How strong are dowel joints?

[Woodchips2]

I’ve been using a Joint Genie dowelling jig for a while making shelving units, stud partitions, cupboard doors and the like and have been very pleased with the results. I use a shooting board to ensure I get accurate matching surfaces for the glued joint. However I wondered how strong a dowelled joint is compared with a traditional mortice and tenon. Also I’ve thought about buying a biscuit jointer.

I had a search on the internet and found this site http://www.dowelmax.com/jointstrength.html where hydraulic tests had been carried out and you can view the videos of the tests. The test was done by Dowelmax which looks a lovely bit of kit but does the same job as a Joint Genie.

The test results were:
20 Biscuit 285 lbs. per square inch
Pocket hole (5 screws) 420 lbs. per square inch
Double Domino 560 lbs. per square inch
Routed mortice & tenon 640 lbs. per square inch
Multiple dowel 890 lbs. per square inch

They only used a 1” depth of penetration so I presume a through mortice and tenon would be stronger than the test results.

Think I’ll stick with my Joint Genie and not bother with the biscuit jointer.

Regards Keith

 

[RogerP]

I use dowels quite a bit but the only snag, unlike other joining methods, there's no "wriggle room" total accuracy is required.

 

[Tetsuaiga]

I imagine it might depend on the size of the dowels and how many you use also if they are hardwood.

The only doweling i've done is where you secure the two pieces together and drill through both pieces in one motion to give guaranteed accuracy.

 

[RogerP]

I imagine it might depend on the size of the dowels and how many you use also if they are hardwood.

The only doweling i've done is where you secure the two pieces together and drill through both pieces in one motion to give guaranteed accuracy.

... yes, that's okay but when they're blind holes things get a little trickier

Of all the gadgetry that's available I still find the old "dowel points" do a good job.

 

[Random Orbital Bob]

I must say one of the only glue joints I've ever had fail was a dowel joint on a piano stool I made near 20 years ago. Maybe I did something wrong but it started to come adrift about 2 years ago. I'm yet to have either pocket screws, dominos or biscuits fail. There again they haven't been out there being sat on etc as long as my dowel joints have!

 

[RogerP]

The modern fluted (straight or spiral) dowels stay put much better that the old plain ones.

 

[Tetsuaiga]

18 years sounds good enough for me.

 

[finish_that]

Not sure that was entirely fair test - in that - from what I could understand one biscuit was up against the others in multiples apart from the M&T - what would be the result with one dowel or one pocket hole ? Not knocking them , but I would also want to look into the speed and ease of accurate work .
It is more about how you like to work and the size of the joints biscuits cannot be used for tiny joints like dowels , but
are faster and more flexible for others .

 

[dzj]

I use dowels. They're OK. But for serious stuff, I go for mortise and tenons.

Problems that might arise with them is that their moisture content might not be the same as the pieces they are connecting. Also, with time, the glue sometimes fails.
Time is what is missing in the 'Joint Strength Test Comparison Videos'.
It's not a longitudinal study.

 

[timber]

I use dowels quite a bit but the only snag, unlike other joining methods, there's no "wriggle room" total accuracy is required.

Quite right Roger !!!!!! I have to start my chair seat all over again (hammer) Also today I am going to look into the quality of some dowels ,they look more like compressed paper, I left one in a glass of water overnight a few days ago and it looks a bit strange well dry now
Richard

 

[Jacob]

The most common (90%?) furniture failure brought in for repair is a failed dowel joint.
M&Ts are belt and braces - glue and wedges and/or pegs. Dowels are glue only, with a small glued surface area- basically a weak joint.

 

[RobinBHM]

I think dowels and biscuits have different applications.

Dowels have been used a lot in manufacture, as they can be drilled accurately on a point to point or through feed boring machine. Also dowels can be inserted automatically. Glue can be applied by a capsule or jet.

The disadvantage of dowels is they require exact centre to centre spacing and they require the right amount of glue. Dowels often fail due to either glue starvation, too much glue or drilling depth wrong (its easy to drill too deep to be sure the joint pulls up, but only to find the dowel then sits down too far when inserted in the first side). I have looked at the joint genie website -it certainly looks a good tool.

Biscuits have significant tolerance in one direction, just requiring a rough pencil mark for positioning. They are very good for bespoke carcase making generally much quicker than dowels.

I havent used a domino machine, but judging by the number of people on here raving about them, perhaps I should try one! Ive managed to avoid Festool so far -Im worried it may the start of an expensive collection.....

 

[Baldhead]

I must say one of the only glue joints I've ever had fail was a dowel joint

+1

Dowels are glue only, with a small glued surface area- basically a weak joint.

Totally agree.

Baldhead

 

[Paul Chapman]

In my experience, dowels are always the worst option. M&Ts, loose tenons, dominos and biscuits are all far better. Dowels just don't stand the test of time.

Cheers :wink:

Paul

 

[John15]

I think dowel joints are OK where there is little stress to the joint, for instance I used them recently to fix a bookcase facia.

John

 

[rafezetter]

Matthias Wandel did tests of his own for dowels vs other joints, be sure to read the additional links at the bottom where he revisits the tests after a dowel jig company complained about his results..

https://woodgears.ca/mortise/strong.html

 

[Chris152]

I found this is interesting - dowels vs mortice and tenon. Obviously they had an axe to grind with Fine Woodworking, but still interesting.
https://www.youtube.com/watch?v=WoOEwEuB1ag
I'm sure real world context changes things, but has anyone tested that?

edit - I came to this question after considering box/ dovetail joints for box-making, and wondered if the reason people use them is appearance/ a romantic attachment to the past rather than efficiency? Not that joints need to be terribly strong for your average box, I guess.

 

[dzj]

Longitudinal studies are missing.
When the glue fails over the course of time, M&Ts will do better.
Dowels, like loose tenon joinery, have their place, but for moving elements, M&Ts is the way to go.

 

[Chris152]

Yep, hadn't thought of that. Do you know how long it takes before the average glue fails? Again, I'm sure it depends how the joint is used?

 

[custard]

Personally I'm a fan of dowels, I use them regularly and regret that they've fallen from favour.

The first argument I'd put in favour of dowels is their affordability for the hobbyist. Yes you can spend a lot of money on some dowel jigs, but traditional dowelling jigs like the Record 148 work very well and are as cheap as chips compared with a Festool Domino or a Lamello Biscuit Jointer. If they have a problem for the hobbyist working with solid wood (rather than sheet goods) then it's the same problem as Dominos and Biscuit Jointers, they all reference directly from the workpiece, so if the workpiece isn't dead square and true then the joint will be gappy. That's just a fact of life.

The second argument is that sometimes nothing else will do the job quite as well as a dowel, so even if you prefer other jointing solutions dowels should still be in your armoury. I could give dozens of examples but I'll just use two.

You'll regularly encounter in cabinetry a rail beneath a drawer secured at either end with twin tusk tenons, but in order to accommodate a traditional drawer stop this rail needs to be deeper, so needs another jointing element. I've tried lots of options but keep coming back to a single dowel. You can just see the arrangement in this photo,

What's even better is that I locate the position for the dowel with the simplest and cheapest device imaginable, the traditional pointed dowel marker shown here. It works for me, and with care it'll work for you too,

A second invaluable application for dowels is with chair making. The most highly stressed joint in a chair is where the side seat rail attaches to the back leg, so you give the majority of the available "meat" in the leg thickness over to this joint. But that leaves a problem, how do you then attach the back seat rail? The solution is a very large, but very shallow stub tenon only about 10mm deep. However to "pin" that tenon securely in place it needs reinforcing with two or three dowels. You can see a typical back rail chair joint here,

Once again the added beauty is it requires a little bit of skill rather than a great deal of money, because for chairs I always make my own dowel jig. Simply a block of hardwood with a mortice on one side and a tenon on the other, shaped to perfectly mate with the corresponding stub mortice and tenon joint, through this I drill three holes and that's the jig made. It won't last forever, but you don't need it to, you only need it to get you through the eight or ten chairs in a set.

Final point. I think debates, about if dowels are stronger than dominos or M&T's, are missing the point. I don't care which is the absolute strongest joint because by and large they're all strong enough for domestic furniture. What matters to me is their practical application within the context of making a piece of furniture. If I was looking for ultimate strength I'd forget about wood and weld the thing up from angle iron.