Are factory edges of plywood straight and square?

If the diagonal measures 5' at the 3' mark of a 4' wide sheet of plywood, then the corner is square. Just remember: Not all plywood is exactly 4' wide.

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A string or a chalkline makes a ready reference for checking the straightness of a sheet of plywood.

Q:

To make shop cabinets, I’m cutting a lot of plywood. Is it safe to consider the factory edges of plywood to be straight and square, or will I need to true them up?
—Jonathan Walters, Bryantsville, Ky.

A:

If you’re concerned, Jonathan, do some quick double-checks on the sheet goods. Sight along the edge to see any curves or wobbles from the manufacturing process. This will also reveal dinged edges or delaminating areas that might not be visible straight-on. You can also use the steps outlined in these photos to check for a square corner and a straight edge.

If you do find problems, your best straightener is your tablesaw. Cut your project pieces to 18 " or more oversize with the factory edge against the tablesaw fence. Then cut them to final size with the newly ripped edge against the fence. Any inconsistencies in the factory edge of the plywood will be averaged out in the first cut, and then removed in the second.

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