Building Big Boxes

[Darren]

Howdy,
I'm new to the forum, and spent some time searching before posting... because I have what I'm afraid is a really silly question: I am building some rather large window boxes (about 7 feet long by 18" high by 24" deep) out of 3/4' finish-grade oak plywood. I am planning on running finger joints down the vertical edges for a little nicer look than butt joints or L-joints. Besides, it's fun:-)

Anyways, my question: I'll be trenching out the finger joints with a 3/4 inch bit... when working on the end of long stock is it advisable to work on the horizontal, or ??? I can't imagine climbing a ladder makes any sense, but haven't used a hand-held router except for edge work.

What do I do? Sorry to be simple.

Thanks!

[Mike]

Darren, you wont want to use finger or box joints for your boxes. The reason is you would be exposing the plywood laminations on the fingers to the weather and your box would come apart in no time flat. Instead consider using a corner block of solid wood that is both glued and screwed in place. You will also want to wrap the exposed edges in solid wood or at the very least apply a veneer of solid wood to help seal the plywood edges from the weather.(A much less expensive method) For your finish you will need to use a good spar varnish with UV inhibitors. Plywood laminations do not react kindly to outside weather, and anything you can do to protect them from the sun and water will increase the life span. If you have questions about different ways to attach corner blocks I will be happy to give you some ideas.

[Darren]

Originally Posted by aniceone2hold

Darren, you wont want to use finger or box joints for your boxes. The reason is you would be exposing the plywood laminations on the fingers to the weather and your box would come apart in no time flat. Instead consider using a corner block of solid wood that is both glued and screwed in place. You will also want to wrap the exposed edges in solid wood or at the very least apply a veneer of solid wood to help seal the plywood edges from the weather.(A much less expensive method) For your finish you will need to use a good spar varnish with UV inhibitors. Plywood laminations do not react kindly to outside weather, and anything you can do to protect them from the sun and water will increase the life span. If you have questions about different ways to attach corner blocks I will be happy to give you some ideas.

Thank you very much, but alas no... my window boxes are perhaps misnamed... as they are intended for inside use instead of outside. They are rather like a box/bench with a cushion on top (I just try to build what I'm told). I fiddled around with finger jointing some of the scrap, and the end-cuts actually look rather nice... and give a cheap plywood box something slightly unique.

So, back to my original puzzle: what do I do with long stock? At an angle? Horizontal? Clamped to a stair rail? I'm still puzzling over this one.

Thanks for your help and any continuing insight.

Cheers,

Darren

[Mike]

Ok Darren, now that we are on the same sheet of music I have a suggestion. Both Shopnotes and Woodsmith have plans for very nice plywood boxes with ideas on dressing them up for different looks, complete with the cushion on top.
There is no way you can freehand your finger joints accurate enough unless you use a template or jig to guide you. The easiest way I can think of is to purchase a box joint guide plate for a dovetail jig. You can screw this to some sacrificial wood and clamp it to the end of a bench, with the "comb" shape facing up. Use a guide bushing with your bit and you should be able to get nice results. You will want to cut both pieces of wood at the same time to ensure a good fit. I would lay one sheet down, apply some double sided carpet tape to it and set the other sheet on top with a 3/4" offset and then clamp it down. Another way would be to build a jig to attach to the bottom of your router. If you look at the Oak Park site you will see Bob & Ricks box joint jig. Normally this type of jig is mounted to a table and you stand your wood on end and move over it. That's not practical for your application, but you can attach a jig like this to your router and using the end of a bench for support should get great results. If you need help building a jig let me know.

[BobandRick]

Darren:

I assume you have done box joints before, right?

The only thing I would add to aniceone2hold is we lay all 4 pieces horizontally on the bench with the correct offset. If your using a 3/4" router bit you need a jig that is 3/4" router bit, 3/4" space and 3/4" fence. Practice on some scrap pieces in the horizontal position before cutting the good pieces.