# Is a Splined Mitre Joint Necessary?



## SleepingFox (Aug 3, 2018)

Hello,

I'm making a small box for watches as a christmas gift and I'm trying to decide if I need to put splines in the mitred corners of the box. I've seen plenty of splines done very beautifully but if possible I want to have the unbroken grain of the wood wrapped around the entire box. I know that splines help strengthen a mitre joint but I don't know if they are necessary for the integrity of a box. Does anyone know if these joints will eventually fall apart if they are left un-splined?

The picture below is the box as it currently is with no splines. The walnut exterior is 13mm thick and cherry interior is 5mm thick. The dark spot on the right side of the box is a small ding thats been filled (dropped a piece on my cement floor :\)


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## Phil32 (Aug 31, 2018)

The spline can run vertically through the miter and be completely hidden when the lid is closed.


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## Snipes (Apr 3, 2012)

i just finished a couple mitered box's that I made longer for the purpose of testing glue strength. I was not able to brake any joint on the glue line. so my opinion is it is not necessary..


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## 000 (Dec 9, 2015)

> The spline can run vertically through the miter and be completely hidden when the lid is closed.
> 
> - Phil32


How would you put those in?


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## wapakfred (Jul 29, 2011)

I've done a few of the vertical spines (flag boxes). It wasn't that hard, tilt the TS blade to 45º and run the box side (end) across it with a miter gauge. the workpiece is flat on the table and the blade cuts 1/2 of the slot you need.


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## 000 (Dec 9, 2015)

But the box is glued together…


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## Phil32 (Aug 31, 2018)

Yes, the splined miter we are describing would be done before assembly.


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## LesB (Dec 21, 2008)

You are essentially gluing "end" grain and that is never a strong joint. Splines or biscuits help strengthen the joint. The alternative is the visible horizontal splines or dove tail splines across the corner of the joint.

Possibly the best idea is router bits that cut a "lock miter" pattern on the miter that greatly improves the strength of the joint. Just google "lock miter router bit".


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## RichT (Oct 14, 2016)

The issue with this box is that it's lidded and the miter is exposed when the lid is removed. I build boxes like this often, and the exposed joint impacts my choices of joinery.

For a box where there is a top covering the joint you can use options like a lock miter or vertical spline. However for my tastes, when the joint is exposed like that shown in the OP, only a clean, straight miter should show. For that, I use either biscuits or miter splines that run across the joint (assuming I'm doing a miter joint and not dovetails or a box joint).

If a biscuit joiner is available, I'm pretty sure #0 biscuits would work in 13mm wood if the slot is cut towards the inside of the miter. I have the PC557 with the optional face frame cutter, and I'm certain FF biscuits would work. Otherwise a slot cutter could be used to make a stopped slot for a vertical spline that wouldn't show through to the exposed area.

Also I'd like to point out that this is not a full end grain joint. The wood is cut at 45º and it falls somewhere between end gain and long grain. While I do always reinforce my joints of this type, I will say that I've tried to break the joint to see how strong they are without reinforcement, and it is very difficult. It's a really strong joint on its own.


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## 000 (Dec 9, 2015)

> Yes, the splined miter we are describing would be done before assembly.
> 
> - Phil32


Yes, I know. Just wondering why it was recommended then?


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## JADobson (Aug 14, 2012)

I don't add splines to my small mitred boxes. I size the joint with a glue/water mixture before gluing and I've never had a problem. I think you'll be fine here.


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## RichT (Oct 14, 2016)

> Yes, I know. Just wondering why it was recommended then?
> 
> - jbay


Good point. I didn't realize the OP was asking about an assembled box, I thought that was a photo of the type of joint he was using.

*Back to the OP*, like I said in my post, I've glued boxes using miters in material much thinner than yours, like 5mm, and tried to break them by hand pressing the corners together. They held together. I'm sure your joint using 13mm stock will be plenty strong if you glued it properly.


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## AAL (Jun 30, 2014)

You could make a jig for a router table that would produce a hidden spline. There are several designs, here's onehttp://www.startwoodworking.com/plans/build-jig-hidden-spline-joinery


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## bndawgs (Oct 21, 2016)

I think that you'll be fine with the box the way it is. I doubt the person it's going to is going to be using it as a football.


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## a1Jim (Aug 9, 2008)

This might help making them, Btw splines are not an absolute necessity but they do add a lot of strength to your miter plus add a nice decorative look.

https://www.woodmagazine.com/woodworking-plans/tablesaw/realign-your-splines


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## ArtMann (Mar 1, 2016)

I normally make boxes out of 1/2 or even 3/8 inch material and mitered corners without some kind of reinforcement is questionable. I would not sell a box like that for fear of having to replace it.


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## splintergroup (Jan 20, 2015)

Doug Stowe did an article in a recent FWW on hidden splines running along the mitered edges so it can/is done.
That aside, I agree that the strength should be ok, especially if the bottom panel is glued in place.
The lock miter router bit is a great solution since the exposed top of the joint actually adds interest in most cases. Box assembly (clamping) is also reduced to a no brainer since the corners won't slide around while gluing.


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## RDan (Jan 14, 2012)

Is the internal box set in the other box? If so and you glued it in, there should not be a problem. Even without that they should be plenty strong as joints. They will not have a lot of stress on a dresser. The other thing I have seen recently is Rockler's dowel pin jig. You could make dowels out of the same material to hide them in the grain. Dan


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## bondogaposis (Dec 18, 2011)

It will probably be fine as long as it it not dropped. Splines will add a lot of strength to a miter joint and I generally add them because you never know how something gets treated after it leaves your shop.


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## Chashint (Aug 14, 2016)

The miters look tight and the thickness looks to be substantial. 
While I don't think splines are structurally necessary I do think splines made out of the same wood as the liner would add interest and still look elegant. 
The box will look great either way though, so it's really just preferences.


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## ArtMann (Mar 1, 2016)

Just to reassure yourself, why not build a few joints with scrap wood from the same build and then see how much force it takes to break them?


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## SleepingFox (Aug 3, 2018)

Thanks so much for all the info guys. I decided to leave the box as is and it is now just awaiting a clear coat.


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## pontic (Sep 25, 2016)

when I just use glue for a miter joint for aesthetic purposes or the stock is just too thin; I "edge glue" first.
I burnish a thin layer of glue into,the endgrain and let it set a little bit. Titebond III works best (in my hands) for this.
This way you get a layer of setting glue in the end grain. So when you apply your glueing layer the end grain doesn't suck up the glue so much and gives you a stronger glue joint.


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