A workbench is unique as the person that uses it. Here are directions to construct a portable workbench. When I say portable, I mean that it is held together with 12 lag screws and can be disassembled for moving, I have included a spreadsheet that allows you to design the size of your bench and automatically generate a cut list.
Step 1: Procure a Bench Top
The size of a workbench is a very subjective thing but it comes down to the length, width, height, and thickness of the bench top. I like a very heavy bench so it doesn't move when I use hand tools. In my opinion I should be able to move it myself, but just barely. I like my bench to be about 20" wide. Some prefer 24" or even 30". 8' is a good length except if you don't have space. I once made a bench 40" by 16" because I just didn't have anymore room or money for something bigger.
First you will need a bench top. You can either build a top to the size you want or find something premade to use as a top. Solid core doors make nice tops at 1-3/4" thick. Glue and screw two of them together and you have a really stout bench. I find them on Craig's List for as low as free. Ikea sells cabinet and desk tops that make nice tops. They sell a LINNMON top that is 78" by 23" by 1-3/8" thick for $45. Glue and screw two of them together and you have a really heavy, rugged bench top that is nearly 3" thick for only $90. You can glue and nail 2x4s together to make an 3-1/2" thick top or 2x6s to make a 5-1/2" thick top.
I am making a bench for son to be stored and used in his garage. He wants it no wider the 20". I made the top from a piece a timber strand beam and some 2x4s I found at a construction site that had finished their last house. The top is 60" long, 19-1/2" wide and 3" thick.
Step 2: Design Your Bench
After you have procured a bench top you need to design the base it sits on. My son is tall and does not use hand tools so he wanted a bench 40" tall. He wants the top to overhang each side by 8", the front by 1" and the back by 2". Since the top is 3" thick this means the base need to be 44" (60 - 8 - 8) long. 16-1/2" (19-1/2 - 1 - 2)wide, and 37" (40 - 3) tall. I have included a spreadsheet that allows you to enter these three values and it will generate a cut list. It even has a large cell to add notes about your specific design.
Step 3: Procure Lumber
The spreadsheet also calculates the amount of 2x6 lumber you will need and displays it in red. For this example the spread sheet calculates that nearly 38" feet of 2x6 will be needed. That would be 5 8' 2x6s at a cost of about $20.
Another option is to scrounge up the wood. I stop by local construction sites several times a week and dumpster dive for scrap wood. The lumber is dirty and full of nails but the price is right. Besides there is a pleasure of making sometime nice from the cast offs of others.
Step 4: Mill the Lumber
From the cut list you can see
that all the pieces are 1-1/4" thick and either 5" or 2-1/2" wide. The pieces have been cut at least 1" longer than the finish dimension. You will have to mill the wood to thickness with a planer or thickness sander. If you do not have one, check the local wood store to see if they will mill wood. Also check in Craig's List as someone is always looking for a few bucks. You can go to the woodshop at the local high school or junior college. They are usually happy to do so. Check local woodworking clubs for sources. If none of this works out then change the dimensions to 1-1/2" thick, and 2-1/2 or 5-1/2" wide and use finish grade 2x3 and 2x6 lumber. Resize cut list accordingly.
Step 5: Assemble B, C, and D
Cut to dimension pieces B, C, and D to form two side leg assemblies.. Drill four, ¼ " holes, 2" deep into each side leg B. This will counter sink the screws so they can grab and hold the rails in place. Place holes 5/8" and 1-7/8" from top. Also place holes, 3-1/8" from bottom. Glue and screw side rails into place. The top rail is flush to the top and the bottom rail is 3" from the bottom. I recommend using SPAX 1-3/4" MDF screws.
Note that I am using some clamping cauls to keep the board aligned while screwing together the pieces. Go see the Instructable on Clamping Cauls for more information
Step 6: Add a to Assemblies
Cut to dimension pieces A and attach to the two side assemblies Glue and screw with 1-3/4 screws. Countersink about 1/2". Do not put screws near the lower rail D.
Step 7: Add C' to Assemblies
Take pieces C' and cut them for a snug fit on the inside of the assemblies, right next to C. Before gluing and screwing into place drill a 5/16" hole about 2" away from each end of the piece. These holes will be use to connect this base to the top and they can be seen in the photo. Countersink the screws about ½".
Step 8: Drill Holes to Attach Long Rails With Lag Screws
On each side of the side pieces, mark 5/8" from the edge of each B leg. Now mark 4-1/4" and 6-3/4 " up from the bottom. Drill two 5/16" hole at these locations. This is where the long rails will bolt into the side assemblies/
Step 9: Bolt Long Rails E' to Assemblies.
Cut to dimension pieces E' and bolt to the assemblies at the newly drilled holes. I recommend using SPAX lag 1/4 " lag screw 4-1/4 " long. They are inexpensive and do not require a pilot hole in the rails. I have turned the assemblies upside down to make construction easier.
Step 10: Add D' to Assemblies
Take pieces D' and cut them for a loose fit on the inside of the assemblies, right next to D. Glue and screw into place making sure not to get any glue on the E' long rails. Countersink the screws about ½".
Step 11: Attach E to E' Rails
Take pieces E and cut them for a snug fit next to the long rail E', between the two assemblies. Glue and screw to E' making sure to only get glue on the E' rail. Countersink the screws about ½".
Step 12: Intermission
You have now completed the base and you have a top. If this bench is going to moved somewhere else after construction, this would be the time to do it. The base is held together with eight lag screws and disassembles into four pieces. When disassembling mark the pieces for easy reassembly.
Step 13: Attach Base to Bench Top
The pieces of the bench have been moved to mu son's garage where it will be assembled. Turn the bench top over and mark the left, right, and front offset. The place base, also up side down, of the bench top and lag screw into place.
Step 14: Finish
Everyone has an opinion of what a bench's finish should be. I like to put on a single coat of oil based sealer on the bench top. I put no finish on the base.