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Over the years, I have come across a few instances of very well respected luthiers who, either in the course of discussion on a forum, or else on their websites, have advocated taking the set-up measurements (relief, string height etc) while the guitar is in "playing position". (Two of these luthiers are occasional contributors to this forum).

I was reminded of this by watching once again the Youtube video of StewMac's space-age neckjig, ( which I had the privilege of being the very first person to view, and comment on.) I did not then, and do not now, understand what difference it makes whether you measure the action, relief etc with the guitar flat on the bench, slung from your shoulder, or stood upright on the floor ... IME (and I have done the experiments), the results are the same in every case.

I could envisage that with something like a Fender bass, there could conceivably be some kind of minute discrepancy in the measurements between flat on the bench and slung round the neck, but on an acoustic guitar? I don't think so.

Still, I could be wrong. I was wrong once before. If I am, doubtless I will be corrected...

Well if you can't measure a difference, there isn't one. Some folk just love to turn things into rocket science. Guitar set up on the atomic level. I half expect them to pull out an electron microscope.

Somewhat related, I think I notice a difference on classicals if the guitar is played for a while, which I attribute to body heat warming up the wood and distorting it a little.

That's something else; 'warming up' or 'playing in'. That is different from the setup, which has to do with the string height off the frets, the neck shape, and so on. We should manfully strive to avoid that discussion in this thread. Please...

I do the final measurement of action in playing position.

I have noticed a difference in string height between flat on the back vs upright. I like not having to crouch or bend down to see the action guage. In playing position you just look down.

Of course, you can do it any old way that works for you....

I like to sight a fretboard surface like I am shooting a rifle in the playing position because it seems to make sense to me that the neck could 'feel' the gravity but... It's a stretch. I vote myth, is this a vote? :p

To what would you ascribe this perceived difference, Ed?

I am assuming that the string height flat on the back is measuring lower than the measurement in playing position.

Is this due to the pull of gravity on the strings, or the weight of the headstock pulling the neck down ... or something else?

A neck will fall forward about 0.010" at the nut from flat to playing position. This is enough to alter set up specs slightly. I generally measure/set up in playing position not for that reason, but cause it's easier than bending down!

If I set up a guitar on the bench, and then play it and find that it's plays wonderfully - who am I to argue?
My point is... if it plays badly, then I'd adjust it again.

I say it's six versus half a dozen. Whatever works, works.

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"Act your age, not your shoe size" - Prince

Interesting ... I am trying to visualize how such a .010" shift could be measured ... I assume that it could only be done by measuring the action at the twelfth fret extremely precisely, with the guitar on the bench, and then measuring again in playing position, and finding an increase of .005" in the action.

Presumably this experiment was done a number of times on different guitars, with the same result each time?

Fascinated as I am by some of the divining that goes on in the world of guitar making, and frustrated as I am by some of the BS out there, I think Al Carruth is sharing some wise words.

LOL. I was wondering the same. I don't even have a ruler scaled in hundreds


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Not quite on topic, but close enough....

Some time ago, I had a guy come in with an old Gibson J45 which needed some serious retrospective intonation work. My usual approach for this type of job is to tune the open strings, create a "map" of cents error, every string, every fret and then use an optimiser program that I put together to figure out what the compensation should be on the nut and saddle to minimise the intonation errors. So I did this and called the customer to come and pick his guitar up. He came, played it and said it sounded even worse than before. I said, I agree! But it was fine yesterday. The difference? He's left handed, I'm right handed. The guitar is strung left handed (bass strings towards his head when he plays it). I did the intonation mapping right handed, i.e. with the guitar "upside down". When I played a few chords upside down it was fine. So we did the error mapping again with him playing left handed, re-did the compensation, all was fine and he left a happy chappy. Before that, I wouldn't have thought it would have made any difference which orientation the guitar was in and I'm pretty sure that on a lot of guitars it doesn't. But, at least occasionally, it does.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

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Do people still use rules to measure action ?

Well I put up a guitar on the bench. When I tune the guitar in playing position to 440, then lay it down on the bench with the neck rest under the nut, the D and A string go flat 4ish cents, and the lo E by 6. The other three strings are more or less the same.

As well, the action at the 12th seems to go up a few thou too. However, I'm using the stew mac guage not a dial guage like you have, so that could simply be a matter of the angle you view the guage.

What I take from it is that the weight of the guitar is enough to bend the neck forward. More so for some guitars than others.

This was something I observed at my last job as well. But it depends on the guitar. On some guitars the action will go down as the weight of the strings pulls them towards the fingerboard and the neck doesn't flex. I do believe that strings bend under gravity like the wires between telephone poles. So protocol was to check action in the upright position.

But the best reason to do it is because you can just flip the guitar vertical and measure instead of bending down with your head and bench height, which, if you do nothing but set ups all day every day becomes most tiresome.

YMMV...

I think that will make a big difference. Upstroke / downstroke.

I've just tried to measure the action at the 12th fret and I can't detect any difference between the two positions. I've tried a few times and I suspect I'm wasting my time. I use a homemade gauge as shown below. Very accurate at both Nut and 12/14 th fret positions, providing you know how to use it. At the Nut position you can feel when the gauge touches the string. At fret 12/14 you have to look at the gap. I use White card as the background and of course you have to be aware of the viewing angle.



I'm shocked that .010" has been cited as being a shift in Neck position. That's a huge amount for a Neck to be flopping about. When a Guitar is laid on it's back the string tension is still pulling the Neck forward. That is also the case when it is in playing position. I should imagine it would take quite a bit of force to alter the Neck geometry such that it can be measured. I honestly can't see gravity/weight of the Neck/headstock doing that. It's not as though we are going from the Guitar lying on it's Back to lying on it's front either.

If you use a neck jig, you can easily measure how much a neck moves under with or with out string tension and you can also see the effects of playing position vs flat. I was shocked the first time I saw it but it is there. It doesn't effect the set up that much was the point I was making

Murrmac, I stand corrected! I didn't even know that thing existed.
But I remain a skeptic that .01 is going to make any noticeable difference. Humidity changes make more effect than that IMO.



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Totally not a myth, especially when setting up thin necked electrics adjusted to extremely tight tolerances.
When the guitar is resting on it's back gravity can pull the headstock down, straightening the neck, and so when the guitar is put in playing position the neck can pull forward, sometimes as much as 1/32 inch. Even a slight pull of 1/64th or 1/128th can have a noticeable effect on feel if the guitar is adjusted to 1/32nd on the treble side and 3/64ths on the bass side (yes, I've done this many a time for the shredders that frequent my shop).
If someone's been playing their guitar that way for a long time they can definitely tell.
Probably not so much of a problem for classical guitars with thick square neck profiles but definitelyso for electrics.
Also, few guys have reported problems to me of their guitars buzzing when they play on the couch but not when they're playing standing up.
It turns out that when they sit doen te guitar was resting on it's back on their belly, this is a problem for large overweight guys rather than skinny guys.
But no, definitely NOT a myth, I always set up all my guitars in playing position for the final checks.

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Old growth, shmold growth!

Electrics are certainly a different ballgame ... you would think however that by the time a large overweight guy gets his large overweight hand round the neck the pressure he is exerting is going to totally negate any kind of precision to 1/128" (or .007" in practical measurement terms))

Hah I don't set EVERY guitar up to that tight a tolerance.

However you'd be surprised at how light a touch some large guys can actually have.

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Old growth, shmold growth!

Really? The weight of the peg head and tuning machines are going to over come these forces and take up slack?

D'Addario, a manufacturer of guitar strings, publishes string tension measurements right on their string packaging. These measurements were taken with the strings tuned to standard pitch and the scale lengths of 25 1/2" for the guitars and 34" for the bass. A set of .010" - .046 electric guitar strings have a combined tension of 103.6 lbs. A set of .012" - .056" phosphor bronze acoustic guitar strings has a combined tension of 178.3 lbs. A set of .050" - .105" medium gauge bass guitar strings has a tension of 192.3 lbs. A medium gauge twelve string acoustic set has the most tension with 322.2 lbs of pull.

Yes. those numbers are misleading. That many pounds of tension in the strings don't translate exactly to direct pull on the neck in all directions.

For instance I can string up any guitar, and by lightly grabbing and moving the neck I can change the pitch of the string and get a fairly dramatic vibrato.

Also, I don't have to press down on the string with 18 or so pounds of force to fret it.

Gravity can easily pull the headstock towards the bench.

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Old growth, shmold growth!

I find that gravity affects the intonation slightly. A guitar intonated on the bench will be off by a few cents when in the playing position.

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Brian

You never know what you are capable of until you actually try.

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