Lock miter bit

 

a BIG +1 for the Lock Miter Bit Jack shows above. I made this table in my projects using one and it did a very good job giving me solid miters for the corners. I bought he Infinity one and also got their set up jig is a great aid in setting up this very fussy bit. If you skip the jig, then make sure that once you've run all of the test pieces to get a good fit, cut yourself some set up blocks to keep for next use.

My biggest mistake when I did my first column was to orient the joints as shown in Jacks image above. I had to throw the first attempt out because I could not get clamp pressure on the joints. You need to make the north & south pieces with the same cuts on both sides and then make the opposite cuts on the east & west pieces. This way you only need to clamp from 2 sides to get the joints closed.

Another good practice is the addition of another board hot glued or 2x taped to the board you're cutting, (shown in jig video above). The sharp edge can get a bit screwed up if you're off a bit with your fence, and the "Guide board" pretty much keeps it fool proof.

 

If you don't want to spend the $ on the lock miter, you can accomplish similar results with splines.

 

Lock miter would work well. But as bilyo said it could be done with splines. I think lock miter would be the easiest between the two methods.

 

What is the best way to glue all of this together so that the inside
hollow dimensions stay as square a possible?

Scott - if your lumber is true and flat, and you build the box straight
and square on the outside, the inside will be just as straight and square.
what species of wood are you using and did you process it yourself
or is it from the box store?

way more information about your project would narrow
down the responses to more accurately fit your needs.
here are some designs for Post Wraps that I offer as options
when wrapping porch columns.
the butt joints give you the option of opening the wrap in the future
if there is a need to without destroying the wrap.
miterer cut, glue and pin nails would be fine for a small project like yours (IMO).
depending on what the post will be used for determines which way to go.
[if you overthink it - it will surely be overthunk].

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Edit: this is how I see your final assembly.

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A lock miter would be great, but a fair amount of work. For what you describe, I'd cut rabbets along both edges of two opposing sides (side width = interior width + double the wall thickness). The narrow sides are just square cut to interior width + double rabbet depth.

The assembly would self-square up but with careful cutting you could clamp a square to the outside and be assured the interior is also square.

 

Edit: this is how I see your final assembly.

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- John Smith

That is correct John. Still testing and prototyping at this point.

 

A couple years ago, I built a replacement cabinet for my vintage amplifier. In doing research on making it as accurate as I could, I figured out that Fender used to use a panel of the correct interior dimension to insure that all fo the cabinets were the same size, while still being able to make the fingers joints a touch oversize… This makes sure the amplifier chassis fits, the cabinet is actually square and the speaker baffles and back panels fit properly.

I would suggest you cut a block or two (or more) to the correct dimension, cover them with packing tape (to keep from glueing them in place) and line them up along the length as you do you clamping and glue up.

Depending on how fancy you need the corners to be, Butt joining or running rabbits would be the easiest.. Not only for machining, but also for assembly.

I love good lock miter joints, but man, those boards better be straight and you better use some feather boards! I really need to pull my lock miter joint bit out and do more with it.

 

my mind's eye sees something like this, with a wood knob on the back side.
and the inside dimensions are not all that critical to function properly.
and it can easily be glued with butt joints and a few pin nails.

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Normally something this size I would just miter the pieces and tape the joints.
But glue squeeze out is the problem here.
So for this, I would just do the rabbits like splintergroup mentioned. As long as your cuts are square the post should end up square. It would be easier to keep your glue out of the inside with the rabbits.