Well, it's not exactly SPF, but I built my workbench mostly out of SYP 2x4's and 2x12's. And to tie into the original poster's question, why not just make the extra effort and have a stable bench that will last? I built mine with the idea that I'd build a "dream bench" later, but now that I've used it for a few years, I expect I'll keep it indefinitely:
SYP is relatively hard, and has served nicely as a top (even if it does make Lar dizzy). It can be difficult to find decent 2x4 stock here (I'm in Texas), but if you pick through the piles, you can sometimes find enough resonably straight material to use. The top was made by ripping 3" strips off of 2x12 stock. The way most of those boards are cut, there is a good strip of tight-grained wood on either edge of a
2x12. I ripped two from each board and then face-glued them to laminate the top.
The leg vise has worked out just great. It handles wood of all different sizes and shapes. The only modification I can see making would be to make me a "board slave" (free-standing board support) for jointing long boards by hand.
And if I ever decide to make my "ultimate" bench, I'll probably turn this one into a sharpening station or carving bench.
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