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Anyone have experience with or an opinion about the bridge plate size for a 12-string dred? I am planning on extending the plate 1/4" towards the tail. I've been looking for a recipe on the net and have come up dry. I will be finishing the box this weekend. So far, I've overbuilt a bit -- the board is 1.2" and braces 5/16" by 9/16" and the plate is standard thickness.

With the caveat that I have never built a 12-string guitar, here is my take on it:

I've built three 6-string guitars and a 10-string cittern - they are all described in the "Blog Your Project" section. I used what would probably be considered oversize bridge plates for all of them, and they all sound very good. So...I don't think you need to worry too much about making the bridge plate too big, assuming you're "reasonable" about it. I don't know what size you're starting with,but + 1/4" shouldn't be a problem at all.

One thing I do is curve and taper the edges so the edges aren't abrupt straight-line stress concentrators. This picture may help convey the idea.

But...what I do may not be the best way of doing it. All I can tell you is that it seems to work acceptably well for me.

Thanks Steve. Good perspective. I'm going to 5/16" bigger and taper, like yours. I been trimming the bracing a bit, but it's still pretty robust. I did a three piece eir back and added a brace -- it should be solid. Now to figure out what to do with the neck. I read that 12 strings are hard on necks. I suppose there I'll start with a convex camber.

I think you may be over-building, though with no personal experience with a 12-string it is hard to say just how much.
The closest I've come is the 10 string cittern, and that has a trapeze tailpiece, not a pin bridge, so it doesn't compare very well.

I don't think I would make the neck deliberately convex. You need to end up with a slight up-bow so the strings don't buzz on the frets. If you want you could embed a couple strips of carbon fiber to stiffen the neck although that can be overdone too, My last project was a neck for a long-neck banjo. I put carbon fiber in that, and the neck is STRAIGHT. Too straight. Even after cranking the truss rod counterclockwise I was hard pressed to get enough up-bow into it. One can have too much of a good thing. The load applied by 5 banjo strings certainly doesn't compare to 12 guitar strings, but don't wildly overestimate.

Ideally you want to build it so it's just on the verge of folding up...but not quite. As a practical matter you probably want to build it somewhat more robust than that so it can survive in the real world. But how much????