When are pocket holes an appropriate joinery technique?

Question

I have come across a lot of designs and plans for things like outdoor furniture, kids' furniture, etc., that call for the use of pocket holes. I can appreciate why this is enticing to a lot of people as it's a lot simpler that mortise and tenon joints or dovetails while still being concealed.

Matthias Wandel has an article on Testing pocket holes against mortise and tenon and dowel joints where he finds that they are indeed significantly weaker than other joint types.

With the exception of small objects, 99lbs as an average breaking force for a pocket joint doesn't seem very strong at all. I could see a tabletop generate forces beyond this with just a few adults leaning on it.

Are there any times when this is an appropriate joinery technique to use, over alternatives? Or are they just typically used when someone doesn't have the skill, time (or maybe cost) to build a more robust joint?

Answer 1

Bear in mind that that 99 lbs is for a single joint with pressure being applied in the manner of a first class lever in Mr. Wandel's experiment. You will have multiple pocket holes in a given construction. Let's look at your table example. Most of that pressure is being distributed through the legs and into the floor, say you have four legs and four boards making up the frame that the tabletop attaches to. it's also being used in conjunction with wood glue (e.g. titebond), so you're not just looking at the strength of the screws but the glue as well.

Even disregarding the fact that you're going to glue your pocket holes, that pressure is distributed over at a minimum of two joints and much of the pressure from someone leaning on the table is going into the legs themselves, not into the class one lever directly applied to the joint like Mr. Wandel used for his experiment.

A pocket hole joint is great for face frames as rob mentioned. A friend of mine used a kreg jig to build his desk and it has not fallen to pieces around him. I probably wouldn't use it for a kitchen table as the sole joint, but I wouldn't be opposed to using them to help clamp mortise and tenon joints.

Frankly, I think Mr. Wandels' experiment is misleading in that it shows that a single joint is stronger, but the impression it gives is that you shouldn't use pocket holes because they're weak, and that simply isn't the case. I am curious to know why his experiment disagrees with Kreg's claims from "independent testing." Kreg claims that a pocket hole joint can sustain more shear load than a mortise and tenon joint. This may be true, since Wandel's test wasn't for a shear load. It might be interesting to see how that experiment was done.

Mostly I think there is opposition to pocket hole joinery because it isn't "classy." Woodworkers like to think of themselves as rustic traditionalists, carrying on a craft passed on for generations. Pocket holes may seem too much like a crutch, or being too "modern," but they're frankly plenty strong for quite a few situations, including light tables and desks.

Answer 2

Pocket hole joinery is commonly used in cabinet face frames, but it can be useful in many other applications, as well. Jay Bates' website has an entire category of projects he's built using pocket hole joinery, ranging from a jewelry cabinet to a bunk bed to a bar stool.

As with many types of joints, pocket hole joinery is strong enough in many applications. For example, there are even tutorials on how to build a workbench using pocket holes.

Pocket hole joinery is really just a very fancy form of toenailing, which is a construction technique commonly used in building houses and cabinets.

You typically wouldn't subject pocket hole joints to the type of racking force demonstrated in Matthias' experiments. If you do want to use pocket holes in such an application, you can reinforce against the racking forces with additional cross members and diagonal braces.

Also keep in mind that a project using pocket screws does not have to use them exclusively as the only joinery method. You can certainly use pocket screws for some parts of a project and some other joinery method for other parts of the project.

Answer 3

Unless we are talking about some fancy glueless japanese joinery, there is a fundamental difference: both mortise + tenon and dove tails are glued together.

Pocket hole joinery is screwed together, which allows you to take it apart again. If the ability to disassemble the result of your work again at some later point in time, pocket holes are in fact superior to the other two, no matter how weak they are or what jig they require.

If that large dining table doesn't fit through the door, strong joints aren't helpful at all. and if you glue the parts together inside the room, you will never get the table back out in one piece.

Answer 4

I have a Kreg pocket hole jig and I find it very useful. Many places where someone might only have a glued joint I will use the pocket holes to strengthen it.

The 99lbs. on a joint is actually quite a lot for many joints, because often the force gets spread out over multiple joints. Not only that by adding more screws you increase the strength. Now after all that, I agree there are plenty of joints I would not use a pocket hole for because I don't feel they are strong enough. I take that on a case by case judgment call.

I have used them often in my book shelves to reinforce glue joints. It also lets me have 'strong' joints that look 'different' if I tried to create them a different way.

One important part is the direction the screws are holding the joint together vs the direction of the normal force being put to them. Anything that would be 'pulling' the screw 'out' of the wood (such as twisting side to side) in general will eventually fail.

Every joint type has its place, and taking things into account such as time, appearance, needed strength and expected life of the joint should go into the decision.

Answer 5

Everything in its place. Years ago, I morticed all my faceframes, and looked askance at guys who used biscuits. Then I switched to biscuits. When pocket holes came available on the street (they'd been in big factory furniture since who knows when) i looked down on those guys. In the last 15 years, pocket holes have become an indispensable part of our fastening repertoire.

Faceframes, yes; table aprons, maybe; chair stretchers, no; flat-edge panel glue-ups - unnecessary, wasteful, and potentially detrimental.

Answer 6

I've used pocket holes. The strength can be improved by using more screws. More importantly, in your design, make sure the wood is supporting the weight, and the joint is holding things in place, and not directly taking the weight.

Nails in the wood frame of your house hold the wood in place, but they are not taking the weight directly, the wood is supporting everything.

Answer 7

99 lbs applied as a first class level 15cm from the join is actually VERY strong. If you have a 4 legged table and sit a 400 lb person on top of it, each leg is carrying the vast majority of the weight to the ground, the pocket hole is not carrying that load, they are simply holding the legs in place. Leaning against the table will impart some level of force that wants to pull/push the legs apart and will test the strength of the pocket hole, but when you are leaning on something once again most of the weight is going through the two legs closest to you.

The worst case scenario would be a shelf in a cabinet where the joint itself is carrying all the weight. But once again if you have 6 pocket holes is your cabinet really going to carry more than 300lbs on a shelf? You would have to have some serious dishes for that to be the case lol.

What you wouldn't want to use a pocket hole for would be something like a chair. People throw themselves into chairs at various angles and often violently drop themselves in and let the chair catch them. No way a chair in constant use would hold up over time.

Answer 8

The best use of pocket holes in joinery I have found is as a replacement for clamping. When enough clamps are not available or the form of the project makes clamping challenging, it is helpful to to glue the joint and instead of clamping use the pocket hole to draw the and hold the pieces together.