Originally posted by: Evadman
You can use the brackets, but be sure to glue the corners together with urethane glue. It will expand slightly and fill in any gaps ( aka mistakes ) Make sure to use 3" gold colored screws ( or another style that will not rust. I would recomend against drywall screws, as the shafts can break over time ) Do not use the piddly little 1.5" screws they give you.
I assume Lowes has a return policy much like Home Depot's where you can return things even after opening them. It is just much easier if it is not open.
If you decide to return them and make the table yourself, this is what I would do. I would use 4 x 4's or doubled up 2 x 4's ( since that would be cheaper tahn 4x4's ) for the corner posts. then use a brace 6-10" from the floor ( the lower the better ) In the corners where the braces attach (which should be 2 x 4's ) you want to notch the 4 x 4 posts so the 2 x 4's fit flush. Then glue them in. this will prevent the "racking" or side to side motion.
here is a crappy drawing Made in paint, so don't kill me
The major problem with the kit is that the 2 x 4 bracing on the bottom just buts up to the corner post. If there is a small gap, the table will shift slightly side to side, and will only get worse as time goes on. Just 2 screws that are not in the plane of this sideways force and a little steel are trying to keep the table steady. For a workbench, this is not good.
Also, instead of plywood, you may want to go with MDF ( medium density fiberboard ) It is much much denser than plywood, and will not have the "bounce" that can happen with regular ply. strenthwize, ply has MDF beat. But for a work surface, MDF is a much better choice. Most workbenches you see will come with MDF instead of ply. MDF does not react well with water though. If it gets wet, the fibers will pull apart, and expand. So if you put a cool drink down on it in summer, you may get a raised ring from the condensation. You can prevent this with some kind of water proofer like polyurethane, but who puts poly on a workbench? I have a few MDF workbenches, and I love them much better than plywood. Up to you though.
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There are other ways of doing the bracing too if you do not want to notch the posts, but they do not look as good, and take up more space. Doing the notching is not that hard though. Just set your circular saw to a 1.5" depth and cut 2 goves 3.5" apart, along with a few more in the center. then knock out the wood with a chisel or a flatblade screwdriver if you do not have a chisel.