What's the point of dovetail joints?

[woodenstx]

I made my first dovetail joint the other week with some scrap 21*190 pine, and yes it was cupped nevermind it was only a quick dive in to see if I had the patience to actually do it. Yes they came out with gaps and the cupping caused the tailboard to snap lenthways when installed, its still a very very strong mechanical joint and has the potential to look awesome

I will do some proper DT's on the bed frame I'm going to make. After buying a coping saw as parting out the waste with a chisel was hard going for me :lol:

 

[MIGNAL]

No knowledge, but is it only modern glue that is stronger than the wood? Were historic glues weaker, if so then the joint structure becomes much more important. Could it just be historic precedent?

F.

That's a good point. In fact, some of the traditional glues are very strong; probably as strong as modern ones under perfect conditions, but they also had disadvantages. Animal glue for example, besides being susceptible to microbe attack, has minimal resistance to moisture or heat and becomes brittle in very dry conditions. Also, until the advent of modern adhesives, a reliable exterior glue was simply non-existent. Joiners of old had therefore to rely on the mechanical strength of their joints and techniques evolved accordingly.

Taking the example of a dovetailed drawer front, due to continual timber movement and stress loading, the hold of the glue - any glue - can weaken over time. How often we see on low class, non-dovetailed work, drawer fronts come loose as soon as the glue fails. Yet in restoration work, it is common to dismantle drawers for repair and I often find that an old but still functioning drawer will come apart very easily when tapped sideways. In other words, the drawer has been continuing to function for years on joint mechanics in the absence of a firm glue hold.

That's just not true. Animal glue can take extreme heat and it will not budge. Far, far greater than any PVA glue. You really need heat and moisture to release animal glue, even then it takes time. I know because I take musical instruments apart and have done so for nearly 30 years. It just isn't that easy to release well glued joints done with animal glue. Of course it can be done but it takes heat, moisture and patience. There are countless thousands of joints that were glued with animal glues 300 years ago and they are still perfectly intact. Neither does it suffer from creep like PVA glues do.

http://www.frets.com/FretsPages/Luthier ... etest.html

 

[Sawyer]

But that was my point: animal glue is a natural thermoplastic, so apply heat and some moisture correctly and apart it comes. A boon for furniture restorers, who often need to get things apart without damaging them. Modern glues conversely, do not have this advantage and are likely to be the bane of 22nd century restorers. Present day restorers often encounter amateurish repairs with modern glue, which can be difficult to put right due to the adhesive's non-reversibility.

Nor am I suggesting that animal glue is bound to fail in time - it just depends on the conditions which, if they have been favourable, will allow a 200 year old joint still to be rock solid.

 

[MIGNAL]

PVA is thermoplastic, which is why you can use that (unreliable) veneering method with it. A bit of heat and it releases. Animal glue won't do that. Regluing is more difficult with PVA because you have to clean the joint, animal glue you just need to apply more glue. If anything it will become stronger because the wood has already been sized. Urea formaldehyde (cascamite) can take serious heat and it's not affected by moisture. That gives it both an advantage and a disadvantage.

 

[Mike Jordan]

It's true that a hand cut dovetail is easily recognisable by other competent woodworkers and usually underlines the quality of the work. To a practised hand they are quick and easy to complete and assemble. I think that cutting box joints by hand would be a longer process and require much more carefull assembly to ensure that the shoulders are closed up in two directions rather than the one for dovetails.
Box comb joints are generally cut by machine, assembled in a jig and glued with RF glue setting systems in mass production use. As suggested either joint correctly cut and glued will last for years.
I have been amazed on occasion by the durability of drawers and other constructions made of weetabix like chip board.
It works but would you feel satisfied with having made it?

 

[AJB Temple]

I am about to cut some dovetails to join green oak tie beams to green oak joists in my timber frame project. There will be no glue and the wood will shrink a bit as it dries. The dovetail will remain secure when compared with a joint minus the angled shoulders.

 

[bugbear]

That's just not true. Animal glue can take extreme heat and it will not budge. Far, far greater than any PVA glue. You really need heat and moisture to release animal glue, even then it takes time.

Laminated bows (as in archery) were made using animal glues - you want to stress test glue? That'd do it.

BugBear

 

[Dan j]

Found this video interesting. Potentially controversial on this thread though.

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

 

[Jacob]

Found this video interesting. Potentially controversial on this thread though.

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

It's a bit beside the point. All those joints are strong enough for the usual applications, but the DT is the easiest and quickest if you only have a few ordinary hand tools.

 

[Jelly]

Found this video interesting. Potentially controversial on this thread though.

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

That was interesting... The box joints failed by the mode I'd anticipated, but the finger joints yielded under tension perpendicular to the grain, which would be the second most likely mode of failure...

I wonder why.

 

[D_W]

Box joints are tasteless and are the mark of cheap manufactured boxes of cheap furniture.

As far as the glue thing, take a chisel and stick it in a butt joint and see how well the glue holds the joint. The whole idea of "modern glues" being the savior of all things is fine in a very short term, but not much else. Dovetailed drawers will last long after the glue has failed. Box joints, especially if they were glued with modern glues, will be a pain.

If you want cheap drawers, just nail them together and put inexpensive guides along their sides. My 40 year old kitchen drawers were pinned together like that with nails and a tiny rebate and they've held up quite well. The ones without guides have needed some repair in the last decade, but I'm sure they're more heavily loaded and opened more often than most furniture will be.

 

[AndyT]

There are plenty of ancient Egyptian coffins in museums, made with dovetail joints, still holding up after a couple of thousand years. As others have said, they are quick and practical to make with a few basic tools. There are alternatives for some purposes now, but they need much greater capital investment in machinery.

 

[Benchwayze]

Simple - dovetails are there to make other woodworkers jealous!

You beat me to it Matt. :mrgreen:

When I did use use box joints on a drawer, (I used ply for economy) I sank a 1.5 " screw down through the fingers from top and bottom. Last I heard the drawers were still in one piece.

 

[Benchwayze]

Box joints are tasteless and are the mark of cheap manufactured boxes of cheap furniture.

As far as the glue thing, take a chisel and stick it in a butt joint and see how well the glue holds the joint. The whole idea of "modern glues" being the savior of all things is fine in a very short term, but not much else. Dovetailed drawers will last long after the glue has failed. Box joints, especially if they were glued with modern glues, will be a pain.

If you want cheap drawers, just nail them together and put inexpensive guides along their sides. My 40 year old kitchen drawers were pinned together like that with nails and a tiny rebate and they've held up quite well. The ones without guides have needed some repair in the last decade, but I'm sure they're more heavily loaded and opened more often than most furniture will be.

DW

Agree; to a point. But sometimes price is a watchword. (Usually when building for myself! ) So I don't say 'cheap'! I use the words 'inexpensive', or 'economy'!

Cheers

John

 

[D_W]

Box joints are tasteless and are the mark of cheap manufactured boxes of cheap furniture.

As far as the glue thing, take a chisel and stick it in a butt joint and see how well the glue holds the joint. The whole idea of "modern glues" being the savior of all things is fine in a very short term, but not much else. Dovetailed drawers will last long after the glue has failed. Box joints, especially if they were glued with modern glues, will be a pain.

If you want cheap drawers, just nail them together and put inexpensive guides along their sides. My 40 year old kitchen drawers were pinned together like that with nails and a tiny rebate and they've held up quite well. The ones without guides have needed some repair in the last decade, but I'm sure they're more heavily loaded and opened more often than most furniture will be.

DW

Agree; to a point. But sometimes price is a watchword. (Usually when building for myself! ) So I don't say 'cheap'! I use the words 'inexpensive', or 'economy'!

Cheers

John

Absolutely - if the price is finger joint price (like manufactured furniture price range), then the buyer gets finger joints.

I think the dovetails that are made by machine here (often in plywood drawers) look no better than finger joints, anyway (in the states, we still have a lot of small furniture manufacturers, but they are amish, etc, and the items tend to be overly rounded, bulky -heavy - and just kind of coarse. For the price they are good, though. The amish aren't much for aesthetics and they like to have things rounded assuming that kids will run into them).

 

[rafezetter]

your friend is a philistine and should be beaten with 2 compound sticks, one dovetailed and one box jointed together, he may choose which one first.

nothing to add above what has been said above.

I don't either, suffice to say - I really like this answer

 

[Benchwayze]

Box joints are tasteless and are the mark of cheap manufactured boxes of cheap furniture.

As far as the glue thing, take a chisel and stick it in a butt joint and see how well the glue holds the joint. The whole idea of "modern glues" being the savior of all things is fine in a very short term, but not much else. Dovetailed drawers will last long after the glue has failed. Box joints, especially if they were glued with modern glues, will be a pain.

If you want cheap drawers, just nail them together and put inexpensive guides along their sides. My 40 year old kitchen drawers were pinned together like that with nails and a tiny rebate and they've held up quite well. The ones without guides have needed some repair in the last decade, but I'm sure they're more heavily loaded and opened more often than most furniture will be.

DW

Agree; to a point. But sometimes price is a watchword. (Usually when building for myself! ) So I don't say 'cheap'! I use the words 'inexpensive', or 'economy'!

Cheers

John

Absolutely - if the price is finger joint price (like manufactured furniture price range), then the buyer gets finger joints.

I think the dovetails that are made by machine here (often in plywood drawers) look no better than finger joints, anyway (in the states, we still have a lot of small furniture manufacturers, but they are amish, etc, and the items tend to be overly rounded, bulky -heavy - and just kind of coarse. For the price they are good, though. The amish aren't much for aesthetics and they like to have things rounded assuming that kids will run into them).

For economy and speed, the multiple drawers in my kitchen were joined with a 'cookie-cutter' Trend dovetail jig. They are still good, and are way better than some of the modern mechanical fixings you get from IKEA and similar houses!
Just saying! (hammer)

 

[Sawyer]

I think the dovetails that are made by machine here (often in plywood drawers) look no better than finger joints, anyway ).

They may not look that great; arguably no better than a finger joint but are still a technically good because of their mechanical resistance to tension. Far superior to a finger or other joint which is only as good as the glue sticking it together.