Best choice for cross-cutting long boards at 45 degrees for a large box?

[wintry crow]

I'm working on just the top frame/box here with this question.

The top and bottom panels of the box are 45" long and all are about 15" wide. I could maybe use the table saw for the longer pieces but I am not confident I have enough clearance and support for the overhang.

I'm currently setting up my circular saw with a guide to do this job and did a few test cuts yesterday, but when putting two pieces together it looked like my jig moved a tiny bit because they were not meeting perfectly.

Looking for any tips on whether this is the right technique and I should just keep practicing until I get it right or is there another way people accomplish large mitered boxes? Or is this dumb and I should just do a simpler joint?

[amber kiln]

I would make a tablesaw sled setup for beveled cuts. Much easier to keep a long piece stable on a sled vs just holding it up against the miter gauge in my opinion

As far as changing the design: I think you could achieve the same look with a rabbeted carcass and then mitered edging on the front

[kind smelt]

You can make a ramp stand for the overhang also, they’re very handy for support at the jointer, planer and TS

[wintry crow]

Ok thank you. I'm hoping they have a sled that accepts 45º at the shop I sometimes use. They also have a rolling stand for supports I suppose I could experiment with if that's what you mean by ramp stand?
And good point on just going with a rabbeted edge if all else fails. It won't be that noticeable with the mitered face edges.

[amber kiln]

That's probably how I would construct it personally

Regardless of the tools I have

[wintry crow]

The rabbeted joint?

[amber kiln]

Just a stronger, less fiddly joint

Yepp

[wintry crow]

Yeah you're probably right there. Also way easier

[kind smelt]

Ages much better too

[wintry crow]

Interesting!

[amber kiln]

Those miters will open up with seasonal expansion and contraction

[wintry crow]

That's good to know– never heard that before

[wintry crow]

I can't see how a rabbeted joint would fade into a 30º front-facing edge

I should mention that my intent was to create a waterfall edge and the 30º edges are already cut

[amber kiln]

I was suggested rabbeted carcass with mitered edging

so you'd have a 3/4" or so thick edging on the front that's mitered

[wintry crow]

Oh that makes sense

I could probably trim what i have now and slap it on there

[amber kiln]

Yepp