# Scale Length Question

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I have a customer who has a 24" scale guitar with a 21 fret neck installed, but he wants it to have a 25.5" scale 21 fret neck installed instead. Before I order the neck and end up with a headache in the shop trying to make this work, is this a possibility?

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I have a customer who has a 24" scale guitar with a 21 fret neck installed, but he wants it to have a 25.5" scale 21 fret neck installed instead. Before I order the neck and end up with a headache in the shop trying to make this work, is this a possibility?

Go to stewmac.com and find the fret calculator.

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I don't know if any of the following will help, but I'll give it a go anyway.

21st fret of a 25.5" scale length will be a little more than 1.05" farther away from the nut than the 21st fret of a 24" scale length.

So given that with the new 25.5" scale, the nut has to be 1.5" farther away from the bridge than the old 24" scale, and assuming you're not moving the bridge, the 21st fret of the 25.5" scale will be about 0.45" farther away from the bridge (and pickups, etc.) than the 21st fret of the old 24" scale neck.

(I rounded...re-do the measurements, of course.)

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Ok... I kindof did the math this way and I think it should work out ok...

Scale length divided by the difference of the 21st fret from the nut and the total scale length would equal the approximate ratio of where on the scale the neck must be placed...

So, I ran a few tests...

25.5 (scale length) - 17.919 (distance of 21st to nut) = 7.581/25.5 = 3.363

24 (scale length) - 16.865 (distance of 21st fret to nut) = 7.135/24 = 3.363

24.75 - 17.392 = 7.358/24.75 = 3.363

28 - 19.676 = 8.324/28 = 3.363

Doesn't this mean that if the heal of the neck of a 21 fret guitar (regardless of the scale length) will most likely bolt into the same place?

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That's a lot of decimals.... Ever tried metric?

Maybe I can convert your country to the decimal system lol.

I can see your predicament it is very confusing.

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Ok... I kindof did the math this way and I think it should work out ok...

Scale length divided by the difference of the 21st fret from the nut and the total scale length would equal the approximate ratio of where on the scale the neck must be placed...

So, I ran a few tests...

25.5 (scale length) - 17.919 (distance of 21st to nut) = 7.581/25.5 = 3.363

24 (scale length) - 16.865 (distance of 21st fret to nut) = 7.135/24 = 3.363

24.75 - 17.392 = 7.358/24.75 = 3.363

28 - 19.676 = 8.324/28 = 3.363

Doesn't this mean that if the heal of the neck of a 21 fret guitar (regardless of the scale length) will most likely bolt into the same place?

Hey Mike,

Not 100% sure I've figure this out yet, I mean your post. What my mind keeps telling me is that number you keep getting is just like a ratio of where the 21st fret is in the scale used. I can't find any way to give it any meaning in terms of this repair, but maybe I'm just not seeing it. I'm tired, so I'm probably missing something important here. But if it is what I think, it really doesn't translate because it remains constant and where you put the heal can be changed in many ways like having an overhang on the fretboard and such, the ratio will remain, but wouldn't be correct.

One issue I'd verify before buying here is fretboard overhang, because if the fretboard has an overhang, then the distance to the bridge is going to be shorten even more, making your problem even worse and I think Rick has it the right idea here, you need to get that nut 25.5" inches away from that bridge period and if you just bolted it up now you'd still be short as Rick pointed out, .446 or .45 rounded as Rick said. If you can move up the heal just less than a half inch, then you'd be fine. If anything, maybe you can just fill the neck pocket and reroute it a .446 of an inch shorter, hopefully you'd still be able to use the same holes in the back of the guitar for bolting on the neck. I just wouldn't want to leave a half inch gap at the end of the neck and the neck pocket, but maybe you can just glue in a small half inch piece to the bottom of the pocket to fill it, instead of filling the whole thing. But I think that's the solution you'll have to use to decide, can you move the neck up .446". It may require more surgery than may be worth it or maybe you can find some other solution. Best of luck and keep us posted. Good to see you around Mike, hope all is going well for you in the job. Jason

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Ok... I kindof did the math this way and I think it should work out ok...

Scale length divided by the difference of the 21st fret from the nut and the total scale length would equal the approximate ratio of where on the scale the neck must be placed...

So, I ran a few tests...

25.5 (scale length) - 17.919 (distance of 21st to nut) = 7.581/25.5 = 3.363

24 (scale length) - 16.865 (distance of 21st fret to nut) = 7.135/24 = 3.363

24.75 - 17.392 = 7.358/24.75 = 3.363

28 - 19.676 = 8.324/28 = 3.363

Doesn't this mean that if the heal of the neck of a 21 fret guitar (regardless of the scale length) will most likely bolt into the same place?

Hey Mike,

Not 100% sure I've figure this out yet, I mean your post. What my mind keeps telling me is that number you keep getting is just like a ratio of where the 21st fret is in the scale used. I can't find any way to give it any meaning in terms of this repair, but maybe I'm just not seeing it. I'm tired, so I'm probably missing something important here. But if it is what I think, it really doesn't translate because it remains constant and where you put the heal can be changed in many ways like having an overhang on the fretboard and such, the ratio will remain, but wouldn't be correct.

One issue I'd verify before buying here is fretboard overhang, because if the fretboard has an overhang, then the distance to the bridge is going to be shorten even more, making your problem even worse and I think Rick has it the right idea here, you need to get that nut 25.5" inches away from that bridge period and if you just bolted it up now you'd still be short as Rick pointed out, .446 or .45 rounded as Rick said. If you can move up the heal just less than a half inch, then you'd be fine. If anything, maybe you can just fill the neck pocket and reroute it a .446 of an inch shorter, hopefully you'd still be able to use the same holes in the back of the guitar for bolting on the neck. I just wouldn't want to leave a half inch gap at the end of the neck and the neck pocket, but maybe you can just glue in a small half inch piece to the bottom of the pocket to fill it, instead of filling the whole thing. But I think that's the solution you'll have to use to decide, can you move the neck up .446". It may require more surgery than may be worth it or maybe you can find some other solution. Best of luck and keep us posted. Good to see you around Mike, hope all is going well for you in the job. Jason

The fret spacing on the neck is fixed at what ever scale it was cut. PERIOD.

Fret spacing is a a function of scale length. And, therefore, might not take well to being messed with...

Edited by imott
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Ok... I kindof did the math this way and I think it should work out ok...

Scale length divided by the difference of the 21st fret from the nut and the total scale length would equal the approximate ratio of where on the scale the neck must be placed...

So, I ran a few tests...

25.5 (scale length) - 17.919 (distance of 21st to nut) = 7.581/25.5 = 3.363

24 (scale length) - 16.865 (distance of 21st fret to nut) = 7.135/24 = 3.363

24.75 - 17.392 = 7.358/24.75 = 3.363

28 - 19.676 = 8.324/28 = 3.363

Doesn't this mean that if the heal of the neck of a 21 fret guitar (regardless of the scale length) will most likely bolt into the same place?

NO!

the bridge to 21st fret distance is governed by the scale length, so they are different for each scale length and are not interchangeable.

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i dont think it will work going from 24-25.5 with anything currently availble to purchase... but if you make a neck then getting it to 25.5 is pretty easy with a few measurements

warmoth makes a few conversion necks but they are designed to go onto guitars designed for 25.5" scales... they offer one to go from 25.5-24 but not the other way around

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The first and most important thing to remember is that, unless you're moving the bridge, the scale length defines the distance from the nut to the bridge. 24" (old) or 25.5" (new) in your case. Nothing you can change there. The frets will fall where they fall and there's nothing you can do about it.

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We know the distance from the nut to bridge (25.5"). That is a fixed point.

Now you have to determine the new distance from the nut to the end of the existing neck pocket. Once you have identified this distance, you know how much neck shaft you can have. Knowing the neck shaft length is key to knowing how long of a fingerboard you can have. It's all related.

Take your new maximum neck shaft length and compare that to your target scale. This is what will give you the number of frets you'll end up with.

I make these conversions a lot, and it's all relatively simple when you get right down to it. Forget the notion of how many frets you want the replacement neck to have, because the maximum length of the new neck shaft will tell you that.

Hope that helps...

-Doug

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So now that I see where I went wrong (actually, as I drove home from the shop tonight I had the epiphany)...

24 - 16.865 = 7.135

So, the distance from the bridge to the neck pocket is 7.135 inches. Well, since I need as close to 7.135 inches to finish the scale length from the heel of what ever neck I use, I calculated this using a 25.5 scale 22-fret neck...

25.5 - 18.344 = 7.156

I think I can do it using this and just adjust the saddles on the bridge to make up for the difference. I am going to give it a shot...

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As I mentioned above be careful of fretboard overhang because this will make everything different. If you look at Stewmacs website and their 22 fret necks, you'll see the 22nd fret is off the fretboard, it overhangs off the neck. If you had the 21 and 22 fret necks side by side they would be exactly the same except the 22 has an overhang of fretboard that allows for the 22nd fret. If this is the same case as the neck you order, ordering the 22fret neck would make no difference and give you no extra length, you must make sure the actual neck itself is longer, because the fretboard being longer will make no difference for you. So, just thought I'd mention that, I'd call the place you are looking at first and make sure the difference isn't just an overhung fretboard. Well, best of luck Mike. Let us know how it goes. J

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Ok yall are making this really hard and its not.

yes it can be done.

no it aint easy.

bolt the neck on the guitar and move the bridge to the correct location to make the scale right.

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Okay, I took the liberty of checking his calculations against actual completed necks in the shop. Based on the 7.135" bridge to neck pocket length, a 21 fret neck will work if the end of the neck shaft (heel) is pretty much right where the 22nd fret would be.

mikevirok, you are on the right track!

As for moving the bridge... experience has demonstrated that people want the neck made to fit whatever body they have. Moving the bridge is generally out of the question because of the refinishing etc. that would follow.

-Doug

OVER 9,000!

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