Okay, I'll do my bit to answer a number of points made so far.
First though, thanks for all the input and discussion, very enlightening and I appreciate you all sharing your knowledge and experiences.
: Thanks, that's a lot of good info. Baltic Birch isn't really available here in Australia so much (I haven't found much) and it's often made into ply with other woods, and not in thin sizes.
: I don't have a slot cutter at this time. Not to say I can't get one, so it's an option.
I am concerned though that if the material I'm working with is only 18mm thick (not quite 3/4") that I would be hogging out quite a bit of material. Would I opt for say a 6mm thick spline?
Biagio: Regarding the position of the glue-line,
1. Will it be visible inside the cabinet? Yes it will
2. Will the board be weight-bearing? Yes it will
3. Are there any other structural members to give support? Yes there are, note I mentioned supports in the original post.
4. Exactly what material are you using? If by laminate you mean melamine-faced, it is darn difficult to get an invisible glue line. In that case, you might want to position the glue line as far towards the back as possible. Also, the factory edges will possibly be more chip-free than you or I can achieve by cutting. Ditto for the edging. If the laminate is wood veneer, it may not matter so much.
Steve: The laminate I refer to is glue-lam beech. No melamine involved
I suspect hiding the glue line won't be an issue, nor will I need to hide the ends as they will be contained within the sides of the cabinet.
I've attached a sample pic of the glue-lam sheet I talk about for reference.
Biagio: I understand it to be that he wants a board 1600mm long and 450mm wide, but the standard width is only 405mm. Hence he wants to join two boards of 405mm along their long edges, and then cut off the extra. The question is whether to have the joint in the middle of the board, or to one side (i.e. one of the joined boards would land up being only 45 mm wide).
If this is the base of the cabinet, and not particularly visible from the inside of the cabinet, I would opt for the simplicity of the unequal widths.
Steve: Correct on the orientation of the board and cutting off the excess. I thought about unequal widths, however my concern about that was about the weight-bearing aspect and whether or not supporting it directly would prove stronger. I've attached also the sketch of the design to provide more clarity.
Note that the sketch is not entirely finished, but it shows the general design idea.