Pocket hole joinery

Someone introduced me to a kreg jig a couple years ago and it seemed pretty handy. When I looked into it, the claim was made that going through the end grain at an angle and using the side grain of the cross piece produces a stronger join than going through the side grain to use the end grain for the threads.

I built a work bench from 2x4s and 2x6s using almost exclusively pocket holes. I'm pretty sure I could drop my pickup on it to rotate the tires if I had to. But it has been pointed out to me that these do not scale up indefinitely for building. It was recommended for connecting 2x6s in a loft/scaffolding project that long screws through the end grain would be stronger than pocket screws in this case. Is there a clear cut way to tell when pocket screws lose their advantage? It is it purely an aesthetic thing at any scale?

I think this is a great question, and unfortunately I don't have a good answer for you. What I can surmise though is that pocket hole joinery has been used in furniture and cabinet making for decades but has not been adopted to framing and home construction. Like you mentioned, it seems that pocket hole joinery is purely for aesthetics.

Yes it is a mostly an aesthetic choice.

How ever screws are not the best choice for framing. Screws are made of a hardened steel that when pushed to their failure point they snap. Where as nails are softer and will bend a great deal without breaking. To use your loft as an example.  If for some reason the space was loaded far beyond its weight limit or twisted in extreme winds,to the point of failure.  The nails will allow for some major deformation before collapse.  In either case a the nails will fail at a slower pace. That may be the difference of being able to see the problem and repair it or just getting  the hell out of the way.

Building for failure seems counter intuitive , how ever everything will  given the right set of circumstances.

I mostly second what James said.

I'm not a professional woodworker or carpenter, but I've never seen screws used for anything structural over furniture size. At that point I think I've usually seen thicker bolts chosen if using metal fasteners. And I haven't even seen that sort of metal hardware used on anything more than a pergola, tree house, or the like. I wonder if you could do pocket holes with bolts? You'd need a lot more width on the hole for the head, and you might sacrifice strength for the amount of material removed.

I did an image search for "metal hardware for timber framing" and it looks like a lot of what comes up are brackets. I would think behind that though the wood is probably joined with mortises and such.

Have you seen the connection that is very old, whereby a ring about 11/2 inch Diameter is placed in a circular groove around the bolt hole.
It sits between the two beams. I just cannot remember its name, but its used on bridges etc.

For my money, I'd prefer to learn how to do proper mortise and tenon joinery. Metal fastenings tend to losen over time especially for something like a workbench which tends to have quite a bit of abuse, but good M&T are incredibly strong. Especially if you learn how to do Drawboring. People have been building buildings with M&T which have lasted literally centuries - my Aunt's house in England was built in the 16th century and uses drawboring M&Ts.

A mortise is a slot or hole in one piece, and a tenon fits snuggly inside that hole. Typically this is at 90degrees, but you can do knee bracing at 45 etc. Drawboring is a technique whereby you drill a hole through the sides of the mortise, and a slightly off centre hole through the tenon towards the shoulder of the tenon. Driving a peg through the holes, sucks the tenon into the mortise creating an incredibly strong joint.

https://www.youtube.com/results?search_query=draw+boring

@ L Johnson: Have you had a look at the traditional Japanese house joinery? It's designed to wiggle in earthquakes without failing (up to a point). I'm not sure it's still practiced, as I suspect that sort of apprenticing took years and "modern" is faster and cheaper, even if it's not better.

That said, Japanese homes were generally smaller than what many people want to build in North American, so the concern with "can this scale up" still applies.

Jay Angler wrote:@ L Johnson: Have you had a look at the traditional Japanese house joinery? It's designed to wiggle in earthquakes without failing (up to a point). I'm not sure it's still practiced, as I suspect that sort of apprenticing took years and "modern" is faster and cheaper, even if it's not better.

That said, Japanese homes were generally smaller than what many people want to build in North American, so the concern with "can this scale up" still applies.

Yes I've seen it and read about it in English and in Japanese. It's still practiced, though most builders combine wood, concrete, and steel for earthquake resilience and fire resistance. All wood homes became a little less popular after several mass fires including the Tokyo fire bombings.

It's still a requirement when rebuilding shrines and temples though. As such carpenters that practice it are referred to as tera-daiku or "temple carpenters".

I think there are a few threads here on permies discussing traditional Japanese timber framing and joinery.

People use pocket hole joinery here these days too. Japan is quite a syncretic culture. As a culture it tends to take in any ideas that people generally find useful, interesting, or good.

For some reference, Matthias Wandel who is a prolific woodworker with pragmatic approach, did a test comparing the strength pocket holes vs mortise and tenon:

https://www.youtube.com/watch?v=apsH8eBfjVA

The thing about pocket holes screws is that it is what is called a 'toenail' attachment. Toenailing, as the name implies, can also be done with nails. There are a number of pro's and con's to toenails versus nailing or screwing straight into a butt joint. I framed houses for a number of years and by far the main reason to using nails was the speed a nail gun can assemble a house. Toenailing is a stronger method of attachment, but with a nail gun it is awfully easy to split the wood, which makes it weaker. Predrilling and not over torquing screws is very strong.

I have also used pocket hole joinery and deck screws to attach 2x4's and 2x6's. I built a large workbench with some pocket hole joinery maybe 15 years ago that is still as solid as the day I made it. Getting the jig positioned properly, adjusting the depth of the drill bit, and getting the appropriate length of screws figured out on scrap pieces before you start is key to success. There are lots of other small but important things to know when attempting to do this. If the head of the screw isn't flat underneath then it can potentially split the wood. This is one of the things that causes failure for most people who attempt to use screws that aren't from Kreg and just use whatever screw they have on hand. I personally just never fully tighten the screws with a drill or impact driver. I drive them most of the way in and then tighten by hand.

Another trick is to get a long (~6") bit of appropriate thickness for the screws (maybe 1/8" to 3/16") to drill the hole the rest of the way through. The Kreg bit has a small nub sticking out that works fine for 1/2" wood, but thicker stuff really needs that hole punched all the way through to avoid splitting the wood, or having threads grabbing to both pieces and not wanting to snug up. This usually gets people to drive it home with a drill, ensuring failure and becoming disheartened with pocket holes. Having a second drill so you don't have to constantly stop and switch bits greatly speeds things up.

Another trick is to glue the end grain. Most people say this never works, but multiple tests on YouTube indicate that it can add substantial strength. The problem with end grain is that it soaks up glue and dries it out before it can set up. If you glue the end grain, let it soak in for ~10 minutes, and add more glue it can add quite a bit of strength. Combining this with pocket screws can be a very strong method of attachment. Assembled incorrectly it won't be very strong at all. I've never tried it, but on a house I'd imagine quality construction adhesive would be a better option than yellow wood glue.

More traditional joinery methods are also extremely valuable. Using a rabbet (or rebate) or mortise and tenon is very strong and doesn't require glue or fasteners. But it often requires special tools and special skills. If you have the time it is great to practice different methods and learn as much as you can. It's virtually impossible to suggest a good course of action without a lot more details for what you have planned.

Emeril Lagasse once said that he could spend his whole life learning to cook and only know a small fraction of what there is to know. Woodworking is very much the same. There are easily thousands of ways to get a project completed so it serves you well, and probably even more ways to do it and fail. The internet is full of people hopping up and down trying to convince others that their way is the only way. If your main goal is to build a loft, find someone who has been successful numerous times and try out their method. If you want to learn how to use pocket hole screws in unconventional ways, there are probably less videos on that. You might want to check out a woodworking forum and ask people that use them regularly.

If you want I can try to get some pictures to give you a better idea how I have gone about using pocket holes with construction lumber.

Daniel Schmidt wrote:It's virtually impossible to suggest a good course of action without a lot more details for what you have planned.

Thanks for the response. I am building the loft to first give access to my yurt ring for repairs, then to serve as extra sleeping and or storage space within once done. I will probably move the whole yurt in a couple of years, and would like to reuse the whole thing or maybe just the lumber, so going with screws instead of nails.

You brought up another important point about pocket screws that I had forgotten to ask about- torquing them in. Kreg doesn't address this in any instructions I've seen. Working on furniture with 1" dimensions I over torqued a few before learning to back off the adjustment on my drill. While hand tightening gives much more feedback for control, it doesn't inform how much effort to actually give. Is it just experimentation? Isn't under torquing problematic? With the drill I ended up using 6 of 20 on 3/4" wood, and 16 on 1 1/2" stuff.

Also, when you use deck screws for pocket holes, are you using a jig to drill the holes? For larger dimensions are you using a regular bit, then following up with the long bit you mention?

Andrew Pritchard wrote:For my money, I'd prefer to learn how to do proper mortise and tenon joinery. Metal fastenings tend to losen over time especially for something like a workbench which tends to have quite a bit of abuse, but good M&T are incredibly strong. Especially if you learn how to do Drawboring. People have been building buildings with M&T which have lasted literally centuries - my Aunt's house in England was built in the 16th century and uses drawboring M&Ts.

A mortise is a slot or hole in one piece, and a tenon fits snuggly inside that hole. Typically this is at 90degrees, but you can do knee bracing at 45 etc. Drawboring is a technique whereby you drill a hole through the sides of the mortise, and a slightly off centre hole through the tenon towards the shoulder of the tenon. Driving a peg through the holes, sucks the tenon into the mortise creating an incredibly strong joint.

https://www.youtube.com/results?search_query=draw+boring

I helped build a timber frame structure last summer using draw boring with only hand tools. I plan to go that way with future construction, but right now I am trying to assemble something better to live in than a camping tent and it is below freezing already here. I had my entire loft structure done with screws before I would have carved the first mortise and tenon out by hand or researched power tool methods. I'm going with the tools and knowledge I already have for now and tweaking that so that I have something usable from which to do a better second iteration.

Hubby built a "loft bed" over a desk area which has a bookshelf at one end, for his room while at college. He mostly assembled it with large bolts and big washers. He disassembled it for transport when he got a job in Ottawa and continued to use it there. He disassembled it for transport when we moved to BC, although he no longer used the bed as a bed since I was then in the picture and it continues as desk + storage. So it's had near continuous use and 2 major moves and is about 40 years old. He used mostly solid wood and didn't skimp - corners are 4"x4"'s some cross supports of 1x8" with two well spaced bolts, however there's no fancy joinery.

It might be the only thing still standing if the big earthquake hits!
I think something like that would meet your need. I can post some pictures if you think that would help.

Here's what I put up so far. I think the bracing will do fine as is, but need to decide whether to add corner bracing, on the side with square crosses only so far, high up to match the other sides or down under the cross brace, or if it matters. Also figuring out if I need to add a second 2x4 to each of the corners to make 4x4 legs.

What prompted this question was the joists I'm putting inside the upper frame. I have three 3" deck screws through the (predrilled) sides and into each of the ends upon advice from a friend, where I was considering three or four pocket screws sized according to Kreg recommendations. I have 2 joists in and they feel more solid than the frame at this point, but need to complete the bracing to have a better idea.

BTW, it is an 8x8' frame with 2x6s on top, the rest are 2x4s. The top of the 2x6s are 7' up.

Coydon Wallham wrote:You brought up another important point about pocket screws that I had forgotten to ask about- torquing them in.

Also, when you use deck screws for pocket holes, are you using a jig to drill the holes? For larger dimensions are you using a regular bit, then following up with the long bit you mention?

My father had me turning wrenches when I was a small child, so I just go by feel. In this case, if you predrill, start light, and keep snugging it up until the joint isn't loose then it should be tight enough. Since you already have screws going straight into the ends, and none of the wood appears to be splitting, it should be plenty strong. I honestly never use the adjustable torque feature on drills. If you predrill everything and slowly increase the torque until the boards tighten together and don't flex apart from basic handling then it is tight enough. I usually will grab scrap pieces to test whenever I change materials or screws to make sure everything appears to be working as expected.

I generally use the jig and just pull it back off the end enough so the screw comes out in the right spot. You don't want it poking through way too far to one side or the other as you can end up with a loose connection. One option is to purposely have it come out a bit offset and then use a pocket hole on either side, this way the diagonal screws in opposite directions complement each other. This doesn't work on end pieces, but the joists in the middle can benefit from this. I've also been known to freehand it by drilling in at 90 degrees and then adjusting to the angle I need when working with pieces that are cut at different angles, such as 2 x 22.5 degree pieces to go around a 45 degree corner.

I have built temporary scaffolds in a similar fashion, and I can tell by looking at it that below the point of the bracing, those 2x4's will flex and will get a bit bouncy when doing certain actions standing on top. All of your legs have the 2x4's in the same orientation (1.5" sides all facing the same way, as are the 3.5" sides). If you take more 2x4's and make them into an L shape, that is, leaving the existing 3.5" side as-is and putting the 3.5" side of new boards to the 1.5" side (making an L shape 5" in one direction and 3.5" in the other) it will be more sturdy than just doubling up the 2x4's into a 3" x 3.5" block. You will have much less flexing below the line where the braces attach. Adding another set of diagonal bracing to the other two sides supporting the joists will further increase rigidity and make it feel quite solid.

I second the "L" shaped posts idea. You definitely need angle bracing on all sides to keep the platform from wobbling, no matter how stiff the posts themselves become. The best would be a single diagonal brace from one top corner to the opposite bottom corner, or double braces from bottom corners to top center.

Daniel Schmidt wrote:I have built temporary scaffolds in a similar fashion, and I can tell by looking at it that below the point of the bracing, those 2x4's will flex and will get a bit bouncy when doing certain actions standing on top. All of your legs have the 2x4's in the same orientation (1.5" sides all facing the same way, as are the 3.5" sides). If you take more 2x4's and make them into an L shape, that is, leaving the existing 3.5" side as-is and putting the 3.5" side of new boards to the 1.5" side (making an L shape 5" in one direction and 3.5" in the other) it will be more sturdy than just doubling up the 2x4's into a 3" x 3.5" block. You will have much less flexing below the line where the braces attach. Adding another set of diagonal bracing to the other two sides supporting the joists will further increase rigidity and make it feel quite solid.

Would it be enough to extend the 'L' 2*4 additions just between the ground and the middle brace? I've burned through my reserve of studs and would need a trip to the lumber yard to make them ground to top. I do have some 1x lumber left, would that be suitable for any of this bracing?

For just working on it as simple scaffolding it is probably fine as-is. Try grabbing it and shaking it back and forth. It probably won't shake much in one direction, but shake a fair bit more in the other. Certain repeated pushing, pulling, or hammering motions will cause it to oscillate more and more until it starts to walk across the floor with continued motion. Make certain to tack down whatever boards you put across the top to walk on. If you need to hold a large amount of material weight (more than your body weight plus yourself), or using it regularly to sleep on in the very near future, then you could probably L brace the bottom and add 1x4 or 1x6 diagonal bracing. If you are just working with a few tools and a few dozen pounds of materials or less, I would just be mindful of how much sway it has and build it up strong later if you want it to last a long time.

Using it as a loft to sleep on or hold a bunch of supplies means it might get awkwardly loaded without much thought. If you have your wits about you and test it out to see how it reacts before working on it temporarily it should be sufficient. I've had to work on much, much scarier scaffolding setups in the past. Fortunately I'm fairly light weight and perhaps a bit lucky.

Andrew Pritchard wrote:For some reference, Matthias Wandel who is a prolific woodworker with pragmatic approach, did a test comparing the strength pocket holes vs mortise and tenon:

https://www.youtube.com/watch?v=apsH8eBfjVA

That's a good test to show how much better a join holds with glue, but why wouldn't he base such a comparison with glued M&Ts by gluing the pocket screw join? The guys who have told me about pocket joins mentioned they used glue on them. Daniel mentions above that 'conventional wisdom' holds that gluing end grain doesn't do anything but various you tube videos display substantial strengthening.

Also, are there ways to form the mortise and tenon that they hold without glue?

Coydon Wallham wrote:
Also, are there ways to form the mortise and tenon that they hold without glue?

Yes! Quite a few actually.

A very tight fit can be sufficient.

Japanese joiners use a round headed hammer to compress the wood fibers of the tenon before inserting and then apply water and heat after inserting to expand the fibers. This makes the joint extremely tight.

I like tusked tenons for a lot of applications.

Dovetails also come to mind.

I can't recall other methods of the top of my head, but they're are dozens of variations.

Coydon Wallham wrote: Also, are there ways to form the mortise and tenon that they hold without glue?

The way people put mallets together is basically that. A slightly wedge shaped mortise with a saw kerf in the tenon to drive a wedge in. You can also put a dowel in from the side but there are some tricks to that so it stays tight and doesn't loosen up easily. Recently I've been playing around with smaller scale stuff and using toothpicks and bamboo skewers and drilling holes a bit too small so it has a solid friction fit. If I make it too tight it won't drive in without breaking. I can always drill it out if I want to pull it apart. The same can be done on a larger scale if you are careful not to go too far and split the work piece.

This structure looks very unsafe.  Several posters have already pointed out the need for extra studs in each corner to make an “L” section. The L-section needs to be full height. Not doing this is asking for the studs to buckle, it’s not just a simple matter of reducing sway. Stability against sway needs proper bracing, of the full height of the studs, not the half bracing you have here.  All four sides need to be braced.  Alternatively, 3 sides, and or even 2 adjacent sides, could be adequate but, in that case, there needs to be bracing of all four studs in the horizontal plane, at both floor and platform level.

The way the horizontal beams of the platform are attached to the studs is not normal timber frame practice.  Such beams should be supported on a solid base, either by lying on the top of the stud, as in a top plate in timber frame construction, checked at least 12 mm into the stud, or on top of a jack stud, as for a lintel. Skew-nailing or screwing is only suitable for stopping the horizontal beam slipping sideways, not supporting vertical loads.  The problem with your approach, and that of most of the commentators here is that you are loading the beams near their ends in ways that are tending to split the grain. This is the weakest aspect of wood.  

I am a retired civil engineer.  I have DIY structurally modified several timber frame houses and had my work approved by council building inspectors over the years.  That being said, I am not a carpenter.  I think you should talk to someone in your locality , either a framing carpenter or an inspector, who is familiar with you local framing timber and good practice in its use.