Lock mitre or splined mitre for ply boxes (entertainment unit)

**rogerwilco** · 15th August 2010, 11:52 PM

Hello,

Doing my first project in a while and have a question about the best type of mitre joint.

It's is fairly straight forward and involves a set of 3 modular boxes in 17mm hoop pine ply which together make up a entertainment unit holding a TV on top with hifi components inside the open-fronted boxes, plus a bit of vinyl storage.

Boxes are about 500mm deep, 460mm high and 300mm, 700mm and 450mm wide respectively.

I want clean joints on the outside corners, but the front facing ply edges will also be exposed, so I don't want anything to odd looking there either. since these boxes are somewhat structural, I know that plain mitres wont be strong enough.

Considering these options:
rabbet mitre
lock mitre
spline mitre

Not sure that rabbet mitre will be enough, and if I'm going to go to the trouble of that, may as well do lock mitre, which will probably be easier to clamp.

Splined mitres I'm guessing will be the strongest, but probably also the trickiest to put together.

Thoughts?

**Gwhat** · 16th August 2010, 09:37 AM

Hi

I think that a Lock Mitre looks great, is relatively easy and is as strong as the plywood. A bit of time making sure the router table and fence are properly set-up and a few practice joints and you will have a good joint. Consider routing the components oversize and trimming on the saw after, if it is too hard to control tear-out.

I hope that this helps>

Regards

Grahame

**rogerwilco** · 18th August 2010, 03:24 PM

That's great advice Grahame, and I was reading something similar about routing oversize then planing the excess off.

I like the look of lock mitre's too. The other advantage is that the boxes can be clamped as a single assembly instead of clamping in sections which i think would be required for the splined mitres.

My only concern is whether lock mitres will be strong enough. Thoughts?

**Glider** · 18th August 2010, 10:53 PM

The lock miters should be plenty strong enough provided the locking channels are positioned vertically rather than horizontally. Certainly as strong as the ply.

What sort of weight will the 700mm span carry?

Mick

**Gwhat** · 19th August 2010, 09:23 AM

Originally Posted by Glider

The lock miters should be plenty strong enough provided the locking channels are positioned vertically rather than horizontally. Certainly as strong as the ply.

What sort of weight will the 700mm span carry?

Mick

I agree with Mick, it depends on the quality of the plywood and the glue, these will be the limiting factors not the joint design. My mind is saying Epoxy glue... but whatever you choose buy good stuff.

Regards

Grahame

**rogerwilco** · 19th August 2010, 10:29 AM

The 700mm span will take a 2 channel hifi amplifier - 9.5 kg.
Didn't realise it was as heavy as that, might need to reinforce the shelf. Might consider having a fixed backing (closed box) for that one, to stabilise the shelf.

Glue - I was planning on standard yellow PVA. Will look into epoxy option.
Ply is 17mm B/B hoop pine, so should hold just fine

**BeanerSA** · 19th August 2010, 10:41 AM

There are many ways to strengthen a plywood shelf. If you need some examples I can send you some scans of a magazine article.

**Gwhat** · 19th August 2010, 11:21 AM

Originally Posted by rogerwilco

Glue - I was planning on standard yellow PVA. Will look into epoxy option.
Ply is 17mm B/B hoop pine, so should hold just fine

Another issue that the epoxy will prevent is glue creep. PVA will move in the joint, epoxy sets rigid.

Regards

Grahame

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Lock mitre or splined mitre for ply boxes (entertainment unit)

Lock mitre for me....

I agree

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