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So I am building a replica of a 1935 O-18K Martin koa Hawaiian guitar I own. It's played lap style. It has a 24.75" scale, with square bar stock, nearly flush frets. I happen to have some precut fretboards for Gibson style instruments of the same 24.75 scale length, so I placed one up against it, and noticed that at the higher frets it no longer matched the vintage fretboard. The precut matches a Gibson Les Paul fretboard I have, so I know it is correct.

I am wondering if the is because the guitar was designed to be played lap style with a bar. The frets on the precut being slightly closer to the headstock, would play flatter than the vintage and likely compensate for the fact the string goes sharp when it is stretched and fretted by a finger, whereas a bar would not stretch it as much. The saddle on the vintage guitar is not slanted for compensation either, just as a dobro is not, which again makes sense as it is played with a bar and not fretted.

What do you guys think?

I just want to double check the knowledge base here before I actually cut the slots for my frets, I am going to inlay MOP instead of using fretwire.

The photo is from the 13th to the 20th fret. As you can see the difference gets larger the further up you go.

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Damon Wack
https://www.facebook.com/LindamonGuitars

A number of different scale are often called 24.75. 24.625 is usually just rounded up and called 24.75 for instance...

There are two possibilities here. First, as MF suggest, there could be very slight differences in the actual scale. Gibson was notorious for changing their "24.75" scale, here is a little blurb from the StewMac website

The Gibson 24-3/4" scale is also very common, but it is also the most confusing of all scale lengths—this is because it rarely ever measures out to be 24-3/4 inches! This scale has gradually changed over the past fifty or so years due to changes in production equipment.

http://www.stewmac.com/images/fretcalc/ ... meline.gif

The other possibility is as you suggest, Martin might have "un compensated" the scale knowing that the instrument would not be fretted. I kind of doubt that because it is so subtle and most lap slide players only use the frets as indicators, you do the actual intoning with that little steel bar.

I've built a couple of Weissenborn style guitars and in that case just used standard fret locations but the saddle is not angled and there is no compensation in its location - it is exactly at the scale length. Many resonators are built the same way which is why the tend to play very sharp when fretted.

Would love to see pictures of your guitar as you build it.

All the older Martin fingerboards are done this way, not just the Hawaiians. The frets past the 12th are set a little closer to the bridge. I don't know the reasoning, other than to compensate for the ear's tendency to hear flat in the upper frequencies. Pianos are tuned to allow for this.

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John

interesting. how many thou would you say the offset is? is it an increasing value from the 12th on up or a constant?

When the rounding is done, I always wonder who is doing the rounding, the originator of the scale or someone else? Next question that comes to mind is, are they creating new scales by doing so?

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Julie Moriarty
http://JulimorCreations.com

24-5/8" to 24-3/4" (an increase of 1/8") man, that's some mighty powerful "rounding-up". i know it's done, but it's also "advertising based" bs math.

What about when the factory does it? Martin currently lists the scale length of a new OM-42 as 25.4. Has anyone played a Martin from the 1970's - was the saddle where you would put it? And of course Gibson is notorious (from LMII)

Notes on Gibson Scale Lengths
The 24.75" scale length is commonly understood as a Gibson scale length. Gibson still advertises this scale length but it is an "abbreviation" of sorts. If you are working on an existing Gibson instrument the actual scale on the instrument may differ due to compensation and/or changes in their product line and production equipment over time. For example, we see instruments made in the early 50's cut to a 24.75" scale, in 1959 and after we find a 24 9/16", in 1969 it was 24 5/8" and after 1992 it was 24 9/16"! LMI offers a 24.75" (24 3/4") scale the 24.625" (24 5/8") scale and the 24.562" (24 9/16") scale.

Maybe that's why they ended up where they are now.

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Julie Moriarty
http://JulimorCreations.com

The dirty little secret is that it doesn't really matter all that much. As long as the frets are located correctly relative to each other, the actual scale can vary (within reason) and no one will know or care. I'm not talking about the difference in "long scale" and "short scale" but the 1/8th difference between 24.75 and 24.625 will only be noticed by someone who measures it. Even then it depends on if they are measuring N-12 and doubling (ignoring compensation) or from nut to saddle.

When I lay out frets (or make a new fret slotting template) I use wfret. My printer prints pretty much dead on when I double check the measurements but even if it didn't I probably wouldn't care. The relative distances would stay correct but the nominal scale length might be off by a 1/16 of an inch (or whatever). I'm locating the saddle using the measurement from nut to 12, adding my compensation and locating the saddle that distance away from the 12th.

That is the beauty of the saddlematic from StewMac (or my shop made equivalent). Even if you are working on a vintage instrument with dubious nominal scale, you don't need to know the scale length to locate the saddle.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

Really interesting. I happen to have a 1972 D-18 I bought new. After I read your post I took it out and using my saddlematic, the saddle is a good 1/16 to 3/32" farther than what the saddlematic indicated. The middle of the saddle scale length is 25 3/8".

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Damon Wack
https://www.facebook.com/LindamonGuitars

I will start another thread with some pictures.

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Damon Wack
https://www.facebook.com/LindamonGuitars

Apparently the most common situation is that Martin didn't put enough compensation in the bridge location - many of them have the high E string right at the scale point. I know its pretty common to fill the saddle slot and reroute it - David Collins at Ann Arbor has an incredibly cool saddle slot milling setup (I have the StewMac version, its adequate but David's is far better). Here is a pretty good discussion by the guy who has worked on my old Marties

http://www.bryankimsey.com/bridges/bridge_scars.htm

arie wrote:
"24-5/8" to 24-3/4" (an increase of 1/8") man, that's some mighty powerful "rounding-up". i know it's done, but it's also "advertising based" bs math."

If you go to the Stew Mac fret position calculator for a scale length of 24 5/8 it shows the compensated string length to be between 24.71 and 24.83. 24.75 seems like a reasonable if not overly precise average. If you ask the average person to measure the scale length of their guitar they will measure nut to saddle and give you that measurement.

Julie, Clay and Damon, here is a very well done explanation of how we got to where we are today. Julie, also note the little section near the end where David talks about the guitar that was built with a fretboard from one source and layout from another - kind of similar to your OM situation

https://youtu.be/0yCLckbp8ps

First of all, thank you for the link. Very informative! When I think of Gibson, I keep remembering a video I saw (can't find it now) where some pros were discussing working on Gibson guitars. Two of the three were in awe of the skills of the third, who said Gibson guitars were awful to work on because of their scales. He attributed Gibson's troubles in part due to that.

And I did note the end of the video comments about the $350 fix due to the builder using both 25.4 and 25.34 scales. When I first noticed the discrepancy between the Stew Mac fret template and the Antes plan, I abandoned the Antes plan for anything to do with the scale.

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Julie Moriarty
http://JulimorCreations.com

Great video, now I want to learn more about the history of scale length and fret placement, thanks!

I went out an checked the Hawaiian, and there is absolutely no compensation in the scale length, it is exactly 24 & 3/4”, with the 12th fret exactly at 12 & 3/8”. So I think I will just copy the fret placement, it sounds fine, although I don’t play it much above the 12th fret, as slide players sometime say, there’s no money up there anyway!

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Damon Wack
https://www.facebook.com/LindamonGuitars