Question about string height above top

Construction and repair of Classical Guitar and related instruments
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rinneby
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Question about string height above top

Post by rinneby » Wed Mar 15, 2017 9:18 pm

I know that the recommended string height above the top at bridge is 9 to 12mm for classical guitars. On one of my guitars I have really low action, about 2.5/2mm, but string height above the top is 11,5-12mm. The setup is done extremely well so this actually works when I'm not plucking too hard. But what if I decide to rise the saddle with lets say 1mm ? Then the string height above the top will be 13mm... Will this put too much stress on the guitar in the long run? When are you out of the "safe zone" so to speak? - I understand this is a matter of how the guitar is built, but in general.

Update: After some careful examination it's safe to say that the guitar was built to work with low action. Adding 0.5mm to the nut and the small buzz on the opens strings were gone.

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/Jon
Last edited by rinneby on Fri Mar 17, 2017 7:44 pm, edited 10 times in total.
1965 - Masaru Kono No.5
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1973 - Ryoji Matsuoka No.80
1978 - Masaru Matano Clase 600

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Aaron Powell
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Re: Question about string height above top

Post by Aaron Powell » Wed Mar 15, 2017 9:46 pm

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Last edited by Aaron Powell on Wed Mar 15, 2017 11:32 pm, edited 1 time in total.

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geoff-bristol
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Re: Question about string height above top

Post by geoff-bristol » Wed Mar 15, 2017 10:17 pm

The 2nd guitar I made I re-topped - and subsequently I ended up with a quite high saddle ( about 14mm over top ) which seems fine. However - the bone upstand is only 4mm max above the slot - and the slot is 4.5mm deep

You do not say what your present string height is at the bridge ? I take your 0.9mm/ 1.2mm to be a typo ? ( 9mm - 12mm ? )

Bear in mind 1mm extra at the 12th = 2mm higher at the saddle. It all depends on what height the saddle is at present above the top ?

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rinneby
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Re: Question about string height above top

Post by rinneby » Thu Mar 16, 2017 6:23 am

geoff-bristol wrote: I take your 0.9mm/ 1.2mm to be a typo ? ( 9mm - 12mm ? )

Correct, typo. The string height at the top at the bridge is approximately 11,5-12mm with 3.5mm saddle sticking up and maybe 4.5mm in the slot. But this gives 2.5/2mm at 12th fret... Sure you could sand down the fretboard, but that must be considered a last option. The guitar is playable as it is, with (almost) no buzzing, quite impressive actually. But a little higher action is preferable.

/Jon
1965 - Masaru Kono No.5
1972 - Yamaha GC-3D
1973 - Ryoji Matsuoka No.80
1978 - Masaru Matano Clase 600

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Michael.N.
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Re: Question about string height above top

Post by Michael.N. » Thu Mar 16, 2017 8:10 am

You must be holding back to get hardly any buzz on a bass action of 2.5 mm's. It's just not possible.
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rinneby
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Re: Question about string height above top

Post by rinneby » Thu Mar 16, 2017 8:35 am

Michael.N. wrote:You must be holding back to get hardly any buzz on a bass action of 2.5 mm's. It's just not possible.

When fretting first position (F) on 6th string I actually don't get any buzz when playing normal. But I can't dig into the guitar very much... I need to get up at least 0.5-1mm in the best of worlds. The question is more how to achieve this without rising the saddle 2mm = 14mm above the top :(

/Jon
1965 - Masaru Kono No.5
1972 - Yamaha GC-3D
1973 - Ryoji Matsuoka No.80
1978 - Masaru Matano Clase 600

You are the instrument, not the guitar

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Michael.N.
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Re: Question about string height above top

Post by Michael.N. » Thu Mar 16, 2017 9:35 am

Well I would say that 3.5 mm is the lowest bass action that the average player can use and even then there will be the odd buzz when trying for forte. Very good set up can only do so much, it can't perform miracles.
if you raise the saddle by 2 mm's it will almost certainly mean that the saddle will have a very high projection over the bridge. The only way to cure that whilst maintaining sub 13 mm string height is by altering the neck geometry, likely an expensive procedure.
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rinneby
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Re: Question about string height above top

Post by rinneby » Thu Mar 16, 2017 9:46 am

Michael.N. wrote:Well I would say that 3.5 mm is the lowest bass action that the average player can use and even then there will be the odd buzz when trying for forte. Very good set up can only do so much, it can't perform miracles.
if you raise the saddle by 2 mm's it will almost certainly mean that the saddle will have a very high projection over the bridge. The only way to cure that whilst maintaining sub 13 mm string height is by altering the neck geometry, likely an expensive procedure.

I think a combination of adjusting the nut (that is also low) and the saddle is the way to go. I will try this first and report back. Thank you for your insights.

All the best
/Jon
1965 - Masaru Kono No.5
1972 - Yamaha GC-3D
1973 - Ryoji Matsuoka No.80
1978 - Masaru Matano Clase 600

You are the instrument, not the guitar

Keith
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Re: Question about string height above top

Post by Keith » Thu Mar 16, 2017 11:09 am

Jon, and others, is there an "over 13mm danger zone"? I know having too much saddle above the slot can be "dangerous" with respect to the front of the slot breaking but if there is close to equal below and above the slot line it seems the extra 1-2mm above the top should not be a problem--or is it? If the bridge is as tall as it seems from the description is there enough wood at the bottom of the slot to remove to lower the saddle there to give more below the line depth? Of course a new saddle would be in order.
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astro64
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Re: Question about string height above top

Post by astro64 » Thu Mar 16, 2017 11:42 am

It just depends on how strong the saddle slot on your bridge is supported. If the slot is supported by a relatively thick layer of wood in front and the slot is relatively deep, the bridge is more likely able to tolerate a tall saddle than when the slot is very close to the front. I have had a guitar where small cracks appeared at the edges of the slot. A drop of superglue took care of that but I also eventually had the fretboard adjusted to get the string height back to normal. On another guitar I do have 14-15mm string height of the top. The bridge can take it, but the stress is enough to make the bridge lean forward (designed that way, apparently, since the guitar plays perfectly in tune with that setup).

SteveL123
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Re: Question about string height above top

Post by SteveL123 » Thu Mar 16, 2017 3:11 pm

Where is string height above top measured? Ooops, just saw the first post that it is measured at the bridge.

Does higher string height at the bridge = higher tension on the top?

Laudiesdad69
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Re: Question about string height above top

Post by Laudiesdad69 » Thu Mar 16, 2017 4:41 pm

How is the set up of the nut. It seems to me that if you have room to raise the action at the nut just a smudge that would lessen the degree of the angle to the higher saddle, if you are concerned about creating too much stress on the top. Not preferable probably but if your action at the first fret is as low as my Ramirez, you would nave room to raise it a little. I would try a shim before I made a new nut though.

Sorry, I guess that you mentioned that earlier. My bad. I guess great minds think alike! :D
Last edited by Laudiesdad69 on Thu Mar 16, 2017 5:26 pm, edited 4 times in total.

Alan Carruth
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Re: Question about string height above top

Post by Alan Carruth » Thu Mar 16, 2017 5:26 pm

The tipping force at the top of the saddle is a function of the break angle of the strings. The actual force on the saddle top runs on the bisector of the break angle, and you can use trigonometry to figure it out. If the string holes in the tieblock are low down you can reduce the break angle by plugging them and drilling new ones. You can also sometimes reduce the angle usably by the way you tie the strings off. Use the loop to pill the break point up toward the top of the tieblock, rather than forcing it down into the channel all the way.

Trevor Gore gave a useful indicator of top stress in his book. String tension pulls the top of the saddle toward the nut, The higher off the top the strings are the greater the leverage and the more forward rotation you'll see. Gore feels that the 'best' guitars tend to show about 2 degrees of bridge rotation under load. It's not too hard to rig up a pointer of some sort and measure this. I've even used a laser pointer taped to the bridge, with the guitar clamped down. Note that, for discussion purposes, the effect should be pretty much linear, so that if you get 1.5 degrees with the strings 12mm off the top then raising them to 16mm should give about two degrees.

Keep in mind that what's being measured here is the ability of the top to withstand the added stress. If the bridge is too small, or glued on poorly, it might very well fly off and kill the cat.

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geoff-bristol
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Re: Question about string height above top

Post by geoff-bristol » Thu Mar 16, 2017 7:14 pm

How thick is the board at the nut and 12th. Can you drop 1mm at the 12th ?
The board does not need to be any particular thickness at the 12th fret - and the extension to the soundhole hardly matters. If its parallel at the moment then 1mm less at the 12th is not going to look odd. It might even make the neck pull up a bit under string tension ?

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rinneby
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Re: Question about string height above top

Post by rinneby » Thu Mar 16, 2017 8:30 pm

geoff-bristol wrote:How thick is the board at the nut and 12th. Can you drop 1mm at the 12th ?
The board does not need to be any particular thickness at the 12th fret - and the extension to the soundhole hardly matters. If its parallel at the moment then 1mm less at the 12th is not going to look odd. It might even make the neck pull up a bit under string tension ?


The fretboard is pretty thick I guess. 6.5-7mm - See 4th picture. I've also attached pictures of how the bridge and saddle looks like. Looking like this the action at 12th is 2.5/2mm.

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/Jon
1965 - Masaru Kono No.5
1972 - Yamaha GC-3D
1973 - Ryoji Matsuoka No.80
1978 - Masaru Matano Clase 600

You are the instrument, not the guitar

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