Belly Reducer

Flatten soundboard bulge before regluing or replacing bridge

(5 customer reviews)
Price: $129.00

Replacing the bridge plate used to be the only way to flatten a top. This tool will reduce, and in many cases, eliminate the common belly behind the bridge. The guitar will retain its full original value and the luthier can avoid the time-consuming task of attempting to carve the bottom of a new bridge to conform to a distorted top. The kit includes two precision-machined aluminum bridge-shaped (convex) cauls and three common bridge plate (concave) shapes.


If you don’t have a hide glue pot, you can submerge cauls in hot water (about 150 degrees) before use. Dampen the bridge area and the entire bridge plate. Install bridgeplate caul with concave side up; hold in place while you install the bridge caul with convex side down. Magnets will hold cauls in place while you install clamps. Clamp with at least as much clamping pressure as you would use to affix the bridge. Leave overnight or longer, depending on the severity of bulge. The convex surface of bridge caul can also be used to flatten cupped wings of an old bridge before regluing.

5 reviews for Belly Reducer

  1. VLE

    Extremely effective!
    I have used this tool on two vintage guitars which would barely have been salvageable without it. Excellent results, and the repair increased the value of the guitars, which wouldn’t have happened if I removed the bridge plates. If you carefully follow the directions it’s as easy to use as hot hide glue. Very glad I have this tool! Now if only stewmac would sell one that would flatten mine…

  2. Steve Kovacik

    worked perfectly
    I have used the Thompson Belly Reducer on several vintage Martins with excellent results on all of them. In each case I followed the instructions as written and left the piece clamped for one week. The tool left each top very flat. I had little trouble with placement or with the plates cooling too fast during placement. I used leather gloves to keep from burning my hands and had no problems.

  3. Joe Konkoly

    Fantastic Tool
    I have been using the Thompson Belly Reducer on numerous guitars for the past year. Results have been excellent on hide glued instruments. The precision machining of the pieces matches the Martin vintage stuff really well. Good results with PVA glued plates and helpful with various other applications too.

  4. Customer

    A Most Excellent Tool!
    I’ve been using these tools for quite some time now on different model guitars with bellying problems and i’m very happy with them. i have the early models without magnets. To position the inside one i insert it cold and mark the desired spot with a permanent marker through two bridgepin holes. I then prepare a wooden post with a string attached to it that will temporarily hold the inside caul once it’s heated up. The string hangs outside the sound hole. i then place the guitar face down with a moistened sponge on the bridgeplate for at least an hour, while i heat up the cauls. Once they’re hot enough and the bridge plate glue is malleable i insert the inside caul with the wooden post which gives me time and space to place the top caul and insert the clamp. pull the string to remove the tempoarary post before tightening the clamp!

  5. Dan McCrimmon, Isle of Skye Guitars (verified owner)

    A lovely tool, well thought out and skillfully made. I used it on a 000 21 that had been rode hard and put to bed wet. The tool functioned perfectly and brought the top back within spec. The magnets are an especially nice touch. Thanks to it and to TJ’s advice about neck resetting, the guitar has returned to playable condition. Thanks, TJ!

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