A Question of Intonation

[Doug Collins]

I have all but finished my first guitar, and I am quite pleased with the results. However, the intonation is not quite correct. I'm afraid I'm going to have to make a new bridge in order to move the saddle back enough. But I can believe just how far it has to move, according to my calculations - nearly 3/16"!

To confirm this, I removed the saddle a placed a piece of fret wire back of the saddle slot to simulate the new saddle position. The intonation measures correctly in this position with the 12 fret, open and harmonic reading pretty close to the same on my tuning device. But it doesn't make mathematical sense to me.

I understand that the 12th fret should theoretically be half way between the nut and the saddle. I also understand that because a string stretches when you fret it, that compensation is needed and increases with the thickness of the string. That is why the saddle angles, giving greater length to the fatter strings. If I measure the distance from my high E string (1:E), the distance from the nut to the 12th fret is 12 - 11/16", while the 12th fret to the saddle is 12 - 3/4". The low E string (6:E) is 12 - 7/8". That is a full 3/16" of compensation, which seems like a lot to me.

The action is admittedly a little high in this temporary setup (4/32" at the 12th fret), but is it possible to require this much compensation, or am I missing something?


Thanks,

Doug

[Rory]

Doug,
FWIW- I noticed this too and am seeing the same problem with my new posting on weissenborn intonation. Does not show up unless you change it to show newest discussions??

Rory

[Doug Collins]

Hi Rory,

Something is amiss. I noticed that the "Tips and Discoveries" thread appears in both "Newest Discussions" and "Latest Activity", but in "Newest Discussions" it says there are 11 replies, while in "Latest Discussions" it says there are 7. I can only see 7 replies under both lists.

Thanks,

Doug Collins

[Doug Collins]

Looks like the forum is fixed - that is if this shows up under "Latest Activity" now.

[Martin Edwards]

I can see it!!

intonation is a funny old thing, but a rough rule of thumb is the scale length plus the diameter of the CORE of the string.

unwound strings thats the diameter of the string, wound, it's less.

that's why you get the wiggle in the saddle

[Doug Collins]

I don't think I understand. According to my measurements, I would have a 3/16" diameter string.

Thanks,

Doug Collins

[Russell Vance]

There are luthiers out there that understand intonation, I'm still 101 after all these years! .....I'm doing electrics which require that sort of intonation everyday, especially when we do the drop tuning 56 -70 gauge strings......acoustics behave much the same - heavy strings, more intonation etc. String wrap to core ratio will affect intonation in different brands and I guess hex core versus round core will have some affect (but not a lot - it's academic) as well.

High actions will also affect intonation more as you correctly observed -

The other issue which is not so apparent is that intonation will depend on your saddle type and nut slots - it gets complicated but the effect is that a string does not start vibrating at exactly the break point on the saddle or the nut - the wire actually stays straight for a short distance past the nut or bridge - effectively shortening the vibrating string length and dicking with the intonation when we progess to a fretted break.
point. You can also see how break angles will also affect intonation across the saddle and sharp saddle tops versus gently rounded tops as well.

But, this is not academic - when we do production setups on our production customs we actually set the bridge intonation position via a dry run with the selected string gauge,action and intonation set (Peterson strobe) before we drill the bridge locating holes - generally the heavy downtuners are a good 1/8 th" back from the max adjustment on the tune-o-matics.

My suggestion is set up the guitar dry, with your usual strings (a new set) with a false saddle (a round, long piece of thick side dot material or similar works - you can roll it back and forth under the strings in place) - use a good tuner, check with your ear anyway, and trust the physics. Hope this helps and maybe encourage an expert to step up . Rusty.

[Doug Collins]

Russell,

You look pretty good for I guy 101 year old! Sorry, couldn't resist.

I am going to take your advice. I'm putting on a new bridge, and this time I will and string it up before cutting the saddle slot.

I kind of already did what you suggested, but I'll try it again with the fresh bridge and let you know how it works out.

If it has to be back that far, I guess I'll have to go with it.

Thanks,

Doug Collins

[Doug T]

To overcome intonation (and frankly, it sounds better, to my ear, than the thin saddle) I build all my guitars with the really thick saddle. I think it is the 1/4" stock from LMI, but I'd have to check the number. I get it pretty close to finish hight and flat all the way across. Then, I listen to where it is at "unadjusted." I shoot for getting the bridge exactly in the midpoint and then I can file from the front or back to adjust the intonation. So far, making this type of saddle I've not had anything go whacky on me. Another thing, it provides a nice space for installing under saddle, and seems to transfer to the top better. Just my 2 cents

[danove]

The fret position formula seldom do take into account the effect from
stretching the string down to the fret and further down to the fretboard.

There are some simplifyed formulas, used by traditional luthiers that do,
to some extent, but the standard 18-rule does not.

Here is a somewhat pretentious layout of the procedure, just in case...
________________

Make sure the strings sit tight in the nut. Wiggle the string sideways
to see that they leave their slots in a proper way.
Check that each string heigth above 12th fret is exactly as you prefer it
- that you love the playability regardless of tone.
________________

Tune to pitch with your favourite gauge, and adjust, for each string,
the 12th harmonic with its fretted note, to a matched position at bridge.
Stewmac “The Intonator” and of course a strobe tuner, come in handy for this.
It is a good idea to test with several gauges, as the string quality differs..
See Avalon bridges, for a hint of the scenario with wound g-strings.
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If not very low frets, it is well worth doing the nut too.
The higher density of the string – the more it is set forward.
I am myself a nylon player, and have no good measures for steel,
but you should be able to find some advice from other luthiers.
________________

A high setup, as with a dead straight fretboard, require extensive
compensation, especially at the basses. More than the string diameter.

If you prefer a drop-D, or some other dropped strings tuning,
there will be extra compensations for those strings, as the
effect from stretching is higher below pitch.
________________

You got a nice guitarone!
Keep us updated...

[Doug Collins]

Just to follow up on this thread, I went ahead and moved the saddle back 3/16" and now the intonation is correct. I was nervous about routing the saddle slot with the bridge attached to the guitar, but it turned out to be no problem. In the future I will always attach the bridge and string it up with a temporary saddle before committing to a slot position.

Thanks for the help,

Doug Collins

[Len Biglin]

Another consideration which I think was not discussed , is that you want the nut slot height (or depth ) close to perfect when evaluating intonation at the bridge , a high nut will still throw you out at the bridge saddle .

[FRANK]

GUITAR 12 TIMES 2 PLUS 1/16TH AND INCLINATION