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Is a Splined Mitre Joint Necessary?

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Forum topic by SleepingFox posted 12-21-2018 08:02 PM 979 views 1 time favorited 22 replies Add to Favorites Watch
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SleepingFox

23 posts in 378 days


12-21-2018 08:02 PM

Topic tags/keywords: question mitre joint joining

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 :\)


22 replies so far

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Phil32

598 posts in 350 days


#1 posted 12-21-2018 08:27 PM

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

-- Phil Allin - There are mountain climbers and people who talk about climbing mountains. The climbers have "selfies" at the summit!

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Snipes

412 posts in 2692 days


#2 posted 12-21-2018 08:48 PM

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..

-- if it is to be it is up to me

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000

2859 posts in 1346 days


#3 posted 12-21-2018 08:52 PM



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

- Phil32


How would you put those in?

View Fred Hargis's profile

Fred Hargis

5630 posts in 2940 days


#4 posted 12-21-2018 08:59 PM

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.

-- Our village hasn't lost it's idiot, he was elected to congress.

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000

2859 posts in 1346 days


#5 posted 12-21-2018 09:08 PM

But the box is glued together…

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Phil32

598 posts in 350 days


#6 posted 12-21-2018 09:12 PM

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

-- Phil Allin - There are mountain climbers and people who talk about climbing mountains. The climbers have "selfies" at the summit!

View LesB's profile

LesB

2149 posts in 3890 days


#7 posted 12-21-2018 09:28 PM

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”.

-- Les B, Oregon

View Rich's profile

Rich

4676 posts in 1036 days


#8 posted 12-21-2018 10:27 PM

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.

-- Knowledge is not skill. Knowledge plus ten thousand times is skill. -- Shinichi Suzuki

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000

2859 posts in 1346 days


#9 posted 12-22-2018 01:04 AM



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

- Phil32


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

View JADobson's profile

JADobson

1445 posts in 2558 days


#10 posted 12-22-2018 01:23 AM

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.

-- No craft is very far from the line beyond which is magic. -- Lord Dunsany — Instagram @grailwoodworks

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Rich

4676 posts in 1036 days


#11 posted 12-22-2018 01:28 AM


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.

-- Knowledge is not skill. Knowledge plus ten thousand times is skill. -- Shinichi Suzuki

View AAL's profile

AAL

80 posts in 1873 days


#12 posted 12-22-2018 03:25 AM

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

-- "Socialism is a philosophy of failure, the creed of ignorance, and the gospel of envy, its inherent virtue is the equal sharing of misery." Winston Churchill

View Steve's profile

Steve

1449 posts in 1029 days


#13 posted 12-22-2018 03:31 AM

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

117688 posts in 4024 days


#14 posted 12-22-2018 03:32 AM

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

View ArtMann's profile

ArtMann

1415 posts in 1263 days


#15 posted 12-22-2018 03:24 PM

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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