How to stop wood from splitting?

[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" 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.
20230126_093526.jpg20230126_093627.jpg
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.