Measuring relief with string vs. straightedge

[Russell Holland]

Before I bought a notched straightedge, I was measuring neck relief using the string (with a capo on the first fret, and I would press down a string on the [bridge side] of whichever fret is where the neck meets the body, then measuring the largest gap with feeler gauges).

When I bought the notched straightedge, I started measuring relief by resting it on the fret tops, and inserting feeler gauges. I much prefer inserting feeler gauges between the frets and a steel straightedge, rather than under a string which moves almost imperceptibly.

It just occurred to me that there should be a difference between results from these methods because the notched straightedge also covers the higher frets, which are part of the 'flatten out area' as Dan Erlewine calls it. If the neck, and therefore the portion of the fingerboard which is free of the body, is curved, and the area from the 10th fret or so up appears basically flat, then measuring the relief using the string method (only from 1st to 14th fret or so on an acoustic) should give a smaller number than using a straightedge which reaches from the first all the way up to the highest fret. I just want to clarify, is the measurement of relief, strictly speaking, generally considered to refer just to the neck? Is this negligible?

I know that I can compare these measurements, and I'm about to do this just now, but I also want to hear anyone's thoughts on this topic anyway. I'm considering buying an unnotched straightedge soon, because I have some general feeling that being able to slide it fret by fret up the fingerboard and clearly see how the neck 'flattens out' will be helpful. Is this a good idea and will it show me anything useful that I don't already know? Maybe buying different lengths would help make things even more clear? Like an 18" and a 12"? Wish these things were cheaper...

Thanks for any thoughts you might have.

[Len Biglin]

I have never seen a reason to measure the relief , I eyeball it holding the string at 1st and 14th , then adjust it for best playabiliy , I guess if the rod is not adjustable or not present , a measurement might be handy before doing neck work ?

[steven gallagher]

Russell,

If you make sure the straightedge is touching the 1st fret, it shouldn't be touching the frets beyond the 14th. The frets in the  'flatten out area' should be on a slightly different plane than the frets in the neck. IOW, if the straightedge is resting on the 1st and last frets only, you need to fix the 'flatten out area'.

[Russell Holland]

I can understand your statements if what you are referring to as the 'flatten out area' is actually the 'fall away' at the extreme upper end. But as I understand it, the 'flatten out area' referred to in Dan Erlewine's book refers to the part of the fretboard from around the 7th or 10th and upward, which he says should be flat (or flat with a slight fall away at the very end). In a situation with no fall away, for example, it seems to me that measuring relief between the 1st and 12th or 1st and 14th would give a different reading than 1st and last. In other words, to my mind it seems to me that a neck with some relief and no fall away would result in the straightedge resting on the first and last frets.

I'm just a beginner and I hope it doesn't sound like I'm arguing! I am only trying to understand. Thanks for your help!

[Russell Holland]

I drew a picture to help explain how I am seeing it.

(1) I drew a curve using a radius gauge to represent the flexible portion of the neck

(2) I extended the line, this time using a straight edge. As I understand it, this straight portion, as well as the tail end of the curve, which would appear basically straight, together constitute the 'flatten out area.' This is why the 'flatten out area' is said to begin around frets 7-10, and not at 12 or 14; because not only could a straightedge rest on the perfectly flat area, but it could be moved a little to the left and still appear to rest flat against the fret tops.

(3) I drew a line representing a straightedge (or string) held against the 1st and 14th (or 12th--wherever neck meets body)

(4) I drew a line representing a straightedge which covers the full length of the fingerboard, showing how it should rest on the firsts and last frets, assuming no fall away is present. This would have to give a slightly greater measurement of relief.

Is there something I am missing here? I ordered a 12" beveled straightedge yesterday so I can inspect the 'flatten out area' on my guitars.

[Russell Kingery]

Russell,
It just so happens I was doing this just yesterday. I'm no "old timer", but I think I've got a good understanding of the process. If all things were perfect, then adjusting the truss rod would only bow the neck between the 1st and 12th frets. I realize that is rarely the case. I string the guitar and tune, and then adjust the truss rod to get it as flat as possible. And using a straight edge I get the relief at the 5th and 6th fret I want. I eyeball it too. It depends on the owner's playing style, the size of the strings, and how perfect the neck is. (Or should I say imperfect?) from the 12th fret on up to the highest fret is what controls string height, or action. Some actually file the frets down hill toward the highest fret, what is called "Fall Away". And, it creates relief on that side of the 12th fret. About the same, maybe less as the relief on the low side. So, the 1st and 12th frets are the two tallest points on the fret board. This allows the lowest action to be dialed in. It's not the low frets keeping the strings high, it's when you fret at the 16th or higher that the strings want to slap frets, fall away allows you to dial it down lower. Anyway, that's how I see the situation, if I'm wrong please correct me! (Speaking to those of greater experience!)

I've made all but one of my straight edges. They are expensive, and so easy to make! If you've got a sheet of thick glass that proves level, you can test with a known straight edge or just stretching a guitar string across it. Or a joiner or table saw with cast iron table works great. Use progressively finer stick-on sand paper until you remove all low spots and polish the edge. Use a Sharpie marker to find and eliminate the low spots. Aluminum works pretty fast, and Stainless takes some time. I had a stainless 12 inch rule, that had a terrible edge! I went from 100 grit to 600, and I also ground the end off so that zero was at the end of the rule, perfectly square. Super useful now! And I've got a 16 inch aluminum straight edge, no rule marks, that was quick and easy to make. And an 8 inch brass one, and I also have a notched one 24 frets long like yours.

In the end, I just play the guitar, keep raising the string until it doesn't buzz, I can't think of a better way to set string height.

I hope I was of some help?

Russ K.

[Murray MacLeod]

" it's when you fret at the 16th or higher that the strings want to slap frets"

I know that was just a typo ... you did mean the  6th fret, didn't you ? ...

[Russell Kingery]

I was referring to the lack of fall away on the frets above the 12th fret. The bass I just leveled the frets on, perfectly level from first to last, so I put a few thousandths worth of relief at the 6th, and set string height rather low. It played wonderful all the way up to the 12th fret, but every fret above that, it was buzzing like crazy! And required a lot more string height to clear those frets, if it were never going to be played above the 12th, I could have gotten away with 2mm string height, but due to the lack of fall away, it needed 3mm (measured at the 12th). I would have gone back and created some fall away, but the frets are too short already. So until it gets a refret 3mm is as low as it's going to get.

[Christopher Parker]

Most basses play like this - sometimes even expensive new ones (and lots of electric guitars too). This is because the flexible portion of the neck bows upward, and the end of it remains staitionary, creating a "ski ramp" at the end of the fingerboard. The best way to correct the problem is to plane the frets (or fingerboard) under simulated string tension. Then you know for a fact that it's perfectly straight at the upper frets, so there is no need to dress in fall away. If you do a precise job of planing under simulated string tension, it will play perfectly and evenly with no buzzing up the neck.

If you dress in fall away without simulating string tension, you're just guessing.  

[Howard Klepper]

I'll keep it brief, since I don't understand all you have written and a full discussion of fret geometry would be far more typing than I'm willing to do.  I think you will get more meaningful information by asking one question at a time.

I never use a guitar string to check relief.  Not only can it be pushed up by the feeler, it can easily be visibly pushed up at its ends by the capo or fretting fingers with the fret as a fulcrum because the string has stiffness. I use a 12" precision bevel edge straightedge (a good professional machinist's tool--many cheap "straightedges" are not straight enough) and feeler gauges and I think there is no need (on a guitar) for a longer straightedge when doing neck work, but shorter ones can be helpful.  I have yet to see any need for a notched straightedge--one plays on the frets, not the fretboard.  I check from the first or second fret (often both, to see if the first fret is higher) to the body joint fret.  Relief (as most people use the word) is not measured above that point.  I check treble, middle and bass areas (across the neck).  A thousandth or two more in the bass than in the treble can be good.

[Russell Vance]

Hi Howard,

Firstly, apples and oranges:  there are acoustic boxes and then there are  electrics with their extended scales, variety of back of neck profiles, fret types and varying neck materials, neck entry points and tunings/string gauges etc which require a broad general approach wrt relief and other neck matters.  For this reason we don't use feeler gauges or measurements to configure or set up guitars however once the job is done we could use them to record where we arrived at. 

My own personal procedure is all eyball and geometry and I use the strings as straightedges all the time (any residual/additional height of the string caused by the bending of the string over the fret is relative and constant).  However, that said, I am familiar with what a couple of thou or more looks like and part of our training is to show the guys what "look" you should expect for various measurements.     

The demo for this is when using the string as short straight edge to set the nut clearance at the first fret we use a white paper string packet tear-off to show the desired clearance at the first string and then double fold it tight to do the 3rd etc.  The joy of this "redneck feeler gauge" (used to stack razor blades to do spark plug gaps when v.young) approach is the paper slides flat under the string and any movement or slight twist does not affect the measure, along with keeping it flat sliding across to do the second and third strings etc.   Another advantage is everyone who is setting up can use this with confidence even in the absence of feeler gauges.  

Furthermore , in our service world, chasing compression "S" problems or neck twists is made easy (ier) by using short section the string as a straight edge from fret 1 to fret 7, fret 7 to 15 sort of thing and then 12 to 24 - allows an easy diagnosis of how the fret plane aligns prior to laying a radius sanding caul over the frets (or other remedies).     

Knotched straight edges are used in our making process (they double as straight edges when the knotches are not used) to check that the fingerboard is behaving after fretting and still true lengthwize and side to side.  This established a base for further particular work that we do on the frets after fretting.  Also, as our boards are machined to within a couple of thou before fretting and maybe a bit more when truing a radius prior to a Service refret its easy enough to find where 'flat' is after fretting using a knotched edge before addressing fret compounding/spot leveling and some drop away.   Note that electrics with their tall frets can often have minor drop away (5-7 thou) and or compounding (typically 9.5 inch to 12 inch, or twelve to 14 inch) in the 15 to 22/24 fret region done via the frets rather than the fingerboard.

Unfortunately, as Howard so rightly puts, these matters are not simple and no one size fits all so the above stuff is just a grab bag of things that are in daily use and may help expand the subject knowledge without going into the great depth of the subject.

Rusty. 

[Christopher Parker]

I'm not sure why you are using a notched straight edge for setup work. It is meant to read the plane of the fingerboard - not the frets. I never use feeler gauges to measure relief, and I almost never use a straight edge. I just use the strings to judge relief and then I play it, and adjust until it plays in a way that best suits the player. A small amount of relief is usually all that's necessary. Depending on the guitar and the player, I usually end up with a relief measurement between .004" and .010". On an acoustic guitar, I fret the first and the fourteenth fret to check relief. On an electric, I fret the first and the seventeenth. I also check relief by fretting at the second fret, because sometimes guitar factories unintentionally leave the first fret high, so sometimes you will get a false reading by using the first fret when checking relief.

A great tool for measuring neck bow is this: http://www.stewmac.com/Luthier_Tools/Tools_by_Job/Tools_for_Necks_a... I don't use it much for setup work, but I actually use it much more than a straight edge when doing refret work. With it, I can plane a fingerboard within .001" of perfection without even touching a straight edge. It's also super handy when working on vintage strats and teles, etc. that need their neck removed to adjust the rod. I use it to read the amount of relief, and then I determine my desired amount of relief, and then subtract the difference. Then I can remove the neck and adjust in the exact amount I want it to change without any guesswork.