# How does a self centering drill bit work?



## charlielo (Apr 2, 2018)

I purchase a bunch of self centering drill bits. The issue I have is, if the metal shaft that covers the drill bit fits the door hinge holes then the drill bit is too big. I don't want to use a huge drill bit. I want to use the metal shaft to self center a smaller drill bit however that is not possible in those that came with mine. Am I using the self centering drill bit wrong? If not, what are some good self centering drill bits brand that I can change the drill bit to different size and the self centering metal shaft would still work?


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## Dave McCann (Jun 21, 2020)

Charlielo,

Are you wanting to drill a clearance hole for the shank (unthreaded portion if there is one) of the screw? or Are you wanting to drill a pilot hole for the screw threads? These two operation will require different size bits. One can also purchase step or tapered bits to accomplish the same thing. You would have to do some measuring to figure out what would be compatible with the centering sleeves you have.


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## _Ogre (Feb 1, 2013)

i'll assume you're working with this type of bit and describing why they don't work well
just use the proper bit for the screw size, even if your off center a little the countersink head will center the screw head


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## charlielo (Apr 2, 2018)

_Ogre said:


> i'll assume you're working with this type of bit and describing why they don't work well
> just use the proper bit for the screw size, even if your off center a little the countersink head will center the screw head


Yes, that's the type of self centering bits I have. If I use the bits that fits the screw, the countersink head is too small so it won't self-centering the bit for me. If I use the countersink head that fits the hole on the hinge than the bit is too big for the screw. That's my dilemma.


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## charlielo (Apr 2, 2018)

Dave McCann said:


> Charlielo,
> 
> Are you wanting to drill a clearance hole for the shank (unthreaded portion if there is one) of the screw? or Are you wanting to drill a pilot hole for the screw threads? These two operation will require different size bits. One can also purchase step or tapered bits to accomplish the same thing. You would have to do some measuring to figure out what would be compatible with the centering sleeves you have.


I'm drilling a pilot hole for the screw.


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## _Ogre (Feb 1, 2013)

i meant... throw those in the trash and use a regular drill bit for the screw


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## kwoodhands (May 1, 2020)

Those bits are called Vix bits. I have 3 or 4 different sizes. For door hinges the drill itself is stationary and the shell is spring loaded. Almost impossible to drill a pilot hole off center, even if you tilt the drill motor. I am a retired carpenter and probably hung more than 1000 doors, more like 2000 I think. Before Vix bits i used a hand held spring loaded center punch similar to a vix bit but hammered instead of drilling. The smallest size is good for piano hinge holes and other small hardware. The next size I do not recall what if ever i used it for. The fourth size is too large for ordinary door screws.
I used this bit on specialty hardware with large screws like Rixon pivots hinges. The third size is most commonly used for door screws.
mike


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## Terry Q (Jul 28, 2016)

You need to pick the vix bit you use based on the size of the screw, not the size of the hole in the hinge.

If there wasn’t a chart that came with your bits, look for one online that shows what pilot size holes are needed based on screw size and hardness of the wood.

The screw head needs to fit in the hole in the door hinge and if is sized properly, will work with the proper sized vix bit. The vix bit only has to center itself in the bottom of the hole in the hinge and I’ve never yet had it not work properly.


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## charlielo (Apr 2, 2018)

Terry Q said:


> You need to pick the vix bit you use based on the size of the screw, not the size of the hole in the hinge.


I'm not sure if I explained this correctly but here's the issue. I pick the vix bit that fit the size the screw but the spring loaded shell is too small for the hole of the hinge; thus, it's not self centering the drill bit at all. And if I choose the counter sink shell that will fit the hole of the hinge then the drill is too big for the screw I want to use. The solution I see is an interchangeable spring loaded shell that allows me to put in different size drill bit but that's not what I got. The one I purchased I can change the drill bit but since the spring loaded shell use an Allen key to tighten the drill bit to the shell, that means the drill bit is going to be off center since shell is way bigger than the bit itself so when I drill the pilot hole, it's not going to be in the center. This is assuming the Allen key that is used to tighten the drill bit to the shell is long enough since the bit is now much smaller size and none of mine Allen screw is long enough.



Terry Q said:


> The screw head needs to fit in the hole in the door hinge and if is sized properly, will work with the proper sized vix bit.


The screw head fits the hole of the door hinge but that does not mean the screw is also big at least those that I use.


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## danrush (Oct 16, 2017)

charlielo said:


> Yes, that's the type of self centering bits I have. If I use the bits that fits the screw, the countersink head is too small so it won't self-centering the bit for me. If I use the countersink head that fits the hole on the hinge than the bit is too big for the screw. That's my dilemma.


I've run into this at times on installs. What I do is use the self censoring bit that fits the hole, but just barely drill into the material. That marks your center. Now switch to the smaller proper size drill to finish your hole freehand.


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