Official Luthiers Forum! :: View topic - OLF OM Mods for 13 Fret Shorter Scale

hmmm ... based on my calculations, moving from a 14 to a 13 fret joint moves the bridge back 16.7mm, or .657 inches .... check your math again to confirm. I am assuming you are doing this as you say you are moving the bridge back

I cant see how you can leave the soundhole in the same spot, and still have 20 frets, unless the FB overhangs - the 19-20 fret delta is approx 12 mm, you are shifting 16mm ...

as for moving the soundhole, if keeping the same number of frets, then yes, move the soudhole the same ammount you are shifting the neck. Same thing for the bracing .. shifts back the same ammount - or you have to play around with closing the X, or making a longer bridge, or a combo ...

13 vs 12 fret .. the 12 fret will be a bit darker/fuller sounding IMO.

Author:	SteveSmith [ Sun Feb 07, 2010 3:17 pm ]
Post subject:	OLF OM Mods for 13 Fret Shorter Scale
I've started a 13 Fret 24.9" scale cutaway based on the OLF OM plans. I suppose the changes would make this a 000. Based on my calculations the bridge needs to move back 0.298". The soundhole can stay in the original location if I use a 20 Fret neck which would be plenty for me. 1. Should I leave the soundhole in the original location and use the 20-fret neck or shift the soundhole towards the tailblock 0.298" to maintain the distance relationship between the bridge and soundhole? 2. Anyone have any comments on a 13-fret versus a 12-fret 000? This will be primarily a rhythm instrument and will be strung with mediums. At least that's the plan. 3. I'm aware I'll need to shift the bracing slightly. Any comments or hints?

Author:	TonyKarol [ Sun Feb 07, 2010 3:35 pm ]
Post subject:	Re: OLF OM Mods for 13 Fret Shorter Scale
hmmm ... based on my calculations, moving from a 14 to a 13 fret joint moves the bridge back 16.7mm, or .657 inches .... check your math again to confirm. I am assuming you are doing this as you say you are moving the bridge back I cant see how you can leave the soundhole in the same spot, and still have 20 frets, unless the FB overhangs - the 19-20 fret delta is approx 12 mm, you are shifting 16mm ... as for moving the soundhole, if keeping the same number of frets, then yes, move the soudhole the same ammount you are shifting the neck. Same thing for the bracing .. shifts back the same ammount - or you have to play around with closing the X, or making a longer bridge, or a combo ... 13 vs 12 fret .. the 12 fret will be a bit darker/fuller sounding IMO.

Author:	SteveSmith [ Sun Feb 07, 2010 5:40 pm ]
Post subject:	Re: OLF OM Mods for 13 Fret Shorter Scale
TonyKarol wrote: hmmm ... based on my calculations, moving from a 14 to a 13 fret joint moves the bridge back 16.7mm, or .657 inches .... check your math again to confirm. I am assuming you are doing this as you say you are moving the bridge back I cant see how you can leave the soundhole in the same spot, and still have 20 frets, unless the FB overhangs - the 19-20 fret delta is approx 12 mm, you are shifting 16mm ... as for moving the soundhole, if keeping the same number of frets, then yes, move the soudhole the same ammount you are shifting the neck. Same thing for the bracing .. shifts back the same ammount - or you have to play around with closing the X, or making a longer bridge, or a combo ... 13 vs 12 fret .. the 12 fret will be a bit darker/fuller sounding IMO. Thanks Tony, always good to recheck the math (previously I included a 0.030" nut compensation but for this calculation I did not). I'm changing the plans from 25.4" to 24.9" scale. Using the StewMac calculator (compensated) the distances are: 1. Bridge moves : - 25.4" scale --> Center of bridge at 25.552", 14 fret at 14.086"". Bridge to body join(25.4 14-fret) = 11.466" - 24.9" scale --> Center of bridge at 25.049", 13 fret at 13.149". Bridge to body join(24.9 13-fret) = 11.9" - 24.9 13-fret bridge moves (11.9" - 11.466") = 0.434" towards the tail block. 2. Soundhole location: - 25.4" 14-fret --> upper edge of soundhole 3.875" from body join but fret board extends ~4.27" (scaled from plan) from the body join and overhangs the soundhole somewhat. - 24.9" 13-fret --> (fret 20 at 17.057") - (fret 13 at 13.149") = 3.908". So far I need to shift the X-brace back and I think I'll shift the soundhole back some as well. Maybe enough to pick up the 21st fret.

Author:	TonyKarol [ Mon Feb 08, 2010 8:27 am ]
Post subject:	Re: OLF OM Mods for 13 Fret Shorter Scale
.. ok .. didnt get the 25.4 14 to 24.9 13 part before ... So eher is what I do when making a new plan .. start from scratch !!!! You just start drawing it out ( you know wher most of the major braces, bridge and soudhole can go), using the other plan as a reference as to what to do with the brace placement .. be adventurous ... make your own and learn how to create a plan for any scale, and neck joint. Other than my first few, all my other plans I have created myself .. its not that hard to do.

Author:	SteveSmith [ Mon Feb 08, 2010 11:29 am ]
Post subject:	Re: OLF OM Mods for 13 Fret Shorter Scale
I do lots of engineering drawings so a new plan would not be a big deal. For this one, I really wanted to work off of the OLF-OM plan as I have not used that and I haven't built enough to have a good understanding of placing and dimensioning the braces and other components. If the existing plans get too marked up then I'll probably have to draw it up separately.

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Author:	Michael Dale Payne [ Mon Feb 08, 2010 4:53 pm ]
Post subject:	Re: OLF OM Mods for 13 Fret Shorter Scale
SteveSmith wrote: I do lots of engineering drawings so a new plan would not be a big deal. For this one, I really wanted to work off of the OLF-OM plan as I have not used that and I haven't built enough to have a good understanding of placing and dimensioning the braces and other components. If the existing plans get too marked up then I'll probably have to draw it up separately. just incase you missed it What Tony was telling you is that my OLF-OM plans is braced for a 25.4 scale OM. The Xbrace center location and splay would need to be adjusted for a shorter scale. this will move the cound hole, tone bar and finger brace locations as well. Not a lot but some. By loosing one fret at the joint you have compesated fo most of it.

Author:	SteveSmith [ Mon Feb 08, 2010 8:05 pm ]
Post subject:	Re: OLF OM Mods for 13 Fret Shorter Scale
Hi Michael - Yes I considered that and figured that going from the 25.4" 14-fret to a 24.9" 13-fret should require minimal adjustments to your plan if I dropped 1 fret off the end of the fretboard. As best I can tell, since I haven't really started working on the bracing yet, nothing should move more than 1/2". I'll know for sure when I get to planning the bracing in the next few days. I'll try to keep everything in balance as move the bridge and X-braces back so if I think its needed, I'll move the soundhole back too. By the way guys - I really appreciate the comments.

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