Underpinner

Underpinner

Definition

Underpinner is a specialized frame-joining machine used in picture framing that secures mitered corners by pressing metal wedges or pins (commonly called V-nails) into the back of the frame, creating a strong mechanical joint.

Characteristics

• Mechanically joins frame corners quickly and consistently.
• Compatible with various frame widths and materials, including hardwoods and softwoods.
• Typically used in combination with adhesives for added strength.

Applications in Framing

• Assembly of custom and readymade frames with precise mitered corners.
• Production environments where speed and consistency are important.
• Ensures durable joints for frames that will carry heavier glazing or artwork.

Best Practices

• Ensure the frame is properly clamped and aligned before underpinning.
• Select the correct size of V-nails or pins based on frame thickness.
• Combine mechanical joining with high-quality wood glue for maximum strength.

Related Terms

• V Nails
• Joinery
• Miter Joint