25.4 scale versus 25.34

[Ray Cutler]

I have a question about the 25.34 scale being referred to as 25.4.  The difference is roughly 0.060" from nut to saddle.  I wouldn't mind using 25.4 as a scale except that the template from SM is actually 25.34.  I'm reading an article from this summer's American Lutherie about intonation and on pg35, Table 2  the author lists measurements to each fret but he's using 25.4 as his scale.  In the Gore Gilet books there are places where they round off the scale to 25.4 also.  If I use the SM template to cut my fret slots won't I be too far off to round anything off to 25.4?  I hope I've made myself clear.  Thanks for any advice

[RMizek]

The “25.4” Martin scale is actually 25.34”. I once knew the story of why Martin called it 25.4, but it’s long forgotten in my memory.

For reference, if you buy a pre-slotted front board from stack, it will come in at 25.34” scale. https://www.stewmac.com/tonewoods/shop-tonewood-by-instrument/acoustic-guitar-wood/acoustic-guitar-fingerboards/slotted-fingerboard-for-martin-guitar/

[Patrick Dewar]

Ray

I too noticed this early on in my building although the SM guys and the videos make this difference very clear.  

Additionally you should take note of Robbie’s “cheat” adding 2mm to the scale length to account for the intonation issues associated with string action.  This is typically done at the B string saddle.  

If you’ve read this blogs’s details around acoustic guitar intonation, as well as some extremely in depth articles in the GAL magazine, you probably know you can spiral down the rat hole of this subject.   

Robbie’s 2mm has worked quite well for me and diving deeper with intonated saddles can also move closer towards “perfection”.  

patd...@yahoo.com

(607)972-9705

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On Nov 6, 2023, at 9:43 AM, Ray Cutler <rcutl...@gmail.com> wrote:

I have a question about the 25.34 scale being referred to as 25.4.  The difference is roughly 0.060" from nut to saddle.  I wouldn't mind using 25.4 as a scale except that the template from SM is actually 25.34.  I'm reading an article from this summer's American Lutherie about intonation and on pg35, Table 2  the author lists measurements to each fret but he's using 25.4 as his scale.  In the Gore Gilet books there are places where they round off the scale to 25.4 also.  If I use the SM template to cut my fret slots won't I be too far off to round anything off to 25.4?  I hope I've made myself clear.  Thanks for any advice

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[Ray Cutler]

Thanks Pat.  I have a terrible way of overthinking things.  I have Robbie's steel string course and in it he converts the 25.4 scale to mm and then adds 2.mm.  When he does the conversion though he uses 25.4, not 25.34.  My sincerest apologies to Robbie if I'm wrong about this.  It doesn't take much but this added to my confusion.  I've found out since posting this subject that though you could make one, there is no 25.4" scale and when I see that written I can be assured that is actually 25.34.  ALWAYS.  Thanks for you help

[Patrick Dewar]

Exactly.  Plus, ALWAYS measure 12th fret actual once on the guitar - just in case gremlins got involved.  Ask me how I know;).  Then 2x plus compensation.  

patd...@yahoo.com

(607)972-9705

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On Nov 6, 2023, at 12:07 PM, Ray Cutler <rcutl...@gmail.com> wrote:

Thanks Pat.  I have a terrible way of overthinking things.  I have Robbie's steel string course and in it he converts the 25.4 scale to mm and then adds 2.mm.  When he does the conversion though he uses 25.4, not 25.34.  My sincerest apologies to Robbie if I'm wrong about this.  It doesn't take much but this added to my confusion.  I've found out since posting this subject that though you could make one, there is no 25.4" scale and when I see that written I can be assured that is actually 25.34.  ALWAYS.  Thanks for you help

To view this discussion on the web visit https://groups.google.com/d/msgid/obrien-forum/90c155a2-27c1-44c6-85c5-967ca046a2ban%40googlegroups.com.

[Patrick Dewar]

Btw, there are many other, more experienced expert luthiers on this stream.  Don’t let me lead Ray astray if I’m not exactly correct!

patd...@yahoo.com

(607)972-9705

Sent from my iPhone

On Nov 6, 2023, at 12:28 PM, Patrick Dewar <patd...@yahoo.com> wrote:

Exactly.  Plus, ALWAYS measure 12th fret actual once on the guitar - just in case gremlins got involved.  Ask me how I know;).  Then 2x plus compensation.  

[Neill Morgan]

Just to clarify: the scale Robbie uses is 645.16 mm, 25.4 inches X 25.4 mm/inch. So, the scale he uses is actually exactly 25.4, not 25.34 as Martin and Stewmac scale rules use for standard scale length. If you ordered pre-slotted fretboards from LMII, you could get 25.4 or 25.34, whichever you preferred, but they were not the same. Before they ran out, I ordered the slotting jig for a 25.4 inch jig, and it is a different scale than the 25.34 inch jig. My measuring tools and eyes are such that either scale length plus 2mm of compensation at high E will get me close enough to intonation to fine tune it at the saddle; but, I wouldn’t cut fret slots for the 25.34” scale and then place the saddle 25.4 (+2mm) from the nut, nor the other way around. The intonation would be off. It’s only a difference of 1.524 mm, but that is too much—you would definitely hear it when you tried to intonate.

If I am wrong, please let me know. I’m looking at the LMII plans and the StewMac plans, and they are just different scale lengths.

Neill

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[windquest_one]

I noticed this early on, and decided to just use 25", and it has worked for me.  so, now I only use 25, and 25.5, accept  for classical which I only use 650mm.  I guess this comes from building steel guitars where I use 22.5", and 25".  This may not be the best solution, but as I said, it works for me.