Is this bridge saddle in the right place?

Issue 185 February 28, 2013

The free Fret Position Calculator at stewmac.com does the math, but can I trust its numbers for placing a Martin bridge? I tested the computer against my "stone age" method. — Dan Erlewine

Video Transcription

Dan Erlewine: [on screen text reads: Dan Erlewine - Stewart MacDonald] Here's a lesson on using the StewMac fret scale calculator to find out where the saddle goes on this Martin guitar.

I had to take the bridge off this, because it was warping up and it split. So now I'm replacing it.

I know where the saddle goes, because I can copy this, but I never trust anything. And I want to check it myself.

Plus, I'm making a new bridge and let's say I didn't have a bridge to copy. How do you know where the saddle goes?

How to find out where the saddle goes

You start by finding out your scale length.

Measure from the nut to the center of the 12th fret. In this case, I'm getting 12-43/64". I'm going to double that and that'll be my scale length.
I want to convert the 43/64" to a decimal. On the back of my action gauge, I've got this little chart of equivalence and it's 43/64" equals 0.6719". I'll round that off to 0.67".

From the nut to the 12th, I get 12.67. And I times that by two. That's 25.34, and that's the scale length. And that's the number that I'm going to enter into the computer.

How to use the StewMac fret scale calculator

Okay. I'm at the StewMac homepage and I'm going to "Free Information."
Then down here, "Calculators."

"How do I calculate a fret scale?"

Number of frets, not that I care, because I'm not making a fret port right now.

The scale length is 25.34. We figured that out.

It's an acoustic guitar.

And calculate. Bingo. At the 12th fret, I see 12.67. That's what I read. And what I want is down here at the bottom, the distance from the fretboard edge of the nut to the break angle of the string at the peak of the saddle. 25.428 to the treble E string. 25.553 to the bass E.

So I'm going to print this out and go to work.

So now I have the measurements to locate the saddle at the two E strings. It'll be a little shorter on the treble, longer on the bass. That's what creates that slanted saddle on a steel string. And it's plus or minus 30 thousandths. The reason we say that, is because the top of your guitar could pull up more than mine. Your action might be taller and mine's a little lower. With the string gauge that you use, it all makes a difference.

If you fall in the center, you're bound to be in tune. And as you gain experience, make more bridges and more saddles, you may decide to go forward a little bit or back a little bit, but you'll have a reason for doing that.
I don't have a ruler that's long enough to measure 25 and whatever number of inches, but I do have a 24-inch straight edge. So here's an idea. Take a couple of magnets and a 6-inch ruler and stick that to your straight edge. Then you can measure out, off the end.

Dan's stone age calculator method

I thought you might like this one. It's my stone age calculator. I made this back in the days before we had computers, before we even had little calculators, and I wasn't all that great with math, like Don McCrosty and Mike Linsgold that came up with this.

I made the tailpiece that would clamp to a guitar. If I was building the guitar or putting a bridge on it and it held the strings, it's padded with a piece of felt and it's got a little block of wood epoxied here, so it won't fly off.

And I'm just clamped to the end block with a padded caul here. And I drilled holes at an angle to come down and up over the saddle.

This way I can play a note and move the bridge and then the saddle around, backwards or forwards, until it plays in tune.

As luck would have it today, this bridge was mounted in the right spot and it agrees with what I found out on the fret scale calculator.

Dan Erlewine

Guitar Repairman and Builder