Another Scale Length Issue

[dave422x]

Hi guys.

I bought a pre-routed body and a neck from the same supplier on eBay. The body's routed for a 22 fret neck (not sure of the exact scale length at this time) and the neck has 24 frets.

I bolted the neck on, put on some strings and checked the intonation, just to see how close it is. On the high E string the harmonic is about 1/4 of an inch closer to the bridge than the actual physical 12th fret.

My initial thought would be to make the neck pocket 1/4" longer so the neck is that much closer to the bridge.

Being lazy(!) I dropped off the guitar at the local music store and asked for the work to be done. The repair guy called me last Friday and said that the neck and bridge have to be 3/4" closer to each other in order for the intonation to be correct.

Can anybody explain why this is the case? Why not the 1/4" I physically observed?

If he's right then fine - I'll put a 22 fret neck on there, but if I'm right I'll route it myself!

Many thanks in advance... I can post pics in the next day or so if required - I need to go and pick the guitar up from the shop first!

Dave

[ihocky2]

I'm not positive here, but I'll take a stab at it. If I am wrong, feel free to tell me I am an idiot. Your scale length is based on 2 times the distance from the nut to the 12th fret. Your 12th fret harmonic is essentially playing half of the string. So to move your harmonic a set distance you will need to double the amount since you are technically playing half the true scale length. You are taking your High E harmonic, when you look at your low E the saddle is always set the furthest back because of the string compensation. That saddle is where the tech is picking up other portion of the extra distance. Again you should need to double the distances to move harmonics, so if that saddle is set back 1/8" beyond the high E (which is reasonable) to move the harmonic you need to move that one back 1/4" as well. So that will get you close to the 3/4".

Again I may be completely wrong so hopefully someone can clarify on this. Plus this is all figuring on the body being setup for the same scale as the neck. If they are different scales, that will changes things as well.

[Mickguard]

First you need to establish the scale length of the neck itself -- i.e., measure from the nut to the crown of the 12th fret, then multiply by 2.

With that measurement, you are now able to establish the distance of the nut to the High E saddle. Doing so will show you exactly where you need to position the neck.

Because the neck needs to be set into the guitar in order for the nut to be exactly the scale length's distance from the bridge.

Which means, in the case of a 24-fret neck, the heel will have to enter deeper into the body than the 22 fret neck --and yes, that measurement will be closer to 3/4 of an inch, given that you have to accommodate for 2 entire frets more than a 22 fret neck in order for the scale length to be right.

Of course, this might then interfere with the neck pickup, since they're often placed fairly close to the heel.

Alternatively, you can set the 24-fret neck the same as the 22 fret neck -- but then you'll have to move the entire bridge that much farther away.

So yeah, you might be better off putting a 22-fret neck on there.

[dave422x]

Now I have the guitar back I see the cause of my confusion.

Nut to 12th fret is 12 3/4", making a scale length of 25 1/2".

Even though the distance between the 12th fret and the harmonic is ~1/4" the total length of the top E string is something like 26 1/4", which is where the repair guy gets his 3/4" from.

I can't argue with the measurements, sigh, so I guess I'll stick a 22 fret neck on this body and buy / build another body for the 24 fretter. Which means two new guitars for me. Heh heh.

Thanks for your answers, guys!

Dave