already drill hole.
Hole saws intended for wood are inexpensive drill bits, starting around $5 a bit. Hole saws intended for masonry and metal are sold in home improvement stores as well.
Reduced Shank Bits Can Be Used Like Traditional Drill Bits
Reduced shank drill bits are traditional twist drill bits that have a smaller base that fits into the chuck of a normal drill. These exist primarily for metal and masonry applications, but reduced shank wood drill bits are sold as well.
The price of these bits largely depends on the material the bit is built for (wood vs metal vs masonry,) but you can typically purchase a set for around $30.
If you’re simply looking to drill a 1/2″ hole through wood or plywood with your 3/8″ drill, I’d grab a spade bit. But if you’re looking to drill a medium sized hole (1″ or less) through metal, reduced shank bits are a good option.
Alter the Drill
The drill bits listed above are truly the best option for drilling holes larger than your drill size. However, if for some reason none of the options work, you can always alter the drill itself.
There are two ways to do this. First off, chuck adapters exist. This one by Makita is a great example. However, these chuck adapters are typically intended to to be used on an impact drill to make them compatible with normal drill bits, not to make a drill accept larger bits.
The problem with using these chuck adapters on a normal drill is that the drill motor might not be strong enough to drill using this system. It’s worth a try, however.
The other option is to replace the chuck entirely with a chuck that has a bigger hole. Drill chucks (the part that holds the drill bit) typically come in either 3/8″ or 1/2″ sizes, so if you have a 3/8″ drill, you can replace the chuck so that it accepts 1/2″ drill bits.
Drill chucks (such as this one by Ryobi) typically cost between $20 and $50.
Final Option: Get a Larger Drill
It probably goes without saying that buying a new drill is always an option. As mentioned above, drills typically come in 2 chuck sizes, 3/8″ and 1/2″. If you want to be able to regularly drill holes with a twist drill bit up to a 1/2″ in diameter, it might be worth getting a new drill.
You also might be looking for an excuse to buy a new drill. This is the excuse you’ve been waiting for. Go for it!