Use 18 2x4s for the top substrate - 57". Glue the 2x4s together in sets of five. After all sets have cured, glue them together to create the complete top substrate assembly. Face glue and pin the 2x4s to get the substrate top.give the appearance of a butcher block top.The substrate gives the bench strength and stability.
Use a belt sander or hand plane to flatten the top of the substrate. Place the substrate, top side down. Align two short 2x8 top rails - 27" - flush with the short sides of the substrate and use 3" wood screws to secure the rails to the substrate.
Align two 2x8 (60") Long Top Rails with the long sides of the substrate. The ends of the Long Top Rails should be flush with the outside face of each Short Top Rail. Attach the Long Top Rails to the substrate with 3" Screws. wood.
Insert two 2x4 - 27" - rail stretchers between the long rails, positioned 1/3 of the way from each end of the bench. Drive 3" wood screws through the long rails to the ends of the rail stretchers.
Build four leg assemblies using eight 2x4 - 30" leg pieces. Place the edge of one 2x4 leg piece on the face of the other and align the ends flush. Screw the leg pieces together with 3" wood screws. ".
Place the legs inside the corners where the long and short top rails meet. The joints between the leg assemblies must be visible from the short sides of the bench. 3/8" hole through top rails and legs. Insert 3/8" x 4" carriage bolts from outside face of top rails through leg pieces. Install washer and nut on the back of each carriage bolt and tighten.
Measure 12" from the bottom of each leg and mark. Align the tops of the two 2x4 long bottom rails - 54" - flush with the marks and use 3" wood screws to secure the rails to the legs.
Insert the two short 2x4 bottom rails - 21" - between the long 2x4 bottom rails. The outside face of the bottom rail should butt up with the inside face of the leg. Attach the short rails to the legs with 3" wood screws .
Lay the workbench right side up. The bench will be heavy, so someone help you. Align the edges of the 1/2" plywood top flush with the edges of the bench. Attach the top to the substrate with 1" flat head screws. If the top of the plywood becomes damaged later, it's a simple task to remove and replace.