4

I don't know if this is the right place to ask this but I saw someone ask a similar question here.

I'm assembling a guitar from a body I bought for cheap. Unfortunately, the body won't line up correctly with any 24.75" scale length neck (Gibson Les Paul style body). To correct the issue I may be able move the neck slightly. However, this would cause the half scale lengths to not match. The distance from the nut to the twelfth fret would be 12.5" while the twelfth fret to the bridge would be approximately 13". Does anyone know if this is a large enough difference to cause intonation problems? I know there is some variability but half an inch seems like it could be significant.

1
  • 3
    Don't have time to write a full answer, but yes, 0.5" is a lot and is likely to be outside of the range of adjustment offered by the bridge. Jan 23 at 4:08

3 Answers 3

5

Building the guitar the way you describe would give you a string length of 25.5". The twelfth fret (for the high E-string) should be at half that: 12.75", so the distance from the bridge to the twelfth fret will be 0.25" too long (about 0.6 cm) which is about a third of the distance between frets at the twelfth fret (about 1.8cm). That means the intonation will be roughly a third of a semitone flat there, too much for almost any kind of music.

The better solution would be to move the bridge 0.5" closer to the neck.

And of course, an even better solution would be to buy parts that fit.

7
  • Do you think moving (I assume) a tune-o-matic bridge is feasible? Jan 23 at 8:41
  • @user1079505 I don't know how far you can move those.
    – PiedPiper
    Jan 23 at 8:47
  • 1
    "too much for any kind of music": surely there is some microtonal experimentalist out there who would have a field day with this (i.e., with the prospect of inventing a new musical system).
    – phoog
    Jan 23 at 9:56
  • @phoog Someone building a guitar from parts and asking a question like this is almost certainly isn't a microtonal experimentalist.
    – PiedPiper
    Jan 23 at 11:49
  • @phoog I'm happy to not call that music :)
    – yo'
    Jan 23 at 13:28
2

The 12th fret must be exactly at the half-way point, aligned with the 12th fret harmonic. Even a smidgeon out will cause intonation problems.

There is around 1/4" difference between the lengths of the top and bottom strings in any case, so take that into account. Adjustable bridges do, but if the bridge is at the absolute limit for one it may not accommodate the other.

So 1/2" differential is waaay too much - even 1/32" is too much, and the only way to sort this out is to buy the correct neck, and make certain there's enough wriggle roo for the two extremes - top and bottom string lengths.

3
  • To put some frequencies on this, if you tune a 25.5-inch string to 220 Hz and then shorten its length to 13 inches, you'll have a frequency of about 431.5 Hz instead of the desired 440 Hz (ignoring effects such as the change in tension, etc.).
    – phoog
    Jan 23 at 10:09
  • You can hear that interval (well, 440 Hz and 863 Hz) at yacavone.net/xen-calc/?q=51/26
    – phoog
    Jan 23 at 10:18
  • 1
    If the twelfth fret needed to be exactly at the halfway point, there would be no need for intonation adjustments at the bridge. On the other hand, it would be fair to say that it must be at "almost exactly"the half-way point., and half an inch off is Just Plain Wrong. No bridge is going to allow enough intonation adjustment, but the distance would probably be large enough to allow new bridge mounting holes to be drilled without interference from old ones.
    – supercat
    Jan 23 at 16:04
0

0.5", that is 12.7mm is a lot. Adjusting the scale by 1mm already makes a significant difference when setting up an instrument.

Electric guitar bridges typically provide some adjustment range. However, normally the bridge is installed in a position, where in the extreme setting the scale is around twice the distance between the nut and 12th fret, and it can be only elongated further by adjusting.

The typical adjustment needed for a guitar in standard tuning and typical string gauges is of order several mm. 0.5" would be perhaps appropriate for a thick bass guitar string (the thicker the string, the more compensation needed). It will be too large for a typical guitar, and the bridge will likely not allow you to shorten the scale enough. But do check to make sure! Maybe your cheap guitar will surprise you once more, in a good way this time?

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.