When repairing wide-seat square we should use Cast iron surface plates.

When repairing and inspecting the wide-seat square using the following methods, the Cast iron surface plates and Inspection surface plates are necessary.

When repairing, use cast iron L-square or cylindrical square check inside and outside 90° angle, use outside micrometer check depth of parallelism of short edge. If there is small error in verticality of long edge, parallelism of short edge and inside as well as outside 90° angle; see little white light when check by cylindrical square, the Junction of sort edge and long edge are in good condition, we can repair it without disassembly, grinding inside and outside 90° angle on cast iron surface plate is ok.

When repairing wide-seat square, we can divide into A, B, C, D four sides: Side A and B are datum planes; grinding side A at first, then side B, as showed on the picture.

We need to check when repairing, after side A and B are parallel to each other, then inside corner side C, it will be more convenient if we use cast iron 90° angle plate and grinding on Cast iron surface plates. At last side D.

When checking inside and outside 90° angle we can use straight edge ruler or cylindrical square. If repair one set wide-seat square, we can inspect on 0 grade cast iron surface plate.