# Rules on Pilot Holes and Why do they work?



## Evil Scotsman (May 30, 2008)

I know the purpose of drilling a pilot hole is to keep the wood from splitting. But how does it keep it from splitting? And what size pilot hole needs to be drilled? For example if drilling a 1/4" hole would an 1/8" pilot be correct?:huh:


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## TS3660 (Mar 4, 2008)

Good question. The pilot hole should be the diameter (or slightly larger) of the root of the screw you're going to use. The best way to measure the root of a screw is with calipers because they can get between the threads. Or, simply hold the screw in front or in back of a drill and eyeball it up. In other words, guess at it. It also depends on what kind of wood it is. The harder the wood, the bigger the drilled hole must be. Basically, when the screw enters the wood, you only want the threads biting into the wood, not the shank of the screw.


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## cabinetman (Jul 5, 2007)

TS3660 said:


> Good question. The pilot hole should be the diameter (or slightly larger) of the root of the screw you're going to use. The best way to measure the root of a screw is with calipers because they can get between the threads. Or, simply hold the screw in front or in back of a drill and eyeball it up. In other words, guess at it. It also depends on what kind of wood it is. The harder the wood, the bigger the drilled hole must be. Basically, when the screw enters the wood, you only want the threads biting into the wood, not the shank of the screw.



That's a very good answer. I don't use any fancy calipers as then I'd have to figure out the size measured to an appropriate drill bit. I just eyeball it like you described. I also don't use any wood screws that are tapered, and prefer screws that are threaded all the way to the head.


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## Juniperlampguy (Nov 11, 2007)

TS3660 said:


> Good question. The pilot hole should be the diameter (or slightly larger) of the root of the screw you're going to use. The best way to measure the root of a screw is with calipers because they can get between the threads. Or, simply hold the screw in front or in back of a drill and eyeball it up. In other words, guess at it. It also depends on what kind of wood it is. The harder the wood, the bigger the drilled hole must be. Basically, when the screw enters the wood, you only want the threads biting into the wood, not the shank of the screw.


Ditto!! Glad to know I'm not the only one that does it like that. Eyeballing and guessing at it is the method I've been using for years.:yes::thumbsup:


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## joesdad (Nov 1, 2007)

Great topic. Great answers.

But the million dollar question is how many curse words do you mutter when you snap a pilot bit off in your project?...:laughing:...:yes:...

On the same note my favorite countersink bits are the Dewalt tapered. But that was when I used to be able to charge them on the old bosses account.
They're a little spendy.:thumbdown:


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## mmwood_1 (Oct 24, 2007)

Evil Scotsman said:


> I know the purpose of drilling a pilot hole is to keep the wood from splitting. But how does it keep it from splitting?


When you try to drive a screw into wood without a pilot hole, the threads will cut in laterally, but the shank (or root, as it was previously called) has to have somewhere to go, hence it forces the wood apart. This is what can lead to splitting. If you have a pilot hole, the shank has an empty space to go into, while the threads cut laterally around that space. 

Softer woods tend to be more forgiving about this, and nails driven into them can often penetrate without splitting. This is why framing can be nailed together without pilot holes for the nails. But harder, drier woods don't give as much.


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## Evil Scotsman (May 30, 2008)

mmwood_1 said:


> When you try to drive a screw into wood without a pilot hole, the threads will cut in laterally, but the shank (or root, as it was previously called) has to have somewhere to go, hence it forces the wood apart. If you have a pilot hole, the shank has an empty space to go into, while the threads cut laterally around that space.


Thank You ALL for your answers, I understand it now. Plus it actually explains how a screw works! Duh on my part. (Never really even thought about it before, just did it!)

I was under the impression that the cutters actually split the wood, but that all makes 100% perfect sense. Thank You all AGAIN for clearing things up for me!:yes:


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