[header] How to crack macadamia nuts [title] Gather tools. [step] You can make a makeshift macadamia nutcracker with a vise grip, an iron bar to set the nut against, and a flat hammer. [substeps] Vise grips are common tools available at any hardware store. 
If you love macadamia nuts and plan to shell them often, it's worth buying a vise grip for this specific purpose (though you'll probably find other uses for it as well). Be sure the hammer has a flat end, rather than a round one.