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How to build a bass guitar – Carving the rear body contour, i.e. the "tummy cut"

In this build step, a contour is cut on the back of the body. This is a cut seen on many different basses and offers additional comfort when playing sitting or standing.

Below: The tools used. Smooth cut files, rasps, surform shaver, microplane, colored sanding blocks, 80-grit sandpaper, sliding arm clamp.

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Below: Rear body contour and forearm contour lines have both been drawn on the body. Both are drawn because it makes for a more symmetrical cut overall for both contours later on. The lines were drawn by hand without any measuring tools, based on other plans seen from other bass instruments.

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Below: Using the surform shaver for shaping.

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Below: Shaving continues and the cut shape is beginning to become visible.

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Below: Shaving continues. Grain lines within the contour cut are now visible.

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Below: Continuing to shave and shape.

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Below: We’re roughly about 50% complete with the contour cut here.

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Below: Continuing to shave and shape.

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Below: Nearing completion. Note: The fact the wood grain lines within the contour cut appear to have an almost perfect ripple effect was pure luck. This body wood is swamp ash, and with this particular piece, the contour cut resulted in very desirable curved grain lines that almost perfectly followed the contour curve. Do not expect this to happen with your contour cut, because as just stated, we got real lucky here.

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Below: Shaping continues, and tool has been switched to the rasp.

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Below: Shaping continues, tool has been switched to 80-grit adhesive back sandpaper.

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Below: Shaping continues, switching to soft contour block (foam block with in-built curve).

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Below: Switched to fine cut file. This is primarily used to make sure surfaces are flat and not bumpy or hilly.

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Below: Back to sanding for further fine shaping.

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Below: The finished rear contour cut.

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Final notes:

The best way to figure out how to determine the shape of a contour cut for your bass is to examine other body shapes first. Yes, you can use measuring tools if you wish, but much of this carving process is just going by feel and shaping the wood in a way you feel works best. It is recommended to examine contour cuts not only from electric bass instruments but also from 6-string guitars. Check the cut depth, the angles, the feel and figure out as best you can what works best for you.

Where are the rest of the build steps?
You can view them all here.

6 thoughts on “How to build a bass guitar – Carving the rear body contour, i.e. the "tummy cut"”

  1. Love the ‘Pure Luck’ grain lines!
    You can save a lot of time by going at it first with a wide chisel and mallet before the surform step, always being aware of the direction of the grain.

    Reply
    • Thanks Rae! Yes that is a fine idea. In fact many ways to cut down on the ‘hog out’. I’ve seen angle grinders, belt sanders and even bandsaws being used for this. I still always recommend the ‘all sure-form’ for first timers as they are easy to control and is good practice for developing fledgling 3d carving skills. Happy building to everyone! 🙂

      Reply
  2. In my experience, the best tummy cut is no tummy cut. The way many basses hang when playing standing up, the tummy cut tends to tilt the bottom edge of the body away from your hip or leg (depending on how high you have it strapped on). That rotates the neck toward you and makes things much harder for your fretting hand if you’re trying to keep your thumb behind the neck instead of alongside the E string. In terms of the overall ergonomics of the instrument, the tummy cut is just not a good idea.
    Contouring the entire back to be concave is much better, but it’s more work than making a tummy cut unless you’re jigged up to do it with a power tool or a machine. To me, it’s worth the effort. The depth of the concavity doesn’t have to be as drastic as what Spector does. Even a shallow scoop makes a worthwhile difference.

    Reply
  3. William, I tend to agree with the no tummy cut. After playing a Spector for the last 8 years, I like the depth of the concavity, and I don’t tote much belly, even though I’m 62. I got my Guild Pilot 5 out and the flat-backed body felt very odd, indeed.

    Reply

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