# Pilot/shank hole



## wsommariva (Jan 3, 2010)

I made a workbench from a nice plan I bought. Called for making shank holes, which I now know are holes that are bigger than the screw.

Question is: When joining two pieces of wood is it always best to drill a shank hole? I always used a bit smaller than the screw, which I called a pilot hole.


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## GeorgeC (Jul 30, 2008)

wsommariva said:


> I made a workbench from a nice plan I bought. Called for making shank holes, which I now know are holes that are bigger than the screw.
> 
> Question is: When joining two pieces of wood is it always best to drill a shank hole? I always used a bit smaller than the screw, which I called a pilot hole.


Theoretically that would be nice. However, practically it would be a pain in the butt.

G


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## jlhaslip (Jan 16, 2010)

A pilot hole larger than the screw shaft will stop the two pieces from 'bridging' as the screw is installed. It also allows some wiggle room for positioning and wood movement.
Predrilling makes the installation of the screw easier and reduces splitting.
The two are used for different purposes. If (relatively) stable material is being used, predrilling will suffice. When you expect movement, or in brittle material, piloting is suggested.

http://www.renovation-headquarters.com/pilot-hole.htm


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## rrich (Jun 24, 2009)

Assuming that you're using the screw to hold two pieces together while the glue sets or for assembly purposes, the shank hole serves an important purpose. The shank hole allows for a greater holding strength and eliminates bridging. All of the screw holding power is applied from the bottom piece toward the piece with the shank hole. Because there is a shank hole, the threads of the screw do not force the wood to bubble where the screw exits the top piece. Thus you're not building a bridge. And yes, drilling body holes (a.k.a. Shank holes) is a PITRE.


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## wsommariva (Jan 3, 2010)

Thanks George

JLhaslip, thanks for the link, very helpful.

Thanks rrich; what's bridging and PITRE? Wait, I figured PITRE out.


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## rrich (Jun 24, 2009)

wsommariva said:


> * what's bridging*


Think of the way that a bridge is built. There is usually a couple of piers with a span between them. When you drive a screw through the top piece, the natural action of the thread pushes a bubble of wood out between the top and bottom piece. 

The bubbles act as piers and the top piece becomes the span.


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## wsommariva (Jan 3, 2010)

If I understand correctly, the bubble is in between the two pieces of wood, compressed when the screw is all the way in?


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## rrich (Jun 24, 2009)

wsommariva said:


> If I understand correctly, the bubble is in between the two pieces of wood, compressed when the screw is all the way in?


Hopefully but usually never happens. Then the screw is over tightened.

It is the principal of two objects trying to occupy the same place at the same time. As the screw threads its way through the wood, the wood displaced has to go someplace. Through a good portion of the top piece, the wood is compressed radial to the screw. As the screw protrudes through the top piece the bubble is created.

As the screw enters the bottom piece a second bubble is created. The two bubbles become the pillar of the bridge.

How to get around the problem. Drill holes, obviously. Also if the two pieces are clamped it is possible to join the pieces without drilling however the clamp should remain in place until the clue cures. If you are going to clamp, why bother to use screws?

The questions for (gawd I hate this term) fine furniture are...
Is the joint going to show? Yes, then you have to drill.
Is the joint in an area where it won't be obvious? Yes, then it's your choice.
Are you assembling something that must be square? Yes, then drill.

Are you building for the shop? Probably don't worry about it.
Are you building a shop jig? ABSOLUTELY drill.

As you can see, it's not an easy true/false decision. You have to think about the final product and your expectations for the result.


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## wsommariva (Jan 3, 2010)

I understand. For good appearance always drill the holes. For a rough item like my shelving I built for my scrap wood, not necessary, but helpful. 

Thanks again to everyone, I learned a lot (from my several posts)


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## BHOFM (Oct 14, 2008)

That is what tapered bits are for. I have used this
set for years and it is faultless! And cheap!

I know ,, I know Harbor Freight! UGH UGH!

But this is one that is a great buy!










http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=7608

Comes in a nice little wooden box too!:laughing:
The damn box is worth the price!:yes:


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## cabinetman (Jul 5, 2007)

I don't use tapered wood screws, but rather straight shank screws like the drywall type. I drill pilot holes, and the size of which is the diameter of the gullet between the threads.

I relieve (slight chamfer), the two places where the drill bit exits one piece and enters the second piece. That way, when the screw goes through both pieces there won't be particulate between the pieces keeping them from pulling up tight. 

I don't drill shank holes, because I use straight diameter screws and prefer them threaded all the way to the head. Threaded like that, the top piece gets locked against the bottom piece. So, you ask where the debris goes as the screw is driven...whatever there is, in between the gullets (theoretically, there shouldn't be any). I use a combo countersink/pilot bit.


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## wsommariva (Jan 3, 2010)

For my workbench project I used the wood screws per the plan. For all my other work, such as building shelves for the basement where pretty isn't important, I use drywall screws. When I go to Home Depot/Lowes I hang around and wait for someone who seems to knows what he's doing - I have received some great advise this way. One guy told me to never use those wood screws, use drywall screws.

I did buy that pilot counersink duo - worked very well


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## jlhaslip (Jan 16, 2010)

Drywall crews are only a number 6 size and are weak. My battery drill snaps them off. I use plated exterior deck screws that are #8 size for almost everything. Predrill with a tapered countersink set about 1/4 shorter than the screw.


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## wsommariva (Jan 3, 2010)

I've had several wood screws snap, the drywall screws seems much stronger. I've used the exterior deck screws for outside work. Will consider them when I need maximum strength.


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