Drilling a Countersunk Pilot Hole In
Today we are going to learn how to make a countersunk pilot hole in wood from our fastener expert, Bob. He told us that he has seen many people attempt to drill this hole and approach it the wrong way. Most people start the same way the would if they were using a standard drill bit. First the pilot hole, then the countersink. This however, does not work with spade bits due to the way the drill bit is engineered.
A countersunk hole is where a secondary larger hole is cut on top of the first hole so that the head of the nut or bolt can sit inside of the material and not be exposed. There are many applications for these types of holes and you probably see them around quite often without even realizing it. Fasteners may be countersunk in furniture, buildings, banisters, decks, etc.
Spade Bits have a triangular tip that digs into the wood before the outer edges of the bit do. This not only acts as a guide for the rest of the bit but as a stabilizing factor as well. Bob told us that if we drill the pilot hole first we would have a hard time drilling the countersunk area and would damage the wood.
He set out to give us an example by showing us the proper way to install a lag screw into some wood.
- 5/16″ Spade Bit (For the pilot hole)
- 1-1/4″ Spade Bit (For the countersink)
- 9/16″ Socket
- 3/8″ Lag Screw
- Safety Gloves
- Safety Glasses
The first step when drilling a countersunk hole with a spade bit was to start with the countersink itself. This will allow both the larger spade bit (countersink) and the smaller (pilot hole) to grip the material and prevent “wobbling”.
So first we drilled the countersunk hole and then we set about drilling the pilot hole inside of the countersunk hole. It was a surprisingly easy task.
We tested this again by doing the process backwards and determined that what our fastener expert had said was true. Not only was it difficult to drill the holes but there was some significant chipping to the surface of the wood. While we were able to drill the hole the result was an unprofessional mess.
Our fastener expert also chose a very large spade bit for the countersink which he later explained was to allow breathing room for the socket that he would use to install the lag screw. Otherwise, it will be difficult to install without the socket getting caught up in the hole.
After comparing the two holes, we determined that the hole we drilled first (properly) was much better. The edges were smoother, barely any chipping on the outside of the wood, everything was in good shape. The second hole was abysmal. With chewed up and chipped edges from the bit bouncing around. Our fastener expert said we can do even better. Pulling out a roll of his trusty blue painters tape, he laid it over the wood and drilled the countersunk pilot hole again. This time there were virtually no chips in the wood at all. The tape re-enforced the edges of the hole being drilled to prevent chipping.
Below are the three drilled holes and the results:
- Hole 1 – Left – Was done properly with no tape. Light chipping occurred around the edges but was still a fairly clean.
- Hole 2 – Middle – This hole had the pilot hole driven first and as a result has heavy chipping around the external edges. The inside edges also weren’t smooth from so much bouncing around.
- Hole 3 – Right – Done by first covering with blue tape, then drilling the countersunk hole and then the pilot hole, this hole is the cleanest of all three with virtually no chipping and clean sides.
How To Drill a Countersunk Pilot Hole With Spade Bits
How To Drill a Countersunk Pilot Hole With Spade Bits Transcript
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Bob: Welcome back to Albany County Fasteners – Fasteners 101. I’m Bob and today I’m going to show you how to properly drill a pilot hole, along with a countersink, using a spade bit. So let’s get started.
I have here two Spade bits. I’m going to drill a pilot hole and a countersink with these two Spade bits. These are wood Spade bits and I’m going to drill for this 3/8″ lag screw I have here. I have my ratchet too.
So, what’s key here about the pilot hole, I’m sorry, about the countersink hole is that you need to have enough diameter to be able to use a ratchet to drive the lag screw. It’s important that you get the right size. So for a 3/8” lag screw, I’m using a 5/16” pilot hole and a 9/16” socket. I’m using an 1-1/4” spade bit to basically give me enough room. So if this moves around, it’s not tight. It makes it very hard to get the socket out. It becomes a real issue.
Now I’m going to use a ratchet to put this in. There’re many other things you can use, such as a pneumatic. They have some cordless drills that you can use today to install the lag screw. This is for demonstration purposes, so I’m just going to do this.
The first thing that you need to do, and what not to do, is you never drill your pilot hole first. If you drill your pilot hole first, which I’m going to demonstrate to you what happens, if you drill your pilot hole first. So using your 5/16” for the 3/8” bolt, when you go to drill your countersink, it’s gonna swash around inside and undo your pilot hole. It won’t guide properly. With a spade bit, this little diamond shaped blade point is what guides the drill bit and holds it in place. If you were to drill this hole with the Spade bit for 5/16”, it’s just gonna be too big. Then this is gonna jump around, and it’s going to jam the drill and you possibly could hurt yourself. So I’m gonna demonstrate this now. I installed my spade bit into the drill, and I’m basically ready to do my countersunk hole. You always have to do your countersunk hole first for the head, and then again for how far you’re gonna go down. Basically, I’m gonna countersink approximately 3/4” to 1” into this wood. Now I have gone down about 3/4”, which will be a nice countersink.
I’m gonna switch out my bit and put my pilot hole in, tighten that up, and put this bit in. I’ll continue drilling until I get through the other side. Always back up to bring the wood shavings out. Well that didn’t work right. Huh. I guess I didn’t tighten it enough. I’ll just tighten it up. I’m gonna take my ratchet and drive it in. There you go. That’s done.
Now I’m gonna demonstrate for you what happens if I drill my pilot hole first. Now this is not a big pilot hole but if you were using a larger size, such as 1/2”, it’s gonna be more severe. I’m gonna drill the pilot hole first. You can see this nicely drills through. No problem. Switch out my bit to do my countersink. As you can see here, this will now wobble around. With that wobbling around, you’re not gonna get a totally centered countersink. It’s gonna want to take off. I have to be cautious. If I go too fast it’s gonna jump around on me and it may wedge the bit in the hole and start to twist at my arm.
You can see already how this is chewing away at the wood. That’s not what we’re looking for. You see how that’s jumping around? You can do it, you can get the countersink done, but it’s not precise. It’s not clean. It doesn’t give you a nice clean finish. So at the end of the day, you really want to drill your countersunk first and then your pilot hole.
Another thing to do, if you wanted to stop the splintering, is to put some blue tape over the area you’re gonna drill. This is very good for marking as well. You can write on blue tape. Let me just find the beginning of this tape…there it is. This will stop splintering from happening when you’re using a spade bit. So I’m going to do another countersink. That gives you a nice clean surface. You can see how nice and smooth that cut is.
I’ve used these bits before. I’m doing this for demonstration. These bits are not brand-new bits. (With) Brand-new bits you would have a nice, sharper point. I think you can see how nice I could drill through here. Then you take off the tape and there you go.
That’s how you properly drill a countersunk with your pilot hole. Thanks for watching.