scale length question - no mandolin content

**James Sanford** · Sep-23-2011, 9:06am

Help,

I am rebuilding a Harmony Sovereign guitar and am replacing the Harmony style bridge with a pin type bridge. In order to get everything back in the right place I have checked the distance from nut to 12th fret (12 5/16") and the distance from 12th fret to bridge (12 5/8"). This does not calculate as the scale length from nut to bridge is 25 1/4".

Can this be correct? I played the guitar before taking it apart and heard no significant problem with intonation.

May be something going on here which is normal but I have little guitar experience.

Any thoughts or help appreciated.

**Audio Artillery** · Sep-23-2011, 9:40am

So... you're saying the original intonation seems to be off by 3/16"? Was this under string tension or no?

**sunburst** · Sep-23-2011, 9:46am

From your post, it sounds like you measured from nut to 12th fret and got 12 5/16", you measured from 12 fret to saddle and got 12 5/8", you measured from nut to bridge and got 25 1/4". In the unlikely event that I am reading that right, I'd say measure again. Otherwise, I'm, not sure I understand the question, could you clarify?

**multidon** · Sep-23-2011, 10:06am

Since your measurements do not add up, and they must, I believe you must have measured incorrectly. Double check and make sure you are reading those marks. Perhaps the bridge got bumped and moved slightly between measurements? Is the original bridge compensated? Or was is installed tilted to approximate compensation? Conventional wisdom says that distance from nut to 12th fret doubled HAS to be the scale length. That makes yours 24 5/8 inches. Of course we have to compensate for string stretching, especially when playing on the high frets. So the relative scale length/bridge placement ends up a tad longer on the bass side thicker wound strings, not as much for the thinner solid strings. I would say that your high E should be not exactly but at least pretty close to the actual scale length, the others a tad longer, with the low E being the longest. If I were you, I would use that movable bridge and an electronic tuner to find individual "ideal" compensated scale lengths for each string one at a time. The actual bridge position would be a compromise of course, and you should install one with a compensated saddle. Just out of curiosity, why not keep the moveable bridge? If there is something wrong with the original it is easy enough to fit a new one. Installing a pin bridge seems like fairly radical surgery to me. I like to keep instruments like that as original as possible under the circumstances. Good luck!

**multidon** · Sep-23-2011, 10:55am

http://www.stewmac.com/shop/Tools/Sp...etails#details

Are you familiar with this tool? I've never used it but it looks very useful. According to the directions, on a "normal" scale guitar (and yours falls into their definition) the front edge of the saddle should be 1/16" longer than actual scale length on the treble side and 5/32" longer than actual scale length on the bass side. If I were going to do this job, especially if there were a possibility I would do it more than once, I would definitely invest in this tool so that there would be no doubt! Gotta love Stew Mac! They have a tool for just about anything you can think of!

**sunburst** · Sep-23-2011, 11:22am

A $30+ gimmick to measure for bridge placement? Intonation is what matters with bridge placement, I have rulers, tape measures, all sorts of measuring devises, but if it plays in tune, that's the correct bridge placement regardless of measurement.
BTW I'm still not trying to answer the original question here because I'm still not sure what the original question is.

**James Sanford** · Sep-23-2011, 11:31am

Originally Posted by sunburst

From your post, it sounds like you measured from nut to 12th fret and got 12 5/16", you measured from 12 fret to saddle and got 12 5/8", you measured from nut to bridge and got 25 1/4". In the unlikely event that I am reading that right, I'd say measure again. Otherwise, I'm, not sure I understand the question, could you clarify?

John,

I went back and rechecked the tape reading. My problem is that the distance from 12 th fret to bridge is 1/4" longer than nut to 12th fret.

The scale length is 25 1/4". From nut to 12th fret is 12 1/2" and from 12th fret to bridge is 12 3/4".

I had the neck out of the guitar for a reset and may have missed the measurement a little because of this although I checked to be sure it was tight against the body.

At any rate the distance which should be the same is off by 1/4". Could this have been extra compensation or just plain manufacturing error?

**sunburst** · Sep-23-2011, 12:30pm

Oh, I see... I think.
The scale length, in theory, is not the same as the compensated string length. Things can get confusing here, so we'll just say the scale length is twice the distance of the distance from the nut to the 12th fret. On a Martin guitar, for example, the scale length is said to be 25.4", and the distance from the nut the 12th fret is half of that, or 12.7". If you actually measure the string length, the distance from nut to center of saddle, you'll find it to be about 3/16" longer than that, and that is to compensate for the stretching of the strings when fretted. That means the distance from the nut to the 12th fret should be a little shorter than half the length from the nut to the saddle on your guitar. The amount of the difference depends upon the scale length, the string gauges, and the action height, so it is generally a compromise setting unless a thorough custom set up has been done.
The scale length of a fretted instrument is not the length you will find by measuring the string length (if the instrument plays in tune).

Scale length =X
Nut to 12th fret = 1/2 X
Distance from nut to saddle = X + compensation factor

(There's a little more to it than that, but that's enough basics to go on. For those picky enough to bring it up, I know that the Martin scale length is not truly 25.4" but the example serves to explain the situation regardless.)

**multidon** · Sep-23-2011, 12:44pm

That extra 1/4 inch could almost be accounted for in compensation but not quite. You state that "there is no significant problem with intonation". Did you check each string's intonation individually with an electronic tuner as I suggested? I'm betting that either A. he bridge is placed incorrectly or B. The action is too high making for more string stretch while fingering, and the bridge was placed further back to compensate.

John gave you great advise. He is a professional and has way more building/repair experience than I do. He is certainly correct in saying that playing in tune is the most important thing regardless of measurement. The measurements just get you in the theoretical ballpark. John, please not the fact that I laid out that procedure in my first post, which you did not address. You seem to have only read my second post. I merely suggested the tool, which I have never used myself, because its design seems fairly "goof proof" and James stated he "doesn't have much experience with guitars". I would never call a well-designed tool a "gimmick". I can see the advantage in using a tool like that but I would never take the results at face value, I would always double check the intonation before cutting any wood.

**sunburst** · Sep-23-2011, 12:59pm

Originally Posted by multidon

...I would never call a well-designed tool a "gimmick"...

Many of Stewmac's dedicated tools are redundant, in that they are simply substitutes for other more common tools that luthiers usually already own and have used for years. There is actually someone on staff at Stewmac who's job it is (among other things) to think up and design tools for lutherie, so they just keep coming. If a luthier bought them all he/she would have a room full of tools for dedicated purposes when the standard tools of the trade are all that is really needed. Gimmick is the word that works for me. It's like those little egg slicers, or bagel slicers, for the kitchen. I've used a knife for years to slice things in the kitchen, and however well designed an egg slicer or bagel slicer is, I think of it as a gimmick and I don't need it; I have a knife.

I should also mention that I do own and use some of Stewmac's "gimmick" tools. If they save me enough time, simplify something enough, don't take up too much space, and aren't too overpriced, I buy one occasionally.

**James Sanford** · Sep-23-2011, 1:45pm

Thanks for the replies.

In response to the question of checking the intonation of each string with a tuner. No, I did not. The guitar's neck needed resetting and I knew that it would have problems because of this. I did a cursory check in the open position and in G, C, D etc.

Based upon John's comments (thank you) what I am seeing appears to be the compensation you refer to. I am used to dealing with mandolins and am just now moving over into guitar learning mode.

I will locate my new bridge in the same place and move on from there. If it works fine, if not I will fix it.

**John Kelly** · Sep-23-2011, 1:55pm

Hi James, just came across this site where someone is re-doing a harmony sovereign and replacing the bridge as you are doing. Some interesting pix on the site. Here is the link:
http://grahamparkerluthier.com/2011/...ony-sovereign/

**multidon** · Sep-23-2011, 4:21pm

Hey James, I apologize, I assumed your original Harmony bridge was a floating bridge. If it's a glued down string through like the one on the Web site John Kelly found, then the intonation should already be correct in that position. Perhaps you should do the neck reset first, then check and measure for ideal string length after that?

**sunburst** · Sep-23-2011, 4:35pm

Don has a point.
There were years when Martin guitars had bridges that were poorly located and intonation suffered (to say the least). One common fix is to replace with a new, unslotted bridge and then cut the saddle slot where it needs to be for accurate intonation. That procedure could give you good intonation on the guitar you're working on. After the neck is re-set, then you can accurately figure it all out. There are several methods for determining the correct position for a saddle in a guitar bridge, (some involving specialty "gimmick" tools from Stewmac

) and you'll probably need a jig to route the slot once the position is determined (again, you can buy, make or improvise the jig).

**James Sanford** · Sep-23-2011, 9:31pm

Originally Posted by John Kelly

Hi James, just came across this site where someone is re-doing a harmony sovereign and replacing the bridge as you are doing. Some interesting pix on the site. Here is the link:
http://grahamparkerluthier.com/2011/...ony-sovereign/

Thanks John,

That is exactly the same model guitar I have even to the missing pick guard. They look just alike.

I have taken the back off and rebraced from the ladder style bracing to martin style x-brace along with the neck reset and bridge change.

Don: I plan to do exactly as you stated regarding the neck reset.

Thanks to both of you for the help.

**multidon** · Sep-24-2011, 8:56am

Wow- you redid the bracing? This is going to be like a completely different guitar when you are done! Keep us posted and let us know how it turns out. Good Luck!

**John Arnold** · Sep-25-2011, 9:14pm

What was the action before? If the action was high, more compensation is required for correct intonation. I use between 0.065" and 0.085" compensation at the first string, depending on the action and the string gauge. High action and/or heavier strings require more compensation.

**James Sanford** · Sep-26-2011, 8:36am

Originally Posted by John Arnold

What was the action before? If the action was high, more compensation is required for correct intonation. I use between 0.065" and 0.085" compensation at the first string, depending on the action and the string gauge. High action and/or heavier strings require more compensation.

John

The guitar has almost no wear on the frets and so has never really been played. I acquired it as a fixer upper to begin learning a little about guitars. The action was obviously too high in the vicinity of the the joint to the body. This model guitar, as best I can determine, is known for needing neck resets after a period of time. The compensation was set at the factory and had never been changed. I intend to reset the compensation as close to factory as I can after resetting the neck. I am used to mandolins and floating bridges so guitars present a really different situation. Not much chance of easily resetting the bridge if needed.

I will try to get it back where it was and hope for the best.

**John Arnold** · Sep-29-2011, 11:22am

Lowering the action will reduce the amount of compensation necessary to play in tune. In other words, if it played in tune before with high action, it will note flat after the reset.
Just because the bridge location was unchanged from the factory setting doesn't mean it is right. Over the last 27 years, I have seen my share of misplaced bridges, even from Martin and Gibson. Some of them have been more than 1/4" off.
You can change the saddle location in an existing bridge by filling the saddle slot and recutting it, but this is only practical if the amount is less than 1/16".
You can also make a new bridge with a different saddle slot location, but reducing the compensation means that the slot may end up too close to the upper edge of the bridge. In that case, the bridge can be widened slightly.
Also, you have a golden opportunity to reduce the amount of compensation during a reset. The heel can be trimmed, shortening the neck itself. In that case, the saddle location can remain unaltered.
Another thought:
If this was one of those Harmony bridges with a straight across saddle, then it was a steel string compromise from the start. Generally, those are positioned for correct intonation on the middle strings. The trebles will be flat, and the bass strings sharp.

**James Sanford** · Sep-29-2011, 11:51am

Originally Posted by John Arnold

Lowering the action will reduce the amount of compensation necessary to play in tune. In other words, if it played in tune before with high action, it will note flat after the reset.
Just because the bridge location was unchanged from the factory setting doesn't mean it is right. Over the last 27 years, I have seen my share of misplaced bridges, even from Martin and Gibson. Some of them have been more than 1/4" off.
You can change the saddle location in an existing bridge by filling the saddle slot and recutting it, but this is only practical if the amount is less than 1/16".
You can also make a new bridge with a different saddle slot location, but reducing the compensation means that the slot may end up too close to the upper edge of the bridge. In that case, the bridge can be widened slightly.
Also, you have a golden opportunity to reduce the amount of compensation during a reset. The heel can be trimmed, shortening the neck itself. In that case, the saddle location can remain unaltered.
Another thought:
If this was one of those Harmony bridges with a straight across saddle, then it was a steel string compromise from the start. Generally, those are positioned for correct intonation on the middle strings. The trebles will be flat, and the bass strings sharp.

John,

Thanks for your thoughts. As noted in a previous post I did not throughly check the intonation of this guitar before removing the neck. (another lesson learned!!!). The original bridge was the Harmony straight bridge and the location from the factory could have been spot on assuming correct neck angle or it could have been off. No way to tell now.

I plan to try to calculate the correct string length based upon Martin medium gauge strings and set my new bridge (pin type) in accord with that since I am replacing it. I wonder if anyone has put a wide saddle in one of these bridges and compensated the strings like a mandolin bridge?

**James Sanford** · Oct-10-2011, 1:15pm

Just finished the guitar. I replaced the bridge with a pin type as noted above and glued it back at the same distance as the original bridge. The neck reset reduced the string height to a good playable condition.

I checked the intonation at 12th fret and found, as John Arnold noted above, that the treble E string is a tad flat but the guitar sounds really good in all of the positions (including with capo) that bluegrassers normally play.

I am going to let our band guitar player try it out at practice tonight. It sounds like a good D-18 to me so I guess I accomplished what I set out to do.

As to my dumb question regarding the wider saddle, I looked at several guitars in the music store and noted that almost all had a compensated saddle. DUH.

Thanks to all who assisted.

**multidon** · Oct-10-2011, 3:24pm

James- Glad all went well. Enjoy the guitar! Tenors are awesome. Did you keep it in CGDA or go for some other tuning? Mine is in GDAE (octave mandolin strings) and I love it there!