# Screws on butt join are making a gap between pieces?



## ng80092a (Mar 7, 2021)

I've bought these screws, but noticed that even when I use clamps to keep the pieces together, these screws will lift up the first piece a little bit, creating a gap.

Is this normal? How can I avoid this?


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## Unfinished Projects (Mar 9, 2021)

How about drilling the first layer and the threads in the second layer will pull it in.


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## m.n.j.chell (May 12, 2016)

If you don't want to pre-drill the top board, then try this.
Drive through the top board and a few threads into the second one. That starts the hole. The back it out until the surfaces are flush again. Press hard and start driving the screw in again. I've done this many times, and it usually works to secure the joint with no gap.


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## NoThankyou (Mar 21, 2018)

You should pre drill the top piece. It does absolutely no good to allow threads to grip in the top piece and may be part of the problem. When you countersink for the head of the flat head screw in the top piece, also do a slight countersink on the exit hole. The reason being that when the screw bites into the bottom piece it also forms a mushroom or volcano around the screw. The back side or exit for the screw is then able to absorb the mushroom and permit a non-interference contact between both pieces.


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## FrankC (Aug 24, 2012)

I don't like using screws with full threads, a smooth length of shank will eliminate your problem most of the time if you don't want to drill the top piece.


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## shoot summ (Feb 21, 2014)

Here's what is happening.

Notice when you drive the screw through the first piece it takes a few revolutions to get it started?

Same thing happens when it tries to drive into the second piece, but with the threads engaged in the first piece the screw is still moving through the first piece, so you get a gap.

I typically just back the screw out, and re-drive it, closes the gap. Pre-drilling the first piece will fix it also.


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## yomanbill (Jul 7, 2020)

I agree with the above. You can easily and quickly fix the issue by drilling the screw hole in the first piece large enough so that the screw can spin freely in it. The screw threads only need to bite into the second piece.

Having said that, there is another way. You say that you clamped the pieces, but you don't say how. Without the larger pilot hole, you need to clamp the pieces together with enough pressure to overcome the tendency of the screw to push them apart. The pressure needs to be enough so that the two pieces act as one. Then the screw will pass through the joint area as if both pieces were a single piece of wood. This, of course, is not always easy or possible to do.


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## kiwi_outdoors (Jan 15, 2020)

True woods screws are designed for wood, using the full-thread types of screw is counter productive - and you can see why with your joints separating.


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## ng80092a (Mar 7, 2021)

Thanks for the great tips guys, I had no idea that was the cause. I always pre drill before screwing, but it makes some sense that the fully threaded screw pulls back the piece.

For example I got these now:

And in my kit I only have drills with 2, 3, 4, 5.

I'm assuming that on the first piece I have make a drill 4, and on the end piece a drill 3. Is this correct? I need the countersink to be as tight as possible.
If so, I'm planning to use a bit of duct tape on drill 4, so that only its thickness is receives the clean part of the screw is drilled. Is this the right technique?


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## Tool Agnostic (Aug 13, 2017)

There are also special tapered drills designed to match the numbered screws. Many of those tapered drills come with countersinks to match the screw heads so they sit flush on the surface of the wood. 

I don't know where you find them in Belgium, but they are easy to find in the US.


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## ng80092a (Mar 7, 2021)

Tool Agnostic said:


> There are also special tapered drills designed to match the numbered screws. Many of those tapered drills come with countersinks to match the screw heads so they sit flush on the surface of the wood.
> 
> I don't know where you find them in Belgium, but they are easy to find in the US.


I'd not be surprised, since the US works much more with wood than european countries, besides I searched trough every of the 24 pages of our main brico store that included the word "drill" in dutch.
And couldn't find one. Either it's lean hole, or you have a little cone shaped, to hide the screw head in the wood (below there's a picture for reference) but I might be wrong.

Résultats de recherche pour 'boor'












Anyways the real question is, for 3.5 and 4 screws, what lean drills should I use for the countersink, and for the screw? 
I've read that in some cases for a fully threaded screw it should be 80% of the diameter, some sources say half the diameter.

But I need the countersink to be as tight as possible, should I use a full hole of 3, for the nº4 screw?


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## yomanbill (Jul 7, 2020)

The method I use is measure the diameter of the smooth shank with my calipers and use that size drill for the first piece and then measure the diameter of the shank between the screw threads and use that size drill (or slightly smaller) for the second piece.


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## FrankC (Aug 24, 2012)

I like these Wolfcraft bits, drill one once and drive the screw.


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## allpurpose (Mar 24, 2016)

Just because..no reason in particular I HATE Spax screws.. They've caused me more trouble than they're worth.. I don't really know what brands I'm currently buying as long as they're not Spax.. maybe I'm Spax cursed or something, but I hate em!


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## woodnthings (Jan 24, 2009)

DaveSmithJr said:


> Hi buddy, I've taken a look at your problem here and I can say with confidence that everything is fine.


Seriously, when 10 other members have suggested how to fix it? You would say "everything is fine" and leave it alone, come on.


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## DrRobert (Apr 27, 2015)

Clamping the pieces prior to drilling or screwing avoids the issue. Tapered countersinks, take the time to adjust them to the correct depth.

AP, I hate Spax too, but I keep buying them. For many years all I used were square drive Robertson, its nice to have a screw that sticks to the bit and doesn't wobble all over. I'm going back to them eventually and when I do, I'm buying 1000 of every size. Make way, McFeeley's, here I come!!!!


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## Rebelwork (Jan 15, 2012)

I just use the dewalt flip bits..Not sure if you can get them at home depot anymore..


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