Acoustic Guitar Construction

Need Advice: Compensation/Saddle/Bridge for Parlor Guitar? 11/15/21

John, put this where it goes, please, I didn't see a defined category.

Deer season started today without us hearing a shot fired. It's shotgun only in lower Lower Michigan, not rifle but every year the hunters decrease, the deer multiply.

My long scale Norman Blake variation of an OM, #9, just completed, is very loud. And this from an unsanded AA grade cedar top (the lowest) from the luthier supply place in Ohio. I'm going to want to build both X-braced and ladder versions as soon as I can get some black ash. Numbers 7 and 8 were black ash and it not only bends well, it sounds good.

But I also want to start some parlor guitars and I'd value your input if you have any expertise building same, which I don't.

Last year my luthier friend here, Kjell, loaned me the top of a 1929 Martin Style 0 and I made a dimensioned drawing with the X-bracing. He has the other parts and will loan me them to document as well. What I may do will be a shorter body but maybe use some of the Martin width dimensions.

When I started trying to make guitars I was told the Martin long scale was 25.4”, so I had my machinist friend make notches for frets at those spacings in a length of 1/8” x 3” 6061-T6 for use with a sled and a machinist's slitting saw to cut fret slots (photo, fretslot_1.jpg). Then somebody told me 25.4” was just the nominal Martin scale and the actual one was 25.34” 'er something. Oh, well, I'm using 25.4”.

But I can still do simple math, and without having a new fretting guide built at a lesser scale, if I use the first fret as the zero fret with the same guide I can achieve a scale of 23.974”, darn near the 24” scale of at least one little Taylor and the Gretsch Jim Dandy, not to mention numerous electric guitars. And I have a couple three mulberry or osage orange fret boards I made earlier that I could shorten.

So here's my questions:

I found several in-print dimensions saying for a 25.4” scale the compensation added to that length ought to be .150”, and have used same with excellent results. If the same ratio, compensation to scale length applies, then with a 23.974” scale the compensation to three decimal places ought to be .142”.

Does that sound right or does using shorter scales result in non-proportional compensation?

And then, I'm suspecting my standard 1/4” wide saddle and 1-1/2” x 6” bridges ought to be reduced to smaller proportions as well?


Elucidate, por favor.

Here is a handy webpage to calculate compensation https://www.liutaiomottola.com/formulae ... sation.htm.

The compensation is pretty much the same. Compensation takes into account action as one is calculating the increased string path down to the fret and then back up to the saddle, instead of the straight path an open note takes. So a shorter scale length with the same action actually needs a touch more compensation.

I would not change the string spacing, as that is set for the player. You can do what you like with the saddle thickness as nothing you are changing is calling out for a difference from what you are happy with.