This student cello came into my shop with a severe bass bar crack that had caused the top to collapse along the left side of the bass bar. Under normal circumstances, this type of damage often requires removing the top to gain access for the repair. In this case, I wanted to see if the crack could be repaired from the outside, avoiding the time, expense, and risk of disassembling the instrument. Using a combination of a balloon bladder, magnets, custom clamping cauls, and a specially made 90-degree cleat, I was able to realign the crack, glue it back together, and reinforce the damaged area entirely through the f-hole. The following photographs document the repair process and some of the simple shop-made tools and techniques that made this unconventional repair possible. - Assess the Damage: The left side of the bass bar had collapsed, causing the top to cave inward.
- Test the Repair: Use a balloon bladder to confirm the top could be lifted back into its original position.
- Glue the Crack: Work hot hide glue thoroughly into the damaged crack.
- Realign the Top: Inflate the balloon bladder and use a cello soundpost measuring tool to lift the crack into alignment.
- Clamp the Repair: Apply clamps and wedges where needed to pull the crack together and level the top.
- Make the Cleat: Build a quick 90-degree box-joint cleat using epoxy.
- Shape the Joint: Use a clamping mold with a rounded bevel to produce a smooth epoxy fillet inside the corner.
- Finish the Cleat: Allow the epoxy to cure overnight, then clean up and shape the cleat.
- Test the Fit: Practice inserting the cleat through the f-hole and shorten one side until it could be positioned easily.
- Add a Positioning Hole: Drill a small hole through the cleat so it could be guided into place with a wire.
- Make an Outside Mold: Shape a small clamping caul to match the arching of the cello top.
- Prepare the Cleat: Soak the cleat to make it slightly more pliable.
- Attach the Magnet: Tie a string to a magnet and secure it to the cleat with a tiny drop of CA glue.
- Apply the Glue: Coat the cleat with wood glue before inserting it into the instrument.
- Position the Cleat: Fish the cleat inside with a bent wire, then use an external magnet to hold it while removing the wire.
- Seat the Cleat: Use a thin piece of brass to push the cleat tightly against the bass bar.
- Secure the Repair: Add additional magnets to stabilize the free end of the cleat.
- Clamp the Assembly: Position the outside mold over the crack and tighten the clamp.
- Remove the Clamps: Allow the glue to cure overnight, then remove the clamp, magnets, and outside mold.
- Retrieve the Magnet: Pull on the string to remove the inside magnet. When it became lodged, a long endpin rod was used to tap it loose while pulling on the string.
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