Official Luthiers Forum!

I know this subject has been posted before, but I can`t seem to locate it in the archives.
I spent all day yesterday working on laying out a template for my fret slotting rig, and I came to realize that I didn`t have a spec for the 21st (or 22nd) fret.
I thought "No big deal, I`ll look it up at the OLF".
No luck here after quite a while, and I do mean quite a while. I checked in on other sites and all that stuff, but still couldn`t find what I was looking for. So I decided to calculate them out myself. How hard could that be? I`ve done it before, and just to compare my numbers to the charts. I thought I had it figured out until I worked with the 24.9" scale.
Now let me tell y`all up front that I had been using the table provided on the Scott Antes "Grand Auditorium Guitar" plan that I started out with a few short years ago.
After checking and rechecking myself on the formulas and numbers, I came to the conclusion that the draftsman`s tables may not be all that accurate if you use the constant 17.817152 (from the Cumpiano book, and other references I gleaned here at home). Yes, I refer to the OLF as Home.
I don`t mean to make this a long post, but...
At first the numbers made sense and compared quite closely, but after I got up to the 10th fret, I found that the difference was 1/1000 different. I took a good strong look at this and continued on.
The 12th fret came right back in line with specs. (What the...?)
After that, the numbers differed just a bit, even after rounding up and down, because .001" isn`t much and I know this can be adjusted with fret crowning.

So my basic question is "Should I go with my own calculations, or stick with the table set before me. I have noticed discrepancies in scale intonation although the nuts and saddles are right on the money, and I won`t count on action height just yet, being a hobby builder so far, and my previous guitars have been laid out painstakenly by hand. Nothing major, but just enough that the real players that come around tell me about it.

While I`m at it, would someone post the positions for the 21st and 22nd frets so I can compare? 24.9" scale.

I made an outstanding template for a 25.4" scale last winter and swear by it, so why not for other scales?

This may be a good place for someone to post the "right" formula for future reference.
Cheers,
Coe Franklin

_________________
Give me 50 cents worth of regular.
Check my oil too, if you don`t mind,,,

Cumpiano's formula is correct. But you could save yourself the trouble of all those manual calculations and just use this: http://www.stewmac.com/FretCalculator

If the difference is only .001" in all cases, then you can just chalk it up to accuracy of calculations and rounding method used. The errors accumulate as you repeatedly multiply by the fret to fret constant, so it's easy to get differences of that much depending on how you execute the formula. Not like you can actually measure and cut that close anyway

Thanks for the reply, Dennis.
I know what you mean by being all too accurate, but I still can`t help but wonder...


Thanks, Todd!
That`s what I origionally went looking for.

Other input would be appreciated.
Coe

_________________
Give me 50 cents worth of regular.
Check my oil too, if you don`t mind,,,

+1 for Wfret. Great software, for nothing!

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Waddy

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