Mitred joints - opening Pandora's Box

**derekcohen** · 7th May 2023, 12:30 AM

A little while ago I posted a progress shot of the two nightstands I am building. These will have Tasmanian Oak cases with a Jarrah base.

The cases are simply mitred to avoid anything distracting the visual flow of the wood grain and figure.

Now I chose to glue these up without any reinforcements using Old Brown hide glue. I could have used splines, biscuits or dominos. Instead, the panels were taped together …

and glued with a sizing technique ...

I came in for a great deal of stick for this at Sawmill Creek. "You can't just glue mitres together - they will come apart!". "Mitres are weak. They need to be reinforced (with dominos, biscuits, etc, etc)". Or, "eventually the joints will fail owing to movement", and "what it they are dropped?".

I think some are a little surprised not to see dovetails, but I did mention that I have made many boxes or cases like this over the years, and they have proved to be strong construction. A few examples ...

I have used this pencil box every day for the past 12 years …

This is a box made for the Veritas Combination Plane. It has been bumped around for the past 5 years …

I lug this tool box to demonstrations. I am not especially gentle with it …

And more recently I built a new plinth and isolation table for a turntable. The isolation table has compound mitres …

I would not have done this if I did not believe in its ability to stay together.

There was a recent video by Patrick Sullivan, which was an assessment of the strength of end grain glueing ...

Frankly, while Patrick did produce a good video, his conclusion that "end grain-to-end grain is twice as strong as side grain-to-side train " is incorrect, but not because the glue joint is not as strong as he depicted. I must admit that I was taken in by this at first, mainly because when all these criticisms were levelled at the joinery, I wanted to avoid further discussion, and just pointed to this. However, there are two take aways from this research project (which would have been better had Patrick included these points):

1. Glue is stronger than wood. None of the joints tested broke at the glue line. This includes end grain-to-end grain. It remained intact under greater forces than side grain-to-side grain. But this is where Patrick gets off track.

2. What Patrick did not account for was that the strength of end grain glue up lay with the grain direction of the boards. The side grain boards broke earlier simply because they were stressed along the grain. It is extremely difficult to break boards across the grain. So, the results of the test really demonstrated that glue joints are stronger than the wood itself, only.
But this is misleading and potentially dangerous information, which is the reason I am writing this post.

Then Rob Cosman, following release of Patrick's video, did his own testing ...

https://www.youtube.com/watch?app=de...=RobCosman.com

Go to the 25-minute mark where a 200 lb Rob Cosman jumps on a dovetailed-and-glued corner and a end grain-glued corner. Both survive. Again, glue wins.

I feel now that it is my duty to clear up any misconceptions about the joinery here:

What Patrick's video demonstrated was that glue is stronger than wood. Most of us have known this for many years. But that does not mean that it is a satisfactory substitute for joinery. At the same time, one does not need to use extreme joinery for everything. It is relevant to differentiate "stressed" from "non-stressed" joints. Panels (as in table tops and frame-and-panels) being glued up are non-stressed. If someone adds biscuits or dominos, it is not for strength; it is for alignment. The glue alone should suffice.

If you plan to hammer on or lever a glued mitre joint verses a reinforced mitre joint, all you are demonstrating is the strength in a non-stressed verses a stressed situation. A small box may have thin sides and thin mitres, but there is relatively less chance of the panels flexing than something structural.

The same situation is present in the mitres for these cases. The only possible stress is from the atmosphere, and I believe that this is negated by the fact that the wood is consistent and the grain of the boards joined are, essentially, coplanar. Will the glue breakdown? Sure, eventually ... in a 100 or so years. Look at vintage furniture using hide glue. These pieces are not intended to last 100 or more years. Fashion will see to that. So ... okay for this situation, not-okay for stressed joinery.

With regard to mitres and biscuits et al, a big reason they are used is to prevent movement when glueing up. Glue is slippery and a misaligned mitre is ugly. Glueing a mitred joint is tricky. The tape method I used here is fantastic for alignment (and it also prevents glue leaking out on bench tops), better than anything else out there (such as other tape, biscuits, dominos, etc). And it is dead easy.

It is important to emphasise that I am not recommending that one use un-reinforced mitres indiscriminately; assess the demands and the determine the risk.

This is a potentially great discussion topic. I would like to hear the views of others.

Regards from Perth

Derek

**double.d** · 7th May 2023, 08:18 AM

Thanks Derek, this is a good topic and one i have often wondered about.

I use mitre joints in my boxes, the method of glueing is to lay the sides out on two rows of tape apply glue to the ends and base groove then fold together. My justification for not clamping was, the tape should be sufficient to hold it tight, the base and lid are glued in and will not move, the glue join should be stronger than the timber..........right?

From here i moved on to wrapping boxes with rubber bands and in most cases a little squeeze out occurred which had me thinking if the tape was indeed enough. I believe glue has no strength on its own and will not hold two pieces together with a void between. I stuck with this method for a while as again my justification was the base and the lid were glued in to hold it together.

We all know that timber moves so glueing a lid in a box can have it's pitfalls, the worst being the lid insert expands and blows the box joins, so the best method is to have a floating lid but this removes one glue point and reliance on glue holding four pieces of 30 x 12 together on end grain is not good insurance.
This was the scenario i was faced with so the next step to ensure tight and strong joins was to glue up with band clamps, two per box, which is now what i do now for further insurance.

I am not a fan of corner keys but do use them if the box i am making is larger than 300 x 200 or if i know the box will be moved around often or be subjected to rapid temperature variation.
Over the years and many hundreds of boxes i have only known of one failure, a box that was returned to me with a join that had come apart but it was clearly obvious by the rounding of one corner that it had been dropped.

In concluding i will say that a four sided timber object with or without legs that for 99.9% of its life will just sit there with no stresses placed on it does not need to be over engineered, a simple well executed glue join will be more than sufficient.

Derek, i would have to agree with all the points you put forward

**Chris Parks** · 7th May 2023, 10:38 AM

Originally Posted by derekcohen

I came in for a great deal of stick for this at Sawmill Creek

Where's Warren?

**auscab** · 7th May 2023, 11:51 AM

Sticking things together will hold things . The length of time it holds things is the question . And how the piece is treated determines that.
A piece of furniture that has good joinery backing up for when the glue lets go will be around in centuries even through long periods of neglect.
A piece just stuck together with minimal joinery will fall apart a lot sooner if neglected. Hide glue wont help either.
If sticking things together to only last as long as you treat it well and you live with it is good enough then that's fine.
I wouldn't proudly be putting a label on it with my name though.

That type of solid timber design on the night stand, even if constructed with the strongest joinery would show movement at the joints at some point in time. Glued mitre joints only, will withstand a lot less.

The design is not the best possible way to build it, if wanting it to last well through time is the goal.

Robert Brown
Cabinet Maker.

**derekcohen** · 7th May 2023, 12:05 PM

Rob, I want 30 years from the two nightstands. They are for a guest bedroom, which gets little use … unless I get kicked out of mine for snoring.

Which will last longer - the tables or me?

Regards from Perth

Derek

**auscab** · 7th May 2023, 01:08 PM

Originally Posted by derekcohen

Which will last longer - the tables or me?

30 years in a room with blinds on windows should be easy.
As long as they don't get an afternoon in the hot westerly setting sun, if that's possible . That wouldn't be good for them .

You however, like any of us, dealing with traffic and driving. Could go at any time.
The tables are safe compared to that.

Rob.

**Fuzzie** · 7th May 2023, 02:40 PM

Well there was always the option of full blind mitred dovetails I suppose. Who needs splines or other reinforcements when you can go truly bonkers on totally hidden serious handwork.

**derekcohen** · 7th May 2023, 02:54 PM

Originally Posted by auscab

30 years in a room with blinds on windows should be easy.
As long as they don't get an afternoon in the hot westerly setting sun, if that's possible . That wouldn't be good for them .

You however, like any of us, dealing with traffic and driving. Could go at any time.
The tables are safe compared to that.

Rob.

That was my reasoning, Rob. These will be nice tables (I hope) but it seemed like a good opportunity to test my level of neuroticism in mitre joints.

This is the case for others, too, I expect. As you know, I am strongly one for traditional joinery, and rarely even use biscuits or dominos. Even now I want to reach for the nail gun and stick a couple of brads in the sides

. But I shall resist this, and watch. Intellectually and rationally, these joints are not coming apart in my lifetime, but emotionally it is harder. I know why so many just plump for the safe choice.

The feedback on Wood Central is unanimously in favour of what I have done. There are some very experienced furniture makers there.

Regards from Perth

Derek

**derekcohen** · 7th May 2023, 02:56 PM

Originally Posted by Fuzzie

Well there was always the option of full blind mitred dovetails I suppose. Who needs splines or other reinforcements when you can go truly bonkers on totally hidden serious handwork.

Fuzzie, these are extra super secret dovetails ... so secret that the dovetails are hidden from themselves

Regards from Perth

Derek

**GRadice** · 8th May 2023, 01:34 PM

Derek, I like the topic for discussion.

I think your analysis is correct for the pieces you have built, their intended use, and a 30 year time horizon. What if you wanted your pieces to last past your lifetime? Say 50, or 100, or 200 years. Would that change your construction method for those pieces? I could imagine just doing the same and expecting a future woodworker to simply re-glue any failures. Or using a different joinery that might last longer without failure.

**derekcohen** · 8th May 2023, 02:43 PM

GR, it is a good question.

If I let my neurotic, perfectionism side get the better of me (

), there are two methods I could go to ... and I would love to hear the thoughts of others ...

1. Add external splines, as per boxes ...

In my case, I would use Tasmanian Oak (to blend in and reduce the visual disruption as much as possible), one at the front and one at the rear.

2. I would shoot in stainless steel nails (#18 or #23) from the side, and then close up the holes with a little warm water.

The questions I have are:

1. While is the least disruptive visually, and ..

2. Which is actually stronger, if at all?

If there is going to be movement, the seam is expected to open up (eventually). All reinforcers (whatever type) may not prevent this.

With regard lasting 150-200 years, I would dovetail the cases, as I have mostly done in the past ...

Mitred through dovetails (for a niece) ...

Thoughts?

Regards from Perth

Derek

**Fergiz01** · 8th May 2023, 06:01 PM

Hi Derek,

Just curious why you went with hide glue?

Thanks, Zac.

**The Spin Doctor** · 8th May 2023, 08:56 PM

Originally Posted by derekcohen

GR, it is a good question.

If I let my neurotic, perfectionism side get the better of me (

), there are two methods I could go to ... and I would love to hear the thoughts of others ...

1. Add external splines, as per boxes ...

In my case, I would use Tasmanian Oak (to blend in and reduce the visual disruption as much as possible), one at the front and one at the rear.

2. I would shoot in stainless steel nails (#18 or #23) from the side, and then close up the holes with a little warm water.

The questions I have are:

1. While is the least disruptive visually, and ..

2. Which is actually stronger, if at all?

If there is going to be movement, the seam is expected to open up (eventually). All reinforcers (whatever type) may not prevent this.

With regard lasting 150-200 years, I would dovetail the cases, as I have mostly done in the past ...

Mitred through dovetails (for a niece) ...

Thoughts?

Regards from Perth

Derek

It also depends on what you want to achieve in looks. If you like exposed joints great, go with dovetails or hardwood accent splines. If you don't want exposed joints, you'd make a poplar or pine box that was dovetailed or splined (or, dare I say it a MDF mitred box), so the joints didn't fail, and veneer it with an exotic wood... It's all about the end result you're looking for.

And once you're dead, you not going to be too concerned if your furniture lasts past that point. After all, you're not making furniture for King Charles' coronation which will be expected to last a couple hundred years, at least.

**auscab** · 8th May 2023, 09:11 PM

This may be a good addition . After its all trimmed flush of course.

DT.jpg

Create Decorative, Strong Boxes with Infinity's Exclusive Tapered Dovetail Spline System

Rob

**derekcohen** · 9th May 2023, 04:09 AM

Originally Posted by Fergiz01

Hi Derek,

Just curious why you went with hide glue?

Thanks, Zac.

Zac, hide glue is reversible if you need to make repairs, and old glue does not need to be removed - just add more glue. It dries clear and does not affect any finishes (unlike yellow glue). Cleans up in water. It does not creep. It is as strong as epoxy (according to Don Williams at the Smithsonian).

Old Brown glue is excellent. I get mine from Chris Vesper. Samml bottles are handy. Pop one in the microwave for 10 seconds, and it flows well. It has an open time of 1 hour, and sets hard in 24 hours.

Regards from Perth

Derek

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