[woofie11]

A problem is that "strength" isn't a scientific term. You have tensile strength, shear strength, torsion strength, and compression strength.

Screws have incredible tensile strength, which this article was testing. Shear strength? Not so much. Hit the joint with a hammer from above, and most screws will just snap. Nails are the opposite -- great shear strength, and no tensile.

Glue is stronger than wood, as several comments indicated, but for how long? I've had many glued pieces of furniture fail after a decade of use.

In a lot of woodworking, I use multiple types of fasteners. It's overengineering, but it doesn't fail.

[jkoudys]

Most of the glued pieces I'll see fail after a decade were using your standard yellow carpenter's glue. It's fine, strong stuff that lasts a while, but it will still soften if it absorbs some water. Some older glues will also brittle over time. There's been a big push recently to waterproof glues that fully cure and can't be re-wet. While it's disheartening to throw out a bottle of clumpy glue (when I've had bottles of the yellow stuff sit around for over a decade and are still good), glues like titebond 2 or 3 should last as long as the wood itself.

I'll still use the yellow glue for anything that doesn't hold a load, like thin panelling. These days my yellow glue mostly gets used to repair pop up books my toddler tore apart.

[exDM69]

On the other hand, if you build heirloom pieces with nice joinery, you want the glue to fail before the wood does. When that happens, it's an easy repair. If there's damage to the wood, it's a much more complex affair.

I use hide glue liquid, which is not very strong and not moisture resistant at all. But it's a pleasure to work with and I know that if it fails, I can put it back together again (doesn't even need the old glue to be cleaned up).

If anyone wants to geek out about historical adhesives for woodworking and other craft, I'll gladly share my experiences about DIY glue cooking at home.

[bluGill]

Hide glue is also stronger than the wood joint.

[exDM69]

It usually is, but that depends on the additives used and the gram strength of the flakes used to cook the glue and the quality of the glue job.

E.g. I cooked a batch of 192 gram strength glue with 50% table salt additive to keep it liquid at room temperature, and I had half of the failures at glue seams in destructive testing. Made an excellent glue for cold winter days, though.

In glue strength tests (like James Wright on YouTube and FWW magazine both), hide glue compares favorably to modern glues.

But all it takes is a few drops of additives to drastically change the qualities of the glue.

[lstodd]

If you absolutely need a joint to not fail before the wood, use epoxy, mix in some glass fiber cuttings. It's indestructible to the point I wasted considerable amount of sandpaper sanding off a joint I needed to remove. Nothing else would so much as cut it.

PVA ("standard yellow carpenter's glue", titebond, etc) is much weaker and moisture kills it over time.

[jimnotgym]

Epoxy comes at a serious cost

1) It costs a lot of $ to begin with

2) Everything you apply it with is ruined within minutes

3) It can cause terrible dermatitis (always wear multiple pairs of nitrile, not latex, gloves). You can become sensitised to the point that you cannot share a room with sanding dust from it!

4) It's open time is short and varies according to the batch size due to the heat it produces. This means you have to spread large batches out in a tray to lose heat or it goes suddenly hard, or indeed melts your tray!

5) Clean up is nigh on impossible. Normally you are left chipping and sanding what is left

6) It has poor resistance to UV light

7) It leaves a residue that can stop paint sticking

8) It is unsuitable for thin glue lines like are used in furniture and traditional joints

But yes it is phenomenally strong and water resistant.

A better glue for joinery is polyurethane, especially the titebond stuff.

[lstodd]

Yes, there are drawbacks.

I'd say multiple pairs of gloves is overkill, plain medical latex ones do just fine for me. Just don't mix or apply it with a finger.

Open time of modern ones is acceptable, Many times I found myself waiting for it to get more sticky than otherwise. And heat is of no concern for joints.

For point 8 I'm not sure what are you talking about. It's great for thin-layer joints, that's where it actually excels.

Never had any problems with UV, but maybe because it was always painted over (and what's the problem with painting? sand it a bit, that's taken as granted as even epoxy itself won't stick to unsanded epoxy)

Besides, knowing you won't be able to get it off once it gets on something trains concentration and fine motor control :)

As for $ well, it costs a bit more, and time spent on weighing and mixing is well over any cost difference in raw materials. Still in the end you get a joint that'll be the last thing that fails.

[jimnotgym]

I used to work in a chemical factory and the head buyer wouldn't have latex gloves in the building, because they are so porous, so no use nitrile or neoprene. Maybe this link will change your mind about the risk of epoxy exposure[0]. There are loads more if you google it. I read an article once about a poor chap who had to wear an NBC suit to finish his boat.

Open time is not an issue if you are mixing enough for a chair leg, but if you were mixing enough to glue a large lamination it kind of sucks when it smokes in the pot and then goes instantly hard or melts your glue pot[3]. Equally if you were trying to glue up a set of stairs, for instance, you would need a helper just to mix the glue fast enough.

point 8. It shows a glue line in thin laminations [1]. I struggle to get where you are saying it 'excels' at thin joints, in fact the main selling point with epoxy is that it is the only wood glue that is strong across a gap. That is where it excels, loose joints and fillets.

> and what's the problem with painting?

It is called amine blushing.Sanding won't do, it has to be washed off [2]

> Besides, knowing you won't be able to get it off once it gets on something trains concentration and fine motor control :)

Buying new rollers, brushes, tubs for every single joint gets old really quickly if you are a pro user. Again fine if you are gluing a chair leg, a pita if you are glueing large joints.

> it costs a bit more,

It costs a lot more! Titebond in bulk is £10 a litre. West system large packs are nearly £50 a kilo!

> Still in the end you get a joint that'll be the last thing that fails.

Is that always a good thing? Wood moves around a lot and sometimes it can crack a glue line that can just be reglued. With epoxy your wood will split instead.

Epoxy has some amazing qualities, gap filling and water resistance in particular. In a hobby shop it might be worth the hassle, in a pro-shop almost never.

[0]:http://www.fram.nl/workshop/controlled_vacuum_infusion/aller...

[1]:http://www.woodweb.com/knowledge_base/Glue_Choices_for_Tight...

[2]:https://www.epoxycraft.com/amine-blush-what-you-need-to-know...

[3]:https://www.epoxyworks.com/index.php/big-batch-mixing-method...

[lstodd]

Well, we must have completely different applications in mind then.

My experience with epoxy is building boats. Mostly spruce stock and birch plywood, fibergrass all around for surface protection and stiffening; 12-16 meters length.

Can't call this a pro operation, there's that.

Still in my experience, thin epoxy joins are the strongest.

We've tested spliced plywood to destruction - not once did it fail along the joint; delamination across factory glue was always the case.

[lstodd]

If screws snap from shear - you undersized the screw diameter.

If nails are in a joint so that they experience pulling-out forces - use barbed nails (and encourage them to rust).

It's all about choosing the right fastener for the job.

[woofie11]

If screws snap from shear, you used the wrong fastener. A bigger screw isn't the right solution. It costs more, makes a bigger hole, and doesn't work as well as the right fastener.

Screws are generally harder steel so that the threads can cut into the substrate. That makes them brittle. Try bending a screw; it won't bend. It will snap.

There are engineered screws designed for high shear strength which I use quite often. They're much more expensive, but I find them worthwhile.

Nails are made of softer, tougher steel. If you try to bend one, it will bend. It won't break.

Conversely, from the video linked, you can see that even a basic screw will handle several times more tension loading than a barbed nail.

[lstodd]

Well, I won't argue. If it snapped, bent or RUDded, engineering is the one to blame :) which is typically me.

[brixon]

Going down that road, the YouTuber ProjectFarm has a good video on the holding power of screws and nails. https://www.youtube.com/watch?v=kAxGAIFbqu4