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Hi - Im just about to glue the bridge on my first guitar build - a HD28 from Blues Creek - and final checking the dimensions, cos theres no second chance!
Ive watched John Halls excellent youtube vid on saddle position and altho he measures to saddle edge, the dimensions correspond exactly to StewMacs scale length/saddle slot calculator, which measure to the middle of the saddle slot.

My question is - the Martin dreadnought scale is usually defined as 25.34", whereas my kit neck and my Martin D-28 both come out at 25.354", based on a nut to middle of 12th fret length of 12.677"(322mm). Have I missed something or is this what all Martin Dreads scale lengths are?

Incidentally my D-28 measures within 0.020" of the StewMac calculations, but the saddle slot is less than 3 degrees...

Thanks for your help guys, Dave

what you want is nut to 12th fret doubled and then add .100 to the center of the slot and 1/8 in to the bass side
that will get you well into the ball park. On initial set up you want to be about 2 cents flat so as the bridge rotates some this will hold you intonation.
feel free to call me my contact info is on my website

Very interesting. StewMac say add 0.088" +or- .030" on the treble e, so I think I will go with your 0.100".
Any comments on the scale length of 25.354"?

John has done hundreds of them. I've done exactly one, so you know who is worth listening to. :) You're right, John's video pretty much tells you all you need to know.

I'll describe what I did. It may help, if only as reassurance that there is a range of acceptability and if you don't get it "perfect" (whatever that is) as long as you are fairly close it will likely be okay.

1. Measure from the nut to the middle of the 12th fret and double it to get the scale length. In my case, I had slotted the fingerboard myself. The nut to the 12th fret is 12.700" so the scale length is 25.400".

2. Add 0.100" to the scale length (in my case, that makes it 25.500".)

3. Measure that distance from the high E string slot on the nut and mark (on a piece of tape) where it lands on the top of the guitar. That is where the center of the saddle slot should be for the high E string.

4. When I made the bridge, I angled the saddle slot by 1/8" so the nut-to-saddle distance for thel low E is 1/8" more than it is for the high E.

There may be more correct ways of locating the saddle, but the results I got doing it that way are certainly acceptable.

Thanks Mainegeezer. I understand the principles, its just that so many luthiers have different measurements for the compensated length. After all these years, I thought it would have been an excact science by now. I will add .100" to the treble e

To help you understand things Dave the variables are many
1 action height
2 bridge rotation
3 string gauge
4 playing style
5 top movement
6 neck relief
all this plays into the position of the saddle and compensation length and angle . When you tune a guitar you are careful to fret clean but in reality when you play you tend to be more aggressive . You should find when you set this up the initial set up a few strings may be a few cents flat but in all they will come into tune. In a few weeks you can then readdress the intonation but allow good settle in time.
Then you can address the saddle and compensate that to make the final address. In some cases you may not need to compensate a saddle.

the first 100 are the hard ones.

Thanks again John!