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Tune-O-Matic bridge placement tip when self-drilling holes
If you've got a kit where holes need drilling for a Tune-O-Matic style bridge and stop tailpiece e.g.
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I found a useful tip for positioning the bridge perfectly in a recent article in the UK's 'Guitar' magazine.
You need to find the right position for drilling the holes so that the strings run down the neck at an equal distance from each side, and at the right distance and angle so that the strings can all be intonated. With no holes drilled for either the bridge or tailpiece posts, (this method also works for wrap-over bridges) then it's all a bit hit-and-miss, regardless of how well you measure up. It's not something you want to get wrong.
A good way to get the bridge in the right position is to first fit a cheap trapeze tailpiece to the guitar. There are plenty on eBay.
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You only need use the the hole for the rear strap pin as it's only a temporary arrangement, and it doesn't need to be a perfect fit if you want to position your strap pin in a slightly different vertical location. With a bare wood body, you could probably just gaffer tape it to the body. The main thing is that you fit the tuners to the headstock (even if only temporarily) so that you can fit a set of strings between the tailpiece and the tuners and be able to bring the strings up to normal tension.
You'll be checking intonation adjustment, so I'd use (and sacrifice) a reasonable set of strings of your normal gauge for this purpose, rather than a rusty old set that won't intonate properly. For the sake of a few dollars, it's a lot easier and less stressful than getting it wrong and having to fill the holes and re-drill them.
You are going to want to check the intonation, so you'll need to temporarily wire up a pickup to an output jack so you can tape the pickup into a cavity and plug the pickup into a tuner.
Then string up the guitar and first make sure the trapeze tailpiece is located so the strings run parallel to the sides of the neck.
Then, push the bare T-O-M bridge under the stings (without posts) and use some packing pieces underneath to raise the bridge up so that the strings are running over the bridge with enough overall height to represent a decent string action across the neck. You can now move the bridge around until the treble and bass strings can be intonated and the strings are still running parallel to the sides of the neck. Then use the bridge post holes to mark the centres of the body post holes, remove the strings, bridge and pickup and you can now drill your bridge post holes safely.
The stop tailpiece holes are easier to drill as the tailpiece is at right-angles to the centreline of the body. As long as the trapeze tailpiece isn't a very long one, whilst everything is still strung up, you can slide it under the strings and mark up a position where the tailpiece holes line up with the strings. Gibson normally have the tailpiece 1-1/2" from the TOM bass side post hole and 1-5/8" on the TOM treble side post hole (centre to centre), though you can move it further back than this if you wish. Just don't put the tailpiece too close to the bridge or you'll have trouble with getting clean string break angles.
