How to stop wood from splitting?

[Wade Lippman]

I am making two nightstands. The legs are made of 3/4x2" cherry and the aprons are 3/4"x1.5". The aprons have 2 pocket screws in either end.
When I screw the aprons into the legs so that it is into the 3/4" thickness, the legs split. I tried clamping them first so they can't split, but they do as soon as I take the clamp off.
I made one already. I got glue into the split and clamped it tight. It held together, so I guess it is fixed, but I would prefer to avoid the split. Any suggestions? I expect a pilot hole would help, but am not sure how that would work. You blunt nails to avoid splitting... would blunting the screws help? I could use 1" screws instead of the proper 1 1/4" screws; but it would weaken the table.
On Facebook I saw a demo of a guy heating the screws in a propane torch first and that stopped them from splitting. Sound silly, but it worked in the demo.
Okay, I shouldn't have made the legs 3/4", but since I did, how can I avoid splitting.

[Mel Fulks]

Bees wax works the best ,but paraffin wax ,or even furniture paste wax helps. Use two sizes of drill bits . Largest size close as possible to size
of beefy part . Smaller diameter bit for the threads. Test on some left over wood scraps, to “be sure you are right, then…go ahead “.

[Michael Burnside]

For sure you need pilot holes with something that small, no question. You barely need the threads to grab and with a little glue they'll be strong enough. I had this happen on some smaller legs made of maple and as an extra step, I had to drill a 3/8 hole and insert a longer dowel with a little glue to shore up the leg. This gave something for the screw to bite into and prevented the leg from spilling again.

[John TenEyck]

What you are doing sounds no different than building face frames. That stock typically is 3/4". So I don't understand why you are having trouble. 1-1/4" screws are the right length, but they need to be the fine thread ones made for hardwood. Is that what you are using? If yes, and the problem is the leg is splitting when you drive the outboard screw, then that means that screw needs to be further away from the end. There should be no need to wax, heat, etc. the screws, but if it helps, so be it.

John

[Mel Fulks]

I see it in a different way. Who among us has not bought knocked down furniture that came with those skinny screws ? Did they hold?

[Tom Levy]

As John said above, you could have an incorrect pocket screw setup. Re-check your drill jig setting and drill bit collar setting, if they are going in too close you'll split even if using the right screws. There isn't a way to pre-drill the leg piece with pocket screws that I'm aware, but they are designed to be used without pre-drilling with the correct screw type/length. The caveat is ensuring the setup/operation procedure is followed exactly as specified.

[Michael Burnside]

Tom, you wouldn’t pre-drill, you would clamp (which you should do with pocket screws anyway) and then drill.

[John TenEyck]

Maybe you haven't used pocket screws, Mel, or perhaps not the Kreg jig. You only pre-drill the piece with the pocket, in this case the rail. The drill has a step in it. When properly set up, it drills both the pocket and pilot hole for the threaded section of the screw, but it does not drill out the end of the piece. Then the two pieces are firmly clamped together, and the screw is inserted and driven through the remaining, unbored section of the first piece and into the also unbored second piece. It's been that way since the invention of the Kreg jig for drilling pocket holes. When set up properly they work w/o splitting, unless you get too close to the end of a piece, as discussed above.

John

[Patty Hann]

Bees wax works the best ,but paraffin wax ,or even furniture paste wax helps. ...“.
Sorry for the minor thread hijack, but I have to ask this...
Why is beeswax superior to paraffin? My Dad kept a chunk of Beeswax in his shop for greasing screws, but I never thought to ask him why he just didn't use an old candle or [canning] paraffin wax.
So why is beeswax the "bees knees" :D when it comes to greasing screws?

[Mel Fulks]

John, thanks for more detail. If I ever used those, it’s forgotten now !

[Myles Moran]

Just to verify, are you using the actual pocket screws? They have self drilling cut in their tip, vs a pan head screw that might not. That feature helps with splitting when driving the screw into something without a pilot hole.

[Kevin Jenness]

When I use pocket screws on dense wood close to the end of a stile I use a 1/8" x 6" aircraft drill to drill a pilot hole. Self-drilling screws help, but they don't clear the swarf. Drill first and there's room for the screw.

[John Kananis]

Is your jig maybe set up for half inch material?

[Lee Schierer]

You only pre-drill the piece with the pocket, in this case the rail. The drill has a step in it. When properly set up, it drills both the pocket and pilot hole for the threaded section of the screw, but it does not drill out the end of the piece. Then the two pieces are firmly clamped together, and the screw is inserted and driven through the remaining, unbored section of the first piece and into the also unbored second piece. It's been that way since the invention of the Kreg jig for drilling pocket holes. When set up properly they work w/o splitting, unless you get too close to the end of a piece, as discussed above.

John


Is your jig maybe set up for half inch material?

Just a slight clarification. The Kreg stepped drill bit drills a clearance hole for the screw head and for the screw. It does not, and is not supposed to, drill a pilot hole in the second piece. The cutter on the screw does that as you screw it in.

I was curious about the dimensions of the work pieces, having joined many pieces in a similar fashion on some of my projects. So, I went out to the shop an located some scrap and prepped it to dimensions identical to those listed by Wade in his post.

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I drilled the holes to the proper depth using my jig

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I inserted two 1-1/4 kreg fine thread screws and drove them in with my drill.
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This photo of the completed joint shows a small crack in the 3/4" piece at the bottom of the photo.
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If you look closely in the photo below to the right on the right hand hole you can see the small crack.
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These are the screws used in this experiment.
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The root problem is the screw nearest the top of the leg is too close to the edge of the board for it not to cause the wood to crack. If you could drill the right size pilot hole for the screw at the proper angle you might be able to prevent the cracking. I'm not sure how you would accomplish this. Any angular error would likely crack the piece.

You might be able to apply some very thin super glue to the end grain where that hole will be. The glue may wick far enough into the wood to prevent the cracking.

[Michael Burnside]

When I use pocket screws on dense wood close to the end of a stile I use a 1/8" x 6" aircraft drill to drill a pilot hole. Self-drilling screws help, but they don't clear the swarf. Drill first and there's room for the screw.

Amen, exactly. Clamp together, drill pilot with 6" bit, insert pocket screw, done. I don't do it often, but in the context of the OP's post, I most certainly would. I'd even do here if I used my Castle pocket hole router that goes in only 3-degrees vs. 15 of Kreg and other versions. I'm sort of shaking my head here thinking people don't realize YES we understand how pocket holes work! We're not the ones confused :rolleyes:

[Lee Schierer]

Sorry for the minor thread hijack, but I have to ask this...
Why is beeswax superior to paraffin? My Dad kept a chunk of Beeswax in his shop for greasing screws, but I never thought to ask him why he just didn't use an old candle or [canning] paraffin wax.
So why is beeswax the "bees knees" :D when it comes to greasing screws?

Bees wax tends to be softer and will stick to the threads. Paraffin tends to be flakey and falls off the screw. Bees wax also has a lower melting point than most candle paraffin

[Michael Burnside]

If you could drill the right size pilot hole for the screw at the proper angle you might be able to prevent the cracking. I'm not sure how you would accomplish this. Any angular error would likely crack the piece.

You might be able to apply some very thin super glue to the end grain where that hole will be. The glue may wick far enough into the wood to prevent the cracking.

It's not more difficult than using the driver and pocket screw which you already know how to do. The key is clamping it where you want it first, which you should always do anyway with pocket hole joinery, drill the pilot using a 6" bit and you're good to go. You can even drill the pocket screws that aren't at risk FIRST. It's really not that difficult and it will prevent cracking in most circumstances.

[Jim Becker]

To add to the discussion, are you using the fine threaded pocket screws intended for hardwoods or the coarse threaded pocket screws intended for softwoods? They are both self-drilling into the non drilled side of the joint, but the former have a bigger bite that can sometimes cause splitting in hardwoods, especially when a piece of wood may have some internal stuff going on.

[Kevin Jenness]

The key is clamping it where you want it first, which you should always do anyway with pocket hole joinery

I don't think many people do it, but clamping endways as well as across the joint face will keep the pieces from creeping while driving screws. Clamps pull the pieces together and screws keep them there. This is especially true with Kreg bits which are not meant to break through the end of the rail. I think that is so the exit crater doesn't keep the joint from coming together, but without end clamping the screw is pushing that last bit of wood ahead of it and trying to push the joint apart before it grabs and starts to pull it back together. The Castle system has the advantage of drilling through from the end as well as a lower angle with less force pulling the joint out of the level.

[Patty Hann]

Bees wax tends to be softer and will stick to the threads. Paraffin tends to be flakey and falls off the screw. Bees wax also has a lower melting point than most candle paraffin

Ah, I see.... thank you.

[Mel Fulks]

And…bees wax is rather gummy and sticky. Certainly not something most people would guess would make things slide. But it DOES make
things slide , for a long time. I really don’t know of anything even remotely similar. It will often allow driving in large screws without any
drilling or splitting of the wood. I was told by an early employer to use it. Of course…I didn’t think the boss knew what he was talking about !
That’s why smart bosses don’t tolerate new hires who are skeptical about their competence !

[Lee Schierer]

Just to check the theory about super glue, I went back out in the shop this morning and placed a couple of drops of thin super glue on the end grain of the "leg" (opposite end of the same piece I used yesterday). I gave it some time to soak in and then a quick spritz of activator before assembling the "apron" to the"leg" with the same hole spacing as before. As you can see in the photos below no cracks occurred.
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Even though the super glue darkened the wood, it would be in an area that would not show. There is no visual sign of the glue on either face.

[Mark Rainey]

In his book Pocket Hole Joinery, Mark Edmundson recommends pre drilling if splitting is a problem, as suggested above.

[glenn bradley]

In his book Pocket Hole Joinery, Mark Edmundson recommends pre drilling if splitting is a problem, as suggested above.

+1. Splitting means the screw shaft being forced into the material is causing too much force for the application. A proper pilot hole is the answer if pocket holes must be used. Since pocket holes are generally used for speed and ease of use a lot of fiddling around decreases their value. They are great problem solvers but, perhaps a dowel or small floating tenon would be a better answer here. My point is that if I have to do a lot of fooling around to make a pocket hole work, it's probably not the right solution.

[Wade Lippman]

I am using official Kreg fine thread screws. I have done hundreds of joints and never had a split before. Perhaps I never used inadequate wood before.

I am not sure how to drill a pilot hole, as it has to be in precisely the right place and angle. I have some screws for the smaller diameter kreg jig; perhaps if I put one of those in first it will act as a guide for the pilot hole.
I will also try the idea of putting CA glue on the end grind first. I expect it will darken the grain, but perhaps not more than the solvent based varnish will anyhow.

You help is appreciated.

[Michael Burnside]

I am using official Kreg fine thread screws. I have done hundreds of joints and never had a split before. Perhaps I never used inadequate wood before.

I am not sure how to drill a pilot hole, as it has to be in precisely the right place and angle. I have some screws for the smaller diameter kreg jig; perhaps if I put one of those in first it will act as a guide for the pilot hole.
I will also try the idea of putting CA glue on the end grind first. I expect it will darken the grain, but perhaps not more than the solvent based varnish will anyhow.

You help is appreciated.

Like you, I've done hundreds (maybe thousands by now) of pockets. I switched from Kreg to Castle last year because I just wasn't happy with the tear out on delicate veneers and the 15-degree angle shift at times drove me batty (there are a few other reasons, but those are the two main ones). Having said that, my process is 100% unchanged. As mentioned I rarely need to drill pilot holes but I've done MANY of them. You simply clamp as you normally would, drill a pilot, then screw as normal. If you're lucky and the same side only has one "at risk" screw, you can do that one first, before drilling the pilot for the "at risk" pocket, which will help hold in place. It's really not that difficult.

You need a 5/32 drill bit that is at least 6" long. The 6" bits are usually called "aircraft" bits though I have no idea why. I think it has to do with the standardized length? You can find them on Amazon for a few bucks.

[Jim Becker]

I have several of the so-called "aircraft" drill bits for my guitar work and while delicate, will let you get into places that are otherwise hard to do, such as a pilot hole if necessary in this particular operation. I do think that sometimes splitting is very much related to the specific piece of wood and clearly, Wade is using the correct screws based on post #25.

[Lee Schierer]

You need a 5/32 drill bit that is at least 6" long.

5/32" is 0.15625 in decimal. The threads on Kreg fine thread screws measure 0.155 dia. so there would be little if and grip in a 5/32 pilot hole. A 0.115 (7/64) inch pilot hole would be more appropriate.

[Kevin Jenness]

+1. Splitting means the screw shaft being forced into the material is causing too much force for the application. A proper pilot hole is the answer if pocket holes must be used. Since pocket holes are generally used for speed and ease of use a lot of fiddling around decreases their value. They are great problem solvers but, perhaps a dowel or small floating tenon would be a better answer here. My point is that if I have to do a lot of fooling around to make a pocket hole work, it's probably not the right solution.

Pre-drilling for a screw is not "a lot of fiddling around". Often pocket screws are a good choice, and a few seconds spent on a pilot hole makes sense. I once denigrated pocket screw joints but after using and seeing them in service for over 20 years, mostly on cabinet face frames, I know they work when done properly.

[Mark Rainey]

I am not sure how to drill a pilot hole, as it has to be in precisely the right place and angle.

My understanding is that you drill the screw hole with the Kreg drill bit, and now you have a predrilled hole which is a jig for your 1/8 inch ( approximate ) pilot drill bit.
Location and angle already set for you. Interestingly, Edmundson, in his book Pocket Hole Joinery, includes a 1/8 inch aircraft drill bit in a picture of the "tools of the trade" for pocket holes.

[Tom Bender]

If clamping prevents the crack until the clamp is removed; do that then remove the screws and run your pilot drill in to open the hole, remove the clamps and assemble.

[Wade Lippman]

I put CA on the end grain and got no splits! On the first table all 4 split. I think we have a winner.

The CA ran over a bit and stained the wood, but after a few hours it was the same color as the wood with varnish, so it is invisible.

Thanks to everyone for your help, but especially whoever suggested the CA.

[Mark Rainey]

I put CA on the end grain and got no splits!

Thanks to everyone for your help, but especially whoever suggested the CA.

It was Lee who made the CA suggestion, so I will thank him for you Wade. Nice idea Lee, I will keep it in mind. In conclusion, CA glue did the trick. A pilot hole or clamping across the grain also are good ideas.