A cutting tool comprising: first and second shearing blades (8, 10) mounted for relative pivotal movement about a blade pivot axis and having respective cutting edges (12, 14) defining therebetween a transverse cutting plane substantially normal to said blade pivot axis, said first and second blades (12, 14) having respective first and second distal blade portions defining a workpiece-admitting gap therebetween when the blades (8, 10) are open and converging transversely as the blades relatively advance to engage a workpiece disposed between the blades; a guide mechanism carried by the first blade and including: a guide member extending toward the second distal blade portion and constrained to move transversely along a prescribed path relative to the first and second distal blade portions between a fully extended position in which said guide member spans at least a portion of said gap and retracted positions in which said guide member spans lesser portions of said gap, said guide member having a distal end and a transverse restraining surface configured to confront a transverse guided surface of the second distal blade portion during cutting to resist axial separation of the cutting edges (12, 14) away from the cutting plane, and a spring biasing said guide member toward said fully extended position, the spring allowing said guide member to retract along its prescribed path to admit a workpiece between the blades and then returning said guide member along its prescribed path to its fully extended position to capture the workpiece between the blades (8, 10); and a resettable catch maintaining constrained movement of said guide member along its prescribed path and yieldable to allow said guide member to move away from its prescribed path and away from said gap when said guide member is urged forcefully against an uncut captured workpiece disposed between the blades (8, 10), thereby releasing the tool from the workpiece. first and second shearing blades (8, 10) mounted for relative pivotal movement about a blade pivot axis and having respective cutting edges (12, 14) defining therebetween a transverse cutting plane substantially normal to said blade pivot axis, said first and second blades (12, 14) having respective first and second distal blade portions defining a workpiece-admitting gap therebetween when the blades (8, 10) are open and converging transversely as the blades relatively advance to engage a workpiece disposed between the blades; a guide mechanism carried by the first blade and including: a guide member extending toward the second distal blade portion and constrained to move transversely along a prescribed path relative to the first and second distal blade portions between a fully extended position in which said guide member spans at least a portion of said gap and retracted positions in which said guide member spans lesser portions of said gap, said guide member having a distal end and a transverse restraining surface configured to confront a transverse guided surface of the second distal blade portion during cutting to resist axial separation of the cutting edges (12, 14) away from the cutting plane, and a spring biasing said guide member toward said fully extended position, the spring allowing said guide member to retract along its prescribed path to admit a workpiece between the blades and then returning said guide member along its prescribed path to its fully extended position to capture the workpiece between the blades (8, 10); and a guide member extending toward the second distal blade portion and constrained to move transversely along a prescribed path relative to the first and second distal blade portions between a fully extended position in which said guide member spans at least a portion of said gap and retracted positions in which said guide member spans lesser portions of said gap, said guide member having a distal end and a transverse restraining surface configured to confront a transverse guided surface of the second distal blade portion during cutting to resist axial separation of the cutting edges (12, 14) away from the cutting plane, and a spring biasing said guide member toward said fully extended position, the spring allowing said guide member to retract along its prescribed path to admit a workpiece between the blades and then returning said guide member along its prescribed path to its fully extended position to capture the workpiece between the blades (8, 10); and a resettable catch maintaining constrained movement of said guide member along its prescribed path and yieldable to allow said guide member to move away from its prescribed path and away from said gap when said guide member is urged forcefully against an uncut captured workpiece disposed between the blades (8, 10), thereby releasing the tool from the workpiece.