Bridge and saddle heights

[sycamore6]

I'm a relative beginner having made 2 kit guitars and 2 scratchbuilds....I'm now on no. 5. I have a general query about bridge and saddle height. I have varied the bridge height at 5/16 in, 3/8 in. and 7/16th on my guitars, and routed the saddle slots deep enough so that 65% or so of the saddle is below the bridge surface. I have tried to set the neck dovetail on each guitar so that a straight edge placed along the top of the frets in the centre of a radiused fingerboard just kisses the top surface of the bridge, thus (in theory) allowing a comfortable action with (say) 3/16th in.(or a little less) saddle height. On two of the guitars I got the neck angle wrong so that these conditions weren't met and as a result I have too low a saddle and too high an action. (I'm going to try neck resets on these). On the other two guitars, I got the neck angle about right and action and saddle heights are good. However, another factor has come into play which I didn't predict. On two of the guitars already completed,(that had good neck angles), on stringing up there was little or no movement of the structure....so the straight edge condition where the fret tops and the bridge top aligned was not compromised (or hardly so). On the other two guitars completed, (the ones with the wrong neck angles) the structure moved appreciably under string tension, so that the sub-optimal high action caused by the incorrect neck angle was made worse as body deflection caused the bridge to rise slightly thus exacerbating the action issue. I seemed to be getting the distortion on first stringing up that happens over 40 years on many acoustic guitars that require neck resets. My guitars are conventionally X braced with "standard" thicknessed and sized spruce braces.

My questions are.....do experienced builders build in a "distortion factor" when setting necks......for example setting the neck such that a straight edge over the frets crosses the bridge 1/16 in above the bridge surface and thus allow for some "pulling up" of the bridge? If so.....how do you predict when this might be necessary? Also....what bridge height should I be using....5/16, 3/8 or 7/16? I should say that these bridge heights are the maximum measurement between the 3rd and 4th pin holes...the bridge curves away in the usual manner towards the 1st and 6th pin holes.

thanks........John

[tippie53]

After 130 guitars I think I have my setting procedure set . It is a guesstimate what the body will do when loaded but I have it so that I can be consistent in getting my 1/2 inch string height. I like a 3/8 bridge and I want to see on initial set up of about .150 to 180 saddle height.
I use a .410 standard martin bridge. and here is a video to what I do .
http://www.youtube.com/results?search_q ... etial&aq=f
My goal is a 3/8 final bridge. I try and hit my fret plane line about 1/16 over the top of the saddle on neck set. After about a week of string load the bridge and top set in. I then do the final set up. With this procedure I usually hit .550 to .500 . So in answer to your question you , yes I do plan for a slight amount of top defection.

[Tony_in_NYC]

After 130 guitars I think I have my setting procedure set . It is a guesstimate what the body will do when loaded but I have it so that I can be consistent in getting my 1/2 inch string height.

After 3.875 guitars (three finished and two under construction, one of which is nearly complete) I do not have my neck setting procedure down as well as you do John. Where are you measuring for the 1/2 inch string height?
I am unfamiliar with that particular measurement and since I am at work, I can't watch the video you linked. And since I have almost nothing to do at work today, I have nothing else to distract me from obsessing on that measurement. Are you measuring the string height from the soundboard at the bridge location? Do you do this with a fretted board on the neck and a straight edge projected out to the bridge location?
If so, and your bridge is .410" thick, that would mean you use a saddle height of .090"? I am certain this is wrong, so before I go looney, please, as Desi Arnaz used to say to Lucy, 'Splain.
See what happens when I am going on vacation at the end of the week and I did not book any appointments? Boredom.

[Ben-Had]

Tony - You asked John.

"Are you measuring the string height from the soundboard at the bridge location?"
Yes he is.

"Do you do this with a fretted board on the neck and a straight edge projected out to the bridge location?"
He has an non-fretted finger board on the neck with the straight edge projected out over the bridge and the str8 edge just kisses the top of the bridge.

[tippie53]

I like to pre dress things when the guitar is in the white as Ben stated . I also play with the stresses a bit. If I am building a guitar for a finger picker , they usually like a softer feel. I will make the set height so I am about 9/16 inch at the front of the bridge and then use a lighter gauge string. This still stresses the top about the same as mediums strings so you get the most of the top , but will the lighter tension , you can get a softer feel.
One key to this is that you set the geometry up so the sides reflect the neck angle and you can then tune it out on the top before finish. I don't like to put the neck angle into the top as you remove wood where you do need it the most , to control that shear force from the fret board extension.
This link shows my method . Yes Martin does in fact do it the same way . The difference is I use a 28 foot disk and martin uses a jig to sand the angle into the sides from the top of the sound hole to the neck block .

http://www.youtube.com/watch?v=QYHPCeVRUA4

[Tony_in_NYC]

DAMN YOU AND YOUR LINKS!!! I can't see them from work. I will try to watch them tonight.
Ben-had, thanks for the info.
John, so you are measuring from the soundboard to the straightedge? And with an unfretted fretboard?

[tippie53]

without the frets I want the straight edge to just touch the top of the bridge . With the frets I want to see 1/32 to 1/16 above the bridge.

[Tony_in_NYC]

Thanks. And thanks for not using a YouTube video to answer!

[Darryl Young]

I'll add a couple of questions and comments.

Just for clarity, John H. is the end goal to have the bottom of the strings 1/2" above the soundboard at the front edge of the bridge?

John (with the original question), if the neck angle is too far forward (high string action) it tends to pull the top up more than it will when the neck angle is corrected so it is pulling more parallel to the soundboard. The further the neck angle is forward of the target, the more the top will likely rise. I had my neck angle a little too far forward when I strung up my first a couple months back. Interesting that is sounded a bit harsh. As I corrected the neck angle the tone seeemed to warm up and the bass improved. Possibly some of this affect was from the guitar getting played and "broken in".......but I think the increased pull upward on the soundboard by the wrong neck angle contributed to the initial "harsh" sound (lots of overtones). Maybe that's a way to get a Delta, bluesy sound loaded with overtones! <smile> So the soundboard "rise" with string tension may be a function of neck angle.

As for bridge height, the higher the bridge the less saddle is needed and vice-versa. The higher the saddle above the bridge, the sharper the break angle of the string over the saddle. The break angle changes the downward force the string tension places on the soundboard (sharper angle increases the downward force and less angle decreases the downward force). Also, the sharper the string angle the more rotation force is placed on the saddle. So a tall saddle above the bridge can place a lot of pressure on the saddle slot since the saddle is trying to rotate forward. If the saddle slot holds, this twisting force is passed from the saddle to the bridge so the bridge rotates forward and the stiffness of the top must resist the bridge rotation. So higher saddle height above the bridge = more pressure on the saddle slot and increased rotation force on the top by the bridge.

Regarding the goal of 1/2" string height, the higher the string height the stiffer the soundboard/bacing must be made to resist the torque placed on the bridge by string tension. Conversely, if you lowered the string height, one could make the soundboard and bracing less stiff (lighter top). So would a lower string height with a lighter soundboard sound different then a similar guitar with higher string height and a stiffer soundboard? I've read statements from both Bryan Kimsey and Mario Proulx (who both played with varying string heights and it's affect on tone) that they prefer the sound of a lighter built top with less string height over the sound of a stiffer top with higher string height. One day I want to test this myself. BTW, if you reduce the string height but don't reduce the soundboard stiffness........don't expect a better sounding guitar, it will sound worse and won't have as much volume. On many/most factory guitars the top is overbuilt so increasing the string height may make them sound better (at least louder).

I'm sure there is a lot of repetitive statements above.......but I've got to get back to work so don' thave time to edit.

[sycamore6]

W-O-W....thanks to John H., Tony and Darryl for informative and thoughtful replies. As ever with guitar building there's a lot more in this topic than I imagined.

John H......thanks for the link to your videos which I hadn't seen. I'll study those carefully. Darryl.....thanks for your thoughts on this topic. I hadn't considered that when the neck angle is too far forward, there is likely to be a greater force on the bridge tending to make the guitar top lift. Strange to say, on my 1st guitar (a 12 fretter), the neck angle is way too far forward giving a high action even with a 5/16 bridge and a minimal saddle height, the tone is soft and mellow.....in fact as nice a tone as I've yet produced (which isn't saying much). The string to top height at the bridge is 7/16 in. on this guitar.

So...in conclusion...suggested average parameters would seem to be.... 3/8 - 7/16 in bridge height, 1/8-3/16 in saddle ht above bridge and around 1/2 in. string height above the top at the bridge front with a neck set that gives a straight edge reading over a fretted board at the bridge about 1/16 in gap over the bridge.....? As we say here in the UK....it's back to the drawing board for me......

thanks again......John