Replies to This Discussion

Permalink Reply by Tom T on October 31, 2016 at 11:18am

Tim!

What's the status here? What have you tried? What results did you have?

The suggestions thus far tend to focus on:

1. Confirming that the bridge is at two times the distance from the front edge of the nut to the 12th fret. Is that confirmed?

2. The string action at the 12th fret is somewhere equal to the thickness of a nickel or less. Has this been confirmed?

3. The middle string is brought into correct intonation then the high and low G strings are adjusted by angling the bridge around the middle string. Have you tried this yet?

At this point, I think we are shooting in the dark without some new test results.

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Permalink Reply by Tim Kuhn on November 6, 2016 at 11:00am

I was stuck in training this week so I have to get back to this this week.  I have tried lowering the nut and the bridge, and also angling the bridge.  I am pretty sure I need to get the nut even lower. I checked it against my Taylor and it is considerably higher.  I am hoping to figure it out because I would like to build a few with frets.  I have an ammo can and a gas can waiting to have necks installed....

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Permalink Reply by Taffy Evans on October 31, 2016 at 5:22pm

Also keep in mind that light strings on high frets can go out of tune if you push down too hard and stretch the string down behind the fret, and so out of tune. I do not know the quality of the neck but is the nut in the correct place.  Also if a nut slot is too tight and grips the string, after tuning the string can slowly slip through under tension and go flat. But I think you said your strings go sharp, so maybe the there is one offending string, a wound one, that goes flat and makes the others seem like they have gone sharp.

 Cheers Taff

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Permalink Reply by Hal Robertson on November 2, 2016 at 5:13am

Hey Tim, I hope you're having some luck on your build. I've attached a couple of pix that may or may not be helpful.

When I first string up a guitar, I get the open strings in tune (placing the bridge at the scale length with a ruler) and then check tuning at of each string at the 1st-4th frets. You don't want to smash the strings down, just enough to get a clear sound. If the tuning goes sharp, the nut is too high on that string. Mine usually end up just a hair sharp on the first fret, then things smooth out. File and test, file and test. Repeat for each string.

Then I move to the bridge, comparing open tuning to the tuning at the 12th fret. If it goes sharp, the bridge needs to move back or get lowered - maybe both. If it's flat, bridge needs to move closer. Either adjustment will probably be small. As others have suggested, getting the outer 2 strings to work by angling the bridge seems to work for me. Middle string might not be 100% but it's really close and this is a CBG after all :-)

This first pic is my very first CBG. Used nails for frets (never again) and it's pretty janky overall. A while back, I modified the oak nut to accept a zero fret (slightly larger nail). Virtually eliminated my weird intonation issues. Just cut the nut slots deeper than the zero fret and used the nut as a string spacer.

Second pic is the angled bridge on that same janky guitar, just for reference. Plays in tune up and down the neck and pretty well stays that way too over time. 

Can't wait to hear how you came out!

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Permalink Reply by Fomhorach on November 2, 2016 at 8:52am

I second this. It shows the intonation angle of a bridge very well. This might not be the problem, only you can find out. But the picture shows how the bridge angle draws backwards slightly for the bass strings. It's all complicated and half because the strings get thicker and tighten and other stuff. If it is the problem, then that angle changes depending on scale length and string thickness.
Hal is correct though. Check this stuff out first. Nice examples hal :)

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Permalink Reply by Taffy Evans on November 2, 2016 at 11:50am

Hi again, I just got one of my three stringers out and played up around the 10 - 14 frets by fretting notes with my fingers, and the intonation was slightly off but not noticeable when playing a riff.
Now I have a higher than normal action at the nut and the 12 fret as I play with a heavy slide, and rarely finger notes up the neck. So even with is higher action I had intonation I could live with.

So your problem is hard to work out, without seeing it.

Minor intonation problems can also be caused by flat frets with no crown on them.

Any way good luck, remember it is nearly impossible to get perfect intonation on a fretted instrument. We try by having compensated saddles and compensated nuts.

Cheers Taff

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Permalink Reply by Tim Kuhn on November 6, 2016 at 10:57am

I just got logged back into the site, between training this week and being locked out I haven't been able to work on my CBG.  This week I will work through all the advice and see what happens. 

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Permalink Reply by Tim Kuhn on November 11, 2016 at 12:04pm

I spent a few more hours with this today. The low G is still the only string that will tune correctly. I have lowered the strings as low as they will go and it is still off on the D and high G. One of the comments mentioned that perhaps it was the strings. I am using 44,18 and 11 gauge for the GDG tuning. I will swap the D and G out to see if that makes a difference. I spent a long time changing the height of the bridge to where it is really low, and even just working with the D it is always sharp until about the 8th fret. The first fret is almost touching the string. I look forward to figuring this out before I lose it and toss it in the fire pit.  If I am measuring correctly its a 25" scale.  1st fret to the middle of the 12th is 12 1/2 inches.   Looking at pictures online, my bridge seems very low to everything I see. I am stumped...

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Permalink Reply by darryl kernaghan on November 11, 2016 at 12:23pm

Try bringing the bridge forward on the high g side till it intonates open and at 12, leaving the low g side as it is, see if that improves it, ignore the d for the time being, as it is going to be a bit of a compromise anyway

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Permalink Reply by Fomhorach on November 11, 2016 at 11:42pm

"and even just working with the D it is always sharp until about the 8th fret." This makes me think that your nut is sitting a little too close to the first fret.
Try putting a capo on the first fret and checking the intonation of the guitar. If you don't have a capo, a little bit of wood and a clamp will do.

Capo the 1st fret, set bridge distance to 2x 1st fret to 13th fret. Check the intonation. If it's decent, do this for the other 2 strings. If they all work out, the problem lies in the nut.

You say it's sharp so if it is the nut, then it's most likely too close to the first fret and needs a little wood shim to pull it back slightly.

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Permalink Reply by Tim Kuhn on November 12, 2016 at 3:33am

Great idea!  I have numerous capos so this will be easy to check.  The nut came pre-cut so it should be in the right spot, but we will see.

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Permalink Reply by Fomhorach on November 12, 2016 at 1:12pm

I wasn't thinking right. If it is the nut and it's too sharp then the nut is too far away and needs to be closer.. Anyway, capo it and see if it is the nut or not.

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