Build a backhoe thumb by welding three steel plates together to form a U-shaped box without a lid. This box is then welded to a steel brace. The entire structure is then mounted to the bottom part of the backhoe arm, where it remains stationary but acts like a hand to pick up objects.
To make the backhoe thumb, place one steel plate measuring 1/4 by 6 by 18 inches on the ground. Place two steel plates, each measuring 1/4 by 6 by 24 inches, on either side. Make sure one end is flush and the other extends 6 inches. Use an arc welder to weld the plates securely together. Once cooled, use an electric drill outfitted with a 3/4-inch drill bit to drill through both corners of both of the 6-inch extending ends.
Put the extending ends around the backhoe arm at an area 18 inches from where the bucket is attached. Tilt the thumb at a 30-degree angle toward the bucket and drill holes in the backhoe arm to correspond with those on the extending ends. Add bolts and secure them with nuts, washers and a 3/4-inch socket and ratchet.
Clamp a steel plate measuring 1/4 by 6 by 18 inches underneath the thumb at a 30-degree angle from its top. Weld it in place to create the thumb's brace. Drill a hole through the steel plate and into the bottom of the backhoe's arm. Secure it with a bolt.