Magnets are helping me do better, more accurate, and cleaner structural acoustic repairs (especially interior) than ever before. Magnets can be fastened onto or inlaid into a variety of cauls and shapes made from wood, teflon, Plexiglas, or brass. Cauls in matched sets of two (photo, right) align perfectly when faced together, magnetically attracting. With a top, side, or back separating them you know exactly which direction the caul is aligned on the inside of an instrument, and where it is. This is a big help in lining up such things as patches, crack reinforcement, and side struts. For example, here's how I'd use magnets to locate the bridge clamping caul. Once glue has been applied to the bridge, you must quickly locate the notched bridge clamping caul over the braces at right angles to the top's centerline so that it parallels the bridge and ends up in the correct position for the clamps. The classical guitar's somewhat small soundhole (3-1/4" diameter average) makes such maneuvers more difficult than in a steel-string guitar. Magnetic “caul stops,” and a magnet taped temporarily to the caul itself, made the job easier… Protect the top around the bridge.
Place interior magnets at (A) and (B) (illustration at right) and attracting magnets (or steel blocks) on the outside. The caul will align as it butts against these interior “stops,” and if the magnets are strong enough, they won't be pushed out of location while you work the caul into position.
I taped a strong magnet to the underside of the caul. With the bridge set in place, I used an outside magnet to position the caul while I applied the first couple of clamps!

There are more uses for magnets. The following are just a few examples: A padded magnet wrapped in cloth and tied-off can be dipped in warm water, squeezed-out, and used wet. It can be drawn along a brace to clean hard-to-reach interior glue squeeze-out during a brace repair (right). Magnets are perfect for locating and then clamping interior patches along glued cracks and seams (lower right). Magnets with sandpaper superglued to their surface do the best job ever of removing old dried glue from an interior surface (right). They're also great for removing dried glue squeeze-out and rough spots along a repaired crack (below). Always use protective tape on the outside of the instrument when you're dragging a magnet over the surface!

Warning: These are seriously strong magnets!
These magnets are made of the rare-earth metal neodymium boride. This is listed in the Guinness Book of Records as the World's Most Magnetic Substance. It is 10 times stronger than modern loudspeaker ceramic magnets.

Use extreme care when handling these magnets since they can magnetize, degauss, or re-polarize any ferrous or magnetic material - including electric guitar pickups! Keep away from magnetic storage media such as floppy discs, cassette and video tapes, as well as pacemakers, computers, CRTs, TVs and watches.

KEEP OUT OF REACH OF CHILDREN If more than one magnet is swallowed, the magnets can attach to each other and cause intestinal perforation or blockage, which can be fatal.