workbench woes...

[myredracer]

If that's only 1 or 2 screws in the corners, that's not enough to hold it tightly together. Are the cuts perfectly square? I would build the top on the floor and then add the legs after. Unless really bad to start with, a bow or twist can be taken out of the long pieces by the cross pieces when it's tightly pulled together with enough screws. Some woodworking clamps may help if gluing the pieces.

I'd use construction adhesive (PL400 or equiv.) along with screws for the top and weight it down if needed to take out any remaining twist while the adhesive sets. The plywood will also act as a diaphragm and help strengthen it up a lot.

With the frame laying on the floor, you could temporarily screw on some 2x4s on the flat extending up about 3-4 feet and then another 2x4 horizontally to tie these together. This will take out twists until you have it all the cross pieces in place. A little adhesive at the ends of the cross pieces won't hurt either. If badly twisted and/or bowed you will be SOL tho.

As in the above diagram, some additional cross and lengthwise pieces will really help to hold it plumb, straight and square. You don't really need 4x4 legs and 2x4 would be fine or even 2x3.

I'd use at least 3/4" ply for the top. Or two layers of 1/2" would be better (glued and screwed). I just built a 12' long workbench with two layers of 3/4" ply and it will be able to take a real beating and handle very heavy stuff.

Once a piece of wood has twisted, cupped and bowed, there is little you can do. Starting with kiln-dried (KD) is the best approach and would help if painted afterwards.

 

[MarkG]

Here's a pic of the end of my bench to illustrate a few key build features:

1. The plywood back screwed to the back of the legs----this WILL prevent ALL 'racking'! It also serves nicely as a back to your lower shelf.

2. The 'captured nut construction'. The stretchers have a short piece of pipe going through them to act as a captured nut type thing. A long bolt goes through leg and about 6" through stretcher and a nut is in the short section of pipe. Now it can be tightened up as tight as you want, where if you DID NOT do this, it would strip out of the endgrain immediately if not sooner!

3. Top---2 layers 3/4" ply and 1 layer 1/4" Masonite all glued up and edge-banded with 3/4" Oak.

4. Leg construction---top and bottom with 2 vertical members doweled and glued. A couple good-sized dowels each end.

5. Last but not least---the whole thing is bolted to the floor! Look midway between the 2 side legs on the foot. Bench does not move, does not rack, does not jiggle at all.