What sort of joints for a plywood box?

[snowyskiesau]

I need to make some storage/carry boxes for a couple of telescopes. As I have a spare sheet of 12mm plywood, I thought I'd use it.
The boxes will be about 600 x 300 x 300.

What would be the best method to joint the edges? Strength is the main criteria.
I like the idea of dovetails but never having tried to make a box using them, I'm not sure that practicing with plywood, would be a good start.

[zenwood]

If strength is the main criterion, use dovetails or finger joints. Plywood is a good start in practicing.

[fletty]

If they are to be 'practical' only then use aluminium angle, double mitred corners, and fix the plywood with self tapping screws. Each face then is a plywood panel with an aluminium frame. Very quick and not expensive!
If they are to be 'practical AND pretty' then there is some very schmick aluminium extrusion with cast corner pieces made to fit plywood panels and there was a recent thread where SOUNDMAN showed us how he does it professionally ... very nice!
To transport (I presume) expensive equipment, I would not use timber to timber jointing using plywood only.
Fletty

[pal]

Just 45 Mitres and contrasting splines .If that gets damaged seriously enough to break I would hate to see the Telescopes

Pal

[AlexS]

What Pal says. On each corner you will then have 17mm wide gluing faces plus the splines. With ply, you can also glue the top & bottom to the sides, which will add to the strength.

I've seen ply boxes with dovetails, and IMHO they always look crappy.

[snowyskiesau]

Thanks for the suggestions.
I think I'll try one using finger joints as I've never done this before. When that fails, I'll try the mitre option. :)

[AlexS]

Finger joints or dovetails will work fine - It's only their appearance in ply that I don't like, but it's subjective.

As Zenwood says, it's all good practice.

[bsrlee]

Use BIG fingers in the joints & cross pin them - then if the glue fails (PVA + water) it won't come apart unexpectedly.

[snowyskiesau]

Use BIG fingers in the joints & cross pin them - then if the glue fails (PVA + water) it won't come apart unexpectedly.

The boxes will be made out of 12mm ply and will vary in size but typically 650mm x 350mm x 350mm
What size fingers would you recommend?

[zenwood]

If you're taking the telescopes outside at night, I'd use a waterproof glue (you could get dew etc.): epoxy or polyurethane.

Conveniently, 25 x 14 = 350 mm, so you could make 14 fingers along each edge. (Add extra for cutting off the lid).

[snowyskiesau]

The box sizes (i need to make 4) are not critical, they just have to be big enough to
allow a certain thickness of foam around the telescope. As the largest size router bit
I have is 19mm, I'll adjust sizes to get an even number of fingers with that size bit.

Now to make a suitable jig to suit my Triton router table....