Acoustic guitar scale on my DIY guitar kit.

[F_Falk]

I have a question regarding the scale on my acoustic guitar.

I got a DIY kit as a gift a while back. In the description it says Scale= 645mm.
When I started to measure I got 325 from top end to 12th fret.
But, when I measured each fret I saw that the 1st fret is to long according to Stewmac fret calculator.

According to this picture (two prints from Stewmac, and my own measuring, measured with a caliper), can you please let me know which is the correct scale?
Should I shorten the fretboard up at the top?



Thank you.

/Fredrik (Sorry for the language, I am from Sweden)

[printer2]

Looks like you may have a 648mm with the first at 38.4 while the calculated length is 36.4, the second and third fret measurements are close to the 648 length.

[redir]

If you are measuring 325 then it looks like you got a 650 board there. I would recommend you measure more then jsut the 1st fret too. Double check at least 3 or 4 more. The reason I say this is because many a pre-cut fretboard I've bought, even from reputable dealers, is off just a little bit. I can cut them more accurate by hand and that's why I only do it that way now. But 5mm is a LOT to be off and that suggests to me that you have a 650 there.

[charles Tauber]

It might be, within the accuracy of your measurements, a 25.5" scale (647.7 mm). That would put the 12th fret at 12.75" (323.85 mm).

Although Stewmac gives the distance between frets, I find it easier to use a ruler and measure all fret locations from a single reference, the end of the fingerboard/nut location.

Also, unless you have a CNC machine, giving numbers to three decimal places in mm is silly "(spurious accuracy").

Last, it is relatively common to shorten the distance from the end of the fingerboard/nut to the first fret. If measuring such a fingerboard from the end of the fingerboard to the 12th fret without accounting for that foreshortening, you will get an incorrect scale length. In such cases, it is necessary to work with the between fret distances to help determine the scale length.

[printer2]

648mm

1 ----36.36945 -----36.36945
2 ----70.69763 -----34.32819
3 ---103.09912 -----32.40149
4 ---133.68206 -----30.58294
5 ---162.54851 -----28.86645
6 ---189.79481 -----27.2463
7 ---215.51189 -----25.71708
8 ---239.78558 -----24.27369
9 ---262.69689 -----22.91131
10 --284.3223 ------21.6254
11 --304.73396 -----20.41166
12 --324 .0000 -----19.26604
13 --342.18472 -----18.18472
14 --359.34882 -----17.16409
15 --375.54956 -----16.20075
16 --390.84103 -----15.29147
17 --405.27425 -----14.43322
18 --418.8974 ------13.62315
19 --431.75594 -----12.85854
20 --443.89279 -----12.13685

[charles Tauber]

Originally Posted by printer2

648mm

The reason I suggested 25.5" is that it is relatively common, while 478 mm is not, though is used on Selmer guitars.

[printer2]

Originally Posted by charles Tauber

The reason I suggested 25.5" is that it is relatively common, while 478 mm is not, though is used on Selmer guitars.

I looked at the fret distances and when the first fret did not match the scale length I took a guess that maybe the board was cut with a mm or two extra on the first fret. So I discounted the first and looked at the second, third and fourth. I then punched in different scale lengths in FretFind2D till I got a reasonable match on the numbers he measured to the calculated ones. I ignored what is common and what he was to get, I just used the numbers to get the best match, ignoring the first fret though. If anyone has a better way of figuring out what he has I am open to it. Taking a measurement from the second fret to the 12th and comparing the distance to a scale would be my next avenue to pursue.

[F_Falk]

Originally Posted by printer2

648mm

1 ----36.36945 -----36.36945
2 ----70.69763 -----34.32819
3 ---103.09912 -----32.40149
4 ---133.68206 -----30.58294
5 ---162.54851 -----28.86645
6 ---189.79481 -----27.2463
7 ---215.51189 -----25.71708
8 ---239.78558 -----24.27369
9 ---262.69689 -----22.91131
10 --284.3223 ------21.6254
11 --304.73396 -----20.41166
12 --324 .0000 -----19.26604
13 --342.18472 -----18.18472
14 --359.34882 -----17.16409
15 --375.54956 -----16.20075
16 --390.84103 -----15.29147
17 --405.27425 -----14.43322
18 --418.8974 ------13.62315
19 --431.75594 -----12.85854
20 --443.89279 -----12.13685

Thank you for your answer. The measurements look good. The thing though, if I should go with this scale, I would need to cut the board 1mm, leaving the first fret still about 1mm to long.

Maybe 646 is the best? In this case I would cut the board 2mm, leaving the 1st fret at 36,43mm
See pic:

[phavriluk]

If OP is going to measure between frets starting at the first fret in order to figure out the scale length, I think it would be a good idea to measure a whole range of frets, like first through twentieth. At least then the numbers will show the largest possible differences. I think measuring between the first and second frets, for example, the identity of the scale length can be lost with very small variations in fret-to-fret distances.

[LouieAtienza]

If you can measure with reasonable accuracy distances between frets you should be able to figure out what the scale length is to some accuracy.

What's little-known, is that the ratio of the first to second fret is theoretically the same as the second to third, third to fourth, etc. So if you divided the measurement between the first and second frets, by the measurement between the second and third frets, you'll get a ratio, that will be the same no matter which adjacent measurements you take. Then you just reverse the process to solve for the theoretical first fret distance. Basic algebra.

[charles Tauber]

If you want to go the algebra route, here's one variation on the formula that I use for fret placement:

Ln=x/[((2**(1/12)**-n)-1]

Where L is the distance from the nut to fret "n", n is the fret number who's position you want and x is the scale length. The 2**1/12 gives equal temperament.

It can be manipulated in a variety ways, including telling you the scale length based on fret distance as well as the difference between two fret distances.

[LouieAtienza]

Originally Posted by charles Tauber

If you want to go the algebra route, here's one variation on the formula that I use for fret placement:

Ln=x/[((2**(1/12)**-n)-1]

Where L is the distance from the nut to fret "n", n is the fret number who's position you want and x is the scale length. The 2**1/12 gives equal temperament.

It can be manipulated in a variety ways, including telling you the scale length based on fret distance as well as the difference between two fret distances.

I think my way is a lit easier on the brain and calculator

[F_Falk]

Hello again and a big thanks for your answers! I now have something to lean on when doing this.

One more question, bridge placement?
Where should the bridge be placed? Should I measure between the nut and the "front to back center" of the saddle slot along the central line of the guitar? I think I have heard of a compensation, +3,80mm if I'm not mistaking.

Thanks!

[redir]

That's the way I do it Falk. From the nut face to the center saddle slot right, down the center of the fretboard, plus .1 inch. That would be closer to 2.5mm. I think 3.8 is a bit much.

[Ned Milburn]

Originally Posted by F_Falk

Hello again and a big thanks for your answers! I now have something to lean on when doing this.

One more question, bridge placement?
Where should the bridge be placed? Should I measure between the nut and the "front to back center" of the saddle slot along the central line of the guitar? I think I have heard of a compensation, +3,80mm if I'm not mistaking.

Thanks!

The required saddle compensation is less for the high E and greater for the Low e. I use 1.5mm compensation on high E and 3.5 on Low e for location of the FRONT of the saddle. Then the saddle gets 2 angles for the peak - high e to b, and G to low E.